Pseudoplusia Includens Research Articles

Spatial Associations of Key Lepidopteran Pests With Defoliation, NDVI, and Plant Height in Soybean

In soybean, Glycine max (L.) Merrill, production, losses to, and control costs for insect pests can be significant limiting factors. Although the heterogeneity of pests has typically been ignored in traditional field management practices, technological advancements have allowed for site-specific pest management systems to be developed for the precise control of pests within a field. In this study, we chose to determine how the in-field distributions of the larvae of three major lepidopteran pests [velvetbean caterpillar Anticarsia gemmatalis (Hübner) (Lepidoptera: Erebidae), soybean looper Chrysodeixis includens (Walker) (Lepidoptera: Noctuidae), and green cloverworm Hypena scabra (Lepidoptera: Erebidae) (Fabricius)] were spatially associated with defoliation, Normalized Difference Vegetation Index (NDVI), and plant height in soybean. Spatial analysis by distance indices (SADIE) of data from two South Carolina soybean fields in 2017 and 2018 revealed a limited number of spatial aggregations for insect datasets. However, 14% and 6% of paired plant-insect datasets were significantly associated or dissociated, respectively. NDVI was found to be more associated with pest distributions than soybean plant heights and defoliation estimates, and the majority of all plant-insect associations and dissociations occurred in the first 4 wk of sampling (late July-early August). If changes are to be implemented regarding how a pest is managed, critical factors explaining the spatial distribution of pests must be identified. Results from this study advocate for the relationship between early-season distributions of pests and important plant variables such as NDVI to be further investigated to better determine the strength of the correlations across years and sites.

Identification of Bacillus thuringiensis Strains for the Management of Lepidopteran Pests

Bacillus thuringiensis (Bt)-based bioinsecticides and transgenic plants expressing proteins with insecticidal activity (Cry and Vip) have been successfully used in several integrated pest management programs worldwide. Lepidoptera comprise some of the most economically important insect pests of the major agricultural crops. In this study, the toxicity of 150 Bt strains was evaluated against Helicoverpa armigera (Hübner) larvae. Eight strains (426, 520B, 1636, 1641, 1644, 1648, 1657 and 1658) showed high insecticide activity against H. armigera and were thereforetested against Anticarsia gemmatalis (Hübner), Spodoptera cosmioides (Walker), Chrysodeixis includens (Walker), and Diatraea saccharalis (Fabricius) larvae. Our results showed that most of the Bt strains were also toxic to these lepidopteran species. The biochemical and molecular analyses of these strains revealed that they had a similar protein profile; however, their cry and vip gene contents were variable. In addition, the median lethal concentration (LC50) of the selected strains indicated that the strains 1636, 1641, and 1658 were the most effective against H. armigera, showing LC50 values of 185.02, 159.44, and 192.98 ng/cm2, respectively. Our results suggest that the selected Bt strains have great potential to control the lepidopteran pests H. armigera, A. gemmatalis, D. saccharalis, S. cosmioides, and C. includes.

Large-scale assessment of lepidopteran soybean pests and efficacy of Cry1Ac soybean in Brazil

The soybean technology MON 87701 × MON 89788, expressing Cry1Ac and conferring tolerance to glyphosate, has been widely adopted in Brazil since 2013. However, pest shifts or resistance evolution could reduce the benefits of this technology. To assess Cry1Ac soybean performance and understand the composition of lepidopteran pest species attacking soybeans, we implemented large-scale sampling of larvae on commercial soybean fields during the 2019 and 2020 crop seasons to compare with data collected prior to the introduction of Cry1Ac soybeans. Chrysodeixis includens was the main lepidopteran pest in non-Bt fields. More than 98% of larvae found in Cry1Ac soybean were Spodoptera spp., although the numbers of Spodoptera were similar between Cry1Ac soybean and non-Bt fields. Cry1Ac soybean provided a high level of protection against Anticarsia gemmatalis, C. includens, Chloridea virescens and Helicoverpa spp. Significant reductions in insecticide sprays for lepidopteran control in soybean were observed from 2012 to 2019. Our study showed that C. includens and A. gemmatalis continue to be primary lepidopteran pests of soybean in Brazil and that Cry1Ac soybean continues to effectively manage the target lepidopteran pests. However, there was an increase in the relative abundance of non-target Spodoptera spp. larvae in both non-Bt and Cry1Ac soybeans.

Mixture compatibility of ChinNPV baculovirus with herbicides and fungicides used in soybean

Chrysodeixis includens Walker, 1858 (Lepidoptera: Noctuidae), commonly known as soybean looper, is one of the main pests that reduces soybean yield due to its defoliation capacity. Population outbreaks of this pest can occur in the vegetative stage of the crop, together with the occurrence of weeds or in the reproductive stage, at the same time as that of diseases. This often requires the use of pesticides against pests and weeds, or fungi at the same time. Thus, the objective of this study was to evaluate the compatibility of baculovirus ChinNPV with different synthetic chemical herbicides and fungicides used in soybean. Four bioassays were carried out, with or without the addition of ChinNPV to different herbicides and fungicides. The artificial diets were immersed in the solutions of the pesticides and their mixture and supplied to the caterpillars of C. includens, immediately and after one and two hours of mixing. The evaluation was performed by quantifying the number of dead caterpillars. The results showed that the ChinNPV baculovirus is compatible for mixing with all studied herbicides and fungicides, even after two hours of mixing. In all the studied scenarios, baculovirus mixed with chemical pesticides triggered the same mortality as sprayed with baculovirus alone, and values of over 80% mortality of C. includens have always been recorded.

Evaluation of Reference Genes and Expression Level of Genes Potentially Involved in the Mode of Action of Cry1Ac and Cry1F in a Susceptible Reference Strain of Chrysodeixis includens.

Simple SummarySoybean looper (a moth species) is a major pest of soybean plants in the American continent and its larvae need to be kept under economic damage thresholds to guarantee sustainable yields. Soybean looper control relies mostly on the use of insecticides and genetically modified crops expressing Bacillus thuringiensis (Bt) insecticidal proteins. Due to the high selection pressure exerted by these control measures, resistance has developed to different insecticides and Bt proteins. Here, we tested the basal sensitivity of a soybean looper laboratory reference strain against two insecticidal proteins and determined the level of expression of potential receptors of these proteins across all (six) larval stages. Furthermore, we identified stable reference genes across all larval stages to normalize gene expression data obtained by quantitative polymerase chain reaction (qPCR). The results presented in this communication are useful to support future studies on insecticide and insecticidal protein resistance in soybean looper.Soybean looper (SBL), Chrysodeixis includens (Walker), is one of the major lepidopteran pests of soybean in the American continent. SBL control relies mostly on the use of insecticides and genetically modified crops expressing Bacillus thuringiensis (Bt) insecticidal Cry proteins. Due to the high selection pressure exerted by these control measures, resistance has developed to different insecticides and Bt proteins. Nevertheless, studies on the mechanistic background are still scarce. Here, the susceptibility of the laboratory SBL-Benzon strain to the Bt proteins Cry1Ac and Cry1F was determined in diet overlay assays and revealed a greater activity of Cry1Ac than Cry1F, thus confirming results obtained for other sensitive SBL strains. A reference gene study across larval stages with four candidate genes revealed that RPL10 and EF1 were the most stable genes for normalization of gene expression data obtained by RT-qPCR. Finally, the basal expression levels of eight potential Bt protein receptor genes in six larval instars were analyzed, including ATP-binding cassette (ABC) transporters, alkaline phosphatase, aminopeptidases, and cadherin. The results presented here provide fundamental knowledge to support future SBL resistance studies.

Bacillus thuringiensis chimeric proteins Cry1A.2 and Cry1B.2 to control soybean lepidopteran pests: New domain combinations enhance insecticidal spectrum of activity and novel receptor contributions.

Two new chimeric Bacillus thuringiensis (Bt) proteins, Cry1A.2 and Cry1B.2, were constructed using specific domains, which provide insecticidal activity against key lepidopteran soybean pests while minimizing receptor overlaps between themselves, current, and soon to be commercialized plant incorporated protectants (PIP’s) in soybean. Results from insect diet bioassays demonstrate that the recombinant Cry1A.2 and Cry1B.2 are toxic to soybean looper (SBL) Chrysodeixis includens Walker, velvetbean caterpillar (VBC) Anticarsia gemmatalis Hubner, southern armyworm (SAW) Spodoptera eridania, and black armyworm (BLAW) Spodoptera cosmioides with LC50 values < 3,448 ng/cm2. Cry1B.2 is of moderate activity with significant mortality and stunting at > 3,448 ng/cm2, while Cry1A.2 lacks toxicity against old-world bollworm (OWB) Helicoverpa armigera. Results from disabled insecticidal protein (DIP) bioassays suggest that receptor utilization of Cry1A.2 and Cry1B.2 proteins are distinct from each other and from current, and yet to be commercially available, Bt proteins in soy such as Cry1Ac, Cry1A.105, Cry1F.842, Cry2Ab2 and Vip3A. However, as Cry1A.2 contains a domain common to at least one commercial soybean Bt protein, resistance to this common domain in a current commercial soybean Bt protein could possibly confer at least partial cross resistance to Cry1A2. Therefore, Cry1A.2 and Cry1B.2 should provide two new tools for controlling many of the major soybean insect pests described above.

Optimization of Large-Scale Production of Chrysodeixis includens nucleopolyhedrovirus for Its Use as a Biopesticide.

The baculovirus Chrysodeixis includens nucleopolyhedrovirus (ChinNPV) is pathogenic to Chrysodeixis includens (Walker) (Lepidoptera: Noctuidae) larvae, known as soybean looper, which is an important pest of soybean and bean. In this study, some parameters were tested to overcome the difficulties in the in vivo production of ChinNPV aiming to increase its use as a biopesticide. First, different combinations of larval instars (3rd and 4th instars), larval incubation temperatures (23 °C and 26 °C), and rearing densities (individually and 10 larvae/cup) were compared for larval weight and the production of occlusion bodies (OBs). A positive correlation (p< 0.001) was observed for OB production and larval weight. Fourth instar larvae produced more OBs than third instar larvae (p<0.05); however, no significant differences in OBs/larva (p>0.05) were observed for larvae kept in groups or individually. Therefore, a second assay was performed using fourth instar larvae incubated at 26 °C and two larval densities (10 larvae/cup and 40 larvae/cup). The losses of insects and OB production were evaluated as well as the influence of storage temperatures post-mortem (-20 °C, 4 °C, and 15 °C) in the OB yield. As expected, insect losses due to cannibalism or microbial contamination were greater (p<0.05) with the increase in larval density, although no difference was observed in OBs/larva (p>0.05). In addition, the storage temperature post-mortem did not influence the OB yield (p>0.05). The average production of ChinNPV OBs was 3×1010 OBs/40 larvae cup. The results demonstrate the viability of rearing C. includens in groups to enhance the mass production and reduce virus production costs.

Water Deprivation Induces Biochemical Changes Without Reduction in the Insecticidal Activity of Maize and Soybean Transgenic Plants.

Like conventional crops, transgenic plants expressing insecticidal toxins from Bacillus thuringiensis (Bt) are subjected to water deprivation. However, the effects of water deprivation over the insecticidal activity of Bt plants are not well understood. We submitted Bt maize and Bt soybean to water deprivation and evaluated biochemical stress markers and the insecticidal activity of plants against target insects. Bt maize (DAS-Ø15Ø7-1 × MON-89Ø34-3 × MON-ØØ6Ø3–6 × SYN-IR162-4) containing the PowerCore Ultra traits, Bt soybean (DAS-444Ø6-6 × DAS-81419-2) with the Conkesta E3 traits, and commercial non-Bt cultivars were cultivated and exposed to water deprivation in the greenhouse. Leaves were harvested for quantification of hydrogen peroxide, malondialdeyde (MDA), and total phenolics and insecticidal activity. Maize or soybean leaf disks were used to evaluate the insecticidal activity against, respectively, Spodoptera frugiperda (J.E Smith) and Chrysodeixis includens (Walker) neonates. Except for Bt soybean, water deprivation increased hydrogen peroxide and MDA contents in Bt and non-Bt plants. Both biochemical markers of water deficit were observed in lower concentrations in Bt plants than in non-Bt commercial cultivars. Water deprivation did not result in changes of phenolic contents in Bt and non-Bt maize. For Bt or non-Bt soybean, phenolic contents were similar despite plants being exposed or not to water deprivation. Water deprivation did not alter substantially insect survival in non-Bt maize or non-Bt soybean. Despite water deprivation-induced biochemical changes in plants, both Bt plants maintained their insecticidal activity (100% mortality) against the target species.

Distribution and invasion risk assessments of Chrysodeixis includens (Walker, [1858]) (Lepidoptera: Noctuidae) using CLIMEX.

Chrysodeixis includens is a polyphagous pest restricted to the American continent. The occurrence of C. includens is allied, among other factors, by favorable conditions such as temperature, humidity, presence of hosts, and migratory behavior. In this work, we built spatiotemporal species distribution models at continental and global levels for the distribution of C. includens using CLIMEX to determine times and regions favorable for year-round survival and migration of this species and in case of invasion on other continents to apply timely and right phytosanitary measures. Our models estimated high climate suitability for C. includens in Central and large proportions of South America throughout the year. Moreover, there is suitability for C. includens growth in all months of the year in Central and northern part of South America. In the northern hemisphere, these conditions range from April to October, while in mid-southern parts of South America, favorable periods comprise October through June. The countries with the highest suitability for C. includens outside the American continent are located on the African and Asian continents. Our results show variable climate suitability for C. includens during the year that help to understand likely migration pattern in North America. This information would direct efforts for appropriate C. includens management during warm and moist periods of the year. Furthermore, our models notify the need for the development of strategies for the inspection and interception of C. includens especially in central Africa, India, South and Southeast Asia, and Northeast Australia.

Big bats binge bad bugs: Variation in crop pest consumption by common bat species

As generalist predators, insectivorous bats exploit fluctuations in prey distribution and abundance. A more nuanced understanding of the influence of bats on arthropod pests requires documentation of the pest species bats consume and of the conditions associated with variation in rates of pest consumption. Here, we used high-throughput metabarcoding of DNA extracted from bat feces to investigate diets of 180 bats representing three Vespertilionidae species common to the southeastern US, a region dominated by agriculture and pine plantations. We detected 23 species of agricultural pests in bat diets, including pests responsible for severe economic damage, such as Helicoverpa zea, Spodoptera frugiperda, Chloridea virescens and Chrysodeixis includens. Incidence of pest consumption was high: 61% of all bats had consumed at least one agricultural pest species, with each bat consuming an average of 1.7 pest species. The likelihood of consumption of pests to row crops and the average size of pests consumed varied by bat species, with a large foliage-roosting species (Lasiurus seminolus) consuming a greater variety of pest species and pest species larger in size than smaller crevice, cavity, and cave roosting bat species (Nycticeus humeralis, Myotis austroriparius). Likelihood of pest consumption also varied among sampling periods (season) and among bats of different sizes (as reflected by wing length and mass). Overall, likelihood of pest consumption was higher in the late summer season than during spring or early summer, and higher among larger bats than smaller bats. Bat characteristics and seasonality were generally more effective than geographic features and weather conditions in predicting pest consumption patterns. Strategies for enhancing pest consumption services by bats in agroecosystems should strive to maintain and enhance diverse bat populations on a landscape scale by protecting and augmenting roost structures appropriate for each species. Our finding of widespread pest consumption by bats contributes to mounting evidence worldwide of the important role bats play in agricultural systems and highlights the value of incorporating bat conservation into integrated pest management programs globally.

Effects of intraguild interactions on Anticarsia gemmatalis and Chrysodeixis includens larval fitness and behavior in soybean.

BACKGROUNDCrop pest management requires an understanding of the complex interactions among species that potentially impact crop yield. In soybean, the velvetbean caterpillar, Anticarsia gemmatalis (Hübner), and the soybean looper, Chrysodeixis includens (Walker), are described as key pests, sharing the same feeding guild. We assessed the intraguild interactions of these species under laboratory conditions. Fitness cost study was conducted to examine the influence of competition on insect development. A video tracking system was used to evaluate behavioral parameters during larval interactions in scenarios with and without food availability.RESULTSIn the fitness cost assay, pupal weight was not significantly affected, regardless of sex. However, larval and pupal survival were influenced by the competition, especially in third versus fifth instar scenarios. We detected 40.00% cannibalism and 46.67% predation when A. gemmatalis and C. includens third instars competed with A. gemmatalis fifth instar, respectively. Distance moved, distance between larvae, body contact (food available) and frequency in food of C. includens larvae were negatively affected by interactions. Anticarsia gemmatalis larvae showed highly active behavior, moving twice or more the distance compared to C. includens larvae, and A. gemmatalis spent more time in body contact with food.CONCLUSIONOur results suggest that A. gemmatalis has a competitive advantage over C. includens. This study provides important information regarding lepidopteran behavior in soybean. We recommended that additional studies are necessary to understand the effects of interactions, especially in field conditions.© 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Thermal Requirements and Population Viability of Chrysodeixis includens (Lepidoptera: Noctuidae).

Development, mortality, fecundity, and longevity of soybean looper Chrysodeixis includens (Walker) (Lepidoptera: Noctuidae, Plusiinae) were examined at six constant temperatures (18, 22, 25, 28, 32, and 36∘C) under laboratory conditions. This set range comprises temperatures observed at soybean- and cotton-producing regions during the growing season. Complete development from egg to adult was observed from 18 to 32∘C. Linear and nonlinear models were fitted to the data to estimate thermal constants and bioclimatic thresholds. Although the development of immature stages of C. includens can be expected across broader temperature ranges, this species is meant to complete the whole cycle and recover from low densities between 19.7 and 30.0∘C. The best fitness is achieved at 25.4∘C. The results can be used to parameterize phenological or mathematical models to forecast the occurrence of different stages of C. includens in the field and help optimize the efforts to control this insect-pest.

Effect of soybean variety and systemic induction on herbivore feeding guilds

Plants are attacked by a variety of herbivores and respond with localized or systemic defenses. Plant defense against one feeding guild (e.g. chewing, piercing/sucking) may also affect alternate feeding guilds. To optimize host plant resistance, interactions between feeding guilds must be understood. Aphids are plant virus vectors whose vector efficiency can be altered by plant defenses. To determine if systemic induction influences aphid feeding behaviors related to virus transmission, three soybean varieties, Davis, Lyon, and Progeny 4906RR, were induced by subjecting plants to soybean looper (SBL) herbivory, or exogenous applications of either jasmonic acid (JA) or salicylic acid (SA). Green peach aphid (GPA) apterae feeding behavior was recorded on induced and control plants using the Electrical Penetration Graph (EPG) technique. SBL growth bioassays were used to assess systemic induction. Previous SBL herbivory reduced SBL larval weights when fed Progeny 4906RR. JA reduced larval weights on Progeny 4906RR and Davis. SA increased SBL larval weights on Lyon. SBL herbivory decreased behaviors associated with nonpersistent virus transmission in Davis and Progeny 4906RR. JA altered behaviors associated with virus transmission in Davis and increased behaviors associated with virus acquisition in Progeny 4906RR. SA delayed probing in Davis, but increased behaviors associated with virus transmission in Progeny 4906RR and Lyon. Inducing host plant resistance with JA may reduce herbivore performance and increase nonpersistent virus transmission. Previous chewing herbivory may decrease nonpersistent virus transmission by aphids but is variety dependent.

MdBVe46 is an envelope protein that is required for virion formation by Microplitis demolitor bracovirus.

Bracoviruses (BVs) are endogenized nudiviruses that braconid parasitoid wasps have coopted for functions in parasitizing hosts. Microplitis demolitor is a braconid wasp that produces Microplitis demolitor bracovirus (MdBV) and parasitizes the larval stage of the moth Chrysodeixis includens. Some BV core genes are homologs of genes also present in baculoviruses while others are only known from nudiviruses or other BVs. In this study, we had two main goals. The first was to separate MdBV virions into envelope and nucleocapsid fractions before proteomic analysis to identify core gene products that were preferentially associated with one fraction or the other. Results indicated that nearly all MdBV baculovirus-like gene products that were detected by our proteomic analysis had similar distributions to homologs in the occlusion-derived form of baculoviruses. Several core gene products unknown from baculoviruses were also identified as envelope or nucleocapsid components. Our second goal was to functionally characterize a core gene unknown from baculoviruses that was originally named HzNVorf64-like. Immunoblotting assays supported our proteomic data that identified HzNVorf64-like as an envelope protein. We thus renamed HzNVorf64-like as MdBVe46, which we further hypothesized was important for infection of C. includens. Knockdown of MdBVe46 by RNA interference (RNAi) greatly reduced transcript and protein abundance. Knockdown of MdBVe46 also altered virion morphogenesis, near-fully inhibited infection of C. includens, and significantly reduced the proportion of hosts that were successfully parasitized by M. demolitor.

Lethal and sublethal effects of Chrysodeixis includens nucleopolyhedrovirus (ChinNPV)-based biopesticide infecting different larval ages of soybean looper

ABSTRACT Laboratory studies that evaluated lethal and sublethal effects of a commercial biopesticide containing Chrysodeixis includens nucleopolyhedrovirus (ChinNPV: Baculoviridae: Alphabaculovirus) infecting different larval ages of soybean looper (SBL), Chrysodeixis includens (Walker) (Lepidoptera: Noctuidae) are presented. Larvae were infected with different concentrations of ChinNPV by droplet feeding (neonates) and diet surface spray bioassays (neonates and third instar). The following biological parameters were evaluated: larval survival at 7- and 14-d post-infection and at moth eclosion; duration of larval, pupal and larval-to-adult periods; larval and pupal weights; sex ratio; moth deformities; fecundity and fertility. A fertility life table was also developed. Results indicated that neonates of SBL did not develop into adults at the highest concentrations of ChinNPV in both bioassays methods. In contrast, a proportion of the exposed larvae survived to adulthood when exposed to the lowest concentrations (neonates) and in all concentrations tested (third instar). SBL neonates surviving exposure to estimated LC50 and LC75 concentrations (droplet feeding bioassays) had low larval weight, reduced fecundity and fertility, altered sex ratio, and produced fewer females per female. Surviving third instar SBL exposed to the highest concentrations showed low weight and sex ratio alterations. Our findings indicated that, beyond lethal effects, the commercially available baculovirus-based insecticide containing ChinNPV also had substantial sublethal effects on neonates and third instar SBL. In field conditions, these sublethal effects can potentially cause a significant impact in the local population dynamics, including reduction in numbers and infestation levels.

Associating Site Characteristics With Distributions of Pestiferous and Predaceous Arthropods in Soybean.

Although site-specific pest management has the potential to decrease control costs and environmental impact associated with traditional pest management tactics, the success of these programs relies on the accurate characterization of arthropod distributions within a crop. Because potential correlation of insect counts with remotely sensed field attribute data could help to decrease the costs associated with and need for fine-scale spatial sampling, we chose to determine which within-field variables would be informative of soybean arthropod counts in an attempt to move toward site-specific pest management in this crop. Two soybean fields were grid-sampled for pestiferous and predaceous arthropods, plant productivity estimates, and abiotic variable characterization in 2017-2018. Negative binomial, zero-inflated models were used to estimate presence and counts of soybean arthropod taxa based on normalized difference vegetation index (NDVI), soybean plant height, soil electrical conductivity (ECa), elevation, and calendar week. Among all variables, calendar week was the most reliable predictor of arthropod counts, as it was a significant predictor for a majority of all taxa. Additionally, counts for a majority of pestiferous taxa were significantly associated with distance from the field edge, elevation, soybean plant height, and NDVI. Although site-specific pest management has the potential for reduced management inputs and increased profitability over conventional management (i.e., whole-field) practices, management zones must first be clearly defined based on the within-field variability for the variables of interest. If site-specific pest management practices are to be applied in soybean, calendar week (and associated soybean phenology), soybean plant height (and associated elevation), and NDVI may be useful for describing the distributions of pests, such as kudzu bug, Megacopta cribraria (Hemiptera: Plataspidae) (Fabricius), green cloverworm, Hypena scabra (Lepidoptera: Erebidae) (Fabricius), velvetbean caterpillar, Anticarsia gemmatalis (Lepidoptera: Erebidae) (Hübner), and soybean looper, Chrysodeixis includens (Lepidoptera: Noctuidae) (Walker).

Temporal Occurrence of Plusiinae on Soybean in the Mississippi River Delta.

The subfamily Plusiinae of the moth family Noctuidae is made up 400 species worldwide. Two species of the subfamily, the soybean looper, Chrysodeixis includens (Walker), and the cabbage looper, Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae), are important defoliating insect pests of various field crops and have been the subject of previous Plusiinae surveys in the Southern U.S. Soybean fields were sampled in the Mississippi Delta from 2010 to 2012 to determine the temporal occurrence of various Plusiinae species on soybean. As in previous surveys, C. includens was the most common Plusiinae species in soybean during the 3-yr survey, especially in late season collections (July-September). Rachiplusia ou (Guenée) (Lepidoptera: Noctuidae) was the predominant species observed in early season collections (May-early July). Populations of R. ou during the first sample dates during 2010 were much higher than those observed during the other years of the survey. Only three collected larvae successfully developed into T. ni adults, one each collected during May, June, and July. Although R. ou was not commonly reported in previous studies on soybean, it occurred in low numbers during June and July during the 3-yr study. The temporal occurrence and species composition followed a predictable pattern in all 3 yr of the study.

Intraspecific variation in the Chrysodeixis includens (Walker) (Lepidoptera: Noctuidae) susceptibility to insecticides

ABSTRACT The looper caterpillar Chrysodeixis includens (Walker) is considered the main defoliating pest in soybean crops, which contributes to yield losses. Delaying its resistance to insecticides is a major challenge in its management. This study aimed to characterize the susceptibility of C. includens to flubendiamide, cyantraniliprole, spinetoram and methomyl, as well as to establish a diagnostic concentration for monitoring resistance. The insecticide was applied to the surface of the artificial diet. For the dose-response curve, concentrations that resulted in 5 to 99 % mortality were used to estimate the lethal concentrations (LC50 and LC99) and resistance ratios (RR50 and RR99). The diagnostic concentrations were based on concentrations that provided 90 to 99 % mortality in the susceptible reference population. For flubendiamide and methomyl, the decrease in the susceptibility resulted in estimated RR50 of 6.2 to 24.2 and 4.4 to 19.6 times, respectively. For cyantraniliprole and spinetoram, there was little difference in susceptibility among the populations, with RR99 lower than 6.1 times. Differences in the susceptibility of C. includens were evident from concentrations of 0.5053, 5.053, 0.1579 and 28.42 μg cm-2, respectively for flubendiamide, cyantraniliprole, spinetoram and methomyl.

Fitness and mating compatibility of Chrysodeixis includens (W.) (Lepidoptera: Noctuidae) populations collected in different provinces and crops in Argentina.

Chrysodeixis includens, is an important Plusiinae pest that feeds on soybean, beans, and cotton. This species has a genetic structure determined by molecular markers in populations collected in soybean crops in Brazil and has developed resistance to insecticides. This had led to an increased interest in the genetic diversity of its populations in Argentina. This study aimed to characterize the fitness parameters and mating compatibility of geographically distant C. includens populations and on different host plants in Argentina. Intra- and inter-population crosses revealed that C. includens populations from Tucumán and Santiago del Estero provinces did not present any evidence of prezygotic and postzygotic incompatibilities, suggesting that both populations collected from soybean plants belonged to a single wide-ranging species. Prezygotic and postzygotic incompatibilities were detected between populations collected from different crops (soybean and bean). These incompatibilities may be caused by the different nutrients that each plant species renders, or the specific pest control strategies which may affect C. includens behavior. Studies of the genetic structure of C. includens populations based on mating isolation on other crops, as well as of the impact of management strategies on the specie, will increase understanding of the reproductive compatibility revealed by the present study.

Current Distribution and Population Persistence of Five Lepidopteran Pests in U.S. Soybean

AbstractThe distribution of lepidopteran pests in soybean (Glycine max (L.) Merr.) is a current knowledge gap limiting accurate prioritization of Integrated Pest Management (IPM) research. Regional characterizations of lepidopteran distribution in soybean are now more than 25 yr old. The goal of this study was to generate a contemporary assessment of the distribution and population persistence of lepidopteran soybean pests. To understand which species are currently infesting soybean and their persistence, we conducted a survey of soybean entomologists with responsibility for approximately 33.6 million hectares of production in 31 U.S. states. Soybean entomologists were asked questions about presence of lepidopteran pests and their persistence in their state. We focused this survey on five lepidopteran pests: corn earworm (Helicoverpa zea Boddie) (Lepidoptera: Noctuidae), green cloverworm (Hypena scabra Fabricius) (Lepidoptera: Erebidae), painted lady (Vanessa cardui L.) (Lepidoptera: Nymphalidae), soybean looper (Chrysodeixis includens Walker) (Lepidoptera: Noctuidae), and velvetbean caterpillar (Anticarsia gemmatalis Hübner) (Lepidoptera: Erebidae). Soybean entomologists also provided insight into regionally relevant or sporadic lepidopteran soybean pests. Participants were also questioned about common scouting practices in each state. Results of this survey highlight dissimilar geographic distribution and relative persistence of lepidopteran pests in soybean. Clear differences in occurrence and abundance among species provide important contemporary distributions and persistence estimates. Assessments of scouting practices demonstrate a need to improve IPM adoption in some states. Results of this study and its complementary pest profile (concurrently published in JIPM) provide a contemporary foundation for studies of lepidopteran soybean pests.