Fecal volatiles as part of the aggregation pheromone complex of the desert locust,Schistocerca gregaria (Forskal) (Orthoptera: Acrididae)

Olfactometric bioassays showed that nymphs of crowded desert locusts,Schistocerca gregaria, aggregated in response to volatiles derived from their feces and to volatiles emitted from the feces of young adults, but were indifferent to volatiles emitted by older adult feces. On the other hand, young and older adults were not only responsive to their own fecal volatiles but also cross-responsive to each other's and that of the nymphs. Charcoal-trapped volatiles from the feces and synthetic blends of the fecal volatiles also elicited similar responses. Young adults responded moderately to a blend of nymphal volatiles and those derived from nymphal feces. GC-EAD and GC-MS analysis of the trapped volatiles revealed the presence of guaiacol and phenol as predominant electrophysiologically active components of nymphal and young adult feces. Fecal volatiles of older adult contained phenylacetonitrile in addition to guaiacol and phenol, which were present in relatively lower proportion. These results suggest that fecal volatiles are part of the aggregation pheromone complex of the desert locust, which includes the pheromone blends produced by nymphs and older adults, respectively.     

Effects of Fifth-Instar Volatiles on Sexual Maturation of Adult Desert Locust Schistocerca gregaria

The effect of the presence of gregarious fifth-instar nymphs on the sexual maturation of newly molted gregarious immature adult males and females of the desert locust S. gregaria was investigated by monitoring color changes (yellowing of body), sexual activity, aggregation–maturation pheromone titers (as measured by phenylacetonitrile levels in males), oocyte length, and oviposition time. Maturation was significantly delayed in adults that were reared together with fifth-instar nymphs (visual, tactile, and chemical signals present) with respect to all parameters measured. Male and female nymphs were equally effective in inducing this delay. Nymphs kept in an upper compartment of two-chamber cages (no visual or tactile contact possible) were similarly effective, but their feces were ineffective, suggesting the mediation of a volatile signal from the nymphs themselves. This was confirmed by examining the effect of volatiles trapped from nymphs and testing synthetic blends of previously identified nymphal aggregation pheromone components (C₆, C₈–C₁₀ aliphatic aldehydes and acids, guaiacol, and phenol) on the sexual maturation of adults. These and previous studies suggest a dual role for nymphal volatiles as nymphal aggregants and adult maturation retardants, similar to the adult volatiles that are known as adult aggregants and maturation accelerants. The results are discussed in terms of the role of the two pheromone systems in synchronizing maturation of the gregarious adults.     

Aggregation pheromone system of nymphal gregarious desert locust,Schistocerca gregaria (forskål)

Hexanal, octanal, nonanal, decanal, hexanoic acid, octanoic acid, nonanoic acid, and decanoic acid were identified in the volatile emissions from fifth instars ofSchistocerca gregaria by coupled gas chromatography-electroantennography (GC-EAD) detection and coupled GC-mass spectrometry (MS). In laboratory assays, synthetic blends of the eight compounds, with acids and aldehydes tested separately, evoked strong aggregation responses from fifth instars, similar to responses evoked by a crude volatile extract of the nymphs. A nymphal fecal volatile phenolic blend of guaiacol and phenol, which we have previously shown to evoke an aggregative response from different stages of the insect, significantly synergized the activity of the blend of eight compounds, suggesting mutually augmentative roles for nymphal and fecal volatiles in evoking aggregation. These results indicate that the aggregation behavior of gregarious second to fifth instars is modulated by three sets of pheromonal compounds: aldehydes and acids emitted by the nymphs themselves and phenols associated with their feces.     

Intra- and Interspecific Aggregation Responses of Locusta migratoria migratorioides and Schistocerca gregaria and a Comparison of Their Pheromone Emissions

Gregarious nymphs of Schistocerca gregaria and Locusta migratoria migratorioides are often seen to march together in common bands in the field. In the present study, the intraspecific aggregation responses of nymphal and older stages of the two insects were compared with their interspecific responses. Unlike S. gregaria, L. m. migratorioides shows a lesser pattern of stage and sex differentiation in its aggregation pheromone biology. Thus, although fifth-instar nymphs did not respond significantly to the adult pheromone, adults responded significantly to the nymph pheromone. No cross-stage aggregative responses occur in S. gregaria. In the adults of S. gregaria, production of the pheromone is male-specific; in L. m. migratorioides both sexes induced a significant level of aggregation from conspecifics. Aggregation assays between corresponding stages of the two species showed stronger interaction between the nymphal stages than between the adults and account for the frequent occurrence of mixed hopper bands in the field. GC-EAD studies of volatiles of nymphal and adult stages by using antennal preparations from both species also showed significant interspecies reactivities. GC-MS analyses showed that of S. gregaria nymphal pheromone components (C₆ and C₈ to C₁₀ straight-chained aldehydes and acids and the fecal phenols, guaiacol and phenol), the acids and phenols constitute the common components of nymphal stages. Phenylacetonitrile, the major component of S. gregaria adult aggregation pheromone, is present in L. m. migratorioides nymphal volatiles, albeit at a lower level. Unlike S. gregaria adult pheromone blend, which is made up wholly of benzene derivatives, the volatile emissions of L. m. migratorioides adults is dominated by aliphatic aldehydes and alcohols. The possible role of cross-aggregation effects in mutually facilitating phase transformation of the two species is discussed.     

Enhancement of Attraction to Sex Pheromones of Spodoptera exigua by Volatile Compounds Produced by Host Plants

We measured the effects of exposure to volatile compounds produced by host plants on the rate of capture of male Spodoptera exigua using synthetic sex pheromones. Exposure to volatile compounds stimulated strong electroantennographic responses of male S. exigua. The behavioral responses of male moths to combinations of sex pheromone and volatile compounds were tested in wind tunnel experiments. When lures were baited with synthetic sex pheromone plus benzaldehyde, phenylacetaldehyde, (Z)-3-hexenyl acetate, or linalool, respectively, the landing rate of S. exigua males was increased by 101.4%, 79.6%, 60.6%, and 34.3%, respectively, compared to sex pheromone alone. In field tests, traps baited with either pheromone + (E)-2-hexenal, pheromone + phenylacetaldehyde, pheromone + (Z)-3-hexenyl acetate, or pheromone + (Z)-3-hexenol enhanced moth catches by 38.8%, 34.6%, 24.6%, and 20.8%, respectively compared to traps baited with pheromone alone. In a second field experiment, more S. exigua males were trapped with a combination of a synthetic sex pheromone blend and several individual host plant volatiles compared to synthetic sex pheromone alone. These results suggest that some host plant volatiles enhance the orientation response of S. exigua male moths to sex pheromone sources.     

Evidence for mediation of two releaser pheromones in the aggregation behavior of the gregarious desert locust,Schistocerca gregaria (forskal) (Orthoptera: Acrididae)

The response of nymphal and adult gregarious phase desert locust,Schistocerca gregaria, to a choice of two columns of air, one permeated with airborne volatiles emanating from nymphs or adults and the other untreated, was investigated in a single-chamber bioassay arena. The nymphs, whether released individually or in groups, preferred to be within the precinct of the air column treated with airborne volatiles of the nymphs but were indifferent to volatiles of the adults. Conversely, older adults responded only to their own volatiles but not to those of the nymphs or young adults. The young adults were responsive only to volatiles of the older adults. Charcoal-trapped volatiles from the nymphs and the adults reproduced the effect of living locusts. These results indicate that there are two different aggregation pheromones inS. gregaria: a juvenile pheromone produced by nymphs and an adult pheromone specific to adults.     

Kairomone from dandelion,Taraxacum officinale,attractant for scarab beetleAnomala octiescostata

The attraction of the scarab beetleAnomala octiescostata to dandelion,Taraxacum officinale, was demonstrated to be chemically mediated by a mixture ofcis-3-hexenyl acetate, benzaldehyde, phenylacetaldehyde, benzyl alcohol, phenethyl alcohol, phenylacetonitrile, and benzyl benzoate, in the ratio 4:8:14:3:5:19:11. Combination of the synthetic kairomone and sex pheromone (buibuilactone + japonilure, 8:2), significantly increased the total catches ofA. octiescostata. Catches of male (but not female) beetles were significantly higher with the kairomone-pheromone blend than with kairomone alone. The synergistic effect of the kairomone from dandelion on the attractiveness did not significantly differ from that of a food-type lure, anethol, geraniol, and phenethyl propionate (9:0.5:0.5). The latter combined with the synthetic sex pheromone resulted in better attraction of female (but not male)A. octiescostata than the sex pheromone alone.     

Saw-toothed grain beetleOryzaephilus surinamensis (L.) (Coleoptera: Silvanidae)

The antennal and behavioral responses of the saw-toothed grain beetle,Oryzaephilus surinamensis, to the three components of its male-produced aggregation pheromone were investigated. EAG recordings showed no differences between the responses of the two sexes to the synthetic pheromone components. In contrast, laboratory behavioral assays demonstrated marked differences between the sexes. More females than males were consistently attracted to mixtures of the synthetic components, and this bias appeared to be caused by one component in the blend. Altering the blend ratio resulted in changes in the ratio of the sexes attracted. Thus, if, as suggested by preliminary work, males vary the blend produced, this should alter the relative response of the sexes to the aggregation pheromone.     

Aggregation Agents in German Cockroach Blattella germanica: Examination of Efficacy

Aggregation behavior and reduced locomotory activity in the German cockroach is known to be caused by chemical compounds in the feces. The attractive and/or arrestant efficacy of three relevant substances was tested in first instars by a two-choice aggregation test and in adults with a locomotion compensator apparatus that allows quantification of taste-directed orientation and walking speed as a function of antennal stimulation. The three substances tested were a feces crude extract; a mixture of six carboxylic acids (mix G) out of a total of 29 that were identified in the feces extract and tested as single compounds and in various combinations; and a steroid glucoside denoted as blattellastanoside A, which has been suggested as an aggregation arrestant pheromone in Blattella germanica. With both of our test methods, feces extract and mix G proved to be very attractive, whereas the effects of blattellastanoside A were, if anything, very poor. Possible reasons for discrepancies are discussed.     

Alarm Pheromone System of the Western Conifer Seed Bug, Leptoglossus occidentalis

The alarm pheromones for adult and nymphal western conifer seed bugs, Leptoglossus occidentalis, were collected from the headspace volatiles of agitated bugs and from extracted adult thoraxes and nymphal abdomens. Adult bugs secreted a blend from the metathoracic glands that consisted of hexyl acetate, hexanal, hexanol, heptyl acetate, and octyl acetate (ratio of 152:103:8:1.5:1). Nymphal alarm pheromone produced by the dorsal abdominal glands consisted of (E)-2-hexenal. Agitated adults emitted 24% of the pheromone contained within the glands, while nymphs released 33% of their constitutive supply. The complete blend from both adults and nymphs, tested in a laboratory headspace bioassay, elicited a dispersal (or alarm) response in >70% of individuals tested. Nymphs in the field exposed to synthetic adult or nymphal pheromones, or a mixture of both, responded with >50% dispersing. When single components were tested on adults reared under summer conditions in a forced-air one-way bioassay, hexanal and hexyl acetate, the major components of the secretion, were responsible for eliciting the alarm response. Adults collected in the fall from the field were unresponsive to the tested blend, suggesting that adults seeking aggregation sites in the fall become refractory to alarm pheromone stimuli that would cause aggregations to disperse. The weak dispersal responses elicited in both adults and nymphs by either nymphal or adult pheromones are consistent with a tradeoff in the advantage gained by avoiding predation and the disadvantage of leaving a food source. Because of these weak responses, use of alarm pheromones as pest management tools against L. occidentalis is unlikely.     

Analysis and Optimization of a Synthetic Milkweed Floral Attractant for Mosquitoes

A pentane extract of flowers of common milkweed, Asclepias syriaca (Asclepiadaceae), elicited significant orientation from both male and female Culex pipiens in a dual-port flight olfactometer. Analysis of the extract by gas chromatography-mass spectrometry revealed six major constituents in order of relative abundance: benzaldehyde, (E)-β-ocimene, phenylacetaldehyde, benzyl alcohol, nonanal, and (E)-2-nonenal. Although not all were collected from the headspace profile of live flowers, a synthetic blend of these six compounds, when presented to mosquitoes in the same levels and proportions that occur in the extract, elicited a response comparable to the extract. Subtractive behavioral bioassays demonstrated that a three-component blend consisting of benzaldehyde, phenylacetaldehyde, and (E)-2-nonenal was as attractive as the full blend. These findings suggest the potential use of synthetic floral-odor blends for monitoring or control of both male and female disease-vectoring mosquitoes.     

Identification of odors from overripe mango that attract vinegar flies,Drosophila melanogaster

Bioassays with a variety of overripe fruits, including mango, plum, pear, and grape, and their extracts showed that odors from overripe mango were most attractive to adult vinegar flies, Drosophila melanogaster. Combined gas chromatography–electroantennographic detection (GC-EAD) analyses of solid-phase microextraction (SPME) and Tenax extracts of overripe mango odors showed that several volatile compounds, including ethanol, acetic acid, amyl acetate, 2-phenylethanol, and phenylethyl acetate elicited significant EAG responses from antennae of female flies. Most of the volatile compounds in the extracts were identified by mass spectral and retention index comparisons with synthetic standards. In cage bioassays, lures with a blend of ethanol, acetic acid, and 2-phenylethanol in a ratio of 1:22:5 attracted six times more flies than any single EAG-active compound. This blend also attracted four times more flies than traps baited with overripe mango or unripe mango. However, in field trials, the blend was not as attractive as suggested by the laboratory bioassay.     

Identification of new sex pheromone components inTrichoplusia ni,predicted from biosynthetic precursors

In addition to the previously identified components (Z)-7-dodecenyl acetate and dodecyl acetate, sex pheromone glands ofTrichoplusia ni release (Z)-5-dodecenyl acetate, 11-dodecenyl acetate, (Z)-7-tetradecenyl acetate, and (Z)-9-tetradecenyl acetate. Bioassays in a flight tunnel showed that a synthetic blend of these six compounds elicited complete flights to the source from 95% of the males tested and elicited hairpenciling responses at the end of the flights from 88% of the males tested. This blend was not significantly different from intact pheromone glands, which elicited complete flights to the source from 98% of the males tested and hairpenciling responses from 91% of the males tested. In contrast, the previously identified two-component blend elicited significantly fewer complete flights to the source (33%) and did not elicit hairpenciling responses from any of the males tested. The search for additional sex pheromone components was prompted by our previous identification of unusual fatty acyl moieties in the gland that seemed to be possible biosynthetic intermediates.     

Identification of floral compounds fromAbelia grandiflora that stimulate upwind flight in cabbage looper moths

Four major volatile components emitted from flowers ofAbelia grandiflora were identified based on retention time using two capillary columns of different polarities and electron impact mass spectrometry. These are phenylacetaldehyde, benzaldehyde, 2-phenylethanol, and benzyl alcohol. A blend of these compounds was as effective as a cluster of flowers in stimulating upwind flight by maleTrichoplusia ni to the source in a wind-tunnel test. Phenylacetaldehyde or 2-phenylethanol were each as effective as the complete blend in stimulating source location by male moths. Attraction to a source of the synthetic blend was demonstrated in virgin males and females and mated males and females, but virgin moths of both sexes were more likely than mated moths to complete the sequence of behavioral responses necessary to locate the odor source.     

Male Phyllotreta striolata (F.) Produce an Aggregation Pheromone: Identification of Male-specific compounds and Interaction with Host Plant Volatiles

The chrysomelid beetle Phyllotreta striolata is an important pest of Brassicaceae in Southeast Asia and North America. Here, we identified the aggregation pheromone of a population of P. striolata from Taiwan, and host plant volatiles that interact with the pheromone. Volatiles emitted by feeding male P. striolata attracted males and females in the field. Headspace volatile analyses revealed that six sesquiterpenes were emitted specifically by feeding males. Only one of these, however, elicited an electrophysiological response from antennae of both sexes. A number of host plant volatiles, e.g., 1-hexanol, (Z)-3-hexen-1-ol, and the glucosinolate hydrolysis products allyl isothiocyanate (AITC), 3-butenyl isothiocyanate, and 4-pentenyl isothiocyanate also elicited clear responses from the antenna. The active male-specific compound was identified as (+)-(6R,7S)-himachala-9,11-diene by chiral stationary phase gas-chromatography with coupled mass spectrometry, and by comparison with reference samples from Abies nordmanniana, which is known to produce the corresponding enantiomer. The pheromone compound was synthesized starting from (-)-α-himachalene isolated from Cedrus atlantica. Under field conditions, the activity of the synthetic pheromone required concomitant presence of the host plant volatile allyl isothiocyanate. However, both synthetic (+)-(6R,7S)-himachala-9,11-diene alone and in combination with AITC were attractive in a two-choice laboratory assay devoid of other natural olfactory stimuli. We hypothesize that P. striolata adults respond to the pheromone only if specific host volatiles are present. In the same laboratory set up, more beetles were attracted by feeding males than by the synthetic stimuli. Thus, further research will be necessary to reveal the components of a more complex blend of host or male-produced semiochemicals that might enhance trap attractiveness in the field.     

Moth Scale-Derived Kairomones Used by Egg–Larval Parasitoid Ascogaster quadridentata to Locate Eggs of Its Host, Cydia pomonella

We determined that location of host (Cydia pomonella) eggs by Ascogaster quadridentata is mediated by kairomones, investigated potential sources of the kairomones and identified a blend of kairomones from the source that was attractive to A. quadridentata. In Y-tube olfactometer bioassays, female A. quadridentata were attracted to Porapak Q-collected volatiles from female C. pomonella scales and eggs, but not to C. pomonella sex pheromone. Scales of C. pomonella were also attractive to male A. quadridentata. Coupled gas chromatographic–electroantennographic detection analysis of scale volatile extracts revealed numerous compounds that elicited responses from male or female A. quadridentata antennae, including heptanal, octanal, nonanal, decanal, undecan-2-one, dodecanal, pentadecan-2-one, (Z)-6-pentadecen-2-one, (Z)-9-hexadecenal, (Z)-6-heptadecen-2-one, and 3,7,11-trimethyl-2E,6E,10-dodecatrien-1-ol acetate. A synthetic blend of these compounds at quantities and ratios equivalent to Porapak Q scale volatile extract was attractive to female A. quadridentata in a Y-tube olfactometer bioassay.     

Sex Pheromone of the Common Sheep Moth, Hemileuca eglanterina, from the San Gabriel Mountains of California

The sex pheromone of Hemileuca eglanterina from the San Gabriel Mountains, California, was determined to be a combination of E10,Z12-hexadeca-10,12-dien-1-yl acetate, E10,Z12-hexadeca-10,12-dien-1-ol, and E10,Z12-hexadeca-10,12-dienal. Ratios of the compounds in extracts of female pheromone glands varied around a mean of 100 : 48 : 1.1 of the acetate, alcohol, and aldehyde, respectively. Field trials with synthetic compounds indicated that the optimum ratio of alcohol to aldehyde was 10 : 1 and that this ratio was more critical than the ratio of either compound to the acetate. A synthetic blend of 100 : 10 : 1 acetatendash;alcoholndash;aldehyde was effective at attracting male moths in the field. Additional compounds found in both extract and aeration samples failed to significantly increase trap catches of male moths, although some of these minor components elicited responses from male moth antennae in coupled gas chromatography–electroantennography studies.     

Behavioral Responses of Adult <Emphasis Type="Italic">Sitophilus granarius</Emphasis> to Individual Cereal Volatiles

The antennae of Sitophilus granarius (L.) (Coleoptera: Curculionidae) adults detect a wide variety of compounds in the odor blend of various cereal grains (Germinara et al., Tec. Molit., 53:27–34, 2002). In the present study, we looked at the behavioral responses of the granary weevil to 20 of these individual volatiles (aliphatic alcohols, aldehydes, ketones, and aromatics) in a two-choice pitfall olfactometer, using the aggregation pheromone and propionic acid as the attractant and repellent controls, respectively. Five doses, ranging from 1 μg to 1 mg, of each compound were tested. At least one concentration of eight compounds attracted beetles but required doses 1,000- to 5,000-fold higher than the concentration of aggregation pheromone to elicit a response. Three compounds, while attractive at lower concentrations, acted as repellents at higher doses. Twelve compounds were repellent at concentrations similar to the quantity of propionic acid that significantly repelled beetles. The data show that granary weevil adults have the ability to respond behaviorally to a wide range of cereal volatiles and that responses may change as a function of concentration. The results suggest that host finding behavior of weevils will depend on the balance of positive and negative volatile stimuli from grain as the relative concentrations of volatiles may change during storage. An understanding of how the weevils respond to such changes could be useful for the development of effective integrated pest management strategies.     

Attraction of male beetles to grubs: Evidence for evolution of a sex pheromone from larval odor

Females of the scarabaeid beetleCyclocephala lurida produce a volatile sex pheromone which attracts conspecific males. Field experiments demonstrated that larvae of both sexes also emit volatile chemicals that stimulate similar responses in adult males, including attempts by the attracted males to mate with the nonreproductive immature stage. Significantly more adult males were caught in traps baited with conspecific male or female larvae or adult females than in blank control traps. Hexane extracts of both male and female grubs were at least as effective as live larvae in trapping male adults, demonstrating that the behavioral responses are mediated by volatile chemicals. Sensory and behavioral responses of males to sex pheromones emitted by adult females are part of the functional communication system. However, their response to grubs is not functional, because grubs are normally temporally and spatially inaccessible to mate-seeking males. In theory, the evolution of a communication system is problematic because it requires the development of a signal in one sex and the sensory and behavioral attributes to respond to that signal in the other sex. The ontogeny of sex pheromone communication inC. lurida suggests a partial solution to this evolutionary problem. We propose that this sex pheromone communication system is probably derived from noncommunicative volatile chemicals that are lost in adult males and retained by adult females.     

Seducin,male sex pheromone of the cockroachNauphoeta cinerea: Isolation,identification, and bioassay

The male sex pheromone of the cockroachNauphoeta cinerea was isolated from adult sternal glands and identified by gas chromatography-mass spectrometry. This pheromone, which attracts females from a distance, is a multicomponent blend. It is composed principally of three compounds: 3-hydroxy-2-butanone (acetoin), 2-methylthiazolidine, and 4-ethyl-2-meth-oxyphenol. A mixture of synthetic compounds in a ratio of 441 (2700 ng) elicits maximal response and short latency of response by receptive females, similar to that induced by male sternal gland extracts. Tested separately, each compound induces a positive response, but the moving times spent by females are generally longer than with the mixture or extracts. These three volatile compounds also are found in small amounts (about 1/40 of sternal glands) in tergal gland secretions licked by females. Acetoin also is found in the sternal and tergal glands of two closely related speciesLeucophaea maderae andHenschoutedenia flexivitta. The biological relationship of each compound and pheromone blend to behavioral response is discussed.