Neotropical Stink Bug Research Articles

Dynamic Energy Budget approach for modeling growth and reproduction of Neotropical stink bugs

Global warming and other climate change drivers have a significant impact on the life cycle of insects which in turn affect their population dynamics and geographic distribution. Among these insects are stink bugs (Hemiptera: Pentatomidae), which are hemimetabolous agricultural pests that cause major damage on crops in many countries. Their life cycle consists of three stages: egg, nymph, and adult. The nymph grows and molts through a small number of instars until reaching emergence, at which point growth ceases. The Dynamic Energy Budget (DEB) theory provides the framework for modeling the life cycle of stink bugs. Nevertheless, determining the most accurate model for nymphal growth and energy allocation during the adult stage remains a challenge, as the best model is not always evident. For two species of the Pentatomidae family, we parameterized and evaluated four DEB models that differ in nymphal growth and the energy allocation rules in adults: isomorphic or V1-morphic nymphal growth combined with the energy allocation scheme in adults that follows the κ-rule or the scheme that the κ-rule is not operational in adults. Overall, all models fit the data, but those with isomorphic nymphal growth reproduce the growth trajectories and instar duration better. However, with the available data we cannot conclude which rule is most likely the energy allocation in adults. Using these models, we further studied the effects of temperature and food availability on individual dynamics and its life cycle. Simulations show that temperature has a higher impact on the duration of life stages and survival, while food availability affects egg production. When simulating a variable environment in terms of temperature for both a summer and a fall generation, the results reveal that the summer generation has higher feeding and egg production rates in comparison to the fall generation. DEB models are valuable tools for simulating individual under various environmental conditions and when combined with appropriate modeling approaches, they can predict population traits and even the potential distribution of a species.

De novo construction of a transcriptome for the stink bug crop pest Chinavia impicticornis during late development.

Chinavia impicticornis is a neotropical stink bug of economic importance for various crops. Little is known about the development of the species, or the genetic mechanisms that may favor the establishment of populations in cultivated plants. Here, we conduct the first large-scale molecular study of C. impicticornis. Using tissues derived from the genitalia and the rest of the body for two immature stages of both males and females, we generated RNA-seq data, then assembled and functionally annotated a transcriptome. The de novo-assembled transcriptome contained around 400,000 contigs, with an average length of 688bp. After pruning duplicated sequences and conducting a functional annotation, the final annotated transcriptome comprised 39,478 transcripts, of which 12,665 were assigned to Gene Ontology (GO) terms. These novel datasets will be invaluable for the discovery of molecular processes related to morphogenesis and immature biology. We hope to contribute to the growing body of research on stink bug evolution and development, as well as to the development of biorational pest management solutions.

A novel trophobiotic interaction between a Neotropical stink bug and an ant species: Insights into potential benefits to the host plant

Trophobiotic interactions occur when phytophagous insects provide a sugary liquid, the honeydew, for ants and obtain defence against predators or parasitoids. The plants may indirectly benefit from an increased ant foraging activity by reducing the herbivorous abundance. These three trophic interactions have been previously studied for several species, but mainly involving plants with extrafloral nectaries, which is a plant structure that also produce attractive substances for ants. Previous studies have reported an ant preference for honeydew over extrafloral nectary content. Therefore, trophobiosis can be an important mediator of ant-plant interactions. In this study, we describe a trophobiotic interaction between Edessa contermina stink bugs and Camponotus blandus ants on the Byrsonima verbascifolia plants occurring in a conservation area of Brazilian savanna. Stink bugs excreted a sugary liquid which was consumed by the ants, and C. blandus ants were observed consuming potential parasitoids. Stink bugs were more abundant in plants containing high food supply and shelter availability. The occurrence of ants depended of the number of inflorescences and trunk circumference of B. verbascifolia. Ant abundance, however, was positively correlated with stink bug abundance and the number of inflorescences. Herbivory was not explained by neither plant architecture nor ant abundance. This high ant activity may benefit plants from a protection against herbivory, but we did not detect this effect during the study period. Hence, the interaction among ants and plants was apparently commensal. We concluded that plant traits were important in ant attraction, but stink bugs foraging also increased ant activity on the plant, but mainly on inflorescences. Therefore, the plant may benefit from an increased defence of inflorescences rather than leaves.

RNAi and CRISPR/Cas9 as Functional Genomics Tools in the Neotropical Stink Bug, Euschistus heros.

Simple SummaryUnderstanding the biology of insect pests is an important step towards developing appropriate control strategies. In this study, a CRISPR/Cas9 gene knockout work flow was established for the first time and was together with RNAi used as tools to study gene functions in the Neotropical stink bug, Euschistus heros. RNAi was first employed to study the function of three genes, abnormal wing disc (awd), tyrosine hydroxylase (th) and yellow (yel). Targeting awd and th resulted in distinct malformed phenotypes such as a deformed wing or a lighter cuticle pigmentation/defects in cuticle sclerotization, respectively. However, no distinct phenotype was observed for yel. To further investigate the function of yel, a CRISPR/Cas9 gene editing protocol was developed for E. heros. A total of 719 eggs were microinjected with single-guide (sgRNA) and Cas9 and total of six insects hatched. Out of these six nymphs, one insect showed mutation in yel but no clear phenotype was visible. Although, we were unable to generate insects with a distinct phenotype for yel, a successful gene editing workflow was established to complement RNAi for future functional gene studies in E. heros. Additionally, we provided recommendations to improve the established gene editing workflow.The Neotropical brown stink bug, Euschistus heros, is one of the most important stink bug pests in leguminous plants in South America. RNAi and CRISPR/Cas9 are important and useful tools in functional genomics, as well as in the future development of new integrated pest management strategies. Here, we explore the use of these technologies as complementing functional genomic tools in E. heros. Three genes, abnormal wing disc (awd), tyrosine hydroxylase (th) and yellow (yel), known to be involved in wing development (awd) and the melanin pathway (th and yel) in other insects, were chosen to be evaluated using RNAi and CRISPR/Cas9 as tools. First, the genes were functionally characterized using RNAi knockdown technology. The expected phenotype of either deformed wing or lighter cuticle pigmentation/defects in cuticle sclerotization was observed for awd and th, respectively. However, for yel, no obvious phenotype was observed. Based on this, yel was selected as a target for the development of a CRISPR/Cas9 workflow to study gene knockout in E. heros. A total of 719 eggs were injected with the Cas9 nuclease (300 ng/µL) together with the sgRNA (300 ng/µL) targeting yel. A total of six insects successfully hatched from the injected eggs and one of the insects showed mutation in the target region, however, the phenotype was still not obvious. Overall, this study for the first time provides a useful CRISPR/Cas9 gene editing methodology to complement RNAi for functional genomic studies in one of the most important and economically relevant stink bug species.

Selective responses of Trissolcus basalis and Telenomus podisi to chemical footprints of preferred hosts

AbstractChemical trails of the hosts (footprints) are important cues for the host searching behaviour of egg parasitoids of the family Scelionidae. The present study aims to determine the influence of the footprints of three neotropical stink bugs (Euchistus heros, Dichelops melacanthus and Nezara viridula) on the foraging behaviour of two parasitoids, Trissolcus basalis and Telenomus podisi, as well as a possible selective response to fooprints of their preferred hosts. Accordingly, Tr. basalis and Te. podisi females are allowed to forage on open arenas where E. heros, D. melacanthus or N. viridula had walked or on open arenas that had been treated with samples of an extract from each stink bug's footprints. Hexane extracts of stink bug footprints are obtained from solvent‐washed Petri dishes where insects were allowed to walk for 24 h, and these extracts were analyzed by gas chromatography‐flame ionization detection and gas chromatography‐mass spectrometry. Each parasitoid responds selectively to the footprints of their preferred host (Tr. basalis to footprints of N. viridula and Te. podisi to footprints of E. heros). Twenty‐six compounds comprising of C18 to C35 (saturated and unsaturated) and methyl branched hydrocarbons were identified in extracts of E. heros, D. melacanthus and N. viridula, respectively. There are significant differences in the total amount of the compounds identified in the footprint stink bug's extracts and also a difference in the amounts of individual compounds. In addition, the behavioural assays showed that footprints of stink bugs are stimuli that are used by egg parasitoids to search, discriminate and selectively locate their preferred host.

Spatial variation in sex ratio and density explains subtle changes in the strength of size-assortative mating in Edessa contermina (Hemiptera: Pentatomidae)

Size-assortative mating (SAM) is usually explained by the mate-choice hypothesis. However, this hypothesis does not consider the effects of variations in the intensity of mating competition on mate choice and SAM. For example, in populations with male-biased operational sex ratios (OSR) and high densities, large males will have more advantages during mating competition and will have access to the most mating opportunities with large, preferred females (i.e. mating competition hypothesis). In this study, we investigated the effects of mating competition and mate choice on the strength of SAM in Edessa contermina (Hemiptera: Pentatomidae). We also described sexual size dimorphism and the mating system of this Neotropical stink bug in a conservation area of the Brazilian savanna. We used density as a proxy for mating competition intensity because it was positively correlated with OSR. Size-assortative mating was more consistent under intense mating competition. However, males copulated with relatively larger females as population density increased. Males assortatively mated based on size in the first and second copulation events observed, while both female matings were random. Thus, male mate choice may promote SAM in E. contermina, but its strength is affected by variations in the intensity of mating competition. Hence, we provided empirical support for mating competition as a potential mechanism promoting subtle changes in SAM. We discussed potential implications of this mechanism on the mating patterns of pentatomids.

Liposome encapsulation and EDTA formulation of dsRNA targeting essential genes increase oral RNAi-caused mortality in the Neotropical stink bug Euschistus heros.

The Neotropical stink bug Euschistus heros is a major pest in soybean fields. Development of highly species-specific pesticides based on RNA interference (RNAi) could provide a new sustainable and environmentally friendly control strategy. Here, the potential of RNAi as a pest control tool against E. heros was assessed. First, target gene selection using a microinjection approach was performed. Seven of the 15 candidate genes tested exhibited >95% mortality after hemolymph injection of 27.5 ng dsRNA. Subsequently, dsRNA was administered orally using different formulations: naked dsRNA, liposome-encapsulated-dsRNA and dsRNA formulated with EDTA. Liposome-encapsulated dsRNA targeting vATPase A and muscle actin led to significant mortality after 14 days (45% and 42%, respectively), whereas EDTA-formulated dsRNA did so for only one of the target genes. Ex vivo analysis of the dsRNA stability in collected saliva indicated a strong dsRNA-degrading capacity by E. heros saliva, which could explain the need for dsRNA formulations. The results demonstrate that continuous ingestion of dsRNA with EDTA or liposome-encapsulated dsRNA can prevent dsRNA from being degraded enzymatically and suggest great potential for using these formulations in dsRNA delivery to use RNAi as a functional genomics tool or for pest management of stink bugs. © 2018 Society of Chemical Industry.

Food diversification with associated plants increases the performance of the Neotropical stink bug, Chinavia impicticornis (Hemiptera: Pentatomidae)

The effect of different diets on the performance of nymphs and adults of Chinavia impicticornis (Stal, 1872) was studied, as well as the effect of switching diets from nymph to adult stages. Three diets were used to rear the insects (d1) 10 green bean pods of Phaseolus vulgaris (L.) plus a mixture of soybean [Glycine max (L.)] and sunflower [Helianthus annus (L.)] dry seeds and shelled raw peanuts [Arachis hypogaea (L.)]; (d2) diet 1 plus a bouquet of the native wild plants, Boldea fragans (Pers.), Bidens pilosa (L.), and Macroptilium atropurpureum (DC.) Urban; and (d3) a bouquet of the native plants. There was no significant difference in the nymphs’ development time when feeding on d1 or d2; however, the survival of the insects was significantly higher when fed on d2. Nymphs did not survive when fed d3. Female fecundity was higher when insects were fed d2 at both nymph and adult stages than when insects fed on other diet combinations. Survivorship and fecundity were negatively affected when adults were reared on d3, independently of the nymph diet. In terms of nutritional requirements for egg production, nymphs’ survival and development, d3 was shown to be the worst food, despite keeping adults alive. We concluded that the native plants evaluated here are associated plants for C. impicticornis. These associated plants in combination with host plants (d1) provide positive effects on some biological parameters relevant to the population dynamics of this stink bug.

Spatial distribution of nymphs and adults of Euschistus heros (Fabricius, 1794) (Heteroptera: Pentatomidae) in transgenic soybean cultivars of different maturing cycles

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.

Biology of a Neotropical Harlequin Stink Bug, Runibia perspicua (F.).

Laboratory and field studies were conducted with nymphs and adults of the Neotropical stink bug Runibia perspicua (F.) to evaluate their biology on plants. Total nymph mortality was ca. 13% on immature fruits of Brunfelsia australis Benth. (IFBA) and 90% on raw shelled peanuts, Arachis hypogaea L. (RSP); no nymphs survived on immature pods of green bean, Phaseolus vulgaris L., or on immature fruits of privet, Ligustrum lucidum Ait. Nymph developmental time was ca. 36 on IFBA and 55days on RSP. Body weight was significantly greater when nymphs were raised isolated compared to those raised in groups. Adult feeding activity was greater than third instars on IFBA. Adult longevity on IFBA + cherry tomato, Solanum lycopersicum L. fruit, reached ca. 150days. On IFBA, fecundity was 2.5 egg masses/female and 48.3 eggs/female; 25.6% of the eggs hatched. Adults did not reproduce on tomato. Body weight gain did not increase significantly for both sexes during the first four weeks of adult life on IFBA. In the field, plants of B. australis were surveyed in Passo Fundo, RS (28°15'S; 52°24'W). The majority of egg masses were deposited on the lower (abaxial) surface of leaves. Nymphs aggregated on immature fruits, and adults were seldom found on the plants. These are the first data on the performance of R. perspicua on B. australis indicating that this plant species is suitable to the bug's biology.

Identification of Soybean Host Plant Resistance to Brown Marmorated Stink Bugs in Maturity Group III Plant Introductions.

Halyomorpha halys (Stål; Hemiptera: Pentatomidae), brown marmorated stink bug (BMSB), is a polyphagous nonnative insect first found in the United States in 1996. As of 2017, BMSB has been detected in 43 states and is a severe agricultural pest in mid-Atlantic states. On soybean, Glycine max (L.) Merr (Fabales: Fabaceae), damage from BMSB infestation ranges from puncture marks with seed discoloration and deformities to seed and pod abortion. Host plant resistance has been used for managing pest populations and mitigating soybean yield losses caused by neotropical stink bugs (Eushistus heros, Nezara viridula, and Piezodorus guildinii) in Brazil and on the U.S. Gulf Coast. We evaluated maturity group III plant introductions (PIs) for resistance to BMSB damage. In 2014, field cage choice tests of 106 PIs revealed a range of both BMSB damage incidence and severity. In field choice tests, PIs 085665 and 097139 showed the lowest incidence of BMSB damage and seed weight loss due to BMSB, while PIs 243532, 243540, and 567252 had the highest. In whole plant no-choice tests, PIs 085665 and 097139 also had high levels of resistance. However, PI 085665 had a higher incidence of damage but lower seed weight loss than PI 097139, which may suggest bimodal resistance. Moreover, PIs 085665 and 097139 are from Japan and North Korea, respectively, two geographically isolated countries where BMSB is native. Thus, further characterization of host plant resistance to BMSB in each of these lines may elucidate distinct mechanisms that could be synergistic if stacked in breeding lines.

Food, shelter or competitors? Overlapping of life stages and host plant selection in a Neotropical stink bug species

ABSTRACTPhytophagous insects may choose host plants based on conditions that enhance offspring performance. However, some insect species may also select plants based on attributes that enhance their own performance regardless of the consequences for offspring survival. An approach evaluating both hypotheses could provide a more comprehensive understanding of the host plant selection by phytophagous insects. In this study, we described the life stages of a Neotropical stink bug, Edessa contermina, co-occurring on Byrsonima verbascifolia plants in a conservation area of the Brazilian Savannah. We also empirically evaluated how food supply, shelter availability and competitors’ density on the host plants affected the densities of nymphs, adults and mating pairs. We identified and described five life stages of E. contermina. The amount of plant resources did not explain the nymph, adult and mating pairs’ density. However, adults and mating pairs chose plants with a low density of nymphs, probably because egg laying on the host plants with a high density of competitors may negatively affect offspring performance.

Vibratory Communication and its Relevance to Reproductive Isolation in two Sympatric Stink Bug Species (Hemiptera: Pentatomidae: Pentatominae)

Communication is in phytophagous stink bugs of the subfamily Pentatominae related to mating behavior that among others includes location and recognition of the partner during calling and courting. Differences in temporal and frequency parameters of vibratory signals contributes to species reproductive isolation. Chinavia impicticornis and C. ubica are two green Neotropical stink bugs that live and mate on the same host plants. We tested the hypothesis that differences in temporal and spectral characteristics of both species vibratory signals enable their recognition to that extent that it interrupts further interspecific communication and copulation. To confirm or reject this hypothesis we monitored both species mating behaviour and recorded their vibratory songs on the non-resonant loudspeaker membranes and on the plant. The level of interspecific vibratory communication was tested also by playback experiments. Reproductive behavior and vibratory communication show similar patterns in both Chinavia species. Differences observed in temporal and spectral characteristics of female and male signals enable species discrimination by PCA analyses. Insects that respond to heterospecific vibratory signals do not step forward to behaviors leading to copulation. Results suggest that species isolation takes place in both investigated Chinavia species at an early stage of mating behavior reducing reproductive interference and the probability of heterospecific mating.

Identification and Synthesis of the Male-produced Sex Pheromone of the Stink Bug, Pellaea stictica.

Stink bugs are major pests of a wide variety of agricultural crops worldwide. The species Pellaea stictica is a Neotropical stink bug found in several South American countries. Chromatographic analyses of volatiles released by adults of this species showed that males produce a sex-specific compound, and bioassays with a Y-tube olfactometer showed that the compound was attractive only to females, confirming that it is a sex pheromone. Gas chromatography coupled to mass spectrometry and Fourier transform infrared analyses of the natural compound and several derivatives suggested that the structure was an alcohol with a saturated carbon chain and several methyl branches. After synthesis of two proposed structures, the pheromone of P. stictica was identified as a novel compound, 2,4,8,13-tetramethyltetradecan-1-ol. Laboratory bioassays showed that the synthesized mixture of stereoisomers of 2,4,8,13-tetramethyltetradecan-1-ol was as attractive to P. stictica females as the natural pheromone.

Transcriptome-Based Identification of Highly Similar Odorant-Binding Proteins among Neotropical Stink Bugs and Their Egg Parasitoid

Olfaction plays a fundamental role in insect survival through resource location and intra and interspecific communications. We used RNA-Seq to analyze transcriptomes for odorant-binding proteins (OBPs) from major stink bug pest species in Brazil, Euschistus heros, Chinavia ubica, and Dichelops melacanthus, and from their egg parasitoid, Telenomus podisi. We identified 23 OBPs in E. heros, 25 OBPs in C. ubica, 9 OBPs in D. melacanthus, and 7 OBPs in T. podisi. The deduced amino acid sequences of the full-length OBPs had low intraspecific similarity, but very high similarity between two pairs of OBPs from E. heros and C. ubica (76.4 and 84.0%) and between two pairs of OBPs from the parasitoid and its preferred host E. heros (82.4 and 88.5%), confirmed by a high similarity of their predicted tertiary structures. The similar pairs of OBPs from E. heros and C. ubica may suggest that they have derived from a common ancestor, and retain the same biological function to bind a ligand perceived or produced in both species. The T. podisi OBPs similar to E. heros were not orthologous to any known hymenopteran OBPs, and may have evolved independently and converged to the host OBPs, providing a possible basis for the host location of T. podisi using E. heros semiochemical cues.

Vibrational communication and mating behaviour of Dichelops melacanthus (Hemiptera: Pentatomidae) recorded from loudspeaker membranes and plants

AbstractVibrational communication is important for successful mating in various stink bugs species. The vibrational signals from males and females of Dichelops melacanthus Dallas (Hemiptera: Pentatomidae) are recorded from a nonresonant substrate (i.e. a loudspeaker membrane) to characterize the temporal and spectral properties of these vibrational signals, as well as on a resonant substrate (i.e. bean plants) to obtain information about how these signals are altered when they are transmitted through the plants. On the loudspeaker membrane, D. melacanthus males and females emit only one male or one female song, respectively. However, when the insects are placed on bean leaves, a more complex repertoire is recorded, with three different songs for each sex. The first female and male songs appear to have calling functions and the third male and female songs are emitted during courtship. The second female and male songs are emitted after the first song, although their functions in mating behaviour are not clear. The identified repertoire is similar to those of other Neotropical stink bugs, starting with songs 1 and 2 and developing into song 3. Frequency modulation is observed in the female songs recorded from the loudspeaker membrane and the plants. The signals recorded from plants present higher harmonic peaks compared with the signals recorded from the loudspeaker membrane. The presence of species and sex‐specific songs during mating confirms the important role of vibrational communication in mate location and recognition. The temporal and spectral characteristic signals are influenced by the substrate used to record the songs emitted by D. melacanthus.

Nymph and Adult Biology on Cultivated and on Non-Cultivated Plants and Seasonal Phenology on Wild Plants of the Neotropical Stink Bug, Euschistus paranticus Grazia (Hemiptera: Heteroptera: Pentatomidae)

Laboratory studies were conducted to evaluate nymph survivorship, developmental time, and fresh body weight at adult emergence, and adult survivorship, total longevity, reproduction, and fresh body weight gain of the Neotropical stink bug, Euschistus paranticus Grazia (Heteroptera: Pentatomidae). In the field, a one-year weekly survey was carried out on the wild plants, Scutia buxifolia Reissek (Rhamanaceae) and Prunus myrtifolia (L.) Urb. (Rosaceae) in Passo Fundo, RS, Brazil (28°15′S latitude; 52°24′W longitude). Results indicated that nymph mortality was very high (range 87-100%) and on only two (green bean pod + raw shelled peanut and green bean pod alone) out of the nine foods, nymphs were able to complete development. Nymph developmental time (2 nd to 5 th stadia) took ≈ 33 days on green bean pod + peanut seed, and ≈ 54 days on green bean pod. Adults E. paranticus fed pods of green bean, raw shelled peanut, mature seed of soybean, and leaf of S. buxifolia in the laboratory showed a total longevity of ≈ 40 to 55 days; 50% females oviposited; the pre-oviposition period was 18.9 days; number of egg masses/female was 9.3; mean total number of eggs/female was 103.6, and their viability was 55.6%. Females were heavier than males. E. paranticus was intercepted mostly during spring-summer on S. buxifolia, and only occasionally on P. myrtifolia.

Egg parasitoid wasps as natural enemies of the neotropical stink bug Dichelops melacanthus

The objective of this work was to determine the potential of five species of Scelionidae wasps - Telenomus podisi, Trissolcus basalis, Trissolcus urichi, Trissolcus teretis and Trissolcus brochymenae - as natural enemies of the neotropical stink bug Dichelops melacanthus, and to determine if the presence of eggs of other stink bug species influences the parasitism and development of the parasitoids. Two kinds of experiments were done in laboratory: without choice of hosts (eggs of D. melacanthus) and with choice (eggs of D. melacanthus and of Euschistus heros). Biological parameters, including proportion of parasitism, immature survivorship, progeny sex ratio, immature stage development period, and host preference were recorded. All the evaluated parasitoids can parasitize and develop on D. melacanthus eggs. The first choice of eggs did not influence the proportion of D. melacanthus eggs parasitized by Tr. basalis, Tr. teretis or Tr. brochymenae. However, D. melacanthus eggs as the first choice of Te. podisi and Tr. urichi increased, respectively, 9 and 14 times the chance for parasitism on eggs of this species. Behavioral and ecological aspects of parasitoids should be considered prior to their use in biological control programs.

Morphology, distribution and abundance of antennal sensilla in three stink bug species (Hemiptera: Pentatomidae)

The neotropical stink bugs, Euschistus heros, Piezodorus guildinii and Edessa meditabunda, are important pests of soybean and other crops throughout Central America and in South America from Northern Argentina to Brazil. Mate finding and host plant location in these species depend largely on their chemical communication, and semiochemicals are important mediators of these behaviors. In this study scanning electron microscopy was used to examine the external morphology, distribution and abundance of antennal sensilla on males, females and 5th instar nymphs of these species. Nine morphologically different sensilla types were found: trichod sensilla, type 1 and 2 (ST1 and ST2), long and short basiconic sensilla (SB1, SB2, and SB3), slit-tipped and knob-shaped basiconic sensilla, long chaetic sensilla (Sch) and coeloconic sensilla (Sco). Differences were detected in the abundance and arrangement of the sensilla over the antennal segments in individuals of the same species and among the species studied. The Sch, Sco and the slit-tipped and knob-shaped basiconic sensilla accounted for the major difference in sensilla types among the species. The ST1 was the most abundant type and was restricted to the flagellum. The pedicel of E. heros differs from the pedicels of P. guildinii and E. meditabunda mainly by the absence of Sch. There was a sexual dimorphism in ST1, SB1 and SB2, and this may be an indicative of their roles in detection of male-produced sex pheromone and odors derived from the host plants. The SB2 was lacking in the antennal tip of both sexes and 5th instar nymphs, but was abundant on the second flagellar segment of females of the three species. The same types of sensilla were found on 5th instar nymphs, but always in significantly lower numbers. The morphology and putative functions of each sensilla were compared and discussed.

Response of the Egg Parasitoids Trissolcus basalis and Telenomus podisi to Compounds from Defensive Secretions of Stink Bugs

We tested the hypotheses that host-searching behavior of the egg parasitoids Telenomus podisi and Trissolcus basalis may be differentially influenced by the different blends of volatiles released from the metathoracic glands of adult stink bug host species. We further studied whether such a differential response is due to different individual components of these glands and whether these responses reflect host preferences. Y-tube olfactometer bioassays were carried out with crude extracts of metathoracic glands of five different host species of neotropical stink bugs. Additionally, we tested the parasitoids' responses to synthetic standards of individual compounds identified in these stink bug glands. Results showed that females of T. basalis and T. podisi responded differentially to crude gland extracts of the different species of host stink bugs and to the compounds tested. The parasitoid T. basalis showed a positive taxic behavior to Nezara viridula methathoracxic gland extracts of a host species preferred in the field, i.e., N. viridula. Furthermore, T. basalis responded positively to 4-oxo-(E)-2-hexenal and (E)-2-decenal, two components of N. viridula glandular secretion. Higher residence time, reduced linear velocity, and higher tortuosity in the arm of the olfactometer supplied with 4-oxo-(E)-2-hexenal showed that this compound modifies the kinetics of some traits of T. basalis walking pattern and suggests that it might stimulate the searching behavior of this parasitoid. The parasitoid T. podisi was attracted to crude gland extracts of the preferred host (Euschistus heros) and also to 4-oxo-(E)-2-hexenal. Additionally, this parasitoid responded positively to (E)-2-hexenal and to the hydrocarbon tridecane, both of which are defensive compounds released from the metathoracic glands by several stink bugs. The results indicate some degree of specialization in the response of two generalist parasitoid species toward defensive secretions of stink bugs.