Neotropical Brown Stink Bug Euschistus Research Articles

Sex‐dependent body mass and respiratory responses on Euschistus heros individuals resistant to imidacloprid

Abstract In insect‐resistant populations, adaptive fitness is intimately related to the physiological responses of males and females to different stressors. By using laboratory‐selected imidacloprid‐resistant individuals of the Neotropical brown stink bug Euschistus heros, one of the most prevalent pests in soybean fields in the Neotropical region, we evaluated whether resistance to imidacloprid (synergized by piperonyl butoxide—PBO) would differentially affect the longevity, body mass and respiratory responses of E. heros males and females. We used an imidacloprid‐susceptible E. heros strain (ImiSusc), whose individuals were reared under controlled and imidacloprid‐free conditions for over a decade, to select the PBO‐synergized imidacloprid‐resistant strain (ImiPBOSel). After eight generations using PBO‐synergized imidacloprid, our results revealed that resistant individuals exposed only to dry residues of imidacloprid (tarsal contact) could survive at concentrations as high as 168 μg a.i./cm2, which is equivalent to 40‐fold the label recommendation for field applications. Furthermore, ImiPBOSel males and females exhibited higher longevity, higher body mass and elevated respiratory activity than ImiSusc individuals. Altogether, the findings described here showed that imidacloprid resistance can select E. heros individuals with better metabolic capacities, which can complicate the management of this pest under field conditions.

Temporal variation and spatial distribution of Euschistus heros (Hemiptera: Pentatomidae) during the soybean grain formation period

The neotropical brown stink bug Euschistus heros (Hemiptera: Pentatomidae) is one of the most important pests in soybean and knowledge of its distribution is necessary to determine the moment of control and enable the appropriate use of strategies to avoid production losses. This research aimed to study the temporal variation and the spatial distribution of E. heros in soybean. The study was carried out in an area of 6600 m2 of soybean, with 60 plots of 100 m2 each, with two sampling points/plot being evaluated weekly by the beat cloth method to count nymphs and adults. The evaluations occurred from fruiting (R3) to physiological maturation (R8). The data were subjected to dispersion indices (variance/mean ratio, Morisita index, and exponent k), theoretical frequency distributions (Poisson, negative binomial, and positive binomial), and spatial analysis by inverse distance weighting (IDW). This study demonstrated the infestation of E. heros throughout the evaluation period, and the dispersion indices showed the trend of nymph aggregation and the sum of nymphs and adults (total population). However, adults tended towards a moderate to uniform aggregation. Theoretical frequency distributions for nymphs and total population indicated randomness at the beginning of the infestation, tending to aggregation from R5 onwards. Aggregation is confirmed in adults, but the population tended towards uniformity at the end of the cycle. The use of the IDW method is an important tool for the rational management of the neotropical brown stink bug in the soybean crop.

Risk assessment of RNAi-based pesticides to non-target organisms: Evaluating the effects of sequence similarity in the parasitoid wasp Telenomus podisi

RNA interference (RNAi)-based pesticides are promising novel pest management products that might reduce environmental impacts compared to other pesticides. Their sequence-guided mode of action facilitates a high species-selectivity, preventing harm on non-target organisms. However, there is currently no consensus on the minimum needed sequence similarity for efficient RNAi in insects and studies have shown that adverse effects in non-targets cannot always be ruled out a priori. This study investigates the effects of exposing the parasitoid wasp Telenomus podisi to double-stranded RNA (dsRNA) which is lethal to its host, the Neotropical brown stink bug Euschistus heros. Feeding T. podisi with wasp-specific dsRNA targeting the vATPase A and actin-2 genes led to 76.4 ± 9.9% and 76.7 ± 8.8% mortality respectively, demonstrating that dietary RNAi is functional in T. podisi. When feeding T. podisi with E. heros-specific dsRNA targeting the same genes, no lethal or sublethal effects were observed. To link sequence similarity to potential gene silencing effects in the parasitoids, the expression of genes showing the highest degree of similarity (17–21 nucleotide matches) with these two target genes was monitored and was found unaffected by the E. heros-specific dsRNA. Our study confirms that RNAi was in this case highly specific and that for E. heros, RNAi-based pesticides can be used complementary to biological control in an integrated pest management context.

Characterization and Comparison of Intestinal Bacterial Microbiomes of Euschistus heros and Piezodorus guildinii Collected in Brazil and the United States.

Background: Herbivorous insects are one of the main biological threats to crops. One such group of insects, stink bugs, do not eat large amounts of tissue when feeding on soybean, but are damaging to the quality of the seed yield as they feed on green developing seeds leading to poorly marketable harvests. In addition to causing physical damage during sucking-feeding activities, the insects can also transmit microbial pathogens, leading to even greater yield loss. Conducting surveys of the insect intestinal microbiome can help identify possible pathogens, as well as detail what healthy stink bug digestive systems have in common.Methods: We used the conserved V4 region of the 16S rRNA gene to characterize the bacterial microbiome of the red-banded stink bug Piezodorus guildinii collected in Brazil and the United States, as well as the neotropical brown stink bug Euschistus heros collected in Brazil.Results: After quality filtering of the data, 192 samples were kept for analyses: 117 samples from P. guildinii covering three sites in Brazil and four sites in the United States, and 75 samples for E. heros covering 10 sites in Brazil. The most interesting observations were that the diversity and abundance of some bacterial families were different in the different ecoregions of Brazil and the United States.Conclusion: Some families, such as Acetobacteraceae, Bacillaceae, Moraxellaceae, Enterobacteriaceae, and Rhodocyclaceae, may be related to the better adaptation in some localities in providing nutrients, break down cellulose, detoxify phytochemicals, and degrade organic compounds, which makes it difficult to control these species.

Sublethal Concentration of Pyriproxyfen Reduces Testicular Connective Tissue Thickness in Euschistus heros Fabr. (Hemiptera: Pentatomidae)

The aim of this study was to determine the effect of the insecticide pyriproxyfen (Tiger™ 100 CE), juvenile hormone analogue, when applied in a sublethal LC30 concentration (0.668 mL a. i. L-1), on the morphological and morphometric parameters of external and internal connective tissue (CT) of the Neotropical-brown stink bug Euschistus heros testicles. The insecticide was applied on nymphs from the 4th instar using a Potter tower with a working pressure of 82.73 kPa (12 lb pol-²) and 1 mL of the emulsion per replicate. A completely randomized experimental design was used, consisting of two treatments (control and pyriproxyfen-treated), five repetitions, and 10 adults of E. heros per experimental unit. The insects were maintained under controlled conditions until the emergence of adults. After 48 h of emergence of adults, the testicles were collected, fixed, and processed for morphological and morphometric analyses. A change was observed in the collagen fibers of the CT of treated insects when compared with those of controls. It was also observed that both types of CT (dense irregular and loose) over the internal tunic of the treated insect were thinner than those in control insects. The analysis showed that pyriproxyfen significantly reduced the external and internal CT width and the conformation of its fibers in all the observed regions when compared with the controls; this may affect the production of the three different types of sperm present in this species.

Imidacloprid-mediated alterations on the salivary glands of the Neotropical brown stink bug, Euschistus heros.

The management of the Neotropical brown stinkbug Euschistus heros (Hemiptera: Pentatomidae) in soybean fields has been heavily dependent on the application of neonicotinoid insecticides. Neonicotinoids act primarily by impairing the function of the nicotinic acetylcholine receptors of the nervous system. These compounds also target specific organs (e.g., salivary glands), which may potentiate their insecticidal efficacy. Here, we evaluated whether the exposure to the neonicotinoid imidacloprid would cause cytomorphological changes in the salivary glands of E. heros. First, we determined the lethal concentrations (LCs) of imidacloprid through contact and ingestion. Subsequently, the cytomorphology of the salivary glands were evaluated in insect groups that survived exposure to the LC5 (3.75 mg a.i./L), LC50 (112.5 mg a.i./L), or LC75 (375.0 mg a.i./L, equivalent to the recommended field rate) doses. Imidacloprid induced apoptosis and necrosis in the salivary gland cells according to the insecticide concentration and salivary gland region. All concentrations increased apoptosis and injured cells (e.g., vacuolization, chromatin condensation, swelling of organelles, and plasma membrane rupture) in the principal and accessory salivary glands. Individuals that survived exposure to the highest concentrations (i.e., LC5 and LC50) were more affected, and exhibited several necrotic cells on their main principal salivary glands. Collectively, our results indicate that imidacloprid exerts toxic effects on the non-target organs, such as the salivary glands, which increases the efficacy of this compound in the management of stink bug infestations.

Spatial distribution and sample size to estimate Euschistus heros population density in wild plants during off-season

The neotropical brown stink bug Euschistus heros (F.) is an important pest for many crops in several countries and its ability to survive on associated plants during winter is one of the main factors contributing to the permanence of this insect in crop areas. The objective of this study was to identify the spatial distribution of E. heros, and the minimum number of samples (tussocks of each plant species) required to estimate their population density in wild plants during winter. Field experiments were conducted in 2014, 2015, and 2016. Tussocks of Eustachys retusa, Andropogon bicornis, and Saccharum angustifolium were assessed in the area surrounding the cropped land. Data on the number of E. heros were categorized in plant species and tussock diameter range. The spatial distribution patterns of E. heros were evaluated using different dispersion indexes. To validate these patterns, the data were fitted to probabilistic distribution models. The minimum number of tussock samples required was determined using a statistical model. The results suggest that E. heros has an aggregate distribution in the three plant species evaluated; however, the distribution varies as a function of the tussock size. The numbers of tussock samples to achieve an accuracy within 30% were 146, 87, and 109 for E. retusa, A. bicornis, and S. angustifolium, respectively.

Parental RNA interference as a tool to study genes involved in rostrum development in the Neotropical brown stink bug, Euschistus heros

In insects, the identity of body segments is controlled by homeotic genes and the knockdown of these genes during embryogenesis can lead to an abnormal development and/or atypical phenotypes. The main goal of this study was to investigate the involvement of labial (lab), deformed (dfd), sex comb reduced (scr), extradenticle (exd) and proboscipedia (pb) in rostrum development in the Neotropical brown stink bug Euschistus heros, using parental RNAi (pRNAi). To achieve this objective, 10-days-old adult females were first microinjected with double-stranded RNAs (dsRNA) targeting these five genes. Then, the number of eggs laid per female, the percentage of hatched nymphs with normal or abnormal phenotype and target gene silencing were evaluated. Except for the dsDfd-treatment, the number of eggs laid per female per day was not affected by the different dsRNA-treatments compared to the control (dsGFP). However, treatment with either dsLab, dsDfd, dsScr or dsExd caused a strong reduction in egg hatching. The dsExd-treatment caused no apparent change in phenotype in the nymphs while hatched nymphs from the dsDfd, dsScr and dsPb-treatment showed abnormalities in the rostrum. Particularly for the dsPb-treatment, 91% of the offspring displayed a bifurcated rostrum with a leg-like structure. Overall, these results indicate that these five genes are involved in E. heros embryonic development and that the knockdown of dfd, scr and pb leads to an abnormal development of the rostrum. Additionally, this study demonstrates the efficiency of pRNAi in studying genes involved in embryogenesis in E. heros, with clear phenotypes and a strong target gene silencing in the next generation, after treatment of the parent female adult with gene-specific dsRNA.

Isolation and evaluation of entomopathogenic fungi against the neotropical brown stink bug Euschistus heros (F.) (Hemiptera: Pentatomidae) under laboratory conditions

ABSTRACT Although the brown stink bug, Euschistus heros (F.) is susceptible to entomopathogenic fungi, only a single formulation is currently available on the Brazilian market for its control. The objective of this work was to isolate entomopathogenic fungi with potential to control E. heros, evaluate their virulence, and determine effective conidial concentrations. Thirty six different fungal isolates were obtained from soil samples and diseased insects and pure cultures of each were established on potato-dextrose agar. Suspensions of 1 × 108 conidia mL−1 were prepared from each isolate and a 5 μL aliquot was inoculated on the dorsum of adult stink bugs (n = 8 replications of 5 bugs each). Three isolates caused 100% mortality of bugs over a 15-day observation period. These were identified by molecular techniques as belonging to the Beauveria bassiana species complex and designated UFSM-1, UFSM-2 and UFSM-26. Further bioassays determined the LC50, LC90 and cumulative mortality functions caused by these three isolates. Isolates UFSM-1 and UFSM-2 stood out as highly virulence, with an LC90 of 5 × 109 conidia mL−1 in 9 days, compared to an LC90 of 8 × 1010 conidia mL−1 for strain UFSM-26. Application of 1 × 108 conidia mL−1 of UFSM-1 and UFSM-2 isolates killed 70% of stink bugs in nine days, whereas the same concentration of UFSM-26 killed only 12%. We conclude that isolates UFSM-1 and UFSM-2 warrant field tests as novel agents for biological control of E. heros.

Synergism and unintended effects of the association between imidacloprid and sodium chloride (NaCl) on the management of Euschistus heros.

The use of insecticidal solutions containing sodium chloride (NaCl) has been proposed as a more environmentally friendly alternative to managing stink bug infestations of Neotropical soybean fields. The potential sublethal and undesirable effects of this practice have, however, been overlooked, especially with novel insecticides. Here, we have evaluated experimentally whether the addition of NaCl (0.5% w/v) to imidacloprid-containing solutions could alter insecticide toxicity and modify the reproductive responses of the Neotropical brown stink bug Euschistus heros. Adding NaCl to imidacloprid solutions significantly increased imidacloprid toxicity against E. heros. The exposure to E. heros to sublethal concentrations of imidacloprid affected the insect's mating abilities in a concentration-dependent manner. The addition of NaCl to solutions containing imidacloprid at concentrations as low as 0.126 μg a.i. cm-2 (i.e. the equivalent to 3% of field rate recommendation) also impacted the sexual behavior of E. heros, reducing mating duration. NaCl-exposed stink bugs, however, exhibited higher fecundity and fertility rates than those insects that were unexposed to NaCl or those that were exposed to sublethal levels of imidacloprid only. The addition of low amounts of NaCl resulted in a higher toxicity of imidacloprid. This practice, however, can also lead to undesirable effects as increasing reproductive output of E. heros that can potentially compromise the management of these insect pests.

Dinâmica populacional de Euschistus heros em cultivares de soja de diferentes ciclos de desenvolvimento

O percevejo-marrom-da-soja Euschistus heros, destaca-se como uma das principais pragas da cultura, sendo fundamental realizar amostragens periódicas para aferir a densidade populacional e auxiliar na tomada de decisão de controle.O objetivo do presente trabalho foi estudar a dinâmica populacional de E. heros em cultivares de soja transgênica de diferentes ciclos de desenvolvimento. Os experimentos foram conduzidos nos anos agrícolas 2013/14 e 2014/15 na FCAV/UNESP, Jaboticabal, SP, Brasil. Foram selecionados três campos, e em cada um foi demarcada uma área de 8.000 m2 (0,8 ha), sendo cada área subdividida em 80 parcelas de 100 m2 (10 m x 10 m). As cultivares de soja transgênica de diferentes ciclos de desenvolvimento utilizadas foram: SYN 1365 RR (precoce), M 7908 RR (média) e BRS Valiosa RR (tardia). As amostragens foram realizadas semanalmente pelo método da batida de pano, registrando-se o número de ninfas e adultos. Foram confeccionadas figuras para demonstrar a dinâmica populacional entre os dados médios de infestação do inseto-praga e o estágio fenológico da cultura, sendo a influência dos fatores meteorológicos analisada por meio da análise de regressão múltipla com seleção de variáveis pelo método “stepwise”. De acordo com os resultados da dinâmica populacional, as maiores densidades populacionais de E. heros foram observadas no estádio fenológico R6 da soja, e a temperatura máxima é o fator meteorológico que mais influenciou na variação da densidade populacional de E. heros.

Virulence of Metarhizium brunneum (Ascomycota: Hypocreales) Strains Against Stinkbugs Euschistus heros and Dichelops furcatus (Hemiptera: Pentatomidae).

Three strains of fungi belonging to the genus Metarhizium Sorokīn (ARSEF 4556, ARSEF 3297, native strain) were assayed against adults and nymphs of the Neotropical brown stinkbug Euschistus heros (F.) and the green-belly stinkbug Dichelops furcatus (F.). The most virulent strain, ARSEF 4556, caused over 90% mortality. The average survival time of the second and fifth instar nymphs and adults following immersion in 1 × 108 conidia ml-1 was 4.8, 5.7, and 5.2 d, respectively. The second instar nymphs were more susceptible than the adults. The LC50 values and median survival times for second instar and adult E. heros were 1.6 × 107 and 3.1 × 107 conidia ml-1 and 6 and 8 d, respectively. Eggs of E. heros and the closely related stinkbug, D. furcatus, were highly susceptible to ARSEF 4556 with the mean mortality of eggs immersed in 1 × 108 conidia ml-1 being 77.4% and 89.7%, respectively. The strain 3297 showed also good aptitudes for stinkbugs control with mortalities higher than 80% against nymphs and adults and eggs mortalities of 75.5% for E. heros and 79.6% for D. furcatus. This study has shown that it is possible to have a two-pronged control strategy, targeting adults and to reduce oviposition and targeting egg clusters to prevent emergence and dispersal of nymphs. Besides early instars of nymphs have been shown to be more susceptible to the fungal strains than late instars and adults.

First transcriptome of the Neotropical pest Euschistus heros (Hemiptera: Pentatomidae) with dissection of its siRNA machinery

Over the past few years, the use of RNA interference (RNAi) for insect pest management has attracted considerable interest in academia and industry as a pest-specific and environment-friendly strategy for pest control. For the success of this technique, the presence of core RNAi genes and a functional silencing machinery is essential. Therefore, the aim of this study was to test whether the Neotropical brown stinkbug Euschistus heros has the main RNAi core genes and whether the supply of dsRNA could generate an efficient gene silencing response. To do this, total mRNA of all developmental stages was sequenced on an Illumina platform, followed by a de novo assembly, gene annotation and RNAi-related gene identification. Once RNAi-related genes were identified, nuclease activities in hemolymph were investigated through an ex vivo assay. To test the functionality of the siRNA machinery, E. heros adults were microinjected with ~28 ng per mg of insect of a dsRNA targeting the V-ATPase-A gene. Mortality, relative transcript levels of V-ATPase-A, and the expression of the genes involved in the siRNA machinery, Dicer-2 (DCR-2) and Argonaute 2 (AGO-2), were analyzed. Transcriptome sequencing generated more than 126 million sequenced reads, and these were annotated in approximately 80,000 contigs. The search of RNAi-related genes resulted in 47 genes involved in the three major RNAi pathways, with the absence of sid-like homologous. Although ex vivo incubation of dsRNA in E. heros hemolymph showed rapid degradation, there was 35% mortality at 4 days after treatment and a significant reduction in V-ATPase-A gene expression. These results indicated that although sid-like genes are lacking, the dsRNA uptake mechanism was very efficient. Also, 2-fold and 4-fold overexpression of DCR-2 and AGO-2, respectively, after dsRNA supply indicated the activation of the siRNA machinery. Consequently, E. heros has proven to be sensitive to RNAi upon injection of dsRNA into its hemocoel. We believe that this finding together with a publically available transcriptome and the validation of a responsive RNAi machinery provide a starting point for future field applications against one of the most important soybean pests in South America.

Prevalence, damage, management and insecticide resistance of stink bug populations (Hemiptera: Pentatomidae) in commodity crops

Abstract Pest management of stink bugs (Hemiptera: Pentatomidae) in soybean [Glycine max (L.) Merr.], corn (Zea mays L.) and cotton (Gossypium spp.) agroecosystems has become a major concern in several countries of the Americas. In this review, we report an overview on geographical distribution, injury, damage and methods used to control (plant resistance mechanisms, biological control) the most important stink bugs in the Americas, with an emphasis on Brazil, the implications of the trend towards decreased susceptibility of stink bug populations to insecticides and the current difficulties of the management of these insect pests. Currently, the Neotropical brown stink bug Euschistus heros (Fabricius) is less susceptible to organophosphate insecticides than in the past. A slight reduction in E. heros susceptibility to pyrethroids and, to a lesser extent, to neonicotinoids has also been observed. In addition, the green‐belly stink bug [Dichelops melacanthus (Dallas)] is more tolerant to the three classes of insecticides (neonicotinoids, organophosphates and pyrethroids) than E. heros. Metabolic detoxification is involved in organophosphate, neonicotinoid and pyrethroid differences in susceptibility. Restricted availability of insecticides with different modes of action could favour the selection of resistant phenotypes in stink bug populations.

The Fitness and Economic Benefits of Rearing the Parasitoid Telenomus podisi Under Fluctuating Temperature Regime.

Successful biological control requires detailed knowledge about the mass rearing conditions of the control agents in order to ensure higher quality of field-released insects. Thus, we investigated whether rearing fluctuating thermal condition would affect the fitness and costs of the parasitoid wasp Telenomus podisi Ashmead (a biocontrol agent used for controlling the Neotropical brown stink bug Euschistus heros (Fabricius)) when compared with parasitoid reared at constant temperature condition, which is commonly used in insect facilities. Parasitoids were reared under either constant (continuous exposure at 25 ± 2°C) or fluctuating temperature conditions (i.e., 30 ± 2°C during day and 20 ± 2°C at night) during four consecutive generations. Our results indicated that tested fluctuating temperature is more suitable for rearing of T. podisi as such temperature condition not only resulted in fitness benefits (e.g., shorter developmental time, longer female longevity, higher fecundity/fertility) but also reduced (approximately 23.5%) the estimated costs for producing the parasitoids. Furthermore, rearing T. podisi under fluctuating temperatures improved tolerance to low constant temperatures (i.e., 20°C) without changing the tolerance to constant high temperatures (30°C) in the fourth generation. Surprisingly, even parasitoids that developed under fluctuating thermal conditions performed better than those reared at constant temperature of 25°C. Collectively, our findings suggest that T. podisi reared under fluctuating thermal condition can tolerate better fluctuating temperatures that normally occur both during long periods of transport and in agricultural ecosystems, which will increase the quality and productivity of mass-reared T. podisi for inundative releases.

Electropenetrography Monitoring of the Neotropical Brown-Stink Bug (Hemiptera: Pentatomidae) on Soybean Pods: An Electrical Penetration Graph-Histology Analysis.

The Neotropical brown-stink bug Euschistus heros (F.) (Hemiptera: Pentatomidae) is the most important pest damaging soybean in the Neotropics, the world largest production area. The alternating current–direct current (AC–DC) electropenetrography (EPG) technology was used to develop an EPG waveform library of adult females feeding on soybean (Glycine max (L.) Merr.) pods at different input resistor (Ri) levels. Thirteen waveform types/subtypes were identified and described. They were divided into non-probing (Z, Np, Dw1, and Dw2), and probing waveforms (Eh1, Eh2, Eh3, Eh4, and Eh5). Probing waveforms were grouped into three phases: 1) pathway (Eh1a, Eh1b, Eh1c, and Eh1w), 2) ingestion (Eh2, Eh3a, Eh3b, and Eh4), and 3) interruption (Eh5). Correlations between waveforms Eh1b, Eh1c, Eh2, Eh3, and Eh4 and stylets tip position and/or salivary sheath in the pod tissue were determined via histological studies. Non-probing waveforms, Z and Np were visually associated with the bug resting and walking on pod surface, respectively. Waveform Dw1 was correlated with egestion, and the ingestion of fluids (droplets) was proposed for Dw2. Eh1a and Eh1b corresponded to initial and deep stylet penetration through pod tissue, and secretion of a salivary sheath. In Eh1c, stylets penetrated the rigid cell layer of sclerenchyma, and during Eh1w they were withdrawn. Eh2 represents sustained xylem sap ingestion. Eh3a corresponded to lacerate and macerate cell rupture feeding behavior in seed endosperm, whereas Eh3b corresponded to ingestion of cellular contents. Eh4 represented short ingestion from an unknown site, and Eh5 represented short interruptions during xylem sap ingestion.

Imidacloprid resistance in the Neotropical brown stink bug Euschistus heros: selection and fitness costs

Neonicotinoid insecticides (e.g., imidacloprid) are some of the most prevalent tools used to control hemipterans that attack soybean crops worldwide. However, the emergence of neonicotinoid-resistant strains of phytosuccivorous soybean pests, such as the Neotropical brown stink bug Euschistus heros, has posed a challenge to the sustainable use of these compounds. Here, we laboratory-selected two E. heros strains for imidacloprid resistance and evaluated the activity of detoxification enzymes (e.g., cytochrome P450, esterases and glutathione-S-transferases) as well as potential adaptive costs associated with resistance (e.g., in survival, fecundity and fertility) in both strains, while laboratory selection for 13 generations in a known imidacloprid-susceptible E. heros strain (ImiSusc) resulted in an imidacloprid-resistant strain (ImiLabSel) with a resistance ratio (RR) of 11.6; similar resistance levels (i.e., RR = 13.5) were also achieved in another imidacloprid-resistant strain, which was field-collected (ImiGoias) and laboratory-selected for only six generations (ImiRes). Regarding enzymatic activity, both resistant strains differed from the imidacloprid-susceptible strain only in the activity of cytochrome P450, where the ImiLabSel and ImiRes strains exhibited higher activity by 72.3% and 40.5%, respectively. Furthermore, severe fitness costs (reductions of 86% for ImiLabSel and 68.0% for ImiRes) were recorded in both imidacloprid-resistant strains. Collectively, our results showed that E. heros rapidly responded to laboratory selection for neonicotinoid resistance, with enhanced cytochrome P450 activity as the likely underlying mechanism, and that they exhibit associated fitness costs, which have direct implications for the management of this insect pest.

Culturable symbionts associated with the reproductive and digestive tissues of the Neotropical brown stinkbug Euschistus heros

Symbionts are widely distributed in eukaryotes, and potentially affect the physiology, ecology and evolution of their host. Most insects harbour free-living bacteria in their haemocoel and gut lumen, intracellular-living bacteria in a range of tissues or bacteria in host-derived specialized cells. Stinkbugs, as do many arthropods, harbour extracellular bacteria in the gut that may affect the fitness of their host. This study identified the culturable symbionts associated with the ovaries, spermatheca, seminal vesicle and posterior midgut region (V4) of males and females of Euschistus heros (F.) (Hemiptera: Pentatomidae). Several culture media were used to isolate the bacteria associated with these structures. The selected colonies (morphotypes) were cultured in liquid medium, subjected to genomic DNA extraction, 16S rRNA gene amplification, and restriction fragment length polymorphism (RFLP) analyses. Morphotypes with distinct RFLP patterns were purified and sequenced, and the sequences obtained were used for putative identification and phylogenetic analysis. Comparison of the sequences with those available in the EzTaxon-e database and the use of a matrix of paired distances grouped the isolates in phylotypes belonging to the Phylum Proteobacteria. Proteobacteria was represented by γ-Proteobacteria phylotypes belonging to Enterobacteriaceae, while Firmicutes had Bacilli phylotypes distributed in Enterococcaceae and Staphylococcaceae. Some of the phylotypes identified were associated exclusively with single structures, such as ovaries, spermatheca and the V4 midgut region of males and females. All culturable bacteria associated with the seminal vesicle were also associated with other tissues.

Area-wide spatial survey of the likelihood of insecticide control failure in the neotropical brown stink bug Euschistus heros

Insecticide resistance is a well-known phenomenon caused by the intensive use of insecticides, which selected resistant individuals and cause large economic losses. The use of area-wide surveys and geostatistical analyses are important management initiatives as they enable the recognition of areas with high risks of insecticide control failure due to insecticide resistance. Here, we surveyed and mapped the risk of insecticide control failure in populations of the neotropical brown stink bug, Euschistus heros, in one of the main soybean-producing areas in the Neotropical region, the state of Goias in central Brazil. Diagnostic bioassays were performed using the recommended label rates and minimum required control efficacy threshold for commercial formulations of the main compounds used against this pest species in the region, namely the pyrethroids beta-cyfluthrin and lambda-cyhalothrin, the neonicotinoids imidacloprid and thiamethoxam, and the organophosphate acephate. The control failure likelihood for the insecticides acephate, lambda-cyhalothrin and thiamethoxam was negligible throughout the surveyed region. However, a low risk of control failure exists for beta-cyfluthrin at localized portions of southwestern Goias and for imidacloprid in the northeast. These findings diverge from the perceived and apparently unjustified notion that the reported insecticide control failure against this stink bug is due to insecticide resistance. Indeed, this problem is currently limited to just two insecticides (i.e., beta-cyfluthrin and imidacloprid) in circumscribed portions of the surveyed area. Thus, resistance management efforts should be specifically designed to address these areas, and more general approaches should continue to be employed in the whole of the region.

Variable Levels of Resistance of Soybean Genotypes on the Performance of Euschistus heros (Hemiptera: Pentatomidae).

The Neotropical brown stink bug Euschistus heros (Fabr.) (Hemiptera: Pentatomidae) is one of the major soybean pests in South America. This species is responsible for high levels of infestation, causes critical damage to seeds, it is associated with leaf retention on plants, and it is extremely difficult to manage. Host plant resistance is a notable technique to assist in reducing the stink bug population in soybean crops. The antibiosis resistance of soybean genotypes to E. heros was evaluated in laboratory. Genotypes L1-1-01, 'IAC 100', 'IAC 23', and 'Coodetec 208' increased the length of nymphal developmental time. PI 274453 and PI 227687 reduced egg viability and also adult body weight. PI 274454, 'IAC 19', PI 227687, and PI 229358 led to low nymphal viability. These results suggest that these genotypes may be useful in soybean breeding programs that focus on the development of genotypes resistant to E. heros.