Dorsal abdominal glands in nymphs of southern green stink bug,Nezara viridula (L.) (heteroptera: Pentatomidae): Chemistry of secretions of five instars and role of (E)-4-oxo-2-decenal, compound specific to first instars

Adaptive changes in pheromone production and release under rearing conditions in stink bugs

BACKGROUND

Healthy cultures of arthropods are important for pest management programs (e.g. biocontrol). Little is known about how rearing conditions may affect pheromonal interactions. We investigated how rearing histories and densities affect pheromone emission/production in two stink bug species (Hemiptera: Heteroptera), the predatory bug Arma custos, a biocontrol agent, and the bean bug Riptortus pedestris, a pest on legume crops.

RESULTS

Nymphs from newly established laboratory colonies of both species produced higher amounts of the defense (dispersal) compound, 4-oxo-(E)-hexenal (OHE), in the presence of conspecific nymphs. Also, when two or more A. custos males were placed together, the dorsal abdominal glands (DAGs) ceased to release aggregation pheromone, whereas the metathoracic glands (MTGs) increased the emission of defensive odors. These changes resulted from exposure to conspecific pheromone odors, as confirmed by exposing bugs to pheromone standards. Hence, pheromone emissions in these stink bugs are readily changed in response to the odors of conspecifics, which may become a problem after long-term rearing. Indeed, an old laboratory colony of A. custos (~30 generations) exhibited less-developed DAGs and reduced pheromone production. Instead, males released significantly more defensive odors from the enlarged MTGs. Furthermore, long-term rearing conditions appeared to favor nymphs that were able to share space with conspecifics by releasing less OHE, which has not yet occurred in the new laboratory colonies.

CONCLUSION

Rearing density affects pheromone release in newly established laboratory colonies of stink bug species, whereas long-term rearing results in new pheromonal compositions coinciding with adaptive changes in gland development. © 2023 Society of Chemical Industry.

Effects of aromatic compounds on movement activity of Pyrrhocoris apterus in the conditions of a laboratory experiment

In the conditions of an urban environment, insects, including Pyrrhocoris apterus (Linnaeus, 1758) (Hemiptera, Pyrrhocoridae), are subject to dozens of volatiles: solvents, food flavorings, cosmetic products. For firebugs, some attract them, some scare them off, and to some they are indifferent. In this article, in the conditions of laboratory experiment, we evaluated the influence of chemical substances on rates of movement of firebugs. Under the influence of the substances we studied, there occurred no significant increase or decrease in the activity of firebugs. The most significant effect on rates of movement of firebugs was exerted by solvent, white spirit and solvent 646 p – firebugs travelled 12 cm distance for 24.2%, 49.6% and 58.7% of the time the control group did. Movement activity of firebugs was insignificantly decreased by aromatic extracts Royаl milk extract, Butcher’s broom extract and chrysalis oil: firebugs travelled 12 cm distance for 132.7%, 135.2% and 146.8% of time the control group. Aromatic substances likely interact with receptors on antennae of firebugs, and therefore the insects need additional time for orienting reactions, deciding whether those substances signal presence of potential food objects in the accessibility zone.

Epicuticular hydrocarbons of the redbanded stink bug Piezodorus guildinii (Heteroptera: Pentatomidae): sexual dimorphism and alterations in insects collected in insecticide-treated soybean crops

BACKGROUND

The redbanded stink bug Piezodorus guildinii (Heteroptera: Pentatomidae) is one of the most important species affecting soybean crops in southern South America. Capillary gas chromatography coupled to mass spectrometry was used to characterize the epicuticular hydrocarbon profiles of field-collected insects, and to identify differences in their composition between fifth-instar nymphs and adults, males and females, and between bugs collected in insecticide-treated and insecticide-free soybean crops.

RESULTS

Straight chain saturated n-C27 and n-C29, and monomethyl and dimethyl chains of C31 and C33 were the most abundant compounds. A group of volatile hydrocarbons with n-C13 and n-C15 as the predominant compounds were also detected. The hydrocarbon pattern was different between nymphs and adults, either males or females. Heneicosene was almost exclusively detected in adult males and was the most important component to differentiate between both sexes, followed by tricosadiene. The total hydrocarbon amount was significantly higher in nymphs, males and females collected in insecticide-treated fields compared with insects obtained from untreated fields.

CONCLUSION

Differences were found in the epicuticular hydrocarbon pattern among nymphs and adults, as well as sexual dimorphism in adult stink bugs. Interestingly, an alteration was also found in the hydrocarbon profile of insects collected in insecticide-treated soybean crops and its relevance is discussed within a pest management context.

Comparative Analysis of Volatile Defensive Secretions of Three Species of Pyrrhocoridae (Insecta: Heteroptera) by Gas Chromatography-Mass Spectrometric Method

The true bugs (Hemiptera: Heteroptera) have evolved a system of well-developed scent glands that produce diverse and frequently strongly odorous compounds that act mainly as chemical protection against predators. A new method of non-lethal sampling with subsequent separation using gas chromatography with mass spectrometric detection was proposed for analysis of these volatile defensive secretions. Separation was performed on Rtx-200 column containing fluorinated polysiloxane stationary phase. Various mechanical irritation methods (ultrasonics, shaking, pressing bugs with plunger of syringe) were tested for secretion sampling with a special focus on non-lethal irritation. The preconcentration step was performed by sorption on solid phase microextraction (SPME) fibers with different polarity. For optimization of sampling procedure, Pyrrhocoris apterus was selected. The entire multi-parameter optimization procedure of secretion sampling was performed using response surface methodology. The irritation of bugs by pressing them with a plunger of syringe was shown to be the most suitable. The developed method was applied to analysis of secretions produced by adult males and females of Pyrrhocoris apterus, Pyrrhocoris tibialis and Scantius aegyptius (all Heteroptera: Pyrrhocoridae). The chemical composition of secretion, particularly that of alcohols, aldehydes and esters, is species-specific in all three pyrrhocorid species studied. The sexual dimorphism in occurrence of particular compounds is largely limited to alcohols and suggests their epigamic intraspecific function. The phenetic overall similarities in composition of secretion do not reflect either relationship of species or similarities in antipredatory color pattern. The similarities of secretions may be linked with antipredatory strategies. The proposed method requires only a few individuals which remain alive after the procedure. Thus secretions of a number of species including even the rare ones can be analyzed and broadly conceived comparative studies can be carried out.

Multifunctional weaponry: the chemical defenses of earwigs

Earwigs protect themselves against predators using pincer-like cerci and/or malodorous exudates secreted from abdominal glands. Little is known about the chemistry of these secretions and their potential functions. However, because earwigs live in aggregations and overwinter in soil, they are exposed to high microbial loads throughout their lifecycle, and we therefore hypothesized that the secretions are used not only to deter predators but also to combat pathogens and parasites in their environment. We analyzed the defensive secretions of the European earwig Forficula auricularia, the short-winged earwig Apterygida media and the woodland earwig Chelidurella guentheri by gas chromatography-mass spectrometry. The secretions of all three species contained 2-methyl-1,4-benzoquinone and 2-ethyl-1,4-benzoquinone, whereas A. media also produced 2,3-dimethyl-1,4-benzoquinone and 2-ethyl-3-methyl-1,4-benzoquinone. The latter has not been identified in the exudates of insects before. The composition and/or quantity of these components were species-specific and partially sex-specific. All secretions showed antimicrobial activity against Gram-positive and Gram-negative bacteria as well as two entomopathogenic fungi. Furthermore, the secretion of F. auricularia displayed nematicidal activity against Caenorhabditis elegans. Our data support the hypothesis that earwig secretions are multifunctional, serving both to deter predators and sanitize the microenvironment.

The metathoracic scent gland of the leaf-footed bug, Leptoglossus zonatus

The metathoracic scent gland of 25-day-old adults of both sexes of the leaf-footed bug, Leptoglossus zonatus (Dallas) (Heteroptera: Coreidae), are described based on optical microscopy analysis. No sexual dimorphism was observed in the glandular composition of this species. The gland is located in the anteroventral corner of the metathoracic pleura between the middle and posterior coxal pits. The opening to the outside of the gland is very wide and permanently open as it lacks a protective membrane. In the internal part, there is a pair of metathoracic glands that consist of piles of intertwined and occasionally bifurcated cellular tubes or columns. These glands discharge their pheromonal contents into the reservoir through a narrow cuticular tube. The reservoir connects with the vestibule via two opposite and assembled cuticular folds that can separate muscularly in order to allow the flow of liquid away from the insect. The external part consists of an ostiole from which the pheromone is emitted. The ostiole is surrounded by a peritreme, a structure that aids optimum pheromone dispersion. The described gland is of the omphalien type.

Synergy versus potency in the defensive secretions from nymphs of two pentatomomorphan families (Hemiptera: Coreidae and Pentatomidae)

One characteristic of true bugs (Heteroptera) is the presence of dorsal abdominal glands in the immature nymphal stages. These glands usually produce defensive chemicals (allomones) that vary among taxa but are still similar in closely related groups. Knowledge of the chemistry and prevalence of allomones in different taxa may clarify the evolution of these chemical defensive strategies. Within the infraorder Pentatomomorpha, the known secretions of nymphs of Pentatomidae tend to contain the hydrocarbon, n-tridecane, a keto-aldehyde, and an (E)-2-alkenal as the most abundant components. In the Coreidae, the dorsal abdominal gland secretions of nymphs often contain little or no hydrocarbon, and the most abundant keto-aldehyde and (E)-2-alkenal are often of shorter chain-length than those of pentatomids. We hypothesized that the long chain compounds would be less potent than their shorter homologs, and that bugs that carry the former would benefit from a synergistic effect of n-tridecane. To test this hypothesis we used three different behavioral assays with ants. A predator-prey assay tested the deterrence of allomones toward predators; a vapor experiment tested the effectiveness of allomones in the gaseous phase toward predators; and application of allomones onto predators tested the effect of direct contact. The results substantiate the hypothesis of a synergistic effect between n-tridecane and longer chain keto-aldehyde and (E)-2-alkenal in deterring predators. The short chain keto-aldehyde 4-oxo-(E)-2-hexenal was highly effective on its own. Thus, it seems that different groups of the infraorder diverged in their strategies involving defensive chemicals. Implications of this divergence are discussed.

Defensive compounds and male-produced sex pheromone of the stink bug, Agroecus griseus

Agroecus griseus is a serious corn pest in Brazil. Contents of the dorsal abdominal glands (DAGs) in nymphs, and the metathoracic gland (MTG) in adults of this species were characterized and quantified. Compounds found were similar to those of other Pentatomidae species and included aliphatic hydrocarbons, aldehydes, oxo-alkenals, and esters. However, two compounds were found in the MTG that have not been described previously for this family. Mass spectrometry, infrared spectroscopy, and gas chromatographic analysis using coinjection with authentic standards confirmed the identities of the compounds as enantiopure (S)-2-methylbutyl acetate and 3-methyl-2-butenyl acetate. The five nymphal instars showed significantly different ratios of components, mainly between those of the first and later instars. No significant differences were detected in MTG contents between sexes. Gas chromatography (GC) analysis of aeration extracts of males and females showed the presence of a compound released exclusively by males. Gas chromatography - electroantennographic detection (GC-EAD) assays indicated that the male-specific compound is bioactive in females, suggesting the presence of an attractant pheromone. The mass spectrum and infrared data for this compound matched with methyl 2,6,10-trimethyltridecanoate, a sex pheromone component previously detected in the stink bugs, Euschistus heros and E. obscurus. The synthetic standard coeluted with the natural pheromone on two different GC stationary phases, confirming the proposed structure. Y-tube olfactometer assays showed that the synthetic standard was strongly attractive to females, and GC-EAD tests produced responses with antennae from females similar to those of the natural pheromone.

Morphology and volatile compounds of metathoracic scent gland in Tessaratoma papillosa (Drury) (Hemiptera: Tessaratomidae)

Tessaratoma papillosa (Drury) (Hemiptera: Tessaratomidae) is a serious insect pest of litchi and longan in South China. When disturbed, this insect could release large quantities of disagreeable odorous volatiles from its scent gland. Knowledge on the scent gland and its secretion is crucial for developing the semiochemical methods to manage this pest. Morphology and ultrastructure of the metathoracic scent glands (MTGs) were studied under stereo and scanning electron microscopy, and the volatile compounds of MTGs from both male and female T. papillosa were analyzed with coupled gas chromatography-mass spectrometry (GC-MS). The MTG complex is located between the metathorax and the first abdominal segment at the ventral surface of the insect, which has a well-developed single double valve cystic-shaped orange median reservoir, paired colorless lateral glands in both sides, and a long and wavy tubular accessory gland that inlays tightly into the ventral edge around the median reservoir. The MTG opens to the body surface through paired ostioles located between the meso- and metacoxae of the evaporatorium with mushroom bodies. The GC-MS analyses showed that female and male adults have nine major volatile components in common. Tridecane is the most abundant in both females and males, reaching up to 47.1% and 51.8% of relative amount, respectively. The minor component is benzophenone with only 0.28% and 0.14%. Furthermore, undecane, tetradecane, 3-methyl-tridecane, and cyclopentadecane were found only in males. The possible function of volatile compounds of MTG contents in T. papillosa is addressed.

4-oxo-aldehydes from the dorsal abdominal glands of the bed bug (Hemiptera: Cimicidae)

Analyses of the dorsal abdominal glands of fourth- and fifth-instar nymphs of the bed bud, Cimex lectularius L. (Hemiptera: Cimicidae), indicated the predominant constituents were (E)-2-hexenal and (E)-2-octenal, with lesser amounts of 4-oxo-(E)-2-hexenal and 4-oxo-(E)-2-octenal. The latter two compounds have not been reported previously as occurring in bed bugs. There were no differences in the chemical composition of the dorsal abdominal glands excised from exuviae left behind by either male or female adults, nor from glands excised from fourth-instar exuviae. Because the two oxo-aldehydes made up at least 16% of the gland contents, further study of the functional role of these chemicals seem advisable.

Inter- and intraspecific variation in defensive compounds produced by five neotropical stink bug species (Hemiptera: Pentatomidae)

The differences in composition of defensive secretions between nymphs, adult males and adult females of Chinavia impicticornis (=Acrosternum impicticorne), Chinavia ubica (=Acrosternum ubicum), Euschistus heros, Dichelops melacanthus and Piezodorus guildinii (Hemiptera, Pentatomidae) were analysed within and between species using compositional log-ratio statistics and canonical variates analysis. Differences in composition between nymphs, males and females were found for all species, as well as when all species were pooled. In particular, tetradecanal appears to be a predominantly nymphal compound in D. melacanthus, E. heros and P. guildinii. In the two Chinavia species 4-oxo-(E)-2-hexenal and an unknown compound were more dominant in nymphs. The interspecific analysis revealed a good separation of defensive compounds according to their taxonomic relationship. Thus, the two Chinavia species grouped together, with (E)-2-decenal and (E)-2-hexenyl acetate, contributing to this separation. The other three species also differed from each other, with (E)-2-octenal associated to D. melacanthus, (E)-2-hexenal to P. guildinii and (E,E)-2,4-decadienal and tetradecanal to E. heros. The pooled analysis of stage ignoring species revealed tetradecanal and 4-oxo-(E)-2-decenal (tentative identification) strongly associated to nymphs. Thus, there are predictable differences between stages, and many of the differences are conserved between species. Consideration of these differences could prove to be important in understanding stink bug-natural enemy interactions, and in optimising biocontrol efforts.

Semiochemicals from the predatory stink bug Eocanthecona furcellata (Wolff): components of metathoracic gland, dorsal abdominal gland, and sternal gland secretions

Volatile compounds from the metathoracic glands (MTG), dorsal abdominal glands (DAG), and sternal setae of the generalist predatory stink bug Eocanthecona furcellata (Wolff) were studied by gas chromatography-mass spectrometry. MTGs of both male and female bugs contained (E)-2-decenal as the major component, with lesser amounts of (E, E)-2,4-decadienal, (E, Z)-2,4-decadienal, and (E)-2,9-decadienal. The relative amount of (E)-2,9-decadienal in the MTGs of female bugs was higher than in male bugs. There was no dimorphism in the morphology of the DAGs of adults. However, the DAG contents of adult bugs were different between the sexes. Geraniol was found only in the DAGs of males, and limonene and alpha-terpineol were found only in the DAGs of females, whereas linalool oxide isomers, linalool, neral, and geranial were found in DAGs of both sexes. The DAG contents of nymphs were also analyzed, with 4-oxo-(E)-2-hexenal, 4-oxo-(E)-2-octenal, tridecane, and tetradecanal being major components. Male bugs but not females possess sternal setae, and 6,10,13-trimethyltetradecyl isovalerate was detected from extracts of the sternal setae of males. The possible biological significance of dimorphism in the contents of the glands in adults is discussed.

Volatile compounds released by disturbed and calm adults of the tarnished plant bug, Lygus lineolaris

Volatile compounds released by disturbed and calm female and male Lygus lineolaris were collected and analyzed. Six major compounds were present in samples from disturbed bugs and from calm females: (E)-2-hexenal, 1-hexanol, (E)-2-hexenol, hexyl butyrate, (E)-2-hexenyl butyrate, and (E)-2,4-oxohexenal. (E)-2-hexenal was lacking in volatiles collected from calm males. Hexyl butyrate accounted for approximately 68% and 66% of volatiles released by agitated and calm females, and 87% and 88% of volatiles released by agitated and calm males, respectively. Blends released by disturbed insects differed quantitatively from blends released by calm insects, with amounts of compounds increasing 75-350 times in samples from disturbed insects. In static air bioassays, both females and males were repelled by natural volatiles collected from females and by five-component [(E)-2,4-oxohexenal excluded] and six-component synthetic blends at doses of 1 and 10 bug-hours, indicating that these volatiles may serve an alarm or epideictic function, as well as a possible role as defensive allomones. Adults also avoided hexyl butyrate, (E)-2-hexenyl butyrate, (E)-2-hexenol, and (E)-2,4-oxohexenal, but not 1-hexanol and (E)-2-hexenal when compounds were assayed individually in static air bioassays at doses equal to 1 bug-hour. When tested over 1 day in two-choice cage trials, adults did not prefer untreated bean plants over bean plants surrounded by vials releasing up to 8.1 mg/hr (= 234 bug-hours) of the five-component synthetic blend. Therefore, the volatiles produced by disturbed adults would not be useful as a repellent for L. lineolaris.