The invasive fly Drosophila suzukii is a pest that can infest a diverse range of intact, ripening fruits, using its serrated ovipositor. This constitutes a different niche compared to the rotting fruits its ancestors use, especially because these intact fruits have limited quantities of microbes and soluble nutrients for the developing larvae. To investigate the potential role of microbial associations in the niche expansion of this invasive fly, we characterized the bacterial and fungal communities of D. suzukii and various wild fruits from which they developed. To assess cross-generational microbial associations, we also lab-reared fly populations and characterized their microbial communities. Diversity metrics of microbial communities differed significantly between flies and fruits. Different fruit types varied substantially in microbial composition, while flies showed relatively uniform bacterial communities, irrespective of the fruit source they developed on. After approximately ten generations of lab-rearing, bacterial communities still showed considerable overlap with those of wild flies. Fungal communities of flies and fruits showed larger resemblance, with a substantial overlap between wild flies and the fruits on which they had developed. Our study thus reports that the fungal community structure in these pests largely reflects those on the breeding substrates, while these flies might have formed more persistent associations with some bacteria and transmit these across generations.
Rising temperatures can enhance foraging activity and accelerate the encounter rate of different predators, which may increase their interference competition strengths. However, limited information is available on such effects of temperature, and on the consequences for their predation rates. We used a functional response approach to experimentally quantify the interspecific interference competition strength of two species of ladybirds, Harmonia axyridis and Propylea japonica (Coleoptera: Coccinellidae), toward their prey Myzus persicae (Hemiptera: Aphididae) at 23 and 33 °C, respectively. The results indicated that high temperature could cause P. japonica to be more active and interfere with H. axyridis more often, and strengthened the interference competition between these two predators. The functional response of H. axyridis was changed from type II in single H. axyridis treatment to type III in paired predator assays at 23 and 33 °C. Moreover, single H. axyridis consumed more aphids than H. axyridis in heterospecific predator trials at aphid densities below 50 and 35 at 23 and 33 °C treatments, respectively. For P. japonica, type II functional responses were detected in all assays. Additionally, when competing with H. axyridis, the predation rate of P. japonica at 23 °C was almost unchanged compared to that of single P. japonica, but fewer aphids were eaten compared with single P. japonica across all aphid densities at 33 °C. Thus, with interference competition, two predator species respond differently to temperature changes in terms of foraging efficiency, which may further affect the population adaptability and control efficiency of these two focal species.
The combination of a companion plant with a cultivated plant is considered an interesting strategy to reduce pest pressure and, hence, the use of pesticides. Although several plants from the Alliaceae and Lamiaceae families are known to be efficient companion plants against aphid pests, only a few plants of the Geraniaceae family have been studied so far. The aim of this work was to investigate the potential effects of Geranium macrorrhizum as a companion plant on the colonization of sweet pepper (Capsicum annuum, Solanaceae) by the green peach aphid (Myzus persicae). Aphid's orientation behavior, probing behavior and life history traits were assessed on sweet pepper using a host choice preference setup, Electrical Penetration Graph technique and clip-cage laboratory bioassays, respectively. The potential disturbance through mechanical stimulation of geranium leaves was also assessed. The composition of VOCs from G. macrorrhizum leaves was analyzed using SPME technic followed by GC-MS. This study revealed that G. macrorrhizum as a companion plant was intrinsically repellent but not enough to completely mask the attractive odor of the sweet pepper host plant. Moreover, G. macrorrhizum negatively impacted the probing behavior, fecundity and survival rate of M. persicae on sweet pepper. The effects were exacerbated when G. macrorrhizum leaves were mechanically stimulated. This could be due to the greater amount of the main VOCs germacrone and β-elemenone emitted by G. macrorrhizum following mechanical stimulation. Our results bring new insights into the use of novel companion plants to regulate aphid pest populations.
Root-knot nematodes (Meloidogyne spp.) are notorious plant-parasitic nematodes that affect agricultural crops. These obligate soil-dwelling parasites typically maneuver the host plant physiology by forming specialized feeding cells resulting in heavy yield losses. Scant management tools are available to effectively combat this pest. In an exploratory attempt of identifying new fungal biocontrol agent(s) for M. incognita from India, a Paecilomyces tenuis isolate from rhizosphere soil was found to incur > 90% mortality of the infective second-stage juveniles (J2s) at 24 h post-exposure to the fungal filtrate with about 87% parasitization. The fungal filtrate also significantly reduced the egg hatching and host-root penetration of M. incognita under in vitro and in vivo conditions revealing its effectiveness in curbing nematode pathogenicity with positive effects on plant growth. Chromatographic analyses revealed the presence of Huperzine A (433.56 mg L⁻¹) in the P. tenuis isolate. Besides, the isolate possessed acetylcholinesterase inhibition attribute with an IC50 of 2.85 ± 0.12 mg mL⁻¹ of the fungal filtrate. Further, GC-MS analysis revealed the production of other nematicidal compounds by the fungus including acetic acid. To conceptualize the mode of nematicidal action, RNA-Seq was done post-treatment of the M. incognita J2s and model worm Caenorhabditis elegans with fungal filtrate and pure Huperzine A. The transcriptomic profile unraveled the molecular intricacies underlying the nematicidal action affecting several biological pathways and developmental checkpoints of the nematode. Thus, the P. tenuis isolate offers significant potential to be used as a biocontrol agent against M. incognita along with its commercial use for Huperzine A production.
Bemisia tabaci species complex (whitefly) is one of the most dangerous pests that destroy many important crops worldwide. It causes damage to the host plant by feeding on phloem sap as well as transmitting a wide range of devastating plant viruses (especially begomoviruses) that cause severe epidemics on crops. To fend off the menace, modern genomic-based strategies have been adapted to minimize the crop losses due to this destructive pest. Genetic engineering techniques, e.g., transgenics and RNA interference (RNAi) have shown promising results in controlling B. tabaci in plants; however, these techniques often face challenges due to the concerns about GMOs in food crops. With the enhanced knowledge about B. tabaci genomics, new technologies, e.g., manipulation of microbiota or CRISPR-based genome editing have shown promising results in several insect pests and could have an instrumental role in controlling agricultural pests including whitefly. Genome editing is an eco-friendly approach that can be employed to suppress or even destroy the target species. In this review, we have discussed B. tabaci as a pest and advancement in control strategies of B. tabaci. Various potential targets for genome editing have also been discussed that could be used in gene-editing technologies for the efficient management of B. tabaci and the viruses it transmits. Finally, we also outlined the future perspective and effective use of genome editing technology in developing CRISPR-based gene drive for whitefly population modification, suppression, and eradication.
Mosquitoes (Diptera: Culicidae) are insect vectors of epidemiologically important arboviruses owing to their behavior, physiology, morphology, and proximity to humans, which require incisive strategies to contain their spread. The failure of current arbovirus management plans and lack of fully effective treatments suggest that vector control by botanical insecticides could be an effective and safe strategy. Botanical insecticides are obtained from renewable sources and have complex chemical compositions, different modes of action, and selective toxicity for target organisms. In this review, we present the main control strategies for insects belonging to the genera Aedes, Culex, and Anopheles and discuss the possibility of using botanical insecticides in the integrated management of vectors. Numerous botanical insecticide formulations are presented, and their potential modes of action during the immature stages include damage to the egg exocorionic network and abnormal disruption of embryos, which result from deficiencies in egg chitinization, impairment of larval morphology, and inhibition or differential expression of enzymes, promoting changes in the digestive tract epithelium and reduced larval mobility, and impairment of external surfaces or the respiratory system of pupae, altering pupal swimming patterns. In adult insects, botanical insecticides can promote incomplete ecdysis, in addition to dysfunction of olfactory receptors, food traffic, and reproductive function. Thus, broad-spectrum botanical insecticides can be used to control the different stages of insect development. The contributions of nanotechnology to vector control should be further explored to enhance the insecticidal activity and stability of botanical insecticides under different conditions.
Telenomus remus (Nixon) is a promising egg parasitoid for the management of Spodoptera frugiperda (J. E. Smith). This species has been successfully reared on alternative hosts under laboratory conditions. However, the production of biocontrol agents is often out of sync with the demands in the field. Appropriate cold storage techniques can drastically prolong their shelf-life to synchronize the release schedule with field needs and reduce production costs. Past studies on the cold storage of T. remus only focused on certain developmental stages, but not all stages. Here, we comprehensively evaluated the impacts of storage temperature (8, 11, and 14 °C) and duration (7, 14, 21, 28, and 35 days) on the maternal emergence and offspring fitness of T. remus stored at different developmental stages (first instar larvae, second instar larvae, prepupae, and pupae) using Spodoptera litura (Fabricius) eggs as alternative hosts. For each developmental stage, emergence percentage and parasitism capacity of parents all decreased with increased storage duration and decreased storage temperature. Maternal female longevity, offspring emergence percentage and percentage of females were barely affected by cold storage. We concluded that storage of the first instar larvae at 14 °C for 21 days was the optimum storage scheme for T. remus. Our findings can be directly used as guidance in mass production and storage of this parasitoid.
Diurnal insects can select suitable oviposition sites by discriminating plant coloration. The long wavelength sensitive opsin (LW) gene is mainly for discriminating long wavelengths of colors in diurnal insects. However, the affection of coloration on oviposition selection and the roles of LW gene in nocturnal insects are unclear. Here, the questions were explored in Helicoverpa armigera (Lepidoptera, Noctuidae) using CRISPR/Cas9 gene editing technology and experiments of oviposition selection under different coloration backgrounds. To different brightness (achromatic white, grey, black), wild moths preferred to oviposit on higher-brightness background, while the LW mutant had no preference. To different colors, wild moths had no oviposition preference, while the LW mutant significantly reduced oviposition on long-wavelengths of colors (red, orange, yellow, and green) compared to blue and violet. When both brightness (white) and color (orange and green) cues were presented for oviposition, wild moths were more attracted to brightness than color, while LW mutant had no significant preference. For the coloration of young and old leaves, wild moths preferred to oviposit on coloration of young leaves that had a brighter light green, while LW mutant had no preference. Electroretinogram recordings showed that the responses of moths to different bright light or different color light were significantly decreased after knockout of LW, especially to the long-wavelengths. These results suggest that brightness is a more reliable cue rather than color for oviposition selection of nocturnal moth H. armigera in changing microhabitats and LW mediates the recognition of different brightness and long wavelengths.
Some plants are able to accumulate on their leaves metals taken from the soil, using this as a defence against herbivorous arthropods. However, herbivore response to metal accumulation in plants is known to be variable. While some species and taxonomic groups are less affected than others, hormetic effects have also been observed in spider mites, herbivorous crop pests. Still, knowledge on the range and causes of intraspecific variation in the response of herbivores to metal accumulation is lacking. Here, using two species of spider mites, Tetranychus urticae and Tetranychus evansi, we tested the variation in 17 populations in response to cadmium-accumulating tomato plants and the drivers of such variation. We observed a nonlinear, hormetic response of mites to plants with cadmium in some, but not all, populations. The same pattern was recaptured in artificial diets with different concentrations of cadmium but not in artificial diets with sugars, which change in the plant in response to cadmium. This indicates that herbivores on metal-accumulating plants respond to metals, not to the variations in leaf carbohydrates. Therefore, metals exert different effects on herbivores according to the amount accumulated, but independently of other studied plant traits. This knowledge is key to the understanding of the mechanisms underlying herbivore responses to metal-based plant defences and to pesticides containing heavy metals. Additionally, our findings draw attention to the need of considering intraspecific variation and nonlinearities when studying the effects of metals and other contaminants on herbivorous arthropods.
The fall armyworm, Spodoptera frugiperda (J.E. Smith), is an invasive pest threatening crop production and food security worldwide. High concerns are linked to the potential establishment of the species in Europe. The high migratory capacity of S. frugiperda causes concerns about the potential impacts of transient populations invading new areas from suitable hotspots. In the present work, we developed and used a physiologically-based demographic model to quantitatively assess the risks of S. frugiperda in Europe. The risks were assessed considering a best-, a median-, and a worst-case scenario. The Mediterranean coastal areas of Southern Europe resulted particularly suitable for the establishment of the species, with suitable areas reaching even higher latitudes, in the worst-case scenario. In Europe, up to four generations per year were predicted. The predicted yearly average number of moths per trap per week (± standard deviation) was 5 (± 4), 17 (± 5), and 139 (± 22) in the best, median-, and worst-case assessment scenarios, respectively. Model results showed that Southern and Central Europe up to the 48th parallel north might be exposed to the risk of transient populations. Depending on the latitude and on the period of arrival of the propagule, 1–2 transient generations per year might be expected. The model can be used to define strategies for reducing the risks of establishment of the pest at the country level. Predictions on the dynamics and phenology of the pest can also be used to support its management at the local level.
Drought affects both crops and their pests, but the effect of the interaction between drought and pests on crops has not been sufficiently understood. The aim of this work is to determine (i) the response of spring wheat (Triticum aestivum) to three watering regimes (soil water capacity of 70, 50 and 40%) and aphid (Metopolophium dirhodum) infestation, and (ii) how drought affect aphid population growth. Seedlings of one drought-susceptible (Quintus) and one drought-tolerant (Septima) cultivar were used, and changes in leaf structural and morphophysiological traits were measured. The age-stage, two-sex life table approach was used to determine aphid population growth. The plant stress and plant vigour hypotheses in this system were tested by analysing correlations between leaf traits and aphid life table parameters. Drought stress negatively affected parameters related to plant vigour (reduced biomass, decrease in Ψπ100 and increased resource allocation in structural defence trichomes) regardless of the stress tolerance of the cultivar, although the level of stress was generally greater in Quintus than in Septima. Plants perceived the stress caused by the aphids as significant only under high drought stress, as the physiological response of increasing growth and osmolyte accumulation was triggered under these conditions. This response also benefited the aphids; hence, the population growth of the aphids was most severely affected under moderate drought stress. The reproductive rate was negatively affected by trichome density and positively affected by leaf biomass and Ψπ100; these findings provide support for the plant vigour hypothesis for the spring wheat seedling–rose-grain aphid study system.
The use of predatory Hemiptera (Pentatomidae: Asopinae) in agroecosystems has increased considerably in the last decades. All Asopinae representatives are obligate predatory stink bugs but they are classified as zoophytophagous because they feed on prey and occasionally feed on plants. They prey on wide variety of insects including the agricultural pests Coleoptera, Diptera, and Lepidoptera. Despite the predatory potential of Asopinae, their use and establishment in the agroecosystems have some restrictions, yet. Here, the aim is to review the advances in biology, feeding strategies, and biological control for using Asopinae species with zoophytophagous-predatory habits (SZP) in the agroecosystems. We discuss four different approaches that can improve the worldwide effectiveness and popularization of SZPs representatives as biocontrol agents in crops,(i) feeding strategies, ingestion, and digestion;(ii) diets for survival during prey shortage;(iii) adaptation of species for biological control in crops; (iv) use of Asopinae in integrated pest management programs.
Reproductive Interference occurs when interactions between individuals from different species disrupt reproductive processes, resulting in a fitness cost to one or both parties involved. It is typically observed between individuals of closely related species, often upon secondary contact. In both vertebrates and invertebrates, Reproductive Interference is frequently referred to as ‘Satyrisation’. It can manifest in various ways, ranging from blocking or reducing the efficacy of mating signals, through to negative effects of heterospecific copulations and the production of sterile or infertile hybrid offspring. The negative fitness effects of Satyrisation in reciprocal matings between species are often asymmetric and it is this aspect, which is most relevant to, and can offer utility in, pest management. In this review, we focus on Satyrisation and outline the mechanisms through which it can operate. We illustrate this by using test cases, and we consider the underlying reasons why the reproductive interactions that comprise Satyrisation occur. We synthesise the key factors affecting the expression of Satyrisation and explore how they have potential utility in developing new routes for the management and control of harmful insects. We consider how Satyrisation might interact with other control mechanisms, and conclude by outlining a framework for its use in control, highlighting some of the important next steps .
Surface treatment is commonly used in controlling the red imported fire ants, Solenopsis invicta Buren. In the present study, the behavioral responses of S. invicta workers to surfaces treated with insecticides were investigated. Toxicological tests showed that beta-cypermethrin had the highest contact toxicity (with the lowest LC 50 value) among nine tested insecticides, followed by thiamethoxam, fipronil, indoxacarb, chlorfenapyr, spinetoram, rotenone, avermectin, and chlorantraniliprole. In the laboratory, surfaces treated with beta-cypermethrin or rotenone significantly reduced the number of foraging ants. In addition, S. invicta workers transported significantly more particles (measured in weight and/or covered area) onto surfaces treated with fipronil (50, 500, and 5000 µg/mL), rotenone (5000 µg/mL), or avermectin (5000 µg/mL) compared with the controls. Similarly, these insecticides significantly triggered the particle-covering behavior of ants in the field. We hypothesized that such behaviors would reduce the contact toxicity of insecticides against S. invicta. When the surfaces treated with fipronil or rotenone (500 or 5000 µg/mL) were artificiality covered with particles, S. invicta had significantly higher LT50 values compared with insecticide-treated surfaces without particles. This study provides the first evidence that S. invicta workers can perform particle-covering behavior to reduce the toxicity of certain insecticides, which constitutes a unique insecticide-resistance strategy in ants.
Fall armyworm (FAW) Spodoptera frugiperda is considered the main defoliating insect pest of maize in many countries. Silicon (Si) applied to plants has been shown to increase the resistance to insects, especially in grasses such as maize. This study characterized the effects of Si fertilization regarding priming, induced resistance, and tolerance to FAW in a landrace variety and hybrid of maize. Si was applied in soil of potted-plants as H4SiO4 at 2 t ha⁻¹ when maize plants were at V2 stage, and when they reached V3 two FAW neonates were placed in the plant’s whorls to cause herbivory. FAW performance was evaluated on excised leaf sections in the laboratory and on plants with larvae infesting V4-stage plants in the greenhouse. Concentrations of H2O2, malondialdehyde, and Si, and the activities of antioxidant enzymes were recorded and correlated to Si-based responses on plant growth, and FAW injury and performance. As main results, there was reduced FAW injury and larval weight gain in Si-treated plants subjected to herbivory. Greater root dry mass was observed in the landrace variety with Si and without herbivory. Landrace plants showed higher shoot weights than the hybrid under FAW infestation. Si-fertilized plants showed higher H2O2 concentrations. The highest peroxidase activities occurred in Si-treated plants without herbivory, and the catalase and superoxide dismutase activities were highest in Si-treated plants without herbivory or herbivory-injured plants without Si. In conclusion, Si-based defense in maize to FAW involve mixed effects of priming and tolerance, and were more pronounced in the landrace variety.
Root-knot nematodes are among the most dangerous plant pathogens. Biological control is a safer and effective way to manage such pests. In this context, bacterial strain KMS-6 was isolated from nematode-affected soil of the research field, CCS HAU, Hisar. It was subjected to morphological and biochemical characterization. The bacterium produced 14.02 ± 0.03 µg/ml of IAA and showed a cyanogenic activity. KMS-6 was identified based on 16S rRNA gene sequence analysis as Bacillus altitudinis (accession no. MT626660). In vitro experiments with fermentation supernatants of KMS-6 resulted in potential hatching inhibition and up to 86% J2s mortality of M. javanica. The bacterium significantly suppressed root-knot nematode infestations in greenhouse and field experiments. During the greenhouse experiment on eggplant, KMS-6 inoculation resulted in a 76% reduction in eggs, 80% reduction in galls, reducing the final nematode population up to 92% compared to control. All trials were significantly more effective than the chemical treatment as well. Also, an enhancement in plant growth was observed in KMS-6 inoculated plants with the highest plant height, maximum fresh and dry weight of root and shoot. Similar results were seen in trials conducted on eggplant (2018) and cucumber (2019) crops in nematode-infested fields. KMS-6 inoculation reduced nematode infestation more effectively than control and carbofuran treatments. The yield was significantly improved in the KMS-6 treatment. Data suggest that B. altitudinis KMS-6 could be an effective biological control agent with plant-growth enhancing properties against root-knot nematodes and a potent alternative to chemical nematicides.
The indirect effect of seminatural habitats on pest suppression has been widely studied in agricultural landscapes. By contrast, the role of crop diversity on pest suppression by predators has seldom been explored, particularly using molecular gut-content analysis (MGCA). In addition, differences between early- and late-season effects of landscape complexity on pest control, crucial to ensure season-long control, have received little attention. During 2014 and 2015, we investigated the effect of agricultural landscape complexity and crop diversity on cereal leaf beetle (CLB, Oulema melanoplus) predation early in the season using sentinel egg cards and late in the season by assessing larval predation using MGCA. Early-season CLB egg predation and late-season abundance of Nabis americoferus and coccinellids in wheat fields were positively correlated with amount of woodland habitat in these landscapes. Contrary to our predictions, crop diversity had negative associations with the late-season frequency of larval predation and the abundance of N. americoferus. Predator diversity and the abundance of Hippodamia lady beetles had negative associations with CLB abundance, highlighting the significant contribution of some generalist predators to CLB suppression. Our results suggest that the proportion of woodland and a few major crops (e.g., canola and non-cereal crops), rather than crop diversity, are associated with higher predation at different temporal scales. Overall, our results suggest that a habitat management strategy could be implemented to adjust the crop rotation regime to add the right kind of crop diversity in the landscape to support the natural control of CLB.
It has become clear that omnivorous predators can induce plant defences that affect the performance and host plant choice of herbivores. They are also known to induce the production of plant volatiles that can affect the behaviour of herbivores searching for plants. These volatiles may also affect the searching behaviour of other predators, which was investigated here. The predatory mite Phytoseiulus persimilis preferred plants previously exposed to the omnivorous mirid Macrolophus pygmaeus over clean plants. The mites were equally attracted to plants previously exposed to the omnivore and subsequently infested by spider mites (Tetranychus urticae, prey of the predatory mite and the omnivore) and plants infested with spider mites alone. Moreover, the mites were more attracted to plants infested with prey and subsequently exposed to the omnivore than plants infested with prey but not exposed to the omnivore. The predatory mites were also significantly more attracted to plants on which the omnivores were still present. Experience of the predatory mites with volatiles from plants previously exposed to the omnivore and without prey resulted in a loss of the preference for volatiles emitted by plants exposed to the omnivore. Analysis of the volatiles showed that plant exposure to omnivores induced qualitative and quantitative changes in the volatile blend. Together, these results suggest that omnivorous predators induce the production of plant volatiles that can interfere with the searching behaviour of other predators. The consequences of such interference for biological pest control remain to be investigated.
Low winter temperatures severely stress newly arriving insect species. Adaptive evolutionary changes in cold tolerance can facilitate their establishment in new environments. Ambrosia artemisiifolia, a noxious invasive plant, occurs throughout China. Ophraella communa, a biological control agent of A. artemisiifolia, mainly occurs in southern China. However, in 2012, it established populations in Beijing (39.98°N, 115.97°E) following introduction from Laibin (23.62°N, 109.37°E), implying cold adaptation. The mechanisms underlying its rapid evolution of cold tolerance remain unknown. We investigated the levels of cryoprotectants and energy reserves in adult O. communa from two latitudes. In high-latitude insects, we found high trehalose, proline, glycerol, total sugar, and lipid levels; five potential genes (Tret1a, Tret1b, Tret1-2, P5CS, and GST), responsible for regulating cold tolerance and involved in trehalose transport, proline biosynthesis, and glutathione S-transferase activation, were highly expressed. These hybridisation changes could facilitate cold temperature adaptation. We demonstrate the genetic basis underlying rapid adaptation of cold tolerance in O. communa, explaining its extension to higher latitudes. Thus, specialist herbivores can follow host plants by adapting to new temperature environments via rapid genetic evolution.
Combinations of entomopathogenic nematode (EPN) species are sometimes more or less effective than individual species for the management of insect pests. We hypothesized that these outcomes are due in part to dispersal rates that differ when EPN species are conspecific or heterospecific. Dispersal rates of three heterorhabditid species, six steinernematid species, and mixtures of some were assessed using image analysis of nematodes on water agar. The dispersal rates between the genera differed significantly and were unrelated to the estimated body mass or the putative foraging strategy, including that of the recently named Steinernema khuongi, characterized here as a cruise forager (actively search for hosts). Heterorhabditis indica dispersed more rapidly on agar when combined with S. diaprepesi, but not with S. glaseri. The presence of S. diaprepesi in soil microcosms also increased the proximity of H. indica to Galleria mellonella host insects, while H. indica presence reduced the number of G. mellonella killed by S. diaprepesi. Nevertheless, increasing the H. indica dispersal rate did not increase its insecticidal effectiveness, likely due to competition with the more virulent S. diaprepesi. Rather, the effect of combining the species on the mortality of G. mellonella was additive. Our results suggest that interspecific EPN communication affects not only orientation but also dispersal rate, with potential impacts on biological control and the subsequent fitness of each species.
Silicon (Si) has a physical barrier effect on plant tissues, decreasing nematode infection in different crops. Notwithstanding, research on lettuce is lacking, especially regarding the chemical mechanisms of action of this beneficial element. This study evaluated the effect of Si supply on lettuce plants infested with 0, 6000, and 12,000 eggs and second stage juveniles of Meloidogyne incognita, both in the absence and in the presence of Si (2 mM) in the nutrient solution. Silicon increased phenolic compounds and ascorbic acid, reducing M. incognita population and decreasing oxidative stress. The element also increased chlorophyll content and the quantum efficiency of photosystem II (FV/FM), favoring lettuce growth and production. The use of Si decreased the number of nematodes and affected their reproduction, decreasing the number of eggs and galls on lettuce roots. This indicates that Si may serve as a sustainable alternative for the control of M. incognita. The benefit of using Si appears to be due to the combined effect chemical action from the increase in phenolic compounds and ascorbic acid in plant tissues, improving plant physiology.
Silicon (Si) enhances rice resistance to various insect herbivores. However, the underlying mechanisms remain unclear. Whereas the salicylic acid (SA) signaling pathway plays a vital role in plant defense responses to sucking insects, its role in Si-enhanced rice resistance has not been investigated. Si transporter mutant OsLsi1 and mutants with antisense expression of ICS (as-ics) and NPR1 (as-npr1) in the SA pathway and their corresponding wild types (WT) were treated with and without Si to determine Si effects on rice resistance to brown planthopper (BPH), Nilaparvata lugens (Stål), as well as on SA accumulation, defense-related enzyme activity and gene expression. Si application significantly affected host preference of BPH, significantly reduced honeydew secretion and inhibited oviposition and hatch rate. Upon BPH infestation, SA content, transcript levels of BPH3, ICS1 and PAL4, and activities of POD, SOD, PPO and PAL were significantly higher in Si-treated than untreated plants. The defense responses were also faster. However, OsLsi1 mutant plants displayed higher susceptibility to BPH and minimal defense responses. Furthermore, simultaneous application of SA and Si in WT plants showed the highest resistance to BPH, but had no obvious effect on OsLsi1, antisense as-ics and as-npr1 plants. Our results suggest that Si enhances rice defense against the sucking insect BPH by defense priming and the Si-mediated priming involves SA signaling pathway.
The adaptation of phytophagous insects to host defense is an important aspect of plant–insect interactions. The reciprocal adaptability between specialist insects and their hosts have been adequately explored; however, the mechanisms underlying the adaptation of tephritid fruit fly specialists, a group of notorious pests worldwide, to unripen host fruits remain elusive. Here, plant metabolomes and insect transcriptomes were analyzed for the first time to explore the interaction between unripe citrus fruits and the Chinese citrus fly Bactrocera minax. Eighteen citrus secondary metabolites, mainly flavones, alkaloids and phenylpropanoids, were identified in the unripe citrus fruit metabolome, and they accumulated during larval feeding. Three detoxification genes (1 P450 gene, 2 ABCs genes) were highly expressed in B. minax larvae collected from unripe citrus fruits compared with the ones fed on artificial diets and ripe citrus fruits. Based on omics data, a novel ABC gene was screened through plant allelopathy tests, and the gene was significantly upregulated in B. minax larvae treated with defensive secondary metabolites (N-Methylcytisine, tryptamine, coixol, limonin, nomilin and quercetin), respectively; additionally, the mortality rate of the larvae reached 51% after silencing the ABC gene by RNAi technique. Overall, these results shed light on the mechanisms underlying the biological interactions between tephritid fruit fly specialists and host fruits.
In order to meet the increasing demands from an exploding human population, sustainable agriculture relies on the availability of crop varieties with high yields and optimal defenses to pests. However, ample work has suggested that domesticated plants could have reduced defenses at the expense of increased biomass or yield, and these potential trade-offs can vary among plant species and genotypes. Herbivory coping mechanisms such as tolerance and resistance can be expressed differently among plant genotypes, with variable relationships and inherent fitness costs. Knowledge of the connection between growth and defense mechanisms in cultivated plants is still limited, especially in tropical crops and is needed to guide theories on plant defenses and crop improvement efforts. Using twenty Sorghum bicolor landraces from the tropics, we evaluated genetic variation in growth and defense measures in response to herbivory from Chilo partellus, a major pest of S. bicolor. Specifically, we tested for trade-offs among tolerance and resistance and their association to growth traits. We found significant genetic differences among landraces in terms of their growth, tolerance, and constitutive resistance to herbivory. There was no apparent trade-off between tolerance and resistance, suggesting that it is possible to enhance both defense strategies in S. bicolor. There were contradictory results in terms of potential growth costs associated with constitutive and induced resistance, and tolerance to C. partellus. Landraces with higher resistance and tolerance had lower biomass, but at the same time had a higher number of stems. Future efforts should be directed at understanding the genetic source of resistance and tolerance, and their inclusion for crop improvement.
The efficacy and high specificity of the RNA interference pathway has prompted its exploration as a potential molecular management tool for many insect pests, including the destructive southern pine beetle, Dendroctonus frontalis Zimmermann, in which gene knockdown and mortality via double-stranded RNAs (dsRNAs) have already been demonstrated in the laboratory. The nucleotide sequence of dsRNAs requires an exact match of at least 16 nucleotides with the targeted messenger RNA to trigger knockdown of that gene. This allows vital genes in a target pest to be silenced and mortality induced while reducing the probability of adverse effects in nontarget organisms. However, prior to utilization in forest ecosystems, demonstration of the specificity of dsRNAs through laboratory bioassays evaluating potential nontarget effects on model insects is required for proper risk assessment analyses. Consequently, we evaluated three SPB-specific dsRNAs for lethal effects, sublethal effects (larval growth rate, adult emergence or adult fecundity), and relative gene expression in three model nontarget insects representing key functional guilds, including a predator, herbivore, and pollinator. The SPB-specific dsRNAs had no effect on survival of our nontarget insects. Additionally, no sublethal effects were found and the gene expression analyses corroborated bioinformatic analyses in finding no gene knockdown. Our findings support the high specificity of RNAi technology and provide support for its development and deployment for protection of conifer forests against SPB with minimal nontarget concerns.
Transgenic plants that express double-stranded RNA (dsRNA) targeting vital insect genes have recently emerged as a valuable new tool for pest control. In this study, tobacco plants were transformed to produce dsRNA targeting Sl 102 gene that is involved in the immune response of Spodoptera littoralis larvae, a serious lepidopteran pest of several crops. Experimental larvae reared on transgenic tobacco lines showed (1) a strongly reduced level of Sl 102 transcripts, which was positively associated with food consumption; (2) a substantial impairment of the encapsulation response mediated by hemocytes; and (3) a marked increase in the susceptibility to Xentari™, a Bacillus thuringiensis -based insecticide. Importantly, this approach may allow a reduction in the doses of B. thuringiensis used for field applications and enhance its killing activity on mature larvae. The results obtained thus support the use of immunosuppressive RNAi plants to enhance the performance of microbial insecticides on lepidopteran larvae.
Varroa destructor is considered a major reason for high loss rate of Western honey bee ( Apis mellifera ) colonies. To prevent colony losses caused by V. destructor, it is necessary to actively manage the mite population. Beekeepers, particularly commercial beekeepers, have few alternative treatments other than synthetic acaricides to control the parasite, resulting in intensive treatment regimens that led to the evolution of resistance in mite populations. To investigate the mechanism of the resistance to amitraz detected in V. destructor mites from French and U.S. apiaries, we identified and characterized octopamine and tyramine receptors (the known targets of amitraz) in this species. The comparison of sequences obtained from mites collected from different apiaries with different treatment regimens, showed that the amino acid substitutions N87S or Y215H in the OctβR were associated with treatment failures reported in French or U.S. apiaries, respectively. Based on our findings, we have developed and tested two high throughput diagnostic assays based on TaqMan technology able to accurately detect mites carrying the mutations in this receptor. This valuable information may be of help for beekeepers when selecting the most suitable acaricide to manage V. destructor .
The tetraploid domesticated emmer wheat, Triticum turgidum L. subsp. dicoccon, expresses α-amylase protein inhibitors of varying sizes and assemblies, i.e. dimers and heterotetramers of polypeptide chains of about 12–15 kDa. Although genetic studies have shown the presence of coding sequences for monomeric inhibitors in tetraploid wheat and whole-seeds proteomic studies have indicated their expression, until now there has been no isolation nor characterization of such proteins. In this study, for the first time, an inhibitory protein of human salivary and Tenebrio molitor, Tribolium castaneum, Sitophilus oryzae, and Ephestia kuehniella α-amylase (EC 126.96.36.199), was isolated from whole flour extracts of a tetraploid wheat and its sequence was determined by MS analyses. The inhibitor acts more strongly against coleopteran α-amylases than against those from E. kuheniella and human saliva. The inhibitory characteristics along with the putative sequence determination reported in the present study, allows for further evaluation towards its utilization as a post-harvest protection strategy against insect infestations.
Our aim was to perform a qualitative review and a meta-analysis with 57 scientific articles (108 assays) published from 1 January 2000 to 31 June 2021 dealing with fumigant toxicity of essential oils (EOs) against Sitophilus zeamais. The studies were obtained from four electronic databases: Web of Science, SCOPUS, PubMed, and Google Scholar. The survey comprised 107 plant species belonging to 26 different families. Lethal concentration values (LC50) of EOs were included in a random-effect model, and two subgroups were defined: “until 24 h” and “more than 24 h”. The EOs more frequently evaluated were those belonging to Lamiaceae (20.18%), Asteraceae (17.43%), Apiaceae (9.17%), and Rutaceae (6.42%). The global mean value was 21.37 (CI95 16.84–27.12), while the summary mean values of the subgroups were 41.45 (CI95 31.10–55.26) for “until 24 h” and 8.45 (CI95 5.72–12.48) for “more than 24 h”. Most species belonging to Apiaceae, Lamiaceae, Asteraceae, and Schisandraceae reported the highest insecticidal effects with mean values that ranged from 1.31 to 27.39 for “until 24 h” and from 0.57 to 5.31 for “more than 24 h”. Additionally, the toxicity of the most effective EOs was discussed by addressing their chemical composition and their major pure compounds chemical features.
The question of whether food webs are resource or predation controlled is crucial for the development of sustainable IPM strategies in agriculture. Many IPM studies focus on top–down control, while little is known about bottom–up effects. Here, we unravelled the bottom–up interactions between rosy apple aphid (RAA) Dysaphis plantaginea and 13 apple cultivars in north-eastern Belgium. Population dynamics, apple leaf damage, preference and performance measurements were used to determine the interactions between RAA and apple cultivars. Seasonal abundances and RAA-infested shoots were significantly affected by the cultivar. The cultivars Fuji, Granny Smith, Jonagold and Cripps Pink harboured clearly higher numbers of aphids compared to other cultivars, especially Red Delicious. Regarding leaf damage degree, Fuji was significantly the most impacted, while the lowest damage was recorded on Red Delicious. The potential apparent competition among apple cultivars was evaluated using RAA overlap diagrams. By acting as a potential source of RAA, a particular cultivar can considerably affect other nearby cultivars. In host selection bioassays, significant differences in the choice behaviour of RAA were found in the laboratory for different apple cultivars. Other important findings from the reproduction–offspring performance bioassays revealed that while Fuji stimulated high production of nymphs, their development remained retarded on Fuji, compared to especially Boskoop on which significantly lower numbers of nymphs occurred. Our study provides a promising insight into the importance of studying apple–RAA interactions within an eco-friendly RAA management tactic.
Evolution of the spread strategies of plant pathogens may be described using the vector manipulation hypothesis (VMH), which posits that pathogens can enhance their transmission to new host plants through their effects on mobile vectors. Barley yellow dwarf virus (BYDV) transmitted by aphid vectors in wheat has become increasingly important as a model pathosystem. However, the role of alate aphids in virus spread has attracted little attention although the migratory morph is a key vector for the long-distance dispersal of plant pathogens. Herein, we first examined the selection preferences of alate or aptera morphs of the vector Schizaphis graminum for healthy/mock-inoculated/BYDV-infected wheat plants and then identified possible volatile components that influenced alate S. graminum selection behavior. The results showed that noninfective S. graminum (either alate or aptera) mainly tended to select BYDV-infected wheat while infective S. graminum (only aptera) preferentially selected noninfected wheat. In addition, we found that the BYDV-infected plants showed significant differences in the content and quantity of volatiles compared with healthy or mock-inoculated wheat plants and that the increased volatiles (trans-2-hexen-1-al or decanal) released by BYDV-infected plants may play a critical role in attracting noninfective alate aphids in a concentration-dependent manner. These findings describe a novel mechanism by which the volatile profiles released by virus-infected plants may influence alate aphid colonization preference, providing further or new evidences for the VMH. This study extends our knowledge base on plant virus transmission to new host plants with potential ramifications for the integrated management of both the vector and disease.
Bemisia tabaci (Gennadius), commonly known as whitefly or sweet potato whitefly, causes feeding-related injuries to plants, and transmits more than 200 different plant viruses, including Tomato chlorosis virus (ToCV). Control of B. tabaci is therefore one of the key measures in the comprehensive prevention and control of ToCV outbreak in tomato fields. Many insects rely on the hydrolysis of trehalose, broken down by the enzyme trehalase, to power their flight and other life-sustaining activities. B. tabaci encodes just one trehalase, making it an attractive target. In this study, the mechanism underlying the involvement of trehalase in the transmission of ToCV by B. tabaci was investigated. Also, the effect of the trehalase inhibitor, validamycin, on ToCV transmission was assessed. Our results showed that trehalase activity was upregulated in B. tabaci fed on ToCV-infected tomato plants. Treating B. tabaci with validamycin decreased the trehalase activity, and significantly reduced its transmission of ToCV. Validamycin treatment also inhibited the flight and feeding ability of B. tabaci. These results indicate that proper function of trehalase is required by whitefly to transmit ToCV with high efficiency. These provides an important theoretical basis for targeting whitefly trehalase as one way to control ToCV transmission.
The invasive, Halyomorpha halys (Hemiptera: Pentatomidae), is a severe economic insect pest native to East Asia. A strong effort has been made to identify natural egg parasitoids of H. halys in invaded regions, but parasitism rates reported from these studies have been inconsequentially low. To determine the species composition, phenology, and efficiency of egg parasitoids in the native region of H. halys, we deployed fresh and frozen sentinel H. halys egg masses from March through December in Kyoto, Japan. Our findings provide valuable insights on the abundance and parasitism rates of native H. halys parasitoids in Japan. A total of seven parasitoid species emerged from the sentinel egg masses, but Trissolcus japonicus had the highest parasitism rate of all parasitoids recovered (84% on fresh egg masses) and maintained the largest portion of the total parasitoid species composition (60% on fresh egg masses). The early season parasitoid community in Kyoto, Japan, is dominated by T. japonicus, with the first parasitism activity occurring in March. Throughout the course of the field study, T. japonicus also sustained a significantly higher parasitism rate on fresh H. halys eggs than frozen. The results from this research help expand the understanding of parasitoids in the native region of H. halys and hold importance for the future development of biological control programs against this invasive pest.
Successful management of invasive forest pests with sustainable approaches, such as biological control, is critical to the restoration of the affected or damaged forest ecosystems. Several parasitoids introduced from Northeast Asia were released between 2015 and 2017 in several northeastern states of the USA for biocontrol of the invasive emerald ash borer (EAB), Agrilus planipennis. Using life tables to estimate the pest population growth rate, we evaluated the impact of two introduced parasitoids (Spathius galinae and Tetrastichus planipennisi) on EAB population dynamics in five ash-dominated hardwood forests in three Northeastern U.S states. We observed ~ 76% decrease in average densities of live EAB larvae to a low density (< 7 live larvae per m² of tree phloem) from 2015 to 2020. This reduction in pest density was driven primarily by the significant increase in parasitism rates (from 35 to 78%) by S. galinae, along with low-to-moderate levels of mortality from local generalist natural enemies, such as woodpeckers. Spathius galinae alone caused a 31–57% reduction in the net pest population growth rate from 2018 to 2020. These findings demonstrate that in the recently invaded ash forests in the Northeastern USA, timely introduction of specialized natural enemies, such as S. galinae, along with local generalist natural enemies, may significantly suppress the invasive pest populations to low densities, allowing surviving trees to recover.
The fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), is a major pest of maize crops and others row crops on the American continent, and this pest has spread to Africa and Asia. Such lepidopteran pest presents resistant populations to synthetic insecticides and to Bacillus thuringiensis (Bt) toxins and, consequently, new (bio) insecticides with distinct modes of action are required. In order to search for derivatives from Solanaceae as a potential source of bioactive compounds, a screening of 38 ethanolic extracts were prepared from 25 Solanaceae species. Using dietary exposure assessment, the ethanolic extracts from leaves of Acnistus arborescens (L.) Schltdl. and Datura stramonium L. were the most promising derivatives. A bioguided fractionation was performed with both plant species. The A. arborescens dichloromethane fraction was the most active, causing sublethal (growth inhibition) and lethal toxicity. Thus, this fraction was submitted to another fractionation procedure resulting in three subfractions (dichloromethane, ethyl acetate and methanol) that were tested against S. frugiperda caterpillars. All subfractions lead to significant sublethal effects, however, without significant mortality. The chemical diversity in the subfractions of A. arborescens was assessed through untargeted approaches, such as molecular networking and the in silico annotation tool NAP, by which two withanolides glycosides were annotated: (22R)-1-Oxo-3beta-(beta-D-glucopyranosyloxy)-14,20,22,27-tetrahydroxyergosta-5,24-diene-26-oic acid delta-lactone and withanoside XI. Therefore, derivatives of Solanaceae present promising compounds that may be useful in the framework of S. frugiperda integrated pest management. In addition, metabolomics is an innovative alternative and powerful approach to facilitate the putative identification of compounds in studies of natural products.
Bemisia tabaci is an important pest affecting agricultural and horticultural crops worldwide and comprises a complex of cryptic species. In China, the introduction of the two invasive cryptic species, Middle East-Asia Minor 1 (MEAM1) and Mediterranean (MED), has considerably affected the ecological niche of the native cryptic species. Based on occurrence records obtained through field surveys and high-resolution environmental data, using maximum entropy modelling, we established ecological niche models to predict the distribution of invasive and native cryptic species of B. tabaci in China and identified the differences in ecological niches. The results showed that the distribution range and niche breadth of the invasive cryptic species exceed that of the native cryptic species in the order of MED > MEAM1 > China1 > Asia1. There are different degrees of niche overlap and range overlap between cryptic species. Moreover, the important environmental variables affecting their distribution were different, as well as their response and adaptation to most environmental variables. Our results suggest that the B. tabaci species complex occupies a complex ecological niche in China. The findings improve our understanding of the ecological characteristics of B. tabaci species complex, which will be useful in the development of prevention and control strategies for this pest in China.
The fall armyworm (FAW), Spodoptera frugiperda, is a polyphagous insect pest feeding on many host plants, including some major crops such as corn and rice. This pest has also developed resistance to many insecticides. Recent genome and transcriptome sequencing efforts identified 117–425 P450 genes in the FAW, but their function in detoxifying plant toxins and insecticides is largely unknown. This study found that a P450 gene, SfCYP321A8, is upregulated in the first instar FAW larvae fed on deltamethrin. A transgenic FAW overexpressing SfCYP321A8 was produced to investigate its function in deltamethrin resistance. Transgenic FAW expressing the gene coding for a P450 known to metabolize deltamethrin in Tribolium castaneum, TcCYP6BQ9, was also produced. P450 genes are highly expressed in different tissues of transgenic larvae. The P450 activity in the midgut and fat body of both transgenic FAW lines is significantly higher than in wild-type larvae. Deltamethrin bioassays showed that the transgenic larvae expressing SfCYP321A8 or TcCYP6BQ9 are 10.3- or 15.3-fold more tolerant, respectively, than the wild-type larvae. These studies report on the production of FAW transgenic lines expressing P450 genes and show that SfCYP321A8 contributes to deltamethrin resistance in FAW. The transformation methods developed could be used in functional genomics studies in FAW and other lepidopteran pests.
Insecticide resistance survey is an in-situ biomonitoring method to assess potential impact of pesticides that exhibit direct economic consequences when leading to control failure of insect pest species. Nonetheless, the latter phenomenon is frequently neglected. Their spatial dependence and mapping are also seldom considered and when complexes of related pest species are involved, such as the rice stink bugs from the Neotropics, Oebalus poecilus, and O. ypsilongriseus, the scenario is even worst. Insecticide use is common against both species, particularly with the neonicotinoid thiamethoxam, and despite suspicion of a shift in O. poecilus historical dominance and complaints of control failure, the role of this insecticide in this context was never tested. Thus, we screened populations from both species for thiamethoxam resistance within rice fields from central Brazil. The levels of thiamethoxam resistance and control failure likelihood were recorded and their spatial dependence was tested and geographically mapped. The thiamethoxam potency was similar between species, which also exhibited overlapping levels of resistance. Thus, this insecticide does not seem involved in eventual shifts in species dominance and the occurrence of O. ypsilongriseus is frequent. Thiamethoxam resistance was detected in both species, nearly half of the populations of O. poecilus and about a third of O. ypsilongriseus, but at low levels (< ten-fold). As a consequence, the risk of control failure with thiamethoxam was also low. Spatial dependence was significant for both species and phenomena (i.e., thiamethoxam resistance and control failure), prevailing in about the same area and likely reflecting the local pattern of insecticide use.
The tomato borer Tuta absoluta is a major pest of tomato mainly controlled by chemical insecticides. However, development of resistance to specific chemical classes has made control of the pest extremely difficult. Emamectin benzoate belongs to the avermectin mode of action and to date, low or no resistance levels against this insecticide have been documented. Recently, reduced efficacy of emamectin benzoate was documented, in a field population from Crete (ninefold resistant ratio (RR)). Subsequent laboratory selections with emamectin benzoate for eight sequential generations resulted in an increase of the RR to 60-fold, the highest resistance level reported to the particular insecticide. Hereby, we are presenting the characterization of emamectin benzoate resistance in T. absoluta. Sequencing of the GluCl and GABA receptor (rdl) genes, the molecular targets of emamectin benzoate indicted absence of non-synonymous SNPs. The use of known enzyme inhibitors (PBO, DEF and DEM) revealed that P450s partially synergized emamectin benzoate resistance, suggesting potential implication of metabolic resistance. RNAseq approach was used to identify differentially expressed genes, from emamectin benzoate resistant and susceptible T. absoluta populations. Twelve libraries were sequenced using the Illumina platform, which generated 81 Gbp, thus substantially increasing the number of publicly available genomic resources for this species. The de novo transcriptome assembly consisted of 549,601 contigs, grouped in 233,453 unigenes. Differential expression analysis and qPCR validation revealed over-expression of one unigene similar to cytochrome P450 (Clan 4) potentially implicated in emamectin benzoate resistance, supporting further the involvement of P450s in the observed resistance phenotype.
Termite bait products that contain chitin synthesis inhibitors (CSIs) protect structures from subterranean termites via colony elimination. A hallmark of CSI baits is their dose-independent lethal time, as workers exposed to a CSI do not die until they initiate the molting process. Due to this mode of action and termite behaviors such as trophallaxis and cannibalism, a relatively small quantity of ingested CSI can spread throughout an entire colony before secondary repellency or avoidance behaviors occur, ultimately resulting in total colony elimination. In the field, only a portion of a subterranean termite colony actively forages upon a CSI bait at any given time, suggesting that only a relatively small proportion of workers may need to feed upon a CSI bait for a colony to be eliminated. In the present study, we used varying proportions of workers from whole four-year-old laboratory-reared Coptotermes gestroi (Wasmann) colonies (~ 62,500 termites/colony on average) to determine what proportion of workers need to feed upon a CSI bait in order to achieve colony elimination. A range of 0% (control), 0.5%, 1%, 2.5%, and 5% of the total worker population of colonies was allowed to feed on a formulated 0.5% noviflumuron bait for five days before being returned to their colonies. Colony elimination was observed for all 5%-fed and four out of six 2.5%-fed colonies by 107 days after CSI exposure. Our results confirm that only a small subset of the worker population of a colony must feed upon a CSI bait to achieve subterranean termite colony elimination.
Native to Southeastern Asia, the ambrosia beetle Xylosandrus compactus is invasive worldwide. Its invasion is favoured by its cryptic lifestyle, symbiosis with a fungus that facilitates a broad range of host plants, and predominant sib-mating reproduction. X. compactus invaded Africa more than a century ago and the Americas and Pacific Islands in the middle of the twentieth century. It was not detected in Europe before 2011, when it was first reported in Italy before quickly spreading to France, Greece and Spain. Despite the negative environmental, agricultural and economic consequences of the invasion of X. compactus, its invasion history and main pathways remain poorly documented. We used COI and RAD sequencing to (i) characterise the worldwide genetic structure of the species, (ii) disentangle the origin(s) of the non-native populations on the three invaded continents and (iii) analyse the genetic diversity and pathways within each invaded region. Three mitochondrial lineages were identified in the native range. Populations invading Europe and the American-Pacific region originated from the first lineage and were only slightly genetically differentiated at nuclear SNP markers, suggesting independent introductions from close sources in or near Shanghai, ca. 60 years apart. Populations invading Africa originated from the second lineage, likely from India or Vietnam.
The tomato red spider mite, TRSM, Tetranychus evansi Baker & Pritchard (Acari: Tetranychidae), is an invasive tomato pest in several countries, with potential to reduce yield by up to 90% in Africa. Solanum habrochaites, access PI 134417 is a wild tomato genotype resistant to several arthropod pests, including TRSM. There is an interest in increasing the resistance of a tomato genotype (Solanum lycopersicum cv. TLCV15) widely cultivated by smallholder western African farmers to TRSM, through interspecific crossings with that wild genotype. For this purpose, after obtaining the F1 progeny and as well as F2 (SPJ-10-2017) and BC1 back-crossed (SPJ-05-2018) genotypes selected for high glandular trichome densities, we characterized their resistance level to TRSM. We quantified the types and densities of trichomes on the abaxial surface of their leaflets, and examined the subsequent bottom-up effects of these progeny plants attributes on behaviour and demographic parameters of the mite. Our results showed that the densities of glandular trichomes inherited from the resistant genotype (PI 134417) by the progenies were highly variable, with types I, IV and VI being the most prevalent. The progeny SPJ-10-2017 was classified as resistant, while the progenies F1 and SPJ-05-2018 were classified as partially resistant. These findings constitute one of the first steps towards advancing breeding programs in African countries to obtain tomato genotypes resistant to TRSM, targeting more sustainable production.
We evaluated the lethal and sublethal effects of azoxystrobin, cyhalofop-butyl, and thiamethoxam on Telenomus podisi after spraying rice plants in a greenhouse, as well as the degradation kinetics of these compounds over time. Pesticides were sprayed at 50 and 100% of the maximum field recommended concentration for the crop (MFRC). At 0, 5, 10, and 20 days after application of the treatments (DAAT), T. podisi was exposed to leaves containing dry pesticide residues. On these same dates, rice leaves from each treatment were collected for determination of pesticide residues by UHPLC–MS/MS. Based on the results for mortality, parasitism, emergence, and sex ratio of T. podisi, the effects were grouped using a reduction coefficient (Ex) and classified according to the scale of the International Organization for Biological and Integrated Control (IOBC). The fungicide azoxystrobin (at 50 and 100% MFRC) was the only one classified as harmless (Class 1). The herbicide cyhalofop-butyl was classified as slightly harmful (Class 2) to T. podisi until 5 DAAT. The insecticide thiamethoxam (50 and 100% MFRC), up to 5 DAAT, was classified as harmful (Class 4) on T. podisi. Regarding residue, the initial concentrations (0 DAAT) of azoxystrobin, cyhalofop-butyl, and thiamethoxam at 100% MFRC in rice leaves were 102.14, 210.09, and 36.93 mg kg⁻¹, respectively. At 50% MFRC, initial waste was approximately half that extracted at 100% MFRC. The estimated half-lives (DT50) were approximately 17, 4, and 5 days for azoxystrobin, cyhalofop-butyl, and thiamethoxam, respectively. Furthermore, we found a positive correlation between effects and residues.
Herbivores select host plants depending on plant quality and the presence of predators and competitors. Competing herbivores change host plant quantity through consumption, but they can also change plant quality through induction of plant defences, and this affects the performance of herbivores that arrive later on the plant. Some herbivores, such as the spider mite Tetranychus evansi , do not induce, but suppress plant defences, and later-arriving herbivores can profit from this suppression. It has been suggested that the dense web produced by this spider mite serves to prevent other herbivores to settle on the plant and benefit from the suppressed defences. Here, we confirmed this by studying the preference and performance of the whitefly Bemisia tabaci , a generalist herbivorous pest. To disentangle the effects through changes in plant defences from the effects of spider-mite web, we included treatments with a strain of the closely-related web-producing spider mite T. urticae , which induces plant defences. Whiteflies did perform worse on plants with defences induced by T. urticae , but, in contrast to other herbivores, did not perform better on plants with defences suppressed by T. evansi . Moreover, the web of both spider mites reduced the juvenile survival of whiteflies, and whiteflies avoided plants that were covered with web. Hence, whitefly performance was not only affected by plant quality and induced plant defences, but also through the web produced by spider mites, which thus serves to protect against potential competitors, especially when these could profit from the suppression of plant defences by the mites.
The common green lacewing Chrysoperla carnea (Neuroptera), also called the aphid lion, is an important predator of pest species, especially aphids that cause serious damage in many crops in agriculture. Neuropeptides are involved in regulating various physiological processes in insects. However, there have not been many studies on the neuropeptides found in C. carnea. This study aimed to assemble and define a whole body- and head-specific transcriptome of C. carnea. Interestingly, we found 41 candidate neuropeptide genes to encode precursors, but 10 neuropeptide genes were not found, including kinin. Based on this original hypothesis that this important neuropeptide was lost during evolution in this important natural enemy, it will lose its effect when we expose C. carnea to kinin neuropeptide analogue. Therefore, we tested three kinin analogues 1728, 2460 and 2139, and assessed their effect on the survival of the important green-peach aphid (Myzus persicae) via topical application. We found that the 2460 analogue [HCA-R(Aib)WGa] effectively controlled aphids, leading to 46% mortality within 5 days post-exposure. In contrast, 2460 showed no significant lethal or sublethal effects on survival, food intake and weight increase, in the beneficial insect C. carnea. In conclusion, this work suggests that kinin analogues may offer biosafe insecticide compounds, and in turn promote the development of more biosafe and sustainable integrated pest management (IPM) pest control strategies that are based on the combination of peptide analogues and natural enemy insects.
Even though the effects of insect pests on global agricultural productivity are well recognised, little is known about movement and dispersal of many species, especially in the context of global warming. This work evaluates how temperature and light conditions affect different movement metrics and the feeding rate of the large lupine beetle, an agricultural pest responsible for widespread damage in leguminous crops. By using video recordings, the movement of 384 beetles was digitally analysed under six different temperatures and light conditions in the laboratory. Bayesian linear mixed-effect models were used to analyse the data. Furthermore, the effects of temperature on the daily diffusion coefficient of beetles were estimated by using hidden Markov models and random walk simulations. Results of this work show that temperature, light conditions, and beetles’ weight were the main factors affecting the flight probability, displacement, time being active and the speed of beetles. Significant variations were also observed in all evaluated metrics. On average, beetles exposed to light conditions and higher temperatures had higher mean speed and flight probability. However, beetles tended to stay more active at higher temperatures and less active at intermediate temperatures, around 20 °C. Therefore, both the diffusion coefficient and displacement of beetles were lower at intermediate temperatures. These results show that the movement behaviour and feeding rates of beetles can present different relationships in the function of temperature. It also shows that using a single diffusion coefficient for insects in spatially explicit models may lead to over- or underestimation of pest spread.
Camphor oil (EO) and its main component (i.e. d-camphor) form specific terpenoid defences in camphor trees, Cinnamomum camphora. However, an emerging insect pest, Pagiophloeus tsushimanus (Coleoptera: Curculionidae) has recently caused serious damage to this intractable plant species, which is largely elusive. To investigate the mechanism underlying the tolerance of this weevil to host-specific terpenoid defences, we carried out the bioassays, RNA-seq, and RT-qPCR analysis based on a simulated diet environment with EO or d-camphor exposure. First, a hormetic response (a highly generalized dose–response phenomenon in toxicology) in the larval overall performance was observed in terpenoid-feeding individuals. Then, genes encoding cytochrome P450 (CYP450) and cuticular protein (CP) were induced by both EO and d-camphor exposures using comparative transcriptome, suggesting that this weevil could deploy the dual mechanism (i.e. CYP450-mediated metabolic resistance and CP-mediated cuticular resistance) to counter host terpenoid defences. Furthermore, temporal expression of CYP450 and CP genes under a low dose of d-camphor exposure indicated that there was a trade-off relationship between the inductions of CYP450 and CP genes. We speculate that the dual mechanism of terpenoid tolerance in this specialist is an essential precondition for the hormetic response in larval growth and development, ultimately contributing to its successful colonization on camphor trees. Additionally, we found a few genes related to glucose transport, juvenile hormone, and odorant binding were fine-tuned under terpenoid exposures. Taken together, our study will open new avenues for understanding insect-plant coevolutionary adaptation and developing durable control strategies for this insect pest.
Several biological control agents of the hemipteran insect families Miridae, Anthocoridae and Pentatomidae, as well as mites of the family Phytoseiidae are known as zoophytophagous predators, a subset of omnivores, which are primarily predaceous but also feed on plants. It has been recently demonstrated that zoophytophagous predators are capable of inducing defenses in plants through their phytophagy. Despite the vast fundamental knowledge on plant defense mechanisms in response to herbivores, our understanding of defense induction by zoophytophagous predators and applied implications is relatively poor. In this review, we present the physiological basis of the defense mechanisms that these predators activate in plants. Current knowledge on zoophytophagous predator-induced plant defenses is summarized by groups and species for the predators of economic importance. Within each group, feeding habits and the effects of their induced-plant defenses on pests and natural enemies are detailed. Also, the ecological implications of how the induction of defenses mediated by zoophytophagous predators can interact with other plant interactors such as beneficial soil microorganisms and plant viruses are addressed. Based on the above, we propose three approaches to exploit zoophytophagous predator-induced defenses in crop protection and to guide future research. These include using predators as vaccination agents, employing biotechnological approaches, as well as applying elicitors to elicit/mimic predator-induced defenses.
Aphids are a major group of crop pests, which directly feed on phloem and indirectly transmit plant virus. The entomopathogenic fungi are essential members of green pest control strategies, and insecticidal RNAi is considered as a new generation of biopesticides. However, the effects of combining entomopathogenic fungus and RNAi-based biopesticides for aphid control are unknown. Here, the responsive genes of Acyrthosiphon pisum were screened from the transcriptomes upon spraying of Beauveria bassiana Bb07 strain (hereafter referred to Bb07). Subsequently, six candidate genes, Ap4714, Ap15782, Ap20844, Ap14741, Ap15105 and Ap16968, were targeted by spray-based RNAi, which produced a range of 20.0, 58.0, 44.0, 27.0, 52.0 and 24.0% gene silencing, respectively. Silencing of single-target (Ap4714, Ap15782, and Ap20844) resulted in increased virulence of Bb07 to Ac. pisum. Importantly, the mortality was increased to 82.1, 76.7, and 60.7% within 7 days to Ac. pisum when double-targets (Ap4714 + Ap15782, Ap4714 + Ap20844 and Ap15782 + Ap20844) were silenced in together with application of Bb07, respectively. This high mortality was also observed in Myzus persicae and Aphis citricidus by co-spray of the combination of dsAp4714 + dsAp15782 together with Bb07. In together, this study demonstrates the potential of a combination of RNAi- and entomopathogenic fungus-based technologies to control aphids, thereby reducing application of chemical pesticides.