Exploration of entomopathogenic bacteria as potential control agents for brown stink bug Euschistus heros (F.) (Hemiptera: Pentatomidae)

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.

Soybeans (Glycine max) can be planted along the upper Texas Gulf Coast from mid-March through May to take advantage of early season rains and to complete harvest before hurricane season and fall rains become a problem. When average to above average rainfall was received in May through July, yields were greater with the early April to mid-April planting; however, under high rainfall conditions throughout the season, the mid-April to early May planting produced the highest yields, with yields of over 4000 kg/ha. When rainfall was below normal, late March to early April plantings produced the greatest yields. When rainfall was above average, soybeans took longer to reach harvestability regardless of cultivar or plant dates, while under drought conditions the interval between planting and harvest was reduced. However, when planting was delayed, there was a greater risk of detrimental late-season effects from southern green stink bug (Nezara viridula) or the brown stink bug (Euschistus heros).

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.

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.

Non-targeted insecticidal stress on the Neotropical brown stink bug 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.

Extracts of the seeds of Tephrosia vogelii Hook. f. were studied in relation to its chemical composition and toxicity to the brown stink bug Euschistus heros (F.). The extracts were obtained in ethyl acetate and ethanol in the sequence according to the polar nature of the solvents. Extracts were sprayed in concentration of 1.0, 2.5, 5.0, 7.5 and 10% on third-instars nymphs and adults, and mortality was recorded. Presence two rotenoids in ethyl acetate was detected, with analyzed with gas chromatography-mass spectrometry (GC-MS). Crude fraction analyses confirmed the presence of these rotenoids (tephrosin - 2.71% in ethyl acetate and 3.66% in methanol; and deguelin - 10.46% in ethyl acetate and 1.22% in methanol) and three other rotenoids in small amounts. Eight days after applications, ethyl acetate caused more stink bugs mortality and on less time than ethanol extract, because great quantity of rotenoids, as polarity. Concentrations above to 1 and 2.5% of the ethyl acetate extracts caused mortality above 80% of the nymphs and adults of E. heros, respectively. Concentration were considered high, thus chemist analyzes demonstrated high rotenoids presence. In conclusion, seed T. vogelli extracts, rich in deguelin and tephrosin (3:1), cause mortality of E. heros, however, high concentration are necessary.

Purification, characterization, and inhibition studies of a new acetylcholinesterase obtained from 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.

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.

Influence of intra- and inter-specific competition between egg parasitoids on the effectiveness of biological control of Euschistus heros (Hemiptera: Pentatomidae)

Entre os insetos que atacam a soja, o percevejo marrom Euschistus heros (Fabricius) é considerado uma das principais pragas. Os objetivos deste trabalho foram avaliar a ocorrência de parasitismo em adultos do percevejo marrom E. hero, no período de cultivo da soja e de entressafra, e identificar seus sítios de diapausa no período de entressafra, na região da Grande Dourados, Mato Grosso do Sul (MS). Foram coletados adultos do percevejo em lavouras de soja, durante as safras 2004/05 e 2005/06, sendo as coletas realizadas semanalmente. No período de entressafra da soja de 2005 e 2006, foram realizadas inspeções em diferentes ambientes vegetais visando a constatar possíveis sítios de diapausa do percevejo, bem como avaliar a ocorrência de parasitismo nesses ambientes. Em cada coleta, foram individualizados 40 adultos em caixas gerbox contendo Ligustrum lucidum Ait. (Oleraceae), sendo os insetos observados durante um período de 40 dias. Os parasitoides foram armazenados em álcool 70% e encaminhados para identificação. O índice natural de parasitismo de adultos de E. heros amostrados no período de safra e de entressafra de soja variou de 0,0 a 5,0%, considerando-se as diferentes coletas realizadas, sendo Hexacladia smithii Ashmead (Hymenoptera: Encyrtidae) a única espécie de parasitoide ocorrente. No período de entressafra, foi verificada maior incidência do percevejo E. heros em folhas secas de mangueira (Mangifera indica L.) caídas no chão, evidenciando que esse ambiente é um importante sítio de diapausa para essa praga na região.

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.

Enhanced reproductive output after sublethal insecticide exposure, including neonicotinoid exposure, has been reported in a diversity of arthropods. Suspicions of such a phenomenon in the Neotropical brown stink bug, Euschistus heros (Hemiptera: Pentatomidae), were sparked by the increasing densities of naturally occurring populations of this insect pest species in Brazilian soybean fields. Here, we tested whether the sublethal exposure to imidacloprid would induce changes in the survival and reproductive performances of E. heros adult females. The imidacloprid estimated LC50 was 0.83 (0.60–1.25) μg a.i./cm2, and the dose recommended for field applications (4.2 μg a.i./cm2) was within the concentration range of the imidacloprid estimated LC80 [2.66 (1.65–5.49) μg a.i./cm2]. Newly emerged (≤24 h) adult females were exposed for 48 h to dry imidacloprid residues (0.042 μg/cm2, equivalent to 1 % of the field rate dose) and exhibited higher levels of cell damage, greater ovariole length, and a larger area of the most developed follicle in their ovaries up to the 6th day of adulthood. Furthermore, these females exhibited reduced rates of survival but higher fecundity and fertility rates compared with untreated females. Our results thus suggest that females of E. heros increased their reproductive output in response to the imidacloprid sublethal exposure. These findings suggest a potential involvement of sublethal exposure to neonicotinoids in the recent outbreaks of the Neotropical brown stink bug E. heros observed in Brazilian soybean-producing regions.

Simple SummaryBiological control programs are used to effectively manage pests in a more sustainable way, such as the case of the microwasp parasitoid Telenomus podisi for managing eggs of the brown stink bug Euschistus heros, a key pest in South American soybean. A biological control program requires continuous production of the parasitoids and thus, artificial diets and freezing of host eggs are necessary. We evaluated the parasitism capacity of T. podisi reared on fresh or previously frozen eggs from E. heros fed on natural or two artificial diets. Seven constant temperatures were tested for each condition. We measured biological parameters of wasps and the rates of parasitism. We found that 24 °C had better parasitism and viability parameters, and was most-favorable to T. podisi production. We also found that both tested artificial diets for E. heros produced eggs that support mass rearing of this egg parasitoid.The parasitoid Telenomus podisi Ashmead, 1893 is used in biological control programs in Brazil against eggs of Euschistus heros (Fabricius, 1798), a key pest of soybean, Glycine max (L.) Merr. To optimize the mass production of parasitoids, artificial diets and storage of host eggs at low temperatures have been developed; however, direct comparisons of the effects of these conditions have not occurred. We assessed a double factorial arrangement composed of six treatments (fresh or cryopreserved E. heros eggs from adults fed on natural or two artificial diets). We evaluated the biological characteristics and parasitism capacity of T. podisi produced from these treatments across seven temperatures. The thermal range between 21 and 30 °C resulted in satisfactory daily parasitism in all treatments tested, with an inverse relationship between temperature and female survival. The best parasitoid biological parameters were found between 21 and 27 °C, where all tested diets supported T. podisi development, with the best results from artificial diets. Fresh eggs and those frozen in liquid nitrogen and stored at −196 °C until use supported parasitoid development. These results suggest that the best method to mass rear T. podisi is to use artificial diets to rear E. heros and store eggs until needed, and then rear parasitoids at 24 °C.