Article

Oviposition Behavior and Development of Aster Leafhoppers (Hemiptera: Cicadellidae) on Selected Host Plants From the Canadian Prairies

Article

Oviposition Behavior and Development of Aster Leafhoppers (Hemiptera: Cicadellidae) on Selected Host Plants From the Canadian Prairies

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Abstract

Some plant pathogens are capable of manipulating their insect vectors and plant hosts in a way that disease transmission is enhanced. Aster leafhopper (Macrosteles quadrilineatus Forbes) (Hemiptera: Cicadellidae) is the main vector of Aster Yellows Phytoplasma (Candidatus Phytoplasma asteris) in the Canadian Prairies, which causes Aster Yellows (AY) disease in over 300 plant species including cereals and oilseeds. However, little is known about the host range of Aster leafhoppers or their host-choice selection behavior in this geographical region. Several crop and noncrop species commonly found in the Canadian Prairies were evaluated as food and reproductive hosts for Aster leafhoppers through no-choice bioassays. To study possible effects of pathogen infection, AY-uninfected and AY-infected insects were used. Cereals and some noncrops like fleabane were suitable reproductive hosts for Aster leafhoppers, with numbers of offspring observed in treatments using both AY-uninfected and AY-infected insects, suggesting an egg-laying preference on these plant species. Development was similar across the different plant species, except for canola and sowthistle, where growth indexes were lower. Sex-ratios of Aster leafhopper adults did not differ among the plant species or with respect to AY infection. Potential fecundity differed across plant species and was affected by the infection status of the insect. These findings have implications for AY epidemiology and suggest that while cereals can be suitable host plants for Aster leafhopper oviposition and development, some noncrop species could act as alternate hosts for leafhoppers that migrate into the Canadian Prairies before emergence of cereal and canola crops.

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... In most years, Aster Yellows (AY) incidence and associated yield losses are minimal yet outbreaks of this disease in canola fields have been documented in 2001in Canada (Alberta Agriculture and Forestry 2014. While an extensive study of the host range and plant use of Aster leafhoppers in the Canadian Prairies exists (Romero et al. 2020), no complementary studies examining host preferences for these species have been performed. Aster leafhoppers are migratory and arrive on wind currents originating in the southern United States (Nichiporik 1965, Olivier et al. 2009). ...
... In this study, we examined the settling behavior of Aster leafhopper adults using a two-choice bioassay approach and multiple domesticated and perennial wild plant species commonly found in the Canadian Prairies. These experiments provide complementary information to a previous characterization of the plant species under study by Romero et al. (2020) and allow for a better understanding of Aster leafhoppers´ host choice selection behavior in more complex environments where more than one plant species is available. ...
... All plants for these experiments were grown according to procedures described by Romero et al. (2020). Plants were watered every three days, with the addition of a 20-20-20 water-soluble fertilizer each time. ...
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Polyphagous insects are characterized by a broad diet comprising plant species from different taxonomic groups. Within these insects, migratory species are of particular interest, given that they encounter unpredictable environments, with abrupt spatial and temporal changes in plant availability and density. Aster leafhoppers (Hemiptera: Cicadellidae: Macrosteles quadrilineatus Forbes) arrive in the Canadian Prairies in spring and early summer and are the main vector of a prokaryotic plant pathogen known as Aster Yellows Phytoplasma (AYp) (Candidatus Phytoplasma asteris). Host choice selection behavior of Aster leafhoppers was evaluated through two-choice bioassays, using domesticated and wild plants species commonly found in the Canadian Prairies. Leaf tissues from these plants were collected and stained to quantify the number of stylet sheaths and eggs. To assess possible effects due to insect infection, two-choice bioassays were repeated using leafhoppers infected with AYp and a subset of plant species. When two domesticated or wild plant species were presented together, similar numbers of uninfected Aster leafhoppers were observed on both plant species in most combinations. In domesticated-wild plant bioassays, uninfected Aster leafhoppers preferred to settle on the domesticated species. There was little to no association between settling preferences and stylet sheath and egg counts. These findings provide a better understanding of AY epidemiology and suggest that after domesticated species germination, leafhoppers could move from nearby wild plants into the preferred cereals (Poales: Poaceae) to settle on them, influencing the risk of AYp infection in some of these species.
... For example, Romero et al. [35] found out that aster leafhoppers (Macrosteles quadrilineatus Forbes) (Hemiptera: Cicadellidae) showed different oviposition behavior when offered multiple host plant species compared to when only one host plant species was given. In a no-choice experiment, no eggs were oviposited on canola by aster leafhoppers [36], but a similar number of eggs was observed on canola as on other more suitable host plant species in a choice experiment. In addition, beet leafhoppers exhibit host plant preference [37] that may affect oviposition behavior depending on vegetation composition. ...
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Phytoplasma diseases are increasingly becoming important in vegetable crops in the Pacific Northwest. Recently, growers in the Columbia Basin and Yakima Valley experienced serious outbreaks of potato purple top disease that caused significant yield loss and a reduction in tuber processing quality. It was determined that the beet leafhopper-transmitted virescence agent (BLTVA) phytoplasma was the causal agent of the disease in the area and that this pathogen was transmitted by the beet leafhopper, Circulifer tenellus Baker (Hemiptera: Cicadellidae). To provide the most effective management of phytoplasmas, timing of insecticide applications targeted against insects vectoring these pathogens should be correlated with both insect abundance and infectivity. Beet leafhoppers were collected from a potato field and nearby weeds in Washington throughout the 2005, 2006, and 2007 growing seasons and tested for BLTVA by PCR to determine the incidence of this phytoplasma in the insects. In addition, overwintering beet leafhoppers were collected throughout Columbia Basin and Yakima Valley and tested for BLTVA to investigate if these insects might constitute a source of inoculum for this phytoplasma from one season to the next. Results showed that 29.6% of overwintering leafhoppers collected near potato fields carried the phytoplasma. BLTVA-infected leafhoppers were also found in both potatoes and nearby weedy habitats throughout the growing season. PCR testing indicated that a large proportion of beet leafhoppers invading potatoes were infected with the phytoplasma, with an average of 20.8, 34.8, and 9.2% in 2005, 2006, and 2007, respectively. Similarly, BLTVA infection rate in leafhoppers collected from weeds in the vicinity of potatoes averaged 28.3, 24.5, and 5.6% in 2005, 2006, and 2007, respectively. Information from this study will help develop action thresholds for beet leafhopper control to reduce incidence of purple top disease in potatoes.
Article
In Poland, a phytoplasma belonging to the subgroup 16SrI-B of ‘Ca. Phytoplasma asteris’ species causes disease in winter oilseed rape (Brassica napus), named rapeseed phyllody (RP). Affected plants exhibit malformations of flowers – phyllody, leading to losses in seed production. However, the potential sources of RP phytoplasma (RPp) outside oilseed rape are poorly understood. A screening survey of non-crop wild plants associated with winter oilseed rape was performed in order to identify alternative plant hosts of RPp. Nested polymerase chain reaction (PCR) and sequencing of PCR-amplified 16S rDNA fragments were employed for the detection and identification of phytoplasma strains affecting oilseed rape crops and adjacent wild plants. Phytoplasmas belonging to subgroups 16SrI-B, 16SrI-L, 16SrI-(B/L)L and 16SrI-C, as well as subgroup 16SrXII-H, were detected in non-crop plants. All investigated oilseed rapes manifesting RP disease were positive to ‘Ca. Phytoplasma asteris’ ribosomal subgroup 16SrI-B or heterogenic variant 16SrI-(B/L)L. Wild plants species were predominantly infected with the same phytoplasma subgroups as oilseed rapes. However, comparative sequence analysis revealed single nucleotide polymorphisms that indicate divergence of 16SrI-B and 16SrI-(B/L)L phytoplasma strains in non-crop species. Surprisingly, most of the weeds which tested positive for phytoplasma did not exhibit any characteristic symptoms of infection. In this study we identified for the first time perennial (Elymus repens, Lolium perenne) and annual (Echinochloa crus-galli, Polygonum aviculare, Viola arvensis, Matricaria perforata, Stelaria media) plants as asymptomatic reservoirs of RPp related strains in the winter oilseed rape agroecosystem. We also confirmed RPp related infections in diseased Apera spica-venti, Sisymbrium officinale, Matricaria discoidea, and Papaver rhoeas. These plants potentially play a significant role in RPp evolution and disease aetiology and epidemiology.
Book
Phytoplasma-associated diseases are a major limiting factor in the context of the quality and productivity of many ornamental, horticultural and other economically important agricultural crops worldwide. Annual losses due to phytoplasma diseases vary, but under pathogen-favorable conditions they have disastrous consequences for the farming community. As there is no effective cure for these diseases, the management options focus on their exclusion, minimizing their spread by insect vectors and propagation materials and on the development of host plant resistance. This book discusses the latest information on the epidemiology and management of phytoplasma-associated diseases, providing a comprehensive, up-to-date overview of distribution, occurrence and identification of the phytoplasmas, recent diagnostics approaches, transmission, losses and geographical distribution as well as management aspects.
Article
Bacteria that are vertically transmitted through female hosts and kill male hosts that inherit them were first recorded in insects during the 1950s. Recent studies have shown these "male-killers" to be diverse and have led to a reappraisal of the biology of many groups of bacteria. Rickettsia, for instance, have been regarded as human pathogens transmitted by arthropods. The finding of a male-killing Rickettsia obligately associated with an insect suggests that the genus' members may be primarily associated with arthropods and are only sometimes pathogens of vertebrates. We examined both how killing of male hosts affects the dynamics of inherited bacteria and how male-killing bacteria affect their host populations. Finally, we assessed the potential use of these microorganisms in the control of insect populations.
Article
Herbivore species sharing a host plant often compete. In this study, we show that host plant-mediated interaction between two insect herbivores – a generalist and a specialist – results in a sex ratio shift of the specialist's offspring. We studied demographic parameters of the specialist Tupiocoris notatus (Hemiptera: Miridae) when co-infesting the host plant Nicotiana attenuata (Solanaceae) with the generalist leafhopper Empoasca sp. (Hemiptera: Cicadellidae). We show that the usually female-biased sex ratio of T. notatus shifts toward a higher male proportion in the offspring on plants co-infested by Empoasca sp. This sex ratio change did not occur after oviposition, nor is it due differential mortality of female and male nymphs. Based on pyrosequencing and PCR of bacterial 16S rRNA amplicons, we concluded that sex ratio shifts were unlikely to be due to infection with Wolbachia or other known sex ratio- distorting endosymbionts. Finally, we used transgenic lines of N. attenuata to evaluate if the sex ratio shift could be mediated by changes in general or specialized host plant metabolites. We found that the sex ratio shift occurred on plants deficient in two cytokinin receptors (irCHK2/3). Thus, cytokinin-regulated traits can alter the offspring sex ratio of the specialist T. notatus.
Article
Models and empirical studies on host selection in plant-insect, algae-amphipod, host-parasite and prey-predator systems assume that oviposition preference is determined by the quality of the oviposition site for offspring development. According to the oviposition-preference-offspring-performance hypothesis, oviposition-preference hierarchy should correspond to host suitability for offspring development because females maximize their fitness by optimizing offspring performance. We show, we believe for the first time, that adult feeding site and related adult performance may explain most of the variation in adult feeding and oviposition site selection of an oligophagous grass miner, Chromatomyia nigra (Diptera). This study advances our understanding of the complex interactions between plants and herbivores because it shows that bust-preference patterns are not only shaped by the optimization of offspring performance, as previously assumed, but also by the optimization of adult performance.
Chapter
This chapter presents a phytoplasma taxonomic scheme that is based on the analysis of two evolutionary markers: the 16S ribosomal ribonucleic acid (rRNA) gene and the spacer region that separates the 16S from the 23S rRNA genes. This chapter provides an outline of the procedures that are available for phylogenetically classifying an unknown phytoplasma strain. Information presented in this chapter includes phytoplasma phylogenetic relationships based on restriction fragment length polymorphisms (RFLP) analysis and sequence analysis of the 16/23S spacer regions. Phylogenetic analyses have provided a coherent framework for the classification of diverse taxa, including the Mollicutes. Another very attractive aspect of this type of analysis is the ability to analyze these phylogenetic markers from non-culturable prokaryotes, such as plant pathogenic mycoplasma-like organisms (MLOs). There are advantages and disadvantages associated with both RFLP and sequence analysis of rDNA for classifying phytoplasmas. RFLP analysis of the polymerase chain reaction (PCR)-amplified 16S rRNA gene is a rapid method to assess the potential affinity of an unknown phytoplasma.
Article
Habitat diversification can influence the interactions of insects with plants and this can be used in agroecosystems for the management of pest populations. Plant diversification can be achieved through planting crops, such as trap crops, or by adjusting weed management. Aster leafhopper, Macrosteles quadrilineatus Forbes (Hemiptera: Cicadellidae), is a polyphagous species that uses cereals, vegetables, and weeds as host plants. The influence of weeds on M. quadrilineatus abundance was investigated experimentally in carrot [Daucus carota L. cv. Canada (Apiaceae)] field plots by adjusting the level of management of two groups of weeds (broadleaf and grass) and by comparing it to weed‐free plots. The preference of M. quadrilineatus for different cereal and weed species relative to carrots was tested in choice test assays. Habitat context influenced the abundance of M. quadrilineatus in the field experiments. The presence of border crops such as oat, rye, barley, wheat, and triticale did not significantly attract or repel this insect to carrot plots compared to the no‐border treatment. However, spelt‐bordered plots had 42% fewer M. quadrilineatus than three treatments, triticale, wheat, and barley, that had the highest insect abundance. The type of weed management affected M. quadrilineatus abundance in carrot plots, but not the frequency of herbicide application. Plots that had carrot growing with broadleaf‐weeds had about 59% fewer M. quadrilineatus compared with those growing with crabgrass or carrot alone. In the greenhouse choice tests, grasses (e.g., cereals) attracted and broadleaf‐weeds repelled M. quadrilineatus relative to carrots. In summary, carrot growers may be able to manage this pest by reducing the interaction of cereal cover crops with carrots and eliminating grassy weeds in commercial production fields.
Article
In studies of the effects of allelochemicals or other factors on the development of different insect species, comparison of growth-inhibiting activities is difficult using the parameters currently employed. We introduce two new parameters, growth index (GI) and relative growth index (RGI), which can unify the quantification of insect development. This quantification can also eliminate the effects of different growth characteristics due to the genetic differences between insect species. By measuring growth-inhibiting effects of two phytochemicals, chaparrin and chaparrinone, on the tobacco budworm,Heliothis virescens, and the beet armyworm,Spodoptera exigua, bioassay procedures and GI and RGI calculations are demonstrated.
Article
The potato/tomato psyllid, Bactericera cockerelli (Šulc) transmits the bacterium, "Candidatus (Ca.) Liberibacter solanacearum" (Lso), also known as "Ca. Liberibacter psyllaurous", which causes zebra chip disease in potato and other solanaceous crops. The authors previously showed that fecundity and nymph survival is significantly reduced in Lso-infected psyllids compared to uninfected psyllids on tomato. However, it is not known whether the level of the pathogen is correlated with concomitant reduction in fitness of the psyllid vector. Using quantitative PCR assays, Lso levels were determined in adult female founders of isofemale lines for whom several life history traits were previously recorded. Analysis of psyllid isofemale lines revealed that Lso infection levels in founders or mothers was negatively correlated with 7-day fecundity, nymph survival percentage, and number of F1 progeny including eggs, nymphs and adults. There was a significant negative density-dependent relationship between Lso level and fecundity. That is, psyllids experienced decreasing levels in fecundity with increasing bacterial titer. There was no apparent negative density-dependent relationship between Lso copies and number of nymphs, nymph survival percentage and number of adults. The negative effect of Lso on psyllid fecundity is likely due to direct effects of the bacteria on the insect host and not via the host plant. Taken together, these findings suggest that the level of Lso in its psyllid vector correlates with reduction in psyllid fitness.
Article
The association of insect herbivores with their host plants is influenced by behaviors governing acceptance of those plants for feeding and oviposition. Behavioral changes accompany and may even precede host range expansion. Characterization and quantification of specific behaviors often form the basis of studies on host plant adaptation and chemical ecology. Behavioral assays of insects are usually designed to measure attraction for feeding or oviposition in relation to their host plants or specific chemistry. We review behavioral assays of insect herbivores with host plants or the volatiles they emit, with special consideration given to design, analysis, and interpretation to maximize ecological relevance. A toolkit of robust assays can help address fundamental issues at the intersection of ecology and evolution, such as the underpinnings of plant-insect interactions and the identification of genes involved in host race formation. Expected final online publication date for the Annual Review of Entomology Volume 59 is January 07, 2014. Please see http://www.annualreviews.org/catalog/pubdates.aspx for revised estimates.
Article
Seven varieties of wheat belonging to the species Triticum aestivum L. and T. durum Desf. were exposed to viruliferous Macrosteles fascifrons (Stal) and found susceptible to a celery-infecting strain (CAYV) and a non-celery-infecting strain (NAYV) of aster yellows virus. The percentages of plants infected with CAYV and NAYV, respectively were: Thatcher 9 and 16; Selkirk 4 and 16; Cascade 10 and 50; Lemhi 10 and 24; Stewart 12 and 70; Ramsey 26 and 63; Pelissier 4 and 52. NAYV infected 42% of the plants tested whereas CAYV infected only 11%. Virus incubation in the plants ranged from 21 to 56 days. Symptoms included dwarfing, chlorotic blotching, chlorosis, necrosis and premature death. No heads developed on severely affected plants but small sterile heads with distorted awns developed on plants infected later. The virus strains could not be distinguished by their symptoms on wheat.
Article
Host-plant selection by phytophagous insects is largely determined by adult insects choosing the developmental location of offspring. Knowledge of natural selection leads to theoretical predictions about how adult behaviour might respond to host quality, the abundance of host-plants, adult egg-load, age and available search time, density-dependence, and stochastic effects. Debates about the value of simple adaptive models can only be settled by repeated testing and reformulation. The theoretical basis of adaptive host selection is quite strong, but several challenges remain. Models are lacking which are both general enough to be applicable to a wide rang of species, and easy to test. The role of variability in plant abundance and other stochastic forces requires clarification. Empirically, good field studies of the effect of host-plants on insect fitness are rare, but without them little progress can be made. The assessment of host-preference also requires attention. Quantitative tests of theory are rare, probably because general models do not encompass enough relevant natural history for each particular species. However much anecdotal and qualitative evidence seems to reflect adaptive predictions. A challenge for the future is to assess the adaptive value of particular mechanisms of host-selection, and to relate these to the predictions made in simple adaptive models.
Article
During the years 1958-1962 studies were conducted to determine the origin of populations of the six-spotted leafhopper, Macrosteles fascifrons (Stal) in a 100-squaremile area in Anoka County, Minnesota, Two sources of infestation were found: eggs produced locally, and adults entering from outlying areas, Some eggs laid in the fall overwintered, while those produced in spring and summer had short incubation periods. In 1961 there was evidence of 3 complete generations and a partial fourth. The host plants on which the leafhopper was found to reproduce arc listed, It is suggested that dispersal flights arc primarily long distance, covering large areas at a time. Local dispersal flights are probably of secondary importance. Leafhoppers originating outside the study area appeared to be more important as initial sources of inoculum than populations produced locally.
Article
When nymphs and adults of Elymana virescens (F.) were caged for 7 days on barley plants, Hordeum vulgare L. var. 'Vantage' infected with aster yellows casual agent (AYCA), 26% and 24%, respectively, of the exposed insects subsequently transmitted AYCA to barley seedlings. In comparable concurrent experiments with the aster leafhopper, Macrosteles fascifrons (Stal), 48% and 78% of the nymphal and adult groups, respectively, transmitted the causal agent. An incubation period of 39-46 days was required before 95% of the inoculative E. virescens could transmit, whereas less than 32 days were needed before 85% of the inoculative M. fascifrons transmitted. However, once the leafhoppers of both species became inoculative they were equally consistent in transmitting. When adult E. virescens and M. fascifrons were injected with an inoculum containing AYCA, 16% and 55% of the injected insects, respectively, became inoculative. The concentration of AYCA in the extracts of inoculative E. virescens was about equal to that of inoculative M. fascifrons when the extracts were prepared on the basis of leafhopper weight.
Article
A 4-year study was made of the aster leafhopper, Macrosteles fascifrons (Stål), and the overwintering host plants of aster yellows to determine reasons for sporadic outbreaks of the disease on susceptible crops grown with the aid of irrigation. This leafhopper overwinters in the egg stage in small grains; no evidence was found of a spring migration from southern overwintering areas. Although populations of the leafhopper remained fairly constant from year to year, abundance of overwintering host plants of the disease was largely dependent upon the timing and abundance of rain in late summer, autumn, and spring.
Article
A study was conducted to identify the strains of aster yellows (AY) disease present in crops of Brassica napus and B. rapa grown near Medstead, Saskatchewan. AY phytoplasma DNA was detected in midrib, stem and root tissues of several symptomless plants as well as plants exhibiting typical AY disease symptoms. Most symptomatic and symptomless, AY-infected plants produced normal-looking and misshapen seeds. However, for both Brassica species, symptomatic plants produced significantly more seeds containing phytoplasma DNA than symptomless, AY-infected plants. Also, significantly more misshapen seeds contained phytoplasma DNA than normal seeds. Phytoplasma DNA belonging to subgroups 16SrI-A and 16SrI-B was detected in symptomatic and symptomless, AY-infected plants and in seed of these plants. The new AY strain sequences were registered in Genbank. The study reports for the first time the detection of AY strains in seedling tissues of both Brassica species. The research also showed that spiral cleaning has the potential to remove seeds that contain phytoplasma DNA in B. napus.
Article
When turnip plants with 3–7 leaves were inoculated with cabbage black ringspot virus (CBRSV) on the 3rd rough-leaf, symptoms only appeared on leaves that had been less than 15 mm long at the time of inoculation, although infection decreased the area and both fresh and dry weight of all leaves. Leaves were ‘aged’ by their appearance and placed in Leaf Age Categories (LACs). Leaves with symptoms senesced (‘aged’) prematurely. CBRSV-infection of cv. Green Top White did not change the distribution of populations of Myzus persicae between LACs, but increased the proportion of the plant suitable for colonisation. All suitable LACs were quickly colonised by adult apterae and nymphs. On CBRSV-infected plants the nymphal period was shorter, F1 adults deposited larvae more frequently and the live body weight and tibial length of the F2 generation was greater, than on healthy plants. The distribution of Brevicoryne brassicae populations on cv. Green Top White differed from that of M. persicae but was also unchanged by CBRSV-infection. On healthy plants the largest colonies were on mature leaves, so that on virus-infected plants premature senescence shortened the life of the colony. On CBRSV-infected plants the nymphal period was prolonged and the live weight of F1 and F2 adult apterae was less than on healthy plants. The differences between the biology of M. persicae and B. brassicae on CBRSV-infected cv. Green Top White were associated with the accelerated senescence of CBRSV-infected leaves. The possibility that CBRSV-infection might reduce the resistance of turnips to aphid infestation was tested. M. persicae and B. brassicae were cultured on two favourable and two less favourable cultivars. No improvement in population growth rate was found when the less favourable host cultivars were infected with CBRSV, but both aphid species weighed less and/or had smaller nymphal populations on cultivars showing the severest symptoms. These results are discussed in relation to the evolution of non-persistent virus transmission by aphids.
Article
In Alberta, Canada, valerian grown for medicinal purposes and sowthistle, a common weed, showed typical aster yellows symptoms. Molecular diagnosis was made using a universal primer pair (P1 / P7) designed to amplify the entire 16S rRNA gene and the 16 / 23S intergenic spacer region in a direct polymerase chain reaction (PCR) assay. This primer pair amplified the DNA samples from valerian and sowthistle and reference controls (AY-27, CP, PWB, AY of canola, LWB). They produced the expected PCR products of 1.8 kb, which were diluted and used as templates in a nested PCR. Two primer pairs R16F2n / R2 and P3 / P7 amplified the DNA templates giving PCR products of 1.2 and 0.32 kb, respectively. No PCR product was obtained with either set of primers and DNA isolated from healthy plants. Restriction fragment length polymorphism (RFLP) was used to analyse the partial 16S rDNA sequences (1.2 kb) of all phytoplasma DNA samples after restriction with four endonucleases (AluI, HhaI, MseI and RsaI). The restriction patterns of these strains were found to be identical with the RFLP pattern of the AY phytoplasma reference control (AY-27 strain). Based on the RFLP data, the two strains are members of subgroup A of the AY 16Sr1 group. We report here the first molecular study on the association of AY phytoplasmas with valerian and sowthistle plants.
Article
Differences in the establishment of the leafhoppers Empoasca devastans and E. kerri motti on different plants are determined by an interaction of the following chief types of their responses in six main stages: (1) Orientation, (2) Feeding, (3) Metabolic utilization of the ingested food determining its nutritive value, (4) Growth, (5) Survival and egg-production, (6) Oviposition. Both the leafhoppers showed equally high attraction and proboscis response to all the six test plants, namely, Gossypium hirsutum, G. herbaceum, G. arboreum, Solanum melongena, S. tuberosum, and Ricinus communis. The quantity and nutritive value of the food ingested by E. devastans decreased in the order: G. hirsutum, S. melongena, S. tuberosum, G. herbaceum, G. arboreum, and R. communis. The growth, particularly in respect of moulting/metamorphosis to adult, also decreased in the same order except that S. melongena was superior to G. hirsutum. But, the suitability of the plants for adult survival decreased in the order: S. tuberosum, S. melongena, G. hirsutum, G. herbaceum, G. arboreum, R. communis. The egg-production and ovipositional response decreased in the order: S. melongena, G. hirsutum, S. tuberosum, G. herbaceum, G. arboreum, R. communis. The interaction of the above responses would render S. melongena most suitable for the establishment of E. devastans and the suitability of the remaining plants would decrease in the order: G. hirsutum, S. tuberosum, G. herbaceum, and G. arboreum, while R. communis would be completely unsuitable.
Article
Source areas for Six-Spotted leafhopper migrations into Manitoba are determined by wind trajectory studies and are found to be mainly in South Dakota, Nebraska and Kansas. There is a high enough frequency of southerly winds for the insects to migrate into Manitoba every spring. Attempts to correlate general weather conditions, both in southern Manitoba and in the source areas,with lettuce crop damage in Manitoba, were inconclusive.This leads to the conclusion that the intensity of aster yellows infestation in Manitoba depends on the environment experienced by the lettuce crop. Favourable meteorological conditions occurring for a few days only, at just the right time, can produce heavy infection in any year.
Article
When theory predicts which phenotypes are well adapted to a given environment, the data do not always match the predictions. Host-plant selection by herbivorous insects is one such example. Herbivorous insects often appear to make poor choices about where their offspring should develop. New evidence presented by Scheirs et al. suggests that adult insects can choose oviposition sites that enhance their own long-term fitness at the expense of their individual offspring. This suggests that herbivorous insects might be genuinely bad mothers, that host choice is nonetheless adaptive, and that theory needs to incorporate new assumptions about host effects on adult performance.