Competition between the phytophagous stink bugs Euschistus heros and Piezodorus guildinii in soybeans

The first extensive analysis of species composition and abundance of stink bugs (Hemiptera: Pentatomidae) on soybean crops in Brazil

BACKGROUND

Soybean is the third-greatest global commodity crop with respect to grain production, Brazil is the largest soybean producer in the world. We performed the first extensive survey including all the five main soybean cultivation regions in Brazil over three seasons (2018/2019, 2019/2020, and 2020/2021). A total of 2386 localities were sampled, corresponding to 145 municipalities in 11 states. Sampling was carried out between the R1 and R8 soybean growth stages, using a beating sheet.

RESULTS

Fifteen species were recorded, with five species accounting for more than 99% of the sampled insects. The Neotropical brown stink bug, Euschistus heros (F.), was the most abundant species (82.4% of the adults and 84.1% of the nymphs overall), with differences in the mean abundance between soybean macroregions. The melacanthus green belly stink bug, Diceraeus melacanthus Dallas was the second most abundant species overall, followed by the brown winged stink bug, Edessa meditabunda (F.), the furcatus green belly stink bug, Diceraeus furcatus (F.) and the red-banded green stink bug, Piezodorus guildinii (Westwood). The relative abundance of each species differed between soybean macroregions. The mean abundance of nymphs and adults of Euschistus heros at different soybean reproductive stages showed an increase from early reproductive stages to the beginning of the late reproductive stages (R5 or R6).

CONCLUSION

This large-scale assessment of stink bugs provides a basis for outlining integrated pest management programs and drives the development of monitoring and control strategies, as well as future studies investigating population dynamics over time and space in soybean fields. © 2024 Society of Chemical Industry.

Comparative Genomics and the Salivary Transcriptome of the Redbanded Stink Bug Shed Light on Its High Damage Potential to Soybean

The redbanded stink bug, Piezodorus guildinii (Westwood) (Hemiptera: Pentatomidae), is a significant soybean pest in the Americas, which inflicts more physical damage on soybean than other native stink bugs. Studies suggest that its heightened impact is attributed to the aggressive digestive properties of its saliva. Despite its agricultural importance, the factors driving its greater ability to degrade plant tissues have remained unexplored in a genomic evolutionary context. In this study, we hypothesized that lineage-specific gene family expansions have increased the copy number of digestive genes expressed in the salivary glands. To investigate this, we annotated a previously published genome assembly of the redbanded stink bug, performed a comparative genomic analysis on 11 hemipteran species, and reconstructed patterns of gene duplication, gain, and loss in the redbanded stink bug. We also performed RNA-seq on the redbanded stink bug's salivary tissues, along with the rest of the body without salivary glands. We identified hundreds of differentially expressed salivary genes, including a subset lost in other stink bug lineages, but retained and expressed in the redbanded stink bug's salivary glands. These genes were significantly enriched with protein families involved in proteolysis, potentially explaining the redbanded stink bug's heightened damage to soybeans. Contrary to our hypothesis, we found no support for an enrichment of duplicated digestive genes that are also differentially expressed in the salivary glands of the redbanded stink bug. Nonetheless, these results provide insight into the evolution of this important crop pest, establishing a link between its genomic history and its agriculturally important physiology.

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.

Larval competition analysis and its effect on growth of Ostrinia furnacalis (Lepidoptera: Crambidae) at natural conditions in Northeast China

The Asian corn borer (Ostrinia furnacalis, Lepidoptera, Crambidae) and Oriental armyworm (Mythimna separata, Lepidoptera, Noctuidae) are 2 major lepidopteran pests of the maize plant, especially the whorls and tassels. The aim of this study was to investigate competition between 2 lepidopteran pests of maize. Intraspecific and interspecific competition occurs when O. furnacalis and M. separata larvae interact with various stages of the maize plant. Therefore, determining whether this competition can decrease larval damage by causing adverse effects on larval growth is crucial. During the maize growing season of 2022, the interaction of these species was assessed in the experimental field of Jilin Agricultural University, China. Interspecific and intraspecific competition of larvae in different maize tissues and the influence of competition on larval development was determined in the fields. The results showed that first, probing behavior was significantly frequent in O. furnacalis larvae; intraspecific and interspecific attack was significant at 4th instar (with leaf, silk, and kernel). Interspecific defense behavior was significant at 3rd instar (without food). O. furnacalis larvae showed attack behavior toward M. separata larvae frequently. Second, competition increased the mortality rate of O. furnacalis larvae (intraspecific, 67%; interspecific, 33%) and decreased pupation emergence rate. Thus, intraspecific and interspecific competition might affect the competitive displacement of pest species sharing the same ecological niche, as well as the prevalence and population dynamics of pests, and help to develop integrated pest management strategies.

The stink bug Dichelops furcatus: a new pest of corn that emerges from soybean stubble

Over the last decades, Argentine and Brazilian farmers have adopted no-tillage cultivation systems and multiple cropping, which have decreased the abundance of traditional pests, such as Nezara viridula, and favored the development of some stink bugs of secondary importance, like Dichelops furcatus, D. melacanthus and Euschistus heros. No-till farming leaves the soil undisturbed, to mitigate erosion, and sufficient crop residue on the field, which is used by D. furcatus as a shelter under unfavorable conditions, and as a shelter against insecticides. Moreover, implementing multiple cropping systems increases crop rotation from soybean to corn, and places overwintering adults of D. furcatus in contact with corn seedlings in spring. Attacks of this stink bug species produce deformation and abortion of corn seedlings, resulting in up to 50% corn yield reduction. The increasing abundance of D. furcatus intensifies the damage on developing pods and seeds of soybean, becoming a primary pest of soybean, and a new pest of corn. Here we summarize the current knowledge about D. furcatus, its biology, life cycle, and geographical distribution pattern in South America. Additionally, we describe the general causes and consequences of D. furcatus as a new pest of corn that emerges from crop stubble. Then, we provide an overview of the chemical control, natural enemies, and possible agronomical practices to improve sustainable crop production methods to control this pest. © 2022 Society of Chemical Industry.

Dynamics in Pest Status of Phytophagous Stink Bugs in the Neotropics

In this review article, we present and discuss the main factors influencing the change in pest status of phytophagous stink bugs (Hemiptera: Heteroptera: Pentatomidae) in the Neotropics. We have surveyed the published records over the past 50 years and divided this timeframe into decades. This was done to rank in time the relative abundance (percentage) of the following species, known pests of commodities, in the Neotropical Region: the Neotropical brown stink bug, Euschistus heros (F.); the green-bellied stink bugs, Diceraeus melacanthus Dallas and D. furcatus (F.); the redbanded stink bug, Piezodorus guildinii (Westwood); the southern green stink bug, Nezara viridula (L.); and the brown-winged stink bug, Edessa meditabunda (F.). The analysis showed that E. heros, D. melacanthus, and D. furcatus, formerly minor pests, in the last decade (2010s) became major pests. The once most important pest species, N. viridula and P. guildinii, decreased their pest status in the last decade. Edessa meditabunda, which never achieved high populations, showed a tendency to increase in abundance in the last two decades (2000s and 2010s). Major factors believed to influence the dynamics of pest populations of stink bugs in the Neotropics include cropping systems (no-tillage replacing conventional soil plowing, and crop rotation); genetically modified (GM) plants (mostly plants expressing insecticidal crystalline proteins derived from Bacillus thuringiensis Berliner - Bt); change in availability of host and associated plants in the new landscape scenario; increased usage of chemicals (insecticides, fungicides, and herbicides); and change in the role of natural enemies in modern day agriculture.

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

BACKGROUND

Crop 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.

RESULTS

In 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.

CONCLUSION

Our 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.

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.

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

BACKGROUND

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.

RESULTS

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.

CONCLUSIONS

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.

Potential for insecticide-mediated shift in ecological dominance between two competing aphid species

Competition is a key structuring component of biological communities, which is affected by both biotic and abiotic environmental stressors. Among the latter, anthropic stressors and particularly pesticides are noteworthy due to their intrinsic toxicity and large use in agroecosystems. However this issue has been scarcely documented so far. In this context, we carried out experiments under laboratory conditions to evaluate stress imposed by the neonicotinoid insecticide imidacloprid on intra and interspecific competition among two major wheat pest aphids. The bird cherry-oat aphid Rhopalosiphum padi L. and the English grain aphid Sitobion avenae F. were subjected to competition on wheat seedlings under varying density combinations of both species and subjected or not to imidacloprid exposure. Intraspecific competition does take place without insecticide exposure, but so does interspecific competition between both aphid species with R. padi prevailing over S. avenae. Imidacloprid interfered with both intra and interspecific competition suppressing the former and even the latter for up to 14 days, but not afterwards when a shift in dominance takes place favoring S. avenae over R. padi, in contrast with the interspecific competition without imidacloprid exposure. These findings hinted that insecticides are indeed able to mediate species interaction and competition influencing community structure and raising management concerns for favoring potential secondary pest outbreaks.

Diversity of Stink Bug Adults and Their Parasitoids in Soybean Crops in Brazil: Influence of a Latitudinal Gradient and Insecticide Application Intensity

Over the last 50 yr, the geographical distribution of soybean crop production in Brazil has expanded from the southern region to Maranhão state in the north. We evaluated if this latitudinal expansion affected the community of stink bugs (Hemiptera: Pentatomidae) and their parasitoids. The fauna of stink bugs and their adult parasitoids were studied in nine soybean production regions in Brazil. Stink bugs were sampled using a shake cloth and and held in laboratory cages with natural diet to await emergence of parasitoids. Stink bug and parasitoid species composition did not shift along the latitudinal gradient. Euschistus heros (Fabricius, 1798) (Hemiptera: Pentatomidae) was the most abundant stink bug and occurred in all sampling regions. Hexacladia smithii Ashmead, 1891 (Hymenoptera: Encyrtidae), Cylindromyia brasiliana (Townsend, 1927), Ectophasiopsis sp., Eutrichopoda sp., Gymnoclytia sp., Phasia sp., and Trichopoda sp. (Diptera: Tachinidae) were the parasitoid adult stink bugs that we registered. Parasitism indexes were low, ranging from 0.77 to 6.05% through the regions. On the other hand, parasitism rates were higher in areas with reduced insecticide application in comparison to areas with intensive insecticide use.

Ultrastructural analysis of salivary glands in a phytophagous stink bug revealed the presence of unexpected muscles

The exceptional abilities of stink bugs (Hemiptera: Pentatomidae) to colonize a diverse group of plants have been attributed to the feeding behaviors and the functions of the salivary complex of these insects. Here, we describe the ultrastructure of the salivary glands of the Neotropical brown stink bug, Euschistus heros, which is a major component of the pentatomid pest complex on soybeans, Glycine max, in the neotropics. Our results revealed a salivary gland complex consisting of two lobes (i.e., anterior and posterior), with a constriction between them (i.e., the hilum), in which the salivary and accessory gland ducts are inserted. The principal gland epithelium has a single layer of cells lining an enlarged lumen filled with saliva, and these cells are cuboidal, rich in rough endoplasmic reticulum and secretory vesicles, with well-developed nuclei, all of which are typical features of protein-secreting cells. We report, for the first time in insects, the presence of a layer of muscle cells surrounding the columnar hilum epithelium. The accessory salivary gland cells are cuboidal with nuclei containing condensed chromatin and cytoplasm rich in vacuoles and rough endoplasmic reticulum, indicating the potential involvement of these glands in water transport/secretion. The lumen content of each lobe of the principal gland suggests that the lobes produce different compounds. Thus, our results suggest that the E. heros salivary complex might have unconventional mechanisms to mix/release saliva, which might help explain the polyphagous abilities of these insects.

What Happened to Nezara viridula (L.) in the Americas? Possible Reasons to Explain Populations Decline

Once abundant in the Americas, the southern green stink bug Nezara viridula (L.) has gradually declined in numbers. Until the 1990s, it was considered the main pest of major crops such as soybean, Glycine max (L.) Merrill, particularly in southern Brazil and southern USA, as well as Argentina, Uruguay, and other countries. In the past 15+ years, a dramatic population decrease was observed to the point of now being considered a secondary pest in these referred countries. In this article, we list and discuss possible reasons which explain the decline in N. viridula population in the Americas. These factors include the following: (1) the steady increase of herbicides used in no-tillage/multiple cropping systems affecting potential hosts such as weeds in crop fields and nearby natural vegetation; (2) the change in cultivation systems, mostly in the Neotropics, favoring other species more adapted to exploit crops in modern day agriculture; (3) competition among several species of stink bugs that colonize major crops; (4) the growing impact of several species of egg parasitoids, some of them laboratory reared and released in crop fields, and other natural enemies (parasitoids and predators); and (5) the impact of global climate change affecting its distribution and biology.