Electroantennogram responses of the cabbage seed weevil,Ceutorhynchus assimilis,to oilseed rape,Brassica napus ssp.Oleifera,volatiles

Electroantennograms (EAGs) were recorded from male and female cabbage seed weevils (Ceutorhynchus assimilis Payk.) in response to volatiles isolated and identified from the odor of oilseed rape (Brassica napus ssp.oleifera DC. cv. Ariana). Relatively large EAGs were obtained on stimulation with volatiles produced by the oilseed rape crop at the time when seed weevils were actively searching for host plants. Artificial rape odor without certain key volatile compounds was in most cases significantly less stimulatory than odor containing these volatiles. There were significant differences in the EAG response of the sexes ofC. assimilis to the green leaf volatiles of oilseed rape and several terpenes present in rape flower odor. The importance of the qualitative and quantitative composition of host-plant odor in host location byC. assimilis is discussed.     

Male-produced aggregation pheromone in pea and bean weevil,Sitona lineatus (L.)

The attraction ofS. lineatus to live baits comprisingS. lineatus feeding onVicia faba (L.) was studied in a field experiment in the early spring. There was clear evidence that maleS. lineatus produced an aggregation pheromone which attracted approximately equal numbers of both sexes from overwintering sites. No evidence was obtained for the production, in the spring, of any semiochemical by female weevils.Coleoptera: Curculionidae.     

Sex attraction in paper wasp,Polistes exclamans viereck (Hymenoptera: Vespidae), in a wind tunnel

A wind-tunnel bioassay was developed to test for the presence of sex attractants in the paper wasp,Polistes exclamans Viereck (Hymenoptera: Vespidae). Males exhibited significant upwind flight and attraction (chemoanemotaxis) in response to airflow passed over unmated females, and to hexane extracts of whole bodies and thoraces of unmated females. Unmated females were attracted to hexane extracts of males and to hexane extracts of each body tagma of males, suggesting distribution of the pheromone over the cuticle by grooming. The ectal mandibular and seventh sternal glands are the likely sources of the male-produced sex attractant(s) since extracts of each elicited female attraction in the flight tunnel. These glands are associated with gastral and mandibular rubbing of perch sites by territorial males ofPolistes species.     

Olfactory reception of potential pheromones and plant odors by tarnished plant bug,Lygus lineolaris (Hemiptera: Miridae)

Olfactory reception of potential pheromones and host-plant odors by male and female tarnished plant bugs (TPBs),Lygus lineolaris (Hemiptera: Miridae), was investigated by utilizing electroantennogram (EAG) techniques. In general, EAGs were similar between the sexes. Among 31 compounds of seven chemical groups tested, insect-produced butyrates and host-plant-containing green leaf volatiles (GLVs) were the most active. Hexyl butyrate and (E)-2-hexenyl butyrate elicited greater EAGs in males than in females. Females responded with significantly greater EAGs to alcohol and aldehyde GLVs than to their acetate derivatives. Among GLVs, sexual dimorphism was also observed in response to (E)-2-hexenol and (E)-2-hexenal. Females were more sensitive to the monoterpene geraniol than were males. While nonanal was the most stimulatory compound tested, no sexual differences in EAGs to this compound were observed. These studies reveal olfactory receptors on TPB antennae responsive to insect and host-plant volatiles that are likely to play a role in host finding and sexual attraction.     

Mating stimulant of the pine weevilHylobius abietis (L.)

Factors eliciting copulatory behavior in mature maleHylobius abietis were studied in the laboratory. Dead female weevils were sexually attractive, while dead mature males and pentane-extracted female weevils were not. The sexual attractiveness of dead females declined with time after death. Pentane extracts of whole female weevils or of the anterior or posterior parts of their bodies elicited a copulatory response when applied to decoys. In contrast, extracts of hindgut or frass were inactive. Juvenile males were sexually attractive for about four weeks, after which their attractiveness gradually declined. The results indicate that the mating stimulant is present on the body surface of female and juvenile male weevils, and it can be extracted with pentane.     

Sex-Related Perception of Insect and Plant Volatiles in Lygocoris pabulinus

We recorded electroantennograms of male and female Lygocoris pabulinus antennae to 63 insect and plant volatiles. EAGs were between 100 and 500 V. Overall, male EAGs were about twice the size of female EAGs. In both sexes, largest EAGs were recorded to (E)-2-hexenyl butanoate and (E)-2-hexen-1-ol. Response profiles were similar in both sexes. However, male antennae were more sensitive to a number of esters, especially the butanoates and pentanoates. Female antennae were more sensitive to nine of the 19 plant volatiles, i.e., to hexan-1-ol, heptan-1-ol, 1-octen-3-ol, 2-heptanone, (R)-carvone, linalool, geraniol, nerol, and methyl salicylate. Sexual differences in responses suggest that males are more sensitive to insect-produced pheromone-type compounds, whereas females are more sensitive to plant compounds for their orientation towards oviposition sites.     

Laboratory and field evidence for maleproduced aggregation pheromone inRhynchophorus cruentatus (F.) (Coleoptera: Curculionidae)

Laboratory and field assays were conducted to determine if palmetto weevil,Rhynchophorus cruentatus (F.), adults produce an aggregation pheromone. Attraction of females in a Y-tube olfactometer to conspecific males was greater than to clean air. Male and female attraction to conspecific male volatiles combined with host-palm,Sabal palmetto (Walter), volatiles was greater than to host-palm volatiles alone. Similarly, more weevils were caught in the field in traps baited with conspecific males plus host-palm tissue than in similar traps baited with only males, or palm tissue, or females, or females plus palm tissue. These results suggest thatR. cruentatus males produce an aggregation pheromone(s) that is highly attractive to conspecific adults of both sexes when combined with host-palm volatiles. This study is an important step towards understanding the chemical ecology ofR. cruentatus.     

Evidence for a short-range sex pheromone in female Maladera matrida beetle

Laboratory studies with live and frozen Maladera matrida female and male beetles showed that males were attracted to chemical substances emanating from the females at dusk. Beetles exhibited sexual activity (including mating) at dusk towards frozen females but not towards frozen males. Frozen females that had been extracted with methanol together with either hexane or dichloromethane or with a mixture of all three solvents did not elicit male sexual activity. Activity was fully restored when a concentrate of the extract was applied to the previously extracted frozen females. Males also responded with vigorous sexual activity to frozen males to which female extract had been applied. Deterrent chemicals appear to be absent from the male body. Males exposed to females that had been frozen during the morning displayed weak sexual activity, indicating that females lack active semiochemicals. Differences between dusk and morning extracts were found with respect to more than 20 compounds, some of which were present in much higher concentrations at dusk than in the morning, while others were not detected in the morning extract. The active component(s) of the short-range sex pheromone of female M. matrida is (are) presumably to be found among these compounds.     

Evidence for volatile male-produced pheromone in banana weevilCosmopolites sordidus

Females of the banana weevil,Cosmopolites sordidus, were attracted to and made longer visits to live conspecific males, trapped volatiles from males, and dissected male hindguts in a still-air olfactometer. Male weevils were attracted to volatiles trapped from males and made longer visits to live males and volatiles from males. Live females, collected volatiles from females and female hindguts, elicited small or no behavioral responses from either sex. Electroantennogram (EAG) responses from both male and female antennae were elicited by collected volatiles from males and by dichloromethane extracts of male hindguts and bodies but not by surface washes of males. No significant EAG responses were given to equivalent material from females. It is therefore suggested that male banana weevils release an aggregation pheromone via their hindgut.     

Response of Cabbage Seed Weevil (Ceutorhynchus assimilis) to Baits of Extracted and Synthetic Host-Plant Odor

The effect of extracted and artificial oilseed rape (Brassica napus ssp. oleifera) odors on the behavioral response of male and female cabbage seed weevils (Ceutorynchus assimilis) was investigated in a wind tunnel. Odor-mediated upwind anemotaxis was induced by leaf extract and its artificial equivalent. Omission of two isothiocyanates from the artificial extract significantly reduced the upwind movement of females. Increasing the wind speed within the tunnel significantly reduced upwind movement in response to the odor of leaf and flower extracts. The artificial baits proved less attractive than simple extracts from oilseed rape. Field trapping confirmed that extracted leaf material was more attractive than artificial equivalents.     

Chemical ecology of the palm weevilRhynchophorus palmarum (L.) (Coleoptera: Curculionidae): Attraction to host plants and to a male-produced aggregation pheromone

Attraction to host plants by adultRhynchophorus palmarum (L.) palm weevils was studied in the field and in the laboratory. Chemical analysis revealed the presence of ethanol and ethyl-acetate in stems of coco palms and in pineapple fruits and of pentane, hexanal, and isopentanol in coco stems. In the olfactometer, the first two compounds and isoamyl-acetate were attractive to the insects and the last three compounds, although not attractive by themselves, increased attractiveness when mixed with the first two compounds. Mixtures of these compounds, in proportions similar to the one occurring in attractive plant tissue, were as attractive as natural coconut tissue. In the field, the chemical compounds, either presented alone or as a mixture, did not attract the weevil. Males produce an aggregation pheromone when smelling ethyl-acetate. Rhynchophorol, 2(E)-6-methyl-2-hepten-4-ol, the known active component of the aggregation pheromone, attracts weevils in the olfactometer and in the field only if plant tissue, ethyl-acetate, or the above-mentioned odor mix are present. We propose that a complex mix of ethanol, ethyl-acetate, pentane, hexanal, isolamyl-acetate, and/or isopentanol serve as a short-range orientation cue to fresh wounds on the plant and that additional host odors, attracting weevils from a distance, have still to be discovered. Rhynchophorol can be considered to be a Synergist, having an anemotactic action at a distance. We recommend the use of retention traps baited with rhynchophorol, ethyl-acetate, and sugar cane as an alternative control method for the pest.     

Effects of host plant,Gossypium hirsutum L., on sexual attraction of cabbage looper moths,Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae)

Unmated female or male cabbage looper moths,Trichoplusia ni (Hübner), were attracted more often in a flight tunnel to a cage with moths of the opposite sex and a bouquet of cotton foliage. Increased sexual attractiveness of females with plants may be a result of stimulation of pheromone release in response to plant odor, since more males were attracted when odor of cotton foliage was passed over females than when odor of females was passed over cotton foliage before venting into the flight tunnel. Increased sexual attractiveness of males with plants is due in part to host odor enhancement of female attraction to male pheromone, since more females were attracted to synthetic male pheromone (a blend of enantiomers of linalool and isomers of cresol) and a cotton leaf extract than were attracted to male pheromone alone. A short synthesis procedure was developed for (S)-(+)-linalool, the major component of the male sex pheromone, isolated from hair pencils, used in these tests.     

Receptor chirality and behavioral specificity of the boll weevil,Anthonomus grandis Boh. (Coleoptera: Curculionidae), for its pheromone, (+)-grandisol

Electrophysiological recordings from antennal olfactory receptors and field behavioral experiments showed both male and female boll weevils,Anthonomus grandis Boh. (Coleoptera: Curculionidae), to respond specifically to (+)-grandisol, an enantiomer of compound I of the boll weevil aggregation pheromone. Single-cell recordings revealed antennal olfactory neurons in both male and female weevils keyed to (+)-grandisol. Electroantennograms in response to serial dilutions of the grandisol enaniiomers showed a threshold 100 to 1000 times lower for (+)-grandisol relative to its antipode. In field behavioral experiments, both sexes were significantly more attracted to (+)-grandisol in combination with the three other pheromone components than the combination with (–)-grandisol. When (–)-grandisol was placed with the (+)-enantiomer at equal dosages, a slight although statistically insignificant inhibition occurred. Subsequent field tests showed that the low level of attraction exhibited by (–)-grandisol in combination with the other three pheromone components could be attributed to the other three components alone. These results are in contrast with an earlier study, which found (–)-grandisol to be as attractive as the (+)-enantiomer.     

Identification of a male-produced pheromone ofAnticarsia gemmatalis (Hübner) (Lepidoptera; Noctuidae) attractive to conspecific males

Observations in the laboratory and in the field indicated that maleAnticarsia gemmatalis (Hübner), the velvetbean caterpillar (VBC), are attracted to conspecific courting males. Male VBC subsequently were found to be attracted to extracts of male abdominal tips including the extrudable hairpencils. The active chemical in these extracts was identified as (Z,Z,Z)-3,6,9-heneicosatriene, which is also one of the major components of the female VBC sex pheromone. Male VBC in a wind tunnel and in the field exhibited a bimodal response distribution to a range of ratios of the (Z,Z,Z)-3,6,9-heneicosatriene and (Z,Z,Z)-3,6,9-eicosatriene, with one maximum at the pure heneicosatriene alone and the other at the 6040 female blend. This demonstrates that the male response to the male hairpencil component is distinct from that to the female sex pheromone.This article reports the results of research only. Mention of a proprietary product does not constitute an endorsement or the recommendation for its use by USDA.     

Identification of male cabbage looper sex pheromone attractive to females

A multicomponent pheromone produced by male cabbage looper moths that is attractive to female moths in a flight tunnel bioassay was isolated and identified. Based on analyses of hairpencil extracts of male cabbage loopers and volatiles emitted by males, the pheromone has been identified as a blend consisting of (S)-(+)-linalool,p-cresol, andm-cresol. The chirality of the major component, (S)-(+)-linalool, is important for behavioral response of females. These pheromonal compounds were also identified as volatiles released by males when males were exposed to the principal pheromone component of female cabbage loopers, (Z)-7-dodecen-1-ol acetate. The amount of male pheromone released was increased significantly when males were exposed to a combination of (Z)-7-dodecen-1-ol acetate and the odor from cabbage. Neither linalool nor the cresols were detected in volatiles from cabbage or from males exposed to cabbage odor.     

Sex-identifying urine and molt signals in lobster (Homarus americanus)

During courtship, premolt female lobsters,Homarus americanus, choose a male and initiate a pair bond by repeated approaches to his shelter. The male allows such a female to share his shelter for about one week. This knowledge formed the basis to search for quantitative evidence for lobster sex pheromone(s) used in courtship: male cues to allow premolt females to identify a preferred male, and female cues to allow males to identify a premolt mature female. In each of four 1500-liter naturalistic aquaria, the behavioral responses of one female and two male lobsters to male and female lobster urine (0.5 ml) and body odor (20 ml) stimuli were observed. These stimuli were injected once or twice per day into a continuously flowing delivery tube attached to lobster shelters. Habituation to stimulus introduction—a serious problem in earlier experiments—was apparently avoided in the more natural social and physical environment we employed in these experiments. We demonstrated that male and female molt body odors contain different chemical substances: females responded to male molt body odor and males responded to female molt body odor but not vice versa. In general, male and female intermolt urine caused strong responses; however, females responded only weakly to male urine. This suggests that male and female urine are chemically different. Female urine and molt body odor caused a typically male high-on-legs response. These results show that molt body odors and intermolt urine contain sex-specific substances, which may be used in lobster courtship as well as other social interactions.     

Characterization of a Female-Produced Courtship Pheromone in the Parasitoid Nasonia vitripennis

Males of the parasitoid Nasonia vitripennis (Walker) (Hymenoptera: Pteromalidae) show a characteristic courtship behavior. We demonstrate that male arrestment and key behavioral elements of the courtship sequence are mediated by a female-derived contact sex pheromone. Males were arrested on paper disks treated with female extracts but not on those treated with male extracts. Male responsiveness was influenced by the surface to which female extracts were applied. Extracts applied to an extracted beetle elytron arrested males more strongly than those applied to filter paper of comparable size. However, more complex behavioral elements, such as head nodding and copulation attempts, were shown only when extracts were applied to extracted male cadavers, suggesting that tactile or visual cues synergize the male response. The chemicals involved are stable, of low volatility, and nonpolar. Dead females arrested males and elicited courtship behavior for at least 8 d. Males showed no sign of attraction to live females at a distance of 3 cm in an olfactometer. Fractionation of female extracts demonstrated that the activity was exclusively located in the nonpolar fraction. Analysis of the active fraction by gas chromatography–mass spectrometry revealed that cuticular hydrocarbons with chain lengths between 25 and 37 carbon units were present. Comparison of hydrocarbon profiles from males and females showed qualitative and quantitative differences. These results suggest that sex-specific cuticular hydrocarbons are the key signals mediating the male courtship behavior in N. vitripennis.     

Importance of bacterial decomposition and carrion substrate to foraging brown treesnakes

Brown treesnakes are an invasive species to the island of Guam that have caused extensive ecological and economic damage. Efforts to control the snake population have included trapping using live mouse lures, but for logistical and economic reasons a synthetic lure is needed. When searching for live food, brown treesnakes use both visual and odor cues. However, when searching for carrion, odor cues are sufficient. Attempts to develop synthetic lures based on chemical reconstruction of the complex carrion odor have not succeeded. We provide evidence that a microbial–substrate interaction is important for bait take by brown treesnakes. Microbial cultures taken from mouse carrion indicate that Enterobacter agglomerans is the predominant bacterium, and field tests suggest that this organism may be important to odor production that attracts brown treesnakes. This information may prove useful in the development of microbial-based biological reactors that could be formulated to produce a continuous stream of odor of sufficient complexity so as to be attractive to foraging snakes.     

Close-range attraction in Lygocoris pabulinus (L.)

Males of the green capsid bug, Lygocoris pabulinus, exhibit a specific courtship behavior, i.e., a vibration of the abdomen. When both live and dead females were offered to males, this vibration behavior was elicited in most of the males tested. When females were dissected into separate body parts, heads, wings, and legs elicited equal responses, while thorax plus abdomen elicited a much lower response. When separate body parts were extracted, the leg extracts elicited significantly stronger responses than any other extract. This suggests that female L. pabulinuslegs are either the source of a close-range sex pheromone or that pheromone is accumulated on the legs due to grooming behavior. The leg extracts contained several hydrocarbons such as n-alkenes, n-alkanes, and some methylalkanes. Female extracts contained more (Z)-9-pentacosene and male extracts contained more (Z)-9-heptacosene. Substrates on which females had walked elicited similar responses as female legs, indicating that the pheromone is deposited on the substrate. This enlarges the functional range of low-volatility compounds, which are thought to function only when sexes are in close vicinity or in contact.     

The attractivity of the female sex pheromone ofPeriplaneta americana and its components for conspecific males and males ofPeriplaneta australasiae in the field

The attractivity of virgin female odors of the American cockroach was examined in field experiments. Crude extracts of the female odor, the isolated sex pheromone fractions, periplanone-A and periplanone-B, and other compounds obtained during the isolation served as stimulants. An extract of male odors, obtained by identical collection methods, was used as a control. Males ofPeriplaneta americana were attracted by the crude extract and periplanone-B; males of the sympatric species,P. Australasiae, by periplanone-A. Experiments in which these components were presented subsequently and as mixtures indicate that, under certain conditions, periplanone-A may also function as an attracting substance forP. americana males and that periplanone-B and possibly some other components act as an inhibitor for males ofP. australasiae.