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

We investigated the exocrine secretions from the five nymphal instars in the southern green stink bug,Nezara viridula, by analyzing separately the contents of the three dorsal abdominal reservoirs. All DAGs 1 produced a mixture of five alkanes with 12, 13, 14, 15, and 16 carbons. No differences were found between DAGs 2 and DAGs 3, for the five instars: the glands of first instars produce the same alkanes as DAGs 1,n-tridecane, traces of (E)-2-decenal, and a specific compound: (E)-4-oxo-2-decenal. In the other instars (second to fifth), (E)-4-oxo-2-decenal is absent from the secretion but another compound is present: (E)-4-oxo-2-hexenal. The kinetics of production of the different compounds were studied, the maximum amounts produced occurring 36 hr after hatching. The biological function of (E)-4-oxo-2-decenal was investigated. Using olfactometry, we showed that this compound acts as an attractant and an arrestant on second instars, at physiological doses. Moreover, this semiochemical was shown to be repellent to the fire-antSolenopsis geminata, a potential predator ofN. viridula and we established the dose-response curve for the repellent activity.     

Identification and synthesis of a male-produced sex pheromone from the stink bug Chlorochroa sayi

The reproductive behavior of the stink bug Chlorochroa sayiwas studied in the laboratory. There was a sexual maturation period of about 10 days before bugs began mating. Sexually mature adult bugs engaged in courtship consisting of antennation and head-butting of the female by the male, before the female adopted a receptive posture and copulation occurred. Both sexes mated multiple times during their life-spans, with the mean duration of copulations of virgin bugs (42.3 ± 19.6 min) and experienced bugs (37.3 ± 28.4 min) being similar. Most matings were initiated in the late afternoon or evening, when pheromone production by males was greatest. Males transferred sperm and nutrients constituting about 17% of their body weight to females during mating. Three male-specific components, methyl geranate, methyl citronellate, and methyl (E)-6-2,3-dihydrofarnesoate in a ratio of 100 : 0.45 : 1.6, were first detected in volatiles collected from male bugs on green beans about 9–12 days after the final molt to the adult stage. In vertical Y-tube bioassays, females were attracted to odors from mature male bugs, and to a blend of the three male-produced components. Low numbers of females also were attracted in field trials with the three-component blend. The relatively weak attraction may be a result of other, as yet unknown cues being required in addition to the pheromone, such as visual or substrate-borne vibrational cues.     

Female-Produced Sex Pheromone of the Predatory Bug Geocoris punctipes

A compound identified from air-entrained volatiles produced by adult female Geocoris punctipes attracted male bugs and stimulated males to investigate nearby moving objects of the appropriate size in their search for females. The compound was identified as (E)-2-octenyl acetate, a relatively common component of the volatile semiochemicals produced by a number of heteropteran species. This compound comprised a significant proportion of the female volatiles, whereas it was detected in only trace amounts in volatiles collected from live males. Other components in the extracts from adults of both sexes included (E)-2-hexenyl acetate, (E)-2-octenal, and several saturated hydrocarbons, but these components were not part of the attractant. These compounds plus (E)-2-hexenal, (E)-4-oxo-2-hexenal, and (E)-2-decenal were found in extracts of homogenized adults, whereas the cast skins from late instar nymphs contained (E)-2-octenal, (E)-4-oxo-2-octenal, (E)-2-octenoic acid, and several saturated hydrocarbons.     

Identification and Synthesis of Male-Produced Sex Pheromone Components of the Stink Bugs Chlorochroa ligata and Chlorochroa uhleri

The reproductive behaviors of the stink bugs Chlorochroa ligata and C. uhleri were studied in the laboratory. Adults of both species became sexually mature about 12–14 days after the final molt, and both sexes mated multiple times during their lifetimes. The mean duration of copulation was 54 ± 24 min for virgin bugs and 46 ± 33 min for experienced bugs for C. ligata and 78 ± 55 min for field-collected C. uhleri of unknown mating status. Male C. ligata were found to transfer a significant fraction of their body mass (19%) to females during mating. Sexually mature C. uhleri males produced three sex-specific compounds, methyl (R)-3-(E)-6-2,3-dihydrofarnesoate, methyl (2E,6E)-farnesoate, and methyl (E)-5-2,6,10-trimethyl-5,9-undecadienoate, in a ratio of 100:0.9:0.6. These three compounds were also produced by sexually mature male C. ligata in a ratio of 100:0.5:0.4. Identifications of the compounds were confirmed by synthesis. Production of the male-specific compounds peaked in late afternoon to early evening, coincident with the peak period of reproductive activity. Laboratory and field bioassays demonstrated that female bugs were attracted to odors from live males and to reconstructed blends of the male-specific compounds.     

Identification of Volatile Synomones, Induced by Nezara viridula Feeding and Oviposition on Bean spp., That Attract the Egg Parasitoid Trissolcus basalis

Bean plants (Vicia faba L. and Phaseolus vulgaris L.) damaged by feeding activity of Nezara viridula (L.) (Heteroptera: Pentatomidae), and onto which an egg mass had been laid, produced volatiles that attracted the egg parasitoid Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae). Extracts of volatiles of broad bean and French bean plants induced by adults of N. viridula as a result of their feeding activity, oviposition activity, and feeding and oviposition activity combined were analyzed by gas chromatography-mass spectrometry (GC-MS), and tested in Y-tube olfactometer bioassays as attractants for T. basalis females. In extracts from undamaged leguminous plants, green-leaf volatiles were absent or scarcely detected, and monoterpenes and sesquiterpenes were present at trace levels. No significant differences were detected in the profiles of volatiles of undamaged plants, and undamaged plants on which bugs were allowed only to lay eggs. In contrast, feeding and oviposition by adults of N. viridula induced in both leguminous plants a significant increase in terpenoids such as linalool, (E)-beta-caryophyllene, (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene, and (3E)-4,8-dimethyl-1,3,7-nonatriene, which was induced only in French bean plants. Quantitative comparisons revealed increased levels of (E)-beta-caryophyllene in extracts from feeding-damaged plants with N. viridula egg masses compared to feeding-damaged plants without egg masses. In Y-tube olfactometer bioassays, T. basalis females were attracted by extracts of both leguminous plants only when N. viridula adults were allowed to feed and oviposit upon them. Fractionation of extracts of volatiles from broad bean plants with N. viridula feeding damage and egg masses yielded two fractions. but only the fraction containing (E)-beta-caryophyllene was attractive to the egg parasitoid. These findings indicate that N. viridula feeding and oviposition induce leguminous plants to produce blends of volatiles that are characterized by increased amounts of (E)-beta-caryophyllene, and these blends attract female T. basalis. The role of (E)-beta-caryophyllene as a potential synomone for T. basalis is discussed.     

Field attraction ofBiprorulus bibax Breddin (Hemiptera: Pentatomidae) to synthetic aggregation pheromone and (E)-2-hexenal,a pentatomid defense chemical

A synthetic blend of the aggregation pheromone [(3R,4S,1E)-3,4-bis(1-butenyl)tetrahydro-2-furanol, linalool, farnesol, and nerolidol] of the spined citrus bug,Biprorulus bibax, and the pentatomid defense chemical, (E)-2-hexenal, both attracted adultB. bibax to individual trees in citrus orchards. Lemon trees containing single glass vials with aggregation pheromone or (E)-2-hexenal were colonized by significantly greater numbers of reproductiveB. bibax than unbaited trees. There was no significant difference between the treatments and bug recruitment was not improved by using both treatments.B. bibax did not enter cylinder/funnel traps baited with aggregation pheromone but colonized trees containing the traps. Orange or lemon trees containing aggregation pheromone on orchard perimeters recruited significantly larger populations of emigrating, nonreproductiveB. bibax during fall than untreated trees. Nonreproductive bugs were not attracted to trees containing (E)-2-hexenal. The potential for using these semiochemicals as management tools forB. bibax is discussed.     

Chemical Ecology of the Defense of Two Nymphalid Butterfly Larvae Against Ants

We analyzed the behavioral responses of the ants Camponotus rufipes and Solenopsis geminata towards all instars of Dione junio and Abananote hylonome. We also analyzed ant behavior towards hexane extracts of larvae and extracts of the spines and neck glands of the fifth instars of both species and identified the chemical compounds present. Larvae of both species were repellent to ants from the first instar onward. Later instars survived ant attacks better than earlier instars. The spines and neck glands of the larvae influenced the behavior of C. rufipes. The chemical compounds contained in the hexane extracts of whole first and fifth instars and in the spines and neck glands of fifth instars were principally carboxylic acids and terpenes. Further bioassays confirmed the repellent effect of some of these acids toward ants.     

Chemical Defense in the Plant Bug Lopidea robiniae (Uhler)

Secretions from the metathoracic glands (MTG) of the black locust bug, Lopidea robiniae (Uhler) (Heteroptera: Miridae) contained six major compounds, including (E)-2-hexenal, (E)-2-hexen-1-ol, (E)-2-octenal, (E)-2-octen-1-ol (E)-2-heptenal, and (Z)-3-octen-1-ol. Males and females did not differ significantly in the relative compositions of identified compounds. In feeding trials, six bird species [robin (Turdus migratorious), blue jay (Cyanocitta cristata), brown thrasher (Toxostoma rufum), killdeer (Charadrius vociferus), starling (Sturnus vulgaris), and house wren (Troglodytes aedon)] demonstrated feeding aversions towards L. robiniae, implying that black locust bugs are chemically defended. Bugs discharged the liquid contents of their MTG when attacked, thereby producing a strong and distinct odor. Some birds immediately ejected bugs out of their mouth after biting them, suggesting that the MTG secretion was a deterrent.     

Chemical Defense in the Stink Bug Cosmopepla bimaculata

Adult Cosmopepla bimaculata discharge a volatile secretion from paired ventral metathoracic glands (MTG) when disturbed. Collected volatiles were similar in both sexes and consisted of n-tridecane (67%), (E)-2-decenal (12%), (E)-2-decenyl acetate (12%), (E)-2-hexenal (3%), hexyl acetate (2%), n-dodecane (2%), a tridecene isomer (1%), and n-undecane, n-tetradecane, and n-pentadecane (all <1%). In addition, undisturbed males produced a novel insect compound, (E)-8-heneicosene, whose function is unknown. The MTG secretion emerges as an enlarging droplet, which is held in place by a cuticular projection and a pleural scent area consisting of specialized rough cuticle surrounding the gland opening. Insects can selectively discharge from either the right or left gland or both glands simultaneously, can control the amount of fluid ejected, and can resorb the ejected secretion droplet back into the gland reservoir. In feeding trials, killdeer (Charadrius vociferous), starlings (Sturnus vulgaris), robins (Turdus migratorius), and anole lizards (Anolis carolinensis) rejected or demonstrated aversion to feeding on the bugs. Furthermore, bugs that lacked the secretion were more susceptible to predation than bugs with secretion, suggesting that the secretion functions in defense against predators.     

A long-range attractant kairomone for egg parasitoidTrissolcus basalis,isolated from defensive secretion of its host,Nezara viridula

A short-chain ,-unsaturated aldehyde, (E)-2-decenal, present in the defensive metathoracic gland ofNezara viridula (L.) (Heteroptera: Pentatomidae), stimulates a behavioral response in the egg parasitoidTrissolcus basalis (Woll.) (Hymenoptera: Scelionidae). Preliminary studies showed thatT. basalis are attracted to an area containing adultN. viridula, but we also found that femaleT. basalis would examine and probe glass beads coated with an acetone extract of the metathoracic gland from males or females. Using this bioassay, the kairomone was isolated by bioassay directed by preparative gas chromatography and identified by NMR and mass spectrometry as (E)-2-decenal. The biological activity of the identified aldehyde was compared with analogs to determine specificity. An unstable Z isomer was found to be more active but not present in detectable or behaviorly relevant levels in the host, based on the bell-shaped dose-response curve of the two isomers. An investigation was also designed to determine if theE isomer was also responsible for the egg recognition kairomone activity previously reported. However, no 2-decenal isomers were detected in host egg extracts and the chemical characteristics of the 2-decenal isomers differ from the unidentified egg recognition kairomone. The role of the (E)-2-decenal in attracting femaleT. basalts toN. viridula was demonstrated in a Y-tube olfactometer; this alk-2-enal appears to act as a long-range kairomone orientingT. basalis toNezara populations.     

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 -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.     

Short and Simple Syntheses of 4-Oxo-(<Emphasis Type="Italic">E</Emphasis>)-2-Hexenal and Homologs: Pheromone Components and Defensive Compounds of Hemiptera

One-step syntheses of 4-oxo-(E)-2-hexenal and 4-oxo-(E)-2-octenal from commercially available 2-ethyl- and 2-butylfuran are described. A two-step synthesis of the homolog 4-oxo-(E)-2-decenal from furan is also reported. These compounds are common components of true bug defensive secretions, and recently have been identified as pheromone components for several species. The simple syntheses reported here will make these compounds readily available for further research.     

Multifunctional communication inRiptortus clavatus (Heteroptera: Alydidae): Conspecific nymphs and egg parasitoidOoencyrtus nezarae use the same adult attractant pheromone as chemical cue

The bean bug,Riptortus clavatus lays scattered eggs (as opposed to the egg masses of pentatomids) on host as well as nonhost plants. Therefore, the first feeding stage (second-instar) nymphs emerging from eggs laid on nonhost plants need a signal that enables them to locate a food source at the lowest energy cost. Male-released (E)-2-hexenyl (E)-2-hexenoate, (E)-2-hexenyl (Z)-3-hexenoate, and myristyl isobutyrate play the double role of attractant pheromone for adults as well as aggregation pheromone, which enables the second-instar nymphs to find the host food plant. These male-specific semiochemicals are released only when foodstuff is available. On the other hand, females ofOoencyrtus nezarae, the most effective parasitoid of the host in Kumamoto, Japan (where the field experiments were conducted), utilize these semiochemicals as kairomones in order to locate the potential host community. Field experiments revealed that the synthetic pheromone rivaled 10 live males in the attraction of adults and second-instar nymphs. Captures of the egg parasitoidO. nezarae females in cylindrical sticky traps were significantly higher in traps baited with the synthetic semiochemicals than in control traps. The number of females captured was significantly higher than the number of males, although the captures in the sticky suction trap system revealed that the populations of male and female were not significantly different.     

Attraction of Piezodorus hybneri to the Aggregation Pheromone Components of Riptortus clavatus

The aggregation pheromone of Riptortus clavatus (Heteroptera: Alydidae) consists of (E)-2-hexenyl (Z)-3-hexenoate (E2HZ3H), (E)-2-hexenyl (E)-2-hexenoate (E2HE2H), and myristyl isobutyrate (MI). Experiments were conducted to examine the attraction of Piezodorus hybneri (Heteroptera: Pentatomidae) to the pheromone components of R. clavatus, individually and in combination, and to determine if P. hybneri produces these compounds. Electroantennogram (EAG) responses of P. hybneri to E2HE2H were significant in a dose dependent manner, while those to E2HZ3H were not significantly different from those to hexane and air. Field trapping tests using E2HZ3H, E2HE2H, and MI, individually or in combination, showed that only E2HE2H was attractive to P. hybneri. E2HE2H was not detected in whole-body extracts or volatile collections from either sex of P. hybneri adults. We propose that the response of P. hybneri adults to the R. clavatus aggregation pheromone may be related to finding suitable host plants.     

Response of the Egg Parasitoids <Emphasis Type="Italic">Trissolcus basalis</Emphasis> and <Emphasis Type="Italic">Telenomus podisi</Emphasis> 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.     

Testing the “new associations” biological control concept with a tachinid parasitoid (Euclytia flava)

Males of the spined soldier bug,Podisus maculiventris (Heteroptera: Pentatomidae), produce an attractant pheromone that is exploited as a host-finding kairomone by a complex of parasitic species. The capability to catch hundreds of a generalist tachinid fly parasitoid,Euclytia flava, alive in traps baited with the pheromone ofP. maculiventris provided an opportunity to test the premise of the new associations biological control concept. The hypothesis that host species newly associated with a parasitoid are maladapted relative to native-native associations was tested by givingE. flava females a choice between native and exotic stink bugs (Heteroptera: Pentatomidae). WildE. flava females preferred to oviposit on exotic pentatomid species rather than indigenous, known host species, both in field traps baited with the pheromone of a native host and in the laboratory. Data presented here demonstrate that an invader may be vulnerable to native parasitoids in one aspect of the parasitism process (acceptance), yet go unrecognized as a potential host.     

Sex Attractant Pheromone from the Neotropical Red-Shouldered Stink Bug, <Emphasis Type="Italic">Thyanta perditor</Emphasis> (F.)

Olfactometer bioassays showed that odors from mature Thyanta perditor males attracted females but not males. Furthermore, odors from females did not attract either sex, indicating that like other phytophagous pentatomid bugs, the males produce a sex pheromone. Attraction appeared to peak in late afternoon to evening. The headspace volatiles collected from male and female T. perditor were analyzed by GC-MS and HPLC. A male-specific compound, methyl (2E,4Z,6Z)-decatrienoate (2E,4Z,6Z-10:COOMe), was identified along with a number of other compounds found in extracts from both sexes. Bioassays carried out with 2E,4Z,6Z-10:COOMe showed it was as attractive to females as the crude extract of male volatiles, suggesting that the male-produced sex pheromone consists of 2E,4Z,6Z-10:COOMe as a single component. Consecutive volatiles collections from males showed that 2E,4Z,6Z-10:COOMe began appearing in extracts from males about 9 d after the final molt, as the males became sexually mature.     

Kairomone strains of Euclytiaflava (Townsend), a parasitoid of stink bugs

Tachinid flies commonly use the pheromones and allomones of stink bugs (Pentatomidae) as host-finding kairomones. Pheromone-baited traps for predaceous (Podisus spp.) and phytophagous (Euschistus spp.) pentatomids were used to obtain tachinid parasitoids in order to study the semiochemical relationships between these parasitic flies and their stink bug hosts. Gas chromatography–electroantennogram detector (GC-EAD) experiments and field tests were conducted to determine if pheromone strains of the tachinids, Euclytia flava and Hemyda aurata, occur in nature and to determine if the EAD-active compound, (E)-2-octenal (a common allomone compound of Heteroptera), affects attraction of tachinid parasitoids to synthetic Podisus pheromones. Addition of (E)-2-octenal to Podisus spp. synthetic pheromones in field traps tended to suppress attraction of the bugs, whereas (E)-2-octenal decreased, did not affect, or increased pheromonal attraction of tachinid parasitoids depending on the host species pheromone being tested and the habitat type in which the traps were deployed. Evidence from GC-EAD experiments of E. flava associated with different stink bug hosts suggested that kairomone-strains of this tachinid parasitoid coexist naturally. The significance of cryptic kairomone strains of parasitoids for classical biological control is disc ussed, and the mechanisms whereby parasitoids evolve kairomonally mediated host-shifts is considered.     

Pheromones of milkweed bugs (Heteroptera: Lygaeidae) attract wayward plant bugs: Phytocoris mirid sex pheromone

The synthetic aggregation pheromone of the large milkweed bug, Oncopeltus fasciatus (Dallas) (Lygaeinae), also attracted males of the plant bug, Phytocoris difficilis Knight (Miridae). Field testing partial blends against the six-component blend comprising the Oncopeltus pheromone showed that cross-attraction of P. difficilis males was due to synergism between (E)-2-octenyl acetate and (E,E)-2,4-hexadienyl acetate. Hexyl acetate was abundant in the metathoracic scent gland (MSG) secretion of P. difficilis males, but because female P. difficilis could not initially be found in the field, further combinatorial tests were guided by prior research on the pheromones of two Phytocoris species in the western United States. The combination of hexyl, (E)-2-hexenyl, and (E)-2-octenyl acetates was as attractive to P. difficilis males as the milkweed bug pheromone, yet no milkweed bugs were drawn to this blend. Gas chromatographic (GC)-electroantennographic detection (EAD) and GC-mass spectrometric (MS) analyses of female P. difficilis MSGs determined that their secretion contained predominantly hexyl, (E)-2-hexenyl, and (E)-2-octenyl acetates (all strongly EAD-active)—the latter two compounds found only in trace amounts from males—plus five minor female-specific compounds, three of which were EAD-active. (E,E)-2,4-Hexadienyl acetate was not detected from P. difficilis females or males. The blend of the three major components, hexyl, (E)-2-hexenyl, and (E)-2-octenyl acetates (2:1.5:1 by volume), was as attractive as the blend of all six EAD-active compounds identified from females, indicating that this ternary blend constitutes the sex pheromone of P. difficilis. Hexyl acetate with (E)-2-octenyl acetate also attracted males of another species, P. breviusculus Reuter, but addition of (E)-2-hexenyl acetate and/or (E,E)-2,4-hexadienyl acetate inhibited attraction of P. breviusculus males. Attraction of P. difficilis males occurred mainly during the first half of scotophase. The possible neurophysiological basis for this asymmetrical cross-attraction is discussed.     

Interspecific Pheromone Cross-Attraction Among Soybean Bugs (Heteroptera): Does Piezodorus hybneri (Pentatomidae) Utilize the Pheromone of Riptortus clavatus (Alydidae) as a Kairomone?

The chemical and ecological function of cross-attraction of Piezodorus hybneri (Pentatomidae) to the Riptortus clavatus (Alydidae) pheromone (a mixture of three components) was studied. In a field attraction test using traps with synthetic pheromone components, P. hybneri was attracted to (E)-2-hexenyl (E)-2-hexenoate, a component of the R. clavatus pheromone. Other components had neither an additive nor a synergistic effect on the attraction of P. hybneri. Neither (E)-2-hexenyl (E)-2-hexenoate nor other components of the R. clavatus pheromone were detected in volatiles or whole-body extracts of P. hybneri adults by gas chromatographic analysis. In addition, (E)-2-hexenyl (E)-2-hexenoate could not be found in volatiles of soybean plants. Therefore, it appears that P. hybneri responds to a component of the R. clavatus pheromone that is not emitted by P. hybneri itself. We discuss this interspecific pheromone cross-attraction of the soybean bug and hypothesize that P. hybneri utilizes the pheromone of its competitor as a kairomone for host location.