Intraspecific and interspecific interaction and fitness cost of stink bugs Euschistus heros, Diceraeus melacanthus, and Piezodorus guildinii in soybean.

BACKGROUND: The most common pentatomid species in soybean crops are Euschistus heros (F.), Piezodorus guildinii (W.), and Diceraeus melacanthus (D.), causing a significant reduction in yield. It is known that these stink bugs inhabit the reproductive structures of soybeans simultaneously; however, there are few studies addressing their intraguild interactions, as well as aspects of possible competition between them in plants. Thus, the interspecific and intraspecific interactions of these stink bugs were evaluated in laboratory and field conditions, throughout the duration of the instars and adulthood, including longevity, mortality, and the number of eggs per female. RESULTS: Euschistus heros had a higher competitive capacity in the interaction with D. melacanthus and P. guildinii, negatively interfering in the abundance or development (duration of instar, fertility, and mortality) of these stink bugs in soybean crops. This interference may act on the natural balance of these insect pests. Mortality of adults in interactions containing E. heros as a competitor or not showed that this species was not affected by the other species under field conditions. In the scenario where D. melacanthus was evaluated, it was observed that the presence of other species caused higher mortality in D. melacanthus. Additionally, higher P. guildiniii mortality was observed in interspecific interactions. CONCLUSION: Our results suggest that E. heros has a greater competitive ability in the soybean crop, followed by D. melacanthus and P. guildinii. Therefore, the results found justified the greater abundance of E. heros and helped to explain the increasing occurrence of D. melacanthus in soybean crops, contributing to new directions for understanding the interaction of the soybean stink bug complex. © 2023 Society of Chemical Industry.

Transcriptomic investigation of the molecular mechanisms underlying resistance to the neonicotinoid thiamethoxam and the pyrethroid lambda-cyhalothrin in Euschistus heros (Hemiptera: Pentatomidae).

BACKGROUND: Laboratory-selected resistant strains of Euschistus heros to thiamethoxam (NEO) and lambda-cyhalothrin (PYR) were recently reported in Brazil. However, the mechanisms conferring resistance to these insecticides in E. heros remain unresolved. We utilized comparative transcriptome profiling and single nucleotide polymorphism (SNP) calling of susceptible and resistant strains of E. heros to investigate the molecular mechanism(s) underlying resistance. RESULTS: The E. heros transcriptome was assembled, generating 91 673 transcripts with a mean length of 720 bp and N50 of 1795 bp. Comparative gene expression analysis between the susceptible (SUS) and NEO strains identified 215 significantly differentially expressed (DE) transcripts. DE transcripts associated with the xenobiotic metabolism were all up-regulated in the NEO strain. The comparative analysis of the SUS and PYR strains identified 204 DE transcripts, including an esterase (esterase FE4), a glutathione-S-transferase, an ABC transporter (ABCC1) and aquaporins that were up-regulated in the PYR strain. We identified 9588 and 15 043 nonsynonymous SNPs in the PYR and NEO strains. One of the SNPs (D70N) detected in the NEO strain occurs in a subunit (α5) of the nAChRs, the target site of neonicotinoid insecticides. Nevertheless, this residue position in α5 is not conserved among insects. CONCLUSIONS: Neonicotinoid and pyrethroid resistance in laboratory-selected E. heros is associated with a potential metabolic resistance mechanism by the overexpression of proteins commonly involved in the three phases of xenobiotic metabolism. Together these findings provide insight into the potential basis of resistance in E. heros and will inform the development and implementation of resistance management strategies against this important pest. © 2023 Society of Chemical Industry.

Ecological zoning of Euschistus heros in Brazil based on the net reproductive rate at different temperatures and relative-humidity levels.

The Neotropical brown stink bug, Euschistus heros (Fabricius, 1798) (Hemiptera: Pentatomidae), is one of the major insect pests in soybean crops, causing severe damage; however, some aspects of its biology that are essential for management remain unknown. To aid in the management of E. heros, the present study investigated the fertility life table of this species at 7 temperatures (18, 20, 22, 25, 28, 30, and 32 ± 1 °C) and 4 relative-humidity levels (30, 50, 70, and 90 ± 10%). Based on the net reproductive rate, R0, we developed an ecological zoning for this pest in Brazil, to identify climatically favorable areas for population growth. Our results indicated that the most favorable range is between 25 and 28 °C and above 70% RH. The ecological zoning indicated that farmers should be more concerned in the northern and Midwest regions, which include the state of Mato Grosso, the largest soybean and corn producer in Brazil. These results provide valuable information, indicating the hotspots most likely to be attacked by the Neotropical brown stink bug.

Development and biological evaluation of nanoencapsulated-based pyrethroids with synergists for resistance management of two soybean pests: insights for new insecticide formulations.

BACKGROUND: Chemical control is commonly used against Euschistus heros (F.) and Chrysodeixis includens (Walker) in soybean fields in South America. However, previous studies reported that these pests have reduced susceptibility to pyrethroids in Brazil. On this basis, we developed and evaluated nanoencapsulated-based bifenthrin (BFT) and λ-cyhalothrin (LAM) with the synergists piperonyl butoxide (PBO) and diethyl maleate (DEM) for insect resistance management (IRM). RESULTS: Nanoformulations of BFT and LAM with PBO and DEM presented good physical-chemical characteristics and were stable. The spherical morphology of all systems and the encapsulation efficiency in nanostructured lipid carriers did not change when synergists were added. Nanoencapsulated BFT with DEM applied topically increased the susceptibility of E. heros to BFT by 3.50-fold. Similarly, nanoencapsulated BFT and LAM with PBO in diet-overlay bioassays increased the susceptibility of C. includens to both chemicals by up to 2.16-fold. Nanoencapsulated BFT and LAM with synergists also improve control efficacy of both species, causing higher mortality than commercial products containing these chemistries. CONCLUSIONS: It is possible to develop nanoencapsulated-based formulations of BFT and LAM with PBO or DEM, and these nanoformulations have the potential to improve control of E. heros and C. includens with recognized low susceptibility to pyrethroids. This study provides updates for designing new insecticide formulations for IRM. © 2022 Society of Chemical Industry.

The Effect of Synergistic Compounds on the Susceptibility of Euschistus heros (Hemiptera: Pentatomidae) and Chrysodeixis includens (Lepidoptera: Noctuidae) to Pyrethroids.

The Neotropical brown stink bug, Euschistus heros (F.), and the soybean looper, Chrysodeixis includens (Walker), are key pests of soybean in South America. Low susceptibility to pyrethroids has been reported for both species in Brazil. Here, we evaluate the addition of synergistic compounds piperonyl butoxide (PBO) and diethyl maleate (DEM) to manage E. heros and C. includens with resistance to λ-cyhalothrin and bifenthrin. The LD50 of technical grade and commercial products containing λ-cyhalothrin and bifenthrin decreased against field-collected E. heros exposed to PBO and DEM relative to unexposed insects; synergistic ratios up to 4.75-fold. The mortality also increased when E. heros were exposed to commercial formulations containing λ-cyhalothrin (from 4 to 44%) and bifenthrin (from 44 to 88%) in the presence of synergists. There was also a higher susceptibility of field-collected C. includens to technical grade λ-cyhalothrin when PBO was used; synergistic ratio of 5.50-fold. High lethally of technical grade λ-cyhalothrin was also verified in the presence of PBO, with mortality increasing from 6 to 57%. Our findings indicate the potential utility of synergists in reversing the resistance to λ-cyhalothrin and bifenthrin in E. heros and C. includens and suggest a significant role of metabolic mechanisms underlying the detoxification of both pyrethroids.

Reproductive Patterns Drive the Gene Flow and Spatial Dispersal of Euschistus heros (Hemiptera: Pentatomidae).

Euschistus heros (Hemiptera: Pentatomidae) has two allopatric strains with a hybrid zone in central Brazil. Asymmetric dispersal and gene flow between these strains of E. heros have been observed, where the South strain (SS) moves more quickly to the northern regions of the country than the North strain (NS) to the southern areas. In addition, SS generally has a bigger body size and presents dark brown coloration, and NS is usually smaller in size and presents light brown coloration. Here, we studied the reproductive behavior and tested for the presence of assortative mating and reproductive barriers between the two allopatric strains of E. heros. Nonrandom mating was observed in the SS strain based on mating choice trials and the reproductive isolation indexes. SS females and males prefer to mate with their co-specific (same strain) partner, while NS insects showed no mating preference. The insect's pronotum width was positively associated with the mating choice suggesting size-assortative mating in E. heros. Reciprocal crosses between strains yielded similar reproductive outputs when compared with pure strain crosses, suggesting similar fitness of hybrid pure strains. The asymmetric gene flow in the hybridization zone that favors SS seems to be associated with the reproductive behavior of the species, which favors the typical phenotype found in the SS populations.

Monitoring Resistance of Euschistus heros (Fabricius) (Hemiptera: Pentatomidae) to Insecticides by Using Encapsulated Artificial Diet Bioassay.

The novel ingestion bioassay method was developed for detecting and monitoring resistance of Euschistus heros by encapsulating an artificial liquid diet using Parafilm®. This methodology was compared with the tarsal contact (vial test) and topical application methods for thiamethoxam, imidacloprid, and lambda-cyhalothrin. The best bioassay method for the neonicotinoid insecticides thiamethoxam and imidacloprid was ingestion. For pyrethroid insecticide lambda-cyhalothrin, the best result was obtained by topical application. Using the best bioassay method for each insecticide, the susceptibility to these insecticides was monitored in 30 populations of E. heros collected from soybean crops in Brazil from 2018 to 2020. High variations in susceptibility to thiamethoxam (resistance ratios, 1.6-22 times), imidacloprid (resistance ratios, 1.6-22 times), and lambda-cyhalothrin (resistance ratios, 5-40 times) were detected among the evaluated E. heros populations. In order to monitor the susceptibility of E. heros to insecticides, diagnostic concentrations were defined based on the LC99 of the susceptible reference population: 5.65 µL of a.i./mL for thiamethoxam, 12.45 µL of a.i./mL for imidacloprid, and 0.20 µg of a.i./insect for lambda-cyhalothrin. Subsequently, we select an E. heros strain resistant to neonicotinoid insecticides and another to lambda-cyhalothrin. The resistance ratios obtained after seven selection cycles were 66, 41 and 44 times for thiamethoxam, imidacloprid and lambda-cyhalothrin, respectively.

Susceptibility of Euschistus heros and Dichelops furcatus (Hemiptera: Pentatomidae) to Selected Insecticides in Brazil.

Euschistus heros (Fabricius, 1798) and Dichelops furcatus (Fabricius, 1775) are key pests of agricultural crops in Brazil. Chemical insecticides are the main control tactic used against these species. Here, we investigated the susceptibility of E. heros and D. furcatus from distinct regions to the mains insecticides used to stink bugs control in Brazil. Field populations of these species were collected throughout the 2017-2019 crop seasons and insects were exposed to insecticides in dip-test bioassays using fresh green bean pods. Populations of E. heros exhibited low variation in the susceptibility to acephate (LC50 = 172.2 to 1,008 µg a.i. per ml), and thiamethoxam (LC50 = 28.8 to 433.9 µg a.i. per ml); resistance ratios were less than 5.9- and 15.1-fold, respectively. In contrast, these populations had higher variation in the susceptibility to bifenthrin (LC50 = 26.7 to 636.1 µg a.i. per ml) and lambda-cyhalothrin (LC50 = 10.0 to 636.1 µg a.i. per ml); resistance ratios reaching 23.8- and 63.6-fold, respectively. Susceptibility monitoring data indicated a higher susceptibility of E. heros to the manufacturers field-recommended rates of acephate, lambda-cyhalothrin + thiamethoxam, and bifenthrin + acetamiprid than lambda-cyhalothrin. Populations of D. furcatus exhibited low variation in the susceptibility to acephate (LC50 = 219.2 to 614.1 µg a.i. per ml), bifenthrin (LC50 = 62.8 to 197.4 µg a.i. per ml), and lambda-cyhalothrin (LC50 = 189.5 to 2,538 µg a.i. per ml); resistance ratios were less than 13.4-fold. In summary, populations of E. heros are less susceptible to pyrethroids, while populations of D. furcatus have similar susceptibility to the insecticides evaluated.

Population Genomics of the Neotropical Brown Stink Bug, Euschistus heros: The Most Important Emerging Insect Pest to Soybean in Brazil.

Recent changes in soybean management like the adoption of transgenic crops and no-till farming, in addition to the expansion of cultivated areas into new virgin frontiers, are some of the hypotheses that can explain the rise of secondary pests, such as the Neotropical brown stink bug, Euschistus heros, in Brazil. To better access the risk of increased pests like E. heros and to determine probabilities for insecticide resistance spreading, it is necessary first to access the levels of the genetic diversity, how the genetic diversity is distributed, and how natural selection is acting upon the natural variation. Using the genotyping by sequencing (GBS) technique, we generated ~60,000 single-nucleotide polymorphisms (SNPs) distributed across the E. heros genome to answer some of those questions. The SNP data was used to investigate the pattern of genetic structure, hybridization and natural selection of this emerging pest. We found that E. heros populations presented similar levels of genetic diversity with slightly higher values at several central locations in Brazil. Our results also showed strong genetic structure separating northern and southern Brazilian regions (FST = 0.22; p-value = 0.000) with a very distinct hybrid zone at the central region. The analyses also suggest the possibility that GABA channels and odorant receptors might play a role in the process of natural selection. At least one marker was associated with soybean and beans crops, but no association between allele frequency and cotton was found. We discuss the implications of these findings in the management of emerging pests in agriculture, particularly in the context of large areas of monoculture such as soybean and cotton.

Macro-elements in the hemolymph of adult Euschistus heros (Fabr.) (Hemiptera: Pentatomidae) treated with pyriproxyfen.

Euschistus heros is an important pest in many crops in Brazil, and different control strategies, mainly involving chemicals, have been evaluated; however, the side effects of these chemicals on the balance of inorganic element levels in the hemolymph are unknown. Thus, the aim of this work was to determine the concentration of inorganic elements (focusing on macro-elements) in the hemolymph of female and male E. heros adults, after applying pyriproxyfen at a sublethal concentration (LC30 = 6.68 mL L-1 diluted in distilled water) to 4th instar nymphs, which were kept in controlled conditions. The hemolymph pool was removed 48 h after adult emergence, centrifuged and placed on an acrylic disk added with Gallium as internal standard for the analysis of total reflection X-ray fluorescence. Most of the elements in the control treatment did not differ between females and males. However, following insecticide application to females and males, respectively, there was a significant increase in sulfur (19 and 51%), chlorine (33 and 137%) and calcium (47 and 82%) in the hemolymph. The significantly higher increase in macro-elements in males' hemolymph indicates that the action of pyriproxyfen may be sex-specific. Phosphorus and potassium concentrations also differed between females and males in the control and treated groups. The observed variation in inorganic elements in the insect's hemolymph may be related to the unknown effects of pyriproxyfen, mainly on immune and reproductive performance.

Diversity of Stink Bugs (Pentatomidae) Associated with Canola: Looking for Potential Pests.

Canola (Brassicaceae: Brassica spp.) is an important feedstock for biodiesel production and a potential ingredient for use in the food industry. In different continents, various arthropod pests damage canola plants. Stink bugs (Heteroptera: Pentatomidae) are present in all zoogeographical regions, and many species are recognized by their economic importance as crop pests. Our aim was to describe the composition, structure, and diversity of the assemblage of stink bugs sampled on canola in southern Brazil. A total of 878 pentatomids were captured, belonging to 27 species. The dominant species were Euschistus heros (F.) (n = 439), Dichelops furcatus (F.) (n = 160), and Nezara viridula L. (n = 79). The species richness estimators indicated the samples correspond from 79.7 to 93.1% of the richness estimated. Comparing canola to other monocultures, the richness of Pentatomidae was much superior. Otherwise, when compared to studies conducted in native vegetation and urban fragments, the richness is similar, and sometimes higher. This relatively high number of associations brings out the vulnerability of the canola fields according to the expansion of its cultivated area. Nine species of Pentatomidae are recorded on canola for the first time in Brazil. The most abundant species reported here are often stressed as stink bugs of economic importance in agro-ecosystems. The economic importance of each species varies greatly depending on the plant attacked. Detailed studies are needed to evaluate the damage caused to canola by stink bugs.

Spatial distribution of nymphs and adults of Euschistus heros (Fabricius, 1794) (Heteroptera: Pentatomidae) in transgenic soybean cultivars of different maturing cycles / Distribuição espacial de ninfas e adultos de Euschistus heros (Fabricius, 1794) (Heteroptera: Pentatomidae) em cultivares transgênicas de soja de diferentes ciclos de desenvolvimento

The neotropical stink bug Euschistus heros is the predominant and most important insect pest affecting soybean cultivation. Knowledge of the spatial pattern of the pest in an area is critical to understanding its behavior. The objective of this work was to study the spatial distribution of E. heros in transgenic soybean cultivars of different maturing cycles. The experiments were conducted in the seasons 2013/14 and 2014/15 in FCAV/UNESP, Jaboticabal, SP. Three fields were selected, and each was marked an area of 8.000 m² (0.8 ha), with each area divided into 80 portions of 100 m2 (10 m x 10 m). The transgenic soybean cultivars of different maturing cycles were: SYN 1365 RR (early), M 7908 RR (average), and BRS Valiosa RR (late). Samples were taken weekly using a beat sheet, registering the number of nymphs and adults of E. heros. To study the dispersion of E. heros, the following indices were used: variance/mean ratio, Morisita index, Green coefficient, and the exponent k of the negative binomial distribution. For studies of special distribution models of E. heros, adjustments of Poisson distribution and negative binomial distribution were tested. The spatial distribution of nymphs and adults was aggregated for all the cultivars studied, indicating that cultivars did not alter the distribution behavior of E. heros.(AU)

O percevejo-marrom-da-soja Euschistus heros, destaca-se como o inseto-praga predominante e mais importante na cultura. O conhecimento do padrão espacial da praga na área é fundamental para o entendimento do seu comportamento. O objetivo do presente trabalho foi estudar a distribuição espacial 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. 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 usando pano de batida, registrando-se o número de ninfas e adultos. Para o estudo da dispersão de E. heros foram utilizados os seguintes índices: razão variância/média, índice de Morisita, coeficiente de Green e o expoente k da distribuição binomial negativa. Para os estudos dos modelos de distribuição espacial de E. heros foram testados os ajustes das distribuições de Poisson e distribuição binomial negativa. A distribuição espacial de ninfas e adultosfoi agregada para todas as cultivares em estudo, ou seja, as cultivares não alteram o comportamento de distribuição de E. heros.(AU)

Spatial distribution of nymphs and adults of Euschistus heros (Fabricius, 1794) (Heteroptera: Pentatomidae) in transgenic soybean cultivars of different maturing cycles / Distribuição espacial de ninfas e adultos de Euschistus heros (Fabricius, 1794) (Heteroptera: Pentatomidae) em cultivares transgênicas de soja de diferentes ciclos de desenvolvimento

The neotropical stink bug Euschistus heros is the predominant and most important insect pest affecting soybean cultivation. Knowledge of the spatial pattern of the pest in an area is critical to understanding its behavior. The objective of this work was to study the spatial distribution of E. heros in transgenic soybean cultivars of different maturing cycles. The experiments were conducted in the seasons 2013/14 and 2014/15 in FCAV/UNESP, Jaboticabal, SP. Three fields were selected, and each was marked an area of 8.000 m² (0.8 ha), with each area divided into 80 portions of 100 m2 (10 m x 10 m). The transgenic soybean cultivars of different maturing cycles were: SYN 1365 RR (early), M 7908 RR (average), and BRS Valiosa RR (late). Samples were taken weekly using a beat sheet, registering the number of nymphs and adults of E. heros. To study the dispersion of E. heros, the following indices were used: variance/mean ratio, Morisita index, Green coefficient, and the exponent k of the negative binomial distribution. For studies of special distribution models of E. heros, adjustments of Poisson distribution and negative binomial distribution were tested. The spatial distribution of nymphs and adults was aggregated for all the cultivars studied, indicating that cultivars did not alter the distribution behavior of E. heros.

O percevejo-marrom-da-soja Euschistus heros, destaca-se como o inseto-praga predominante e mais importante na cultura. O conhecimento do padrão espacial da praga na área é fundamental para o entendimento do seu comportamento. O objetivo do presente trabalho foi estudar a distribuição espacial 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. 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 usando pano de batida, registrando-se o número de ninfas e adultos. Para o estudo da dispersão de E. heros foram utilizados os seguintes índices: razão variância/média, índice de Morisita, coeficiente de Green e o expoente k da distribuição binomial negativa. Para os estudos dos modelos de distribuição espacial de E. heros foram testados os ajustes das distribuições de Poisson e distribuição binomial negativa. A distribuição espacial de ninfas e adultosfoi agregada para todas as cultivares em estudo, ou seja, as cultivares não alteram o comportamento de distribuição de E. heros.

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.

Sequential sampling of Euschistus heros (Heteroptera: Pentatomidae) in soybean

Integrated pest management programs for soybean (Glycine max (L.) Merrill) must be based on efficient sampling plans for estimating the pest population. Based on the spatial distribution of the Neotropical brown stink bug Euschistus heros (Fabricius, 1794) found on soybean, it was possible to construct a sequential sampling plan for the survey of this insect found on soybean. The experiment was carried out during two growing seasons, 2010/2011 and 2011/2012, using the transgenic soybean cultivar M 7908 RR, in plots of 10,000 m² subdivided into 100 plots of 100 m² (10 m × 10 m). Nymphs > 0.5 cm (4th and 5th instars) plus adults were counted weekly from five drop cloth technique samplings per plot. To evaluate insect dispersion in the area, the following indices were used: variance/mean ratio, Morisita's index, Green's coefficient, the k exponent of the negative binomial distribution, and estimation of the common exponent k (kc). To study probabilistic models to describe the spatial distribution of the insects, adjustments of the Poisson and negative binomial distributions were tested. Two sequential sampling plans for separate fields, one for grain production and the other for seed production, were prepared. The data fitted a negative binomial distribution and a sampling plan was drawn up using the sequential likelihood ratio test (SLRT). The maximum sampling unit number expected for control-related decision making was six in grain production fields, and nine in seed production fields.(AU)

Sequential sampling of Euschistus heros (Heteroptera: Pentatomidae) in soybean

Integrated pest management programs for soybean (Glycine max (L.) Merrill) must be based on efficient sampling plans for estimating the pest population. Based on the spatial distribution of the Neotropical brown stink bug Euschistus heros (Fabricius, 1794) found on soybean, it was possible to construct a sequential sampling plan for the survey of this insect found on soybean. The experiment was carried out during two growing seasons, 2010/2011 and 2011/2012, using the transgenic soybean cultivar M 7908 RR, in plots of 10,000 m² subdivided into 100 plots of 100 m² (10 m × 10 m). Nymphs > 0.5 cm (4th and 5th instars) plus adults were counted weekly from five drop cloth technique samplings per plot. To evaluate insect dispersion in the area, the following indices were used: variance/mean ratio, Morisita's index, Green's coefficient, the k exponent of the negative binomial distribution, and estimation of the common exponent k (kc). To study probabilistic models to describe the spatial distribution of the insects, adjustments of the Poisson and negative binomial distributions were tested. Two sequential sampling plans for separate fields, one for grain production and the other for seed production, were prepared. The data fitted a negative binomial distribution and a sampling plan was drawn up using the sequential likelihood ratio test (SLRT). The maximum sampling unit number expected for control-related decision making was six in grain production fields, and nine in seed production fields.

Photophase influence on the reproductive diapause, seasonal morphs, and feeding activity of Euschistus heros (Fabr., 1798) (Hemiptera: Pentatomidae)

Laboratory studies were conducted to verify the influence of photophase on diapause incidence in the Neotropical brown stink bug, Euschistus heros (Fabr., 1798), fed with soybean [Glycine max (L.)] Merrill pods. Nymphs were maintained at three different photophases: 10 h, 12 h, and 14 h, with constant temperature of 25 ± 1ºC and relative humidity of 65 ± 5%. With 14 h, aproximately 100% of the adults showed mature reproductive organs; the shoulder (spine) length was significantly greater (2.96 and 2.79 mm for females and males, respectively) than those of bugs maintained at the photophase of 12 h (2.60 mm for females and males) and 10 h (2.59 and 2.53 mm for females and males). At the longer photophase (14 h), E. heros showed better reproductive performance and greater feeding activity than insects reared at 10 h and 12 h; in all photophases bugs tended to reduce feeding from the 1st to the 6th week of life. Body color was considered an unreliable parameter to indicate diapause incidence. However, at 14 h, 60% of the insects were dark brown and 40% were reddish brown. These results indicate that E. heros enters reproductive diapause with photophase of 12 hours or less, showing immature reproductive organs or with intermediate development, with shoulder (spine) less developed and reduced feeding activity.

A influência da fotofase na diapausa do percevejo-marrom Euschistus heros (Fabr.) alimentado com soja [Glycine max (L.)] Merrill foi estudada em laboratório. Os experimentos foram conduzidos sob três fotofases, 10 h, 12 h e 14 h, mantendo-se constantes a temperatura (25 ± 1ºC) e a umidade relativa (65 ± 5%). Sob 14 h, cerca de 100% dos insetos apresentaram órgãos reprodutivos maduros; os espinhos pronotais, medidos aos 10 dias de vida adulta, foram significativamente maiores (2,96 e 2,79 mm para fêmeas e machos, respectivamente) que os espinhos dos insetos mantidos sob 12 h (2,60 mm para fêmeas e machos) ou 10 h (2,59 e 2,53 mm para fêmeas e machos, respectivamente). Com a fotofase mais longa, ocorreu desempenho reprodutivo e atividade alimentar maiores do que o observado para adultos criados sob fotofase de 10 h ou 12 h. Em todas as fotofases observou-se tendência de diminuição da atividade alimentar dos percevejos da 1ª à 6ª semana. A coloração do corpo mostrou-se como um parâmetro não confiável para indicar a diapausa, mas, sob 14 h, cerca de 60% dos insetos apresentaram corpo marrom-escuro e os demais marrom-avermelhado. Esses resultados demonstram que esse percevejo entra em diapausa reprodutiva sob fotofase de 12 horas ou menos, apresentando órgãos reprodutivos imaturos ou com desenvolvimento intermediário, espinhos pronotais menos desenvolvidos e redução na atividade alimentar.

Photophase influence on the reproductive diapause, seasonal morphs, and feeding activity of Euschistus heros (Fabr., 1798) (Hemiptera: Pentatomidae)

Laboratory studies were conducted to verify the influence of photophase on diapause incidence in the Neotropical brown stink bug, Euschistus heros (Fabr., 1798), fed with soybean [Glycine max (L.)] Merrill pods. Nymphs were maintained at three different photophases: 10 h, 12 h, and 14 h, with constant temperature of 25 ± 1ºC and relative humidity of 65 ± 5%. With 14 h, aproximately 100% of the adults showed mature reproductive organs; the shoulder (spine) length was significantly greater (2.96 and 2.79 mm for females and males, respectively) than those of bugs maintained at the photophase of 12 h (2.60 mm for females and males) and 10 h (2.59 and 2.53 mm for females and males). At the longer photophase (14 h), E. heros showed better reproductive performance and greater feeding activity than insects reared at 10 h and 12 h; in all photophases bugs tended to reduce feeding from the 1st to the 6th week of life. Body color was considered an unreliable parameter to indicate diapause incidence. However, at 14 h, 60% of the insects were dark brown and 40% were reddish brown. These results indicate that E. heros enters reproductive diapause with photophase of 12 hours or less, showing immature reproductive organs or with intermediate development, with shoulder (spine) less developed and reduced feeding activity.

A influência da fotofase na diapausa do percevejo-marrom Euschistus heros (Fabr.) alimentado com soja [Glycine max (L.)] Merrill foi estudada em laboratório. Os experimentos foram conduzidos sob três fotofases, 10 h, 12 h e 14 h, mantendo-se constantes a temperatura (25 ± 1ºC) e a umidade relativa (65 ± 5%). Sob 14 h, cerca de 100% dos insetos apresentaram órgãos reprodutivos maduros; os espinhos pronotais, medidos aos 10 dias de vida adulta, foram significativamente maiores (2,96 e 2,79 mm para fêmeas e machos, respectivamente) que os espinhos dos insetos mantidos sob 12 h (2,60 mm para fêmeas e machos) ou 10 h (2,59 e 2,53 mm para fêmeas e machos, respectivamente). Com a fotofase mais longa, ocorreu desempenho reprodutivo e atividade alimentar maiores do que o observado para adultos criados sob fotofase de 10 h ou 12 h. Em todas as fotofases observou-se tendência de diminuição da atividade alimentar dos percevejos da 1ª à 6ª semana. A coloração do corpo mostrou-se como um parâmetro não confiável para indicar a diapausa, mas, sob 14 h, cerca de 60% dos insetos apresentaram corpo marrom-escuro e os demais marrom-avermelhado. Esses resultados demonstram que esse percevejo entra em diapausa reprodutiva sob fotofase de 12 horas ou menos, apresentando órgãos reprodutivos imaturos ou com desenvolvimento intermediário, espinhos pronotais menos desenvolvidos e redução na atividade alimentar.

Nymphal and Adult Performance of Euschistus heros (Fabr. ) (Hemiptera: Pentatomidae), as a Potential Alternative Host for Egg Parasitoids Multiplication / Desempenho de Ninfas e Adultos de Euschistus heros (Fabr. ) (Hemiptera: Pentatomidae), Como Hospedeiro Alternativo Potencial na Multiplicação de Parasitóides de Ovos

Este trabalho teve como objetivo avaliar o potencial de Euschistus heros (Fabr.) (Hemiptera: Pentatomidae) como hospedeiro na multiplicação de parasitóides de ovos, através da determinação do desempenho de ninfas e de adultos, de laboratório e campo, de E. heros, comparativamente a Nezara viridula (L.) (Hemiptera: Pentatomidae), em condições massais. A partir de 100 ovos colocados entre as folhas de uma planta de soja contida em gaiola (50x50x70 cm), determinou-se o número de ninfas que atingiram a fase adulta e o tempo de desenvolvimento ninfal. As ninfas foram alimentadas com vagens verdes de soja e grão secos de soja e amendoim. Para estudar a sobrevivência e o desempenho reprodutivo, 100 casais de E. heros e N. viridula, provenientes do campo e laboratório, foram alocados em gaiolas contendo a mesma dieta das ninfas e observados durante 13 semanas (fevereiro a maio - 1999). Verificou-se que o tempo de desenvolvimento das ninfas de E. heros e N. viridula foi 33,0 e 34,0 dias e que 65,0 por cento e 71,3 por cento das ninfas atingiram a fase adulta, respectivamente. Adultos de E. heros criados em laboratório produziram 2,5 vezes mais ovos (5547,0 ovos/gaiola) do que aqueles provenientes do campo (2262,7 ovos/gaiola). Os adultos de E. heros provenientes do campo apresentaram redução na sobrevivência e no número de ovos produzidos devido ao elevado índice de parasitismo por Hexacladia smithii Ash. (Hymenoptera: Encyrtidae). Os adultos de N. viridula provenientes do campo apresentaram produção de ovos 1,7 vezes maior (6304,9 ovos/gaiola) do que a dos percevejos criados em laboratório (3609,2 ovos/gaiola). E. heros criado em laboratório é um promissor hospedeiro na multiplicação de parasitóides de ovos, quando comparado com N. viridula coletado no campo.

This research aimed to evaluate the potential of Euschistus heros (Fabr.) (Hemiptera: Pentatomidae) as host for multiplication of egg parasitoids, by determining the nymphal and adult performance of E. heros from laboratory and the field, comparing with Nezara viridula (L.) (Hemiptera: Pentatomidae), under mass conditions. One hundred eggs of E. heros and N. viridula were placed among the leaves of soybean plants contained in cages (50x50x70 cm) and observation were made until adult emergence. The nymphs fed on soybean pods, dry soybean and peanuts seeds. The number of nymphs that reached adulthood and the development time were calculated. The survivorship and reproduction performance of laboratory and field populations of E. heros and N. viridula were evaluated during 13 weeks in February-May 1999. The number of eggs produced by 100 pairs of stink bugs per cage containing the same diet was recorded. Nymphal development time of E. heros and N. viridula was 33.0 and 34.0 days and 65.0 percent and 71.3 percent of nymphs reached adulthood, respectively. Adults of E. heros reared under laboratory conditions produced 2.5 times more eggs (5547.0 eggs/cage) than those collected in the field (2262.7 eggs/cage). The adult field population of E. heros had reduced reproduction and longevity due to parasitism by Hexacladia smithii Ash. (Hymenoptera: Encyrtidae). The N. viridula adults collected in the field produced 1.7 times more eggs (6304.9 eggs/cage) than those reared in the laboratory (3609.2 eggs/cage). E. heros laboratory reared is a promising host for egg parasitoids multiplication when compared with N. viridula collected in the field.