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.     

Flight-mediated attraction ofBiprorulus bibax breddin (Hemiptera: Pentatomidae) to natural and synthetic aggregation pheromone

The attraction of female spined citrus bugs,Biprorulus bibax, to natural and synthetic aggregation pheromone was studied using an olfactometer and a large flight cage. No locomotory response by postdiapause, prereproductive females to heptane extracts of male dorsal abdominal glands (DAGs) (site of pheromone production) was recorded in the olfactometer study. However, postdiapause, prereproductive females showed significant attraction to sites baited with DAG extracts in the flight cage (1.9–3.0 times that of unbaited sites). Prereproductive and reproductive females showed greatest attraction to sites baited with a synthetic blend of pheromone [(3R,4S,1E-3,4-bis(1-butenyl)tetrahydro-2-furanol, linalool, farnesol, nerolidol] (2.3–4.7 times the attraction of unbaited sites). Females also responded significantly to sites baited with the hemiacetal major component alone (1.7–2.2×). Diapausing females collected from fall populations did not respond to natural or synthetic pheromone baits. Potential applications of the synthetic aggregation pheromone are discussed with respect toB. bibax management.     

Identification,synthesis, and bioactivity of a male-produced aggregation pheromone in assassin bug,Pristhesancus Plagipennis (Hemiptera: Reduviidae)

Pristhesancus plagipennis, a large Australian assassin bug, possesses three pairs of dorsal abdominal glands (DAGs). In the male, the anterior and posterior glands are hypertrophied and secrete an attractant pheromone. Gas chromatography-mass spectrometry (GC-MS) analyses of male DAG extracts and airborne volatiles emitted from calling males showed the pheromone signature to be dominated by a novel component. Subsequent chemical manipulations, GC-MS, and chiral-column analyses established its identity as (Z)-3-hexenyl (R)-2-hydroxy-3-methylbutyrate. Minor components included 3-methylbutanol, 2-phenylethanol, (Z)-3-hexenol, decanal, (E)-2-hexenoic acid, and three minor hexenyl esters. Bioactivity studies using laboratory olfactometers and outdoor flight cages demonstrated attraction by femaleP. plagipennis to calling males, heptane extracts of male posterior DAGs and a synthetic formulation of the (Z)R enantiomer of the major ester, alone or in combination with other components of male anterior and posterior DAGs. Males were also attracted to the major ester. The racemate andS enantiomer of the ester were not attractive. Contamination of the (Z)R enantiomer with 30–60% of theE isomer also made the compound nonattractive. This is the first report of an aggregation pheromone in the Reduviidae. The prospects for pheromonal manipulation ofP. plagipennis populations to enhance the value of this predator in horticultural ecosystems, are discussed.     

Chemistryvis-à-vis maternalism in lace bugs (Heteroptera: Tingidae): Alarm pheromones and exudate defense inCorythucha andGargaphia species

The hawthorn lace bug,Corythucha cydoniae, and the eggplant lace bug,Gargaphia solani, possess alarm pheromones that are produced in dorsal abdominal glands (DAGs). WhenG. solani nymphs are grasped, they emit secretion from both DAGs; the posterior DAG secretion alone elicits alarm, but the anterior DAG secretion may hasten the response. InC. cydoniae, the response is due to a synergism between the anterior and posterior DAG secretions, and nymphs are apparently unable to voluntarily release their DAG secretions; both DAGs must be ruptured for the pheromone to escape. The alarm pheromones are interspecifically active in patterns matching the intraspecific activities. Compounds identified from tingid DAG secretions that are involved in the alarm messages are: (E)2-hexenal, (E)-4-oxo-2-hexenal, acetaldehyde, geraniol, and linalool. A new natural product of unknown function (designated nerolidol aldehyde) was identified from the anterior DAG secretions of both species.     

Multichemical defense of plant bugHotea gambiae (westwood) (Heteroptera: Scutelleridae)

Chemical defense in larvae of the plant bugHotea gambiae has been investigated. Results of analyses (GC, GC-MS) on the secretions from the three dorsally situated larval abdominal defense (scent) glands are reported. The secretion from the first abdominal gland consists of a mixture of C₁₀ and C₁₅ isoprenoids: (C₁₀) -pinene, -pinene, limonene, -phellandrene; (C₁₅) -caryophyllene, caryophyllene oxide, -humulene, and (the major component) humulene epoxide II. The secretions from the second and third abdominal glands are similar mixtures consisting of (E)-2-decenal, (E)-4-oxohex-2-enal, andn-tridecane together with lesser amounts of (E)-2-hexenal,n-dodecane, and other materials. Isoprenoid defense is now known from four species of plant bugs (Heteroptera) associated with Malvaceae.     

Pentatomid natural products

In addition to the primarily defensive metathoracic glands, adult Pentatomoidea possess a pair of active exocrine glands that open between the III and IV abdominal tergites. In the southern green stink bug,Nezara viridula, and other phytophagous species examined, the glands are small (< 10 g secretion/individual) and of approximately equal size in both sexes. In some, but not all, of the predaceous pentatomids (Asopinae), the III-IV dorsal abdominal glands are small in females (< 10 g secretion/individual) and extremely large in males (>500 g secretion/individual). Using a GC-MS system, the secretion from both males and females ofN. viridula (Pentatominae) was found to contain (E)-2-hexenal, hexanal, 1-hexanol, andn-tridecane. Females contained about three times moren-tridecane than males. The capacious glands ofPodisus maculiventris (Asopinae) males produce (E)-2-hexenal, benzyl alcohol, -terpineol, linalool, terpinen-4-ol, andcis-piperitol. The composition of the previously unanalyzed secretions from the adult III-IV dorsal abdominal glands is compared and contrasted to that of secretions from the metathoricic gland, and the role of coexisting exocrine glands in adult Heteroptera is discussed.     

Volatile compounds from the predatory insectPodisus maculiventris (Hemiptera: Pentatomidae)

In the predatory spined soldier bug,Podisus maculiventris, the dorsal abdominal glands are much smaller in adult females than males. Females produce a mixture of (E)-2-hexenal, (E)-2-octenal, (E)-2-hexenoic acid, benzaldehyde, and nonanal in these glands. The female dorsal abdominal gland secretion may be a close-range pheromone since the dorsal abdominal gland secretion from males has been shown to be a long-range aggregation pheromone in this species. The metathoracic scent gland secretions of male and female spined soldier bugs are apparently identical, and similar to that of other pentatomids, except for the presence of the monoterpene alcohol, linalool.Mention of a commercial product does not constitute an endorsement of this product by the USDA.     

Volatile glandular secretions of three species of new world army ants,Eciton burchelli,Labidus coecus,andLabidus praedator

The Dufour glands of workers ofEciton burchelli contain a mixture of small quantities of oxygenated compounds, some of which are derived from terpenes, and C₁₇-C₂₅ hydrocarbons. The secretion of the Dufour glands of soldiers was either similar to that of workers, with geranylacetone a significant component, or they contained geranyllinalool in large amounts. The glands of workers and soldiers ofLabidus praedator andLabidus coecus contained (E)--ocimene, a new substance for the Dufour glands of ants. 4-Methyl-3-heptanone was the dominant compound in the mandibular glands ofE. burchelli andL. coecus. Skatole and indole were found in the gasters ofL. praedator, and skatole was present in the venom glands of some soldiers ofE. burchelli.     

Multichemical defense of plant bugHotea gambiae (Westwood) (Heteroptera: Scutelleridae): (E)-2-hexenol from abdominal gland in adults

The occurrence inHotea gambia adults of a sexual dimorphism in the divided dorsal abdominal scent gland (dg 1)is reported. Counts made of ducted secretory units indicate that female dg 1 regresses at the end of larval development, unlike male dg 1 which undergoes no regression. Other dorsal abdominal scent glands (dg 2, dg 3) which function in the larvae cease to function during the imaginai moult. From gas chromatographic, mass spectrometric and [¹H]NMR data, the identity of the secretion from male adult dg 1 was established as virtually pure (E)-2-hexenol (a 100-mg mature male adult contains 0.5–1 l of secretion). 2-Hexenol was also found in the reduced female adult dg 1. In the sexually monomorphic metathoracic scent gland, (E)-2-alkenals (C₆, C₈) and (E)-4-oxohex-2-enal, together with monoterpenes (-pinene, limonene) but not 2-hexenol, were identified. The vapor of (E)-2-hexenol is repellent to both sexes ofHotea adults and toxic to blowfly (Calliphora) eggs.     

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.     

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.     

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.     

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.     

Chemistry and Defensive Efficacy of Secretion of Burrowing Bug (Sehirus cinctus cinctus)

Adult Sehirus cinctus cinctus emit a volatile secretion from their metathoracic scent glands when tactually stimulated. We identified the volatile components by gas chromatography, high-performance liquid chromatography, and mass spectrometry. The secretion of both sexes contained (1R)-(+)--pinene, (1S)-(–)--pinene, -myrcene, (R)-(+)-limonene, and -terpinolene. Two additional compounds were found in only female secretions: (E)-2-hexenyl acetate and (E)-2-octenal. We also tested the defensive capability of this insect by offering it to various predators. Anoles, starlings, and a killdeer rejected S. c. cinctus after an initial sampling. These findings suggest that the secretion plays a defensive role.     

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.     

(Z,E)-α-farnesene: Major component of secretion from metathoracic scent gland of cotton seed bug,Oxycarenus hyalinipennis (Costa) (Heteroptera; Lygaeidae)

The isolation and identification of (Z,E)--farnesene[(3Z, 6E)-3,7,11-trimethyldodeca-1,3,6,10-tetraene] (III) as the major component of the secretion from the metathoracic scent gland of the cotton seed bug,Oxycarenus hyalinipennis, is reported. The compound was identified by a combination of [1H] NMR, [¹³C] NMR, UV, and mass spectral data and by comparison with a synthetic sample, prepared by dehydration of (E)-nerolidol. (Z,E)--Farnesene (III) has been recorded previously in insects (ants and termites), but this is the first report of its occurrence in a member of the Heteroptera. (E)2-Octenyl acetate (XIII) and 2-octenal (XIV) were identified as minor components of the secretion. In addition, three minor monoterpenoid and two other sesquiterpenoid components were detected and tentatively identified.     

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.     

Metasternal Gland Volatiles and Sexual Communication in the Triatomine Bug, Rhodnius prolixus

Twelve compounds produced by the metasternal glands (MGs) of the triatomine bug Rhodnius prolixus were identified by solid phase microextraction (SPME) combined with coupled gas chromatography-mass spectrometry (GC-MS) using achiral and chiral columns. All substances were ketones or alcohols, and the same compound profile was found in the secretions produced by either sex. The most abundant compounds were 2-methyl-3-buten-2-ol, (2S)-pentanol, (3E)-2-methyl-3-penten-2-ol, and (2R/2S)-4-methyl-3-penten-2-ol. Emission of these compounds was detected more frequently from females than males, and females released them more frequently during the early hours of the scotophase, the period when sexual activity in this species is at its peak. These compounds were also detected in the headspace above mating pairs. Finally, the occlusion of the MG orifices of male or female bugs with paraffin resulted in a significant decrease in copulation frequency compared to sham-operated insects. Together, these data suggest that the MG secretions of R. prolixus may be involved in sexual communication.     

Nitroalkenes and Sesquiterpene Hydrocarbons from the Frontal Gland of Three Prorhinotermes Termite Species

Frontal gland contents of soldiers of three Prorhinotermes species, Prorhinotermes canalifrons, Prorhinotermes inopinatus, and Prorhinotermes simplex, consisted of two groups of compounds: nitroalkenes and sesquiterpene hydrocarbons. Analysis by gas chromatography-mass spectrometry revealed (E)-1-nitropentadec-1-ene as the major component of the glands with mean values of 152, 207, and 293 μg/individual for P. canalifrons, P. inopinatus, and P. simplex, respectively. Four other 1-nitroalkenes (C13, C14, C16, and C17), and two nitrodienes (C15 and C17) were also detected in the three species. The C17:1 nitroalkene was identified as (E)-1-nitroheptadec-1-ene. The sesquiterpene composition of the gland was species-specific: P. simplex contained (3Z,6E)-α-farnesene (mean of 39 μg/individual), while P. canalifrons and P. inopinatus contained the same compound (means of 0.5 and 1.5 μg/individual, respectively) as well as the (3E,6E) isomer (means of 1.8 and 0.7 μg/individual, respectively). Two other sesquiterpenes, trans-β-bergamotene and (Z)-γ-bisabolene, were also found in low quantities in the frontal gland of P. canalifrons.     

The Male Abdominal Glands of <Emphasis Type="Italic">Leucophaea maderae</Emphasis>: Chemical Identification of the Volatile Secretion and Sex Pheromone Function

In Leucophaea maderae, male calling behavior involves the release of a sex pheromone from the abdominal sternal glands. An extract of sternal glands attracted conspecific females over a distance. The compounds present were identified as hydroxy-3-butan-2-one, (2R, 3R)-butanediol, senecioic acid, and (E)-2-octenoic acid. The same components are also present in male tergal glands. The identified compounds were tested on their own and in mixtures. Their biological function is discussed.