Renata C. Santos’s research while affiliated with Federal University of Minas Gerais and other places

There has been an excitement toward novel eco-friendly alternatives to pest management, particularly formulations based on essential oils (EOs). Here, the biological activity of an EO-based emulsion derived from patchouli, Pogostemon cablin, was assessed against Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), a devastating and invasive pest in tomato crops worldwide. Laboratory bioassays were carried out to determine and compare lethal doses, lethal times, oviposition of treated individuals, and oviposition of T. absoluta on treated leaves of tomato to pure patchouli essential oil or its emulsion containing 18% of oil. The LD50 were 10.06 and 2.57 µg of patchouli per mg of insect for the EO and emulsion, respectively. Oviposition was reduced in adults derived from the second instar treated with LD10 by 78.5% (EO) and 85.4% (emulsion). The EO and its emulsion conferred similar avoidance to adults when sprayed on tomato leaves. Therefore, both formulations present similar lethal and sublethal effects against T. absoluta. This study demonstrated a remarkable potential of an emulsion containing 18% of P. cablin oil to be employed for T. absoluta management on tomato crops. Further studies are needed to assess and guarantee open field applications.

Erthesina fullo (Thunberg) (Hemiptera: Pentatomidae) is an invasive pest that has recently been detected in Europe (2017) and South America (2021). Due to polyphagia and temperature adaptation, this pest has a high risk of establishing in introduced areas. However, despite recent invasion events, there are no data on potentially suitable areas for E. fullo occurrence outside its native range. In this study, we presented a model for the potential distribution of E. fullo based on the CLIMEX algorithm. We built the model using global species occurrence (1424 points), three climate scenarios (current, 2030, and 2080), and available biological data. The ecoclimate index and weekly growth index were then estimated to determine the suitability of regions in a general scenario over time. Our model shows suitable areas for E. fullo in America, Africa, Europe, and Oceania under the current climate scenario. These regions have tropical and subtropical climates. However, the suitability was reduced (-28%) in those climates under future climate scenarios while increasing in temperate regions. In addition, we found that the weekly growth index of E. fullo was positively correlated with photoperiod. Our findings can help guide future efforts to prevent potential invasion and establishment of E. fullo beyond its current range.

1. Terrestrial gastropods (slugs and snails, Mollusca: Eupulmonata) are destructive pests of brassica crops. These organisms defoliate plants and contaminate the har-vest, leading to reduced crop yield and marketability. Losses caused by molluscs have escalated in recent years in Brazil. 2. We aimed to determine the seasonal activity of gastropods in brassica fields and unravel the environmental variables associated with these dynamics. Gastropod abundance, assemblage and within-plant distribution were also compared among Brassica oleracea cultivars (broccoli, cabbage and cauliflower). 3. Mild temperatures and rainy periods were found to coincide with gastropod peaks. Regression analyses confirmed a positive association of rainfall and humidity with gastropod abundance, whereas gastropod abundance increased with decreasing temperature. Deroceras laeve (Müller) (Agriolimacidae) and Bradybaena similaris (Férussac) (Bradybaenidae) were the most constant species. Mollusc abundance and assemblage differed amid B. oleracea cultivar; cabbage had the highest abundance and its species composition differed from broccoli and cauliflower. Slugs and snails were more concentrated on lower plant portions, regardless of the cultivar. 4. Management efforts should be reinforced in mild-temperature and rainy periods to reduce damage by gastropods, and cabbage should be monitored more closely than other cultivars.

The cabbage looper, Trichoplusia ni Hübner (Lep.: Noctuidae), is a destructive pest of Brassica crops. Their larvae defoliate plants, leading to reduced crop yield. Understanding and modeling pest seasonal dynamics is central to management programs because it allows one to set up sampling and control efforts. This study aimed to train, with field-collected data, artificial neural networks (ANN) for T. ni forecasting on Brassica crops. ANNs were used due to their suitability to fit complex models with multiple predictors. Three weather variables (air temperature, rainfall, and relative humidity lagged at different intervals from the day of pest assessment) and three host plants (broccoli, cabbage, and cauliflower) along with another plant-related variable (days after transplanting) were used as input variables to build ANNs with different topologies. Two outputs (T. ni eggs or larvae) were tested to verify which one would yield more precise models. ANNs forecasting T. ni eggs performed better, based on Pearson's correlation (r v) of observed with fitted values. The winning ANN (r v = 0.706) had weather data lagged by 15 days, 2 neurons in the hidden layer, hyperbolic tangent as the activation function, and resilient propagation as the learning algorithm. Broccoli and cauliflower were the hosts with major contributions for T. ni occurrence. Rainfall was the primary environmental predictor and affected T. ni negatively. Therefore, the winning ANN may be used to forecast T. ni egg densities 15 days in advance, allowing for timely management of this pest.

Soybean (Glycine max) is the world's most cultivated legume. In recent years, the thrips Caliothrips phaseoli and Frankliniella schultzei (Thysanoptera: Thripidae) have caused >15% yield reduction in soybean crops. Conventional sampling plans serve as the starting point for the establishment of decision-making systems for integrated pest management (IPM) programs. These plans establish the sampling methodology, the number of samples, and the time and cost required. They must be simple, representative, accurate, fast, inexpensive, and suitable for different field sizes and plant growth stages. The objective of this research was to determine a conventional sampling plan to facilitate IPM of thrips in soybean crops. For this purpose, a 2-year study in 29 commercial soybean fields was performed to determined the best sampling technique, the optimal number of samples, and the time and cost requirements for fields of different sizes. Our sampling plan can be used for fields of different sizes, plants of different growth stages, and thrips infestations of different densities. It involves beating the apical part of 40 soybean plants per field on a white plastic tray. The time and cost of sampling ranged from 21 min and US $0.78 (1-ha fields) to 129 min and US$4.78 (100-ha fields). This sampling plan is feasible for incorporation into IPM programs because it is representative, accurate, fast, and inexpensive.

The diamondback moth (DBM), Plutella xylostella (Lep.: Plutellidae), causes significant losses in Brassica crops. Leaf consumption by the larvae reduces plant yield and causes the contamination of heading brassicas. Chemical control usually provides unsatisfactory results due to the quickly developed resistance of DBM populations to insecticides. Thus, natural control by biotic factors (predators, parasitoids, and entomopathogens) is crucial and should be managed upon knowledge of their role as DBM regulators. The leading mortality factors of DBM across the annual seasons in southeast Brazil were investigated by conducting 57 field life tables for 2 years. The highest and lowest total mortalities of DBM occurred in winter (99.7%) and autumn (94%). Predation was the main mortality factor in all seasons. Marginal parasitism rates were higher in spring and lower in autumn, and Oomyzus sokolowskii (Hym.: Eulophidae) accounted for almost 90% of total parasitism. The highest mortalities by rainfall were recorded in spring (44.5%), while physiological death and infection caused low mortalities (≤ 6%) throughout the seasons. In addition, models were built to investigate the main predators acting on the DBM life stages; Araneae, Brachymyrmex bruchi, and Tetramorium simillimum (Hym.: Formicidae) were the predators associated with egg/L1 predation whereas Solenopsis saevissima, T. simillimum and Camponotus spp. (Hym.: Formicidae) were the ones responsible for L4/pupa predation. The L2/L3 stage was the least affected by predation, and the final model for this stage did not include any predator. In light of these findings, habitat manipulation and insecticide selectivity are discussed as measures to preserve the main predators and parasitoid.

In this study, we evaluated the causes of mortality in immature stages of Ascia monuste orseis Godart 1918 (Lepidoptera: Pieridae) over each of four seasons, for 2 years, on an experimental cabbage plot using life tables. We addressed two key questions: (1) Do the mortality rates caused by a factor vary by season? And (2) how does the local weather contribute to such variation? We identified five causes of mortality (failure, pathogens, parasitism, predation and rainfall) that together tended to be higher during wet–warm conditions with values up to 94%. However, each cause and its mortality rate varied among seasons. Failure was observed in all stages and tended to increase during cold conditions with a negative relationship with air temperature and relative humidity and positive for precipitation. Larval and pupal predation increased during warm conditions and was positively associated with both air temperature and relative humidity. Conversely, in seasons with intense precipitation, pupal predation was reduced and had a negative relationship. Rainfall caused mortality of eggs and larvae, mostly during intense events, and egg mortality also showed a positive and significant association with precipitation. Larval parasitism was low, and pathogens were noted in larvae and pupae, but we did not find variation by season for these factors. Our results indicate that mortality caused by failure, predation and rainfall on immature stages of A. monuste orseis can vary among seasons and appear to be related to local weather. These findings improve our comprehension of how local weather affects the immature stages of a neotropical pest and the associated mortality factors.

Ascia monuste orseis Godart (Lepidoptera: Pieridae) is a neotropical butterfly distributed in South America. During the larval stage, this insect causes economic losses on Brassica crops. Wet and warm conditions are known to increase subspecies occurrence, but it remains unclear why these conditions are more suitable. In this study, we have shown that both conditions are highly favourable for A. monuste orseis. We determined the thermal requirements for immature development and then created models for A. monuste orseis occurrence using Climex algorithm. Two models were built: one for the year-round presence and other for seasonal suitability. We validated the models using subspecies occurrence records and monitoring in two Brazilian regions (Northeast and Southeast). The minimum, optimum and maximum temperature for immature development were estimated at 16.37, 29.16 and 34.95 °C, respectively. The model for year-round presence indicated tropical areas as highly suitable for A. monuste orseis occurrence (with 88% of accuracy) and the seasonal models showed unsuitable areas in some parts of South America during cold and dry periods. Such predictions were observed in the monitored areas where A. monuste orseis was not found. These results can be associated with the mortality caused by low temperature to immature stages and drought conditions that may induce adult migration to moist habitats. Thus, we suggest that A. monuste orseis occurs mainly during wet and warm seasons on Brassica crops due to deleterious effects caused by cold and dry conditions. This information can be used to improve A. monuste orseis management in Brassica crops.

Essential oils (EO’s) have been investigated as a safe alternative to pest management. The toxicity of an EO can vary due to abiotic and biotic factors. The individual compounds of different EO’s have shown promise to insect control and they may present toxicity similar to or greater than the EO’s. In this study, we determined the toxicity of Corymbia citriodora EO compounds against Ascia monuste (Linnaeus, 1764) and Plutella xylostella (Linnaeus, 1758). Citronellal, trans-caryophyllene, and citronellol (LD50 = 23.24, 24.17 and 27.84 μg/mg, respectively) were the most toxic compounds to A. monuste. On the other hand, α-pinene and β-pinene presented low toxicity to this pest. For P. xylostella, citronellol and citronellal were the most toxic compounds (LD50 = 22.36 and 25.53 μg/mg, respectively). The other compounds presented lower toxicity with similar doses. Thus, the individual compounds of C. citriodora EO can be an alternative for A. monuste and P. xylostella control.