Identification of food volatiles attractive toGlischrochilus quadrisignatus andGlischrochilus fasciatus (Coleoptera: Nitidulidae)

Seven volatile compounds identified from the headspace of whole wheat bread dough were investigated for their role in attractingGlischrochilus quadrisignatus andG. fasciatus in the field. Traps baited with either whole wheat bread dough or a synthetic seven-component bread dough odor caught similar numbers of these beetles, suggesting that the seven-compound combination could simulate the behavioral effect of bread dough. A series of trials using traps baited with various combinations of these chemicals showed that five compounds were significantly active in attractingG. quadrisignatus andG. fasciatus, but not all were essential for maximum response. The simplest blend eliciting a level of response comparable to the seven-component combination included ethyl acetate, acetaldehyde, ethanol, and racemic 2-methylbutanol, of which ethyl acetate, ethanol, and acetaldehyde were essential and 2-methylbutanol was replaceable with 2-methylpropanol forG. quadrisignatus attraction. Ethyl acetate and ethanol were essential for comparable attraction ofG. fasciatus. The chemical mediation of food finding in G.quadrisignatus andG. fasciatus is discussed in the context of volatile blends characterized for other nitidulid species.     

Chemical characterization of fruit and fungal volatiles attractive to dried-fruit beetle,Carpophilus hemipterus (L.) (Coleoptera: Nitidulidae)

The chemical basis underlying orientation to fruit and fungal odors was investigated for the dried-fruit beetle,Carpophilus hemipterus (L.). In wind-tunnel bioassays of walking and flight response from 1.8 m, beetles were attracted to odors of the yeastSaccharomyces cerevisiae on agar, aseptic banana, or banana inoculated withS. cerevisiae, although both banana substrates elicited greater response than the yeast alone. When presented in a two-choice bioassay, the yeast-inoculated banana attracted approximately twice as many beetles as did the aseptic banana. GC-MS analysis of the headspace volatiles above these odor sources revealed a somewhat more complex and concentrated volatile profile for yeast-inoculated banana than for aseptic banana. The odor from yeast on agar had fewer components, and these were present at lower concentrations than the odors of either banana substrate. By blending mineral-oil or aqueous solutions of the 18 components of inoculated-banana odor in varying concentrations, it was possible to mimic closely the headspace profile of the natural odor. This synthetic odor also elicited beetle attraction in the wind tunnel at levels comparable to the inoculated banana. Through a series of bioassays in which individual components were subtracted from or added to a synthetic odor blend, it was determined that ethyl acetate, acetaldehyde, 2-pentanol, and 3-methylbutanol comprised the simplest blend of compounds evoking full behavioral response. However, 2-methylpropanol or butanol were apparently interchangeable with 3-methylbutanol in this blend, and comparable response could also be elicited by replacing acetaldehyde with a combination of both 2-pentanone and 3-hydroxy-2-butanone. Thus, our results suggest that this generalist insect herbivore locates its hosts by a long-range response to a variety of blends of common fruit volatiles, whose concentrations are enhanced by fungi.     

A Versatile and Quantitative Volatile-Delivery System for Laboratory Bioassays

A versatile moving-air system is described for delivering volatiles into a wind tunnel or other bioassay device. The system controls up to four volatile sources at one time. There is a calibrated, adjustable splitter for each source so that any percentage of a source's airstream, or none of it, can be directed to the system outlet at any moment. Thus, the system allows the sample volatiles to be bioassayed in any order and at any level or in mixtures of any desired proportions. Volatile sources of many types can be used, including single chemicals in slow-release formulations, mixtures of chemicals, or volatiles from living organisms. The volatile stream can be sampled by solid-phase microextraction (SPME) just before it enters the wind tunnel. Analysis of the SPME sample by gas chromatography allows absolute delivery rates of volatile components to be calculated. System performance was characterized with physical measurements and with bioassay experiments involving Carpophilus humeralis (F.) (Coleoptera: Nitidulidae). One bioassay experiment demonstrated how volatiles from a microbial culture (fermenting bread dough) and a synthetic counterpart (an aqueous solution of acetaldehyde, ethanol, 1-propanol, isobutanol, 3-methyl-1-butanol, 2-methyl-1-butanol, and ethyl acetate) could be compared at a range of dose levels, with just one sample of each type. These natural and synthetic volatile sources delivered very similar amounts of the above compounds and produced nearly identical dose–response curves. In another experiment, three bread dough volatiles (ethanol, acetaldehyde, and ethyl acetate) were tested in mixtures. Each component was used at four different levels (giving a total of 64 experimental treatments), but just one physical sample was needed for each chemical. The experiment provided clear information about response thresholds and interactions among these host volatiles. The volatile delivery system is versatile, easy to operate, and can be constructed from inexpensive materials.     

Female-Biased Attraction of Oriental Fruit Fly, Bactrocera dorsalis (Hendel), to a Blend of Host Fruit Volatiles From Terminalia catappa L.

Coupled gas chromatography-electroantennogram detection (GC-EAD) analysis of volatiles from tropical almond fruit, Terminalia catappa L., revealed 22 compounds that were detected by antennae of oriental fruit fly females, Bactrocera dorsalis (Hendel). Both solid-phase microextraction (SPME) and Porapak Q were used for sampling odors in fruit headspace, with SPME collections producing larger EAD responses from a greater number of compounds. Geranyl acetate and methyl eugenol elicited the largest EAD responses. A synthetic blend containing SPME collected, EAD stimulatory compounds showed female-biased attraction in laboratory wind tunnel bioassays, but heavily male-biased trap captures in a larger olfactometer arena. A nine-component subset of compounds eliciting relatively small EAD responses (EAD minor) and consisting of equal parts ethanol, ethyl acetate, ethyl hexanoate, hexyl acetate, linalyl acetate, ethyl nonanate, nonyl acetate, ethyl cinnamate, and (E)-β-farnesene, attracted mainly females. This EAD minor blend was as attractive to females and much less attractive to males when compared to torula yeast in field cage experiments using glass McPhail traps. Similar results were obtained with outdoor rotating olfactometer tests in which the EAD minor blend was almost completely inactive for males.     

Aggregation pheromone ofCarpophilus antiquus (Coleoptera: Nitidulidae) and kairomonal use ofC. lugubris pheromone byC. antiquus

Males ofCarpophilus antiquus Melsheimer (Coleoptera: Nitidulidae) emit an aggregation pheromone that was found to be a novel hydrocarbon, (3E,5E,7E,9E)-6,8-diethyl-4-methyl-3,5,7,9-dodecatetraene. A synthetic scheme and spectra (mass and proton NMR) are given for the compound. Beetles produced the pheromone when feeding on a variety of media, including the brewer's yeast-based artificial diet, fermenting whole-wheat bread dough, corn, and prunes; live baker's yeast was generally added to the food media. Males held individually produced, on average, 25 × more pheromone per beetle than males held in groups of 10 or more. Pheromone was not produced until males were at least 5 days old but was still detected from the oldest beetles tested (47 days). In field tests, the pheromone was attractive to both sexes ofC. antiquus, and it was synergized by food volatiles: A combination of pheromone and fermenting whole wheat dough attracted 2.5× more beetles than pheromone alone, but dough by itself was not significantly more attractive than the control. Semiochemical interactions were studied amongC. antiquus and two other sympatric species for which pheromones are known,C. lugubris Murray andC. freemani Dobson.C. antiquus responded readily to the pheromone ofC. lugubris, but all other interspecific responses to the pheromones were weak. In a sample of naturally infested corn ears, the presence ofC. antiquus was strongly associated with the presence ofC. lugubris, as would be expected if the pheromone ofC. lugubris serves as a kairomone forC. antiquus.     

Identification and Field Evaluation of Fermentation Volatiles from Wine and Vinegar that Mediate Attraction of Spotted Wing Drosophila, Drosophila suzukii

Previous studies suggest that olfactory cues from damaged and fermented fruits play important roles in resource recognition of polyphagous spotted wing Drosophila flies (SWD), Drosophila suzukii (Matsumura) (Diptera: Drosophilidae). They are attracted to fermented sweet materials, such as decomposing fruits but also wines and vinegars, and to ubiquitous fermentation volatiles, such as acetic acid and ethanol. Gas chromatography coupled with electroantennographic detection (GC-EAD), gas chromatography-mass spectrometry (GC-MS), two-choice laboratory bioassays, and field trapping experiments were used to identify volatile compounds from wine and vinegar that are involved in SWD attraction. In addition to acetic acid and ethanol, consistent EAD responses were obtained for 13 volatile wine compounds and seven volatile vinegar compounds, with all of the vinegar EAD-active compounds also present in wine. In a field trapping experiment, the 9-component vinegar blend and 15-component wine blend were similarly attractive when compared to an acetic acid plus ethanol mixture, but were not as attractive as the wine plus vinegar mixture. In two-choice laboratory bioassays, 7 EAD-active compounds (ethyl acetate, ethyl butyrate, ethyl lactate, 1-hexanol, isoamyl acetate, 2-methylbutyl acetate, and ethyl sorbate), when added singly to the mixture at the same concentrations tested in the field, decreased the attraction of SWD to the mixture of acetic acid and ethanol. The blends composed of the remaining EAD-active chemicals, an 8-component wine blend [acetic acid + ethanol + acetoin + grape butyrate + methionol + isoamyl lactate + 2-phenylethanol + diethyl succinate] and a 5-component vinegar blend [acetic acid + ethanol + acetoin + grape butyrate + 2-phenylethanol] were more attractive than the acetic acid plus ethanol mixture, and as attractive as the wine plus vinegar mixture in both laboratory assays and the field trapping experiment. These results indicate that these volatiles in wine and vinegar are crucial for SWD attraction to fermented materials on which they feed as adults.     

Aggregation pheromone of driedfruit beetle,Carpophilus hemipterus Wind-tunnel bioassay and identification of two novel tetraene hydrocarbons

A male-produced aggregation pheromone was demonstrated inCarpophilus hemipterus (L.) (Coleoptera: Nitidulidae) using a wind-tunnel bioassay. Both sexes responded to the pheromone, but the beetles flew in the wind tunnel only after they had been starved for at least several hours. The attractiveness of the pheromone was greatly enhanced by volatiles from a food source, and combinations of pheromone and food volatiles typically attracted 3–10 times more beetles than either source by itself. A variety of food-related sources of volatiles were effective. These included apple juice; a mixture of baker's yeast plus banana; the pinto bean diet used for rearing this beetle; the chemicals propyl acetate, ethanol; and a mixture of acetaldehyde, ethyl acetate, and ethanol. The pheromonal activity resided with a series of 10 male-specific, unsaturated hydrocarbons of 13, 14, and 15 carbon atoms. These were partially separated by HPLC. No single compound was absolutely required for pheromonal activity to be observed, and various subsets of these compounds were active. The most abundant component was (2E,4E,6E,8E)-3,5,7-trimethyl-2,4,6,8-decatetraene. One minor component was (2E,4E,6E,8E)-3,5,7-trimethyl-2,4,6,8-undecatetraene. These structures were proven by synthesis. Together, the synthetic compounds were as active in the wind tunnel as the beetle-derived pheromone.     

Male-produced aggregation pheromone ofCarpophilus obsoletus (Coleoptera: Nitidulidae)

Males ofCarpophilus obsoletus Erichson produce an aggregation pheromone to which both sexes respond. The pheromone was identified by GC-MS as (2E,4E,6E,8E)-3,5,7-trimethyl-2,4,6,8-undecatetraene (1), which is also a minor constituent of the pheromone blends ofC. hemipterus (L.),C. freemani Dobson, andC. lugubris Murray. The pheromone was synergized in wind-tunnel bioassays by propyl acetate, a host-type coattractant. In a dose-response study, 50 pg of1, plus propyl acetate, was significantly more attractive than just propyl acetate. Pheromone emission from groups of 65 males, feeding on artificial diet, averaged 2.2 ng/male/day. Emissions from individual males were larger, averaging 72 ng/day and ranging as high as 388 ng/day. Synthetic1 was tested in a date garden in southern California (500 µg/rubber septum), using fermenting whole-wheat bread dough as the coattractant. The pheromone plus dough attracted significantly more beetles than dough alone (means were 4.2 and 0.0 beetles per week per trap). Captured beetles were 54% females. Field trap catches were highest during the months of July and August.All programs and services of the U.S. Department of Agriculture are offered on a nondiscriminatory basis without regard to race, color, national origin, religion, sex, age, marital status, or handicap. Mention of firm names or trade products does not imply endorsement by the U.S. Department of Agriculture over similar firms or products not mentioned.     

Attractants for synanthropic flies

Fermented molasses or sucrose solutions are known to attract several species of filth-breeding flies. To identify the volatile attractants produced in fermenting sucrose solutions with yeast, these solutions were fractionated, and the chemical constituents identified and bioassayed against filth-breeding flies includingFannia canicularis (L.),Muscina stabulans (Fallén), andMusca domestica (L.). Distillation of a fermented sucrose solution gave an active distillate and an inactive residue. Gas Chromatographic analysis of the distillate showed the presence of acetaldehyde, ethyl acetate, ethanol, 1-pro-panol, 2-methyl-l-propanol, and 3-methyl-l-butanol. Ethanol constituted by far the greatest proportion of compounds present in the distillate. An aqueous solution of ethanol exhibited the same level of attractancy as the distillate, the fermented sucrose solution, and a reconstituted distillate containing all compounds identified. Ethanol was thus identified as the sole attractant emanated from fermented carbohydrate solutions that elicited positive responses in pest flies, especially inF. canicularis.Diptera: Muscidae.     

Identification of Pheromone Synergists in American Palm Weevil, Rhynchophorus Palmarum, and Attraction of Related Dynamis Borassi

Thirteen host-plant kairomone blends, including 28 compounds, were tested and showed moderate to high synergy with rhynchophorol. The blends plus rhynchophorol also attracted the related Dynamis borassi. Ethanol–ethyl acetate blends in various ratios showed moderate synergy. Two blends, including "characteristic coconut" odor molecules, were as efficient as sugarcane in synergizing rhynchophorol and field luring American Palm weevils (APWs). Preliminary olfactometer tests of natural host-plant volatiles demonstrated the role of fermentation in primary APW attraction. The synergists were chosen from a comparative study of the odors emitted by four plant materials attractive to the APW: sugarcane, coconut, Jacaratia digitata tree and Elaeis guineensis (Oil palm). The volatiles were isolated during 6 days of sequential trappings onto Supelpak-2 adsorbent. The highly volatile fraction of sugarcane volatiles was sampled by solid-phase microextraction (SPME). Odors were analyzed and identified by gas chromatography and mass spectrometry. Electroantennogram responses to the plant odors were recorded to help in screening for bioactivity. The odor compositions between plants prior to and during fermentation were compared using a principal component analysis (PCA) to determine common odor features of the plants and to design simplified blends for field activity screening. About 100 components were identified in the >4-carbon fraction of the odors, among which 65% were fermentation volatiles. Fermentation generated a strong increase in the amount and variety of the volatiles emitted. The palm materials emitted two- to threefold greater odor amounts than the other plants. The odors from each plant were distinct according to PCA, with few common abundant components: isopentanol, 2-methylbutanol, their acetates, acetoin, isobutyl acetate, 2,3-butanediol, and 2-phenylethanol. Ethanol and ethyl acetate accounted for 80–90% in the highly volatile fraction of sugarcane odors. Coconut odor was mainly characterized by phenol, guaiacol, 1,2-dimethoxybenzene, ethyl esters of tiglic and 3,3-dimethylacrylic acids, 2-hexanone, 2-nonanone; and, to a lesser extent, by 2-heptanone, menthone, -phellandrene, ethyl octanoate and decanoate, which were also present in other plants.     

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.     

Semiochemical-mediated flight responses of sap beetle vectors of oak wilt,Ceratocystis fagacearum

The sap beetle, Colopterus truncatus (Coleoptera: Nitidulidae), is one of the primary vectors of the oak wilt pathogen, Ceratocystis fagacearum, in the north-central United States. Field behavioral assays utilizing various release rates and blends of three methyl-branched hydrocarbon aggregation pheromone components showed that flight responses of this beetle were similar in Illinois and Minnesota populations. In both locations, both sexes of the beetle responded synergistically to a combination of the three-component pheromone and fermenting whole-wheat bread dough. Further, Colopterus truncatus preferred a high release rate over a low release rate of the three-component blend. In both locations, the response of C. truncatus to a simplified version of the pheromone consisting of (2E,4E,6E)-3,5-dimethyl-2,4,6-octatriene (1) and (2E,4E,6E,8E)-3,5,7-trimethyl-2,4,6,8-decatetraene (3) was not significantly different from the response to the three-component blend. An experiment in Illinois with all possible combinations of the components demonstrated that the decatetraene (3) was the crucial component in the blend; of all treatments, the maximal response was elicited by 3 + dough. Chipped bark, phloem, and xylem from northern pin oak, Quercus ellipsoidalis, was not attractive to C. truncatus in Minnesota. During a weekly survey over two seasons in Minnesota, C. truncatus flew in response to the three-component pheromone between early April and early July, with the maximum responses coming on May 4, 2000 and April 20, 2001. During both years, more than 98% of the beetles were trapped between April 14 and June 1. During the same survey, Glischrochilus spp. (Nitidulidae) flew during longer periods of the summer, particularly in 2001. The sex ratio of C. truncatus responding during all experiments was female-biased (1.8:1, female–male), which is characteristic of other male-produced coleopteran aggregation pheromones. Other sap beetles that play a minor role in the pathobiology of C. fagacearum also responded in experiments conducted in Minnesota. Carpophilus brachypterus Say was cross-attracted to the two- and three-component blends of the C. truncatus pheromone and dough, whereas two Glischrochilus spp. were attracted to all treatments that contained dough.     

Male-produced Aggregation Pheromone of Colopterus truncatus: Structure, Electrophysiological, and Behavioral Activity

A male-produced aggregation pheromone was demonstrated in Colopterus truncatus Randall (Coleoptera: Nitidulidae) by gas chromatographic comparisons of male and female volatile emissions. Male-specific compounds were identified with coupled gas chromatographic–mass spectrometric (GC-MS) analysis and GC and MS comparison of authentic standards. Physiological activity was evaluated by coupled gas chromatographic–electroantennographic (GC-EAG) recordings, and electroantennographic (EAG) assays of standards. The male-produced volatiles eliciting responses from male and female antennae (and relative abundance) were (2E,4E,6E)-3,5-dimethyl2,4,6-octatriene (1) (1.8), (2E,4E,6E)-4,6-dimethyl-2,4,6-nonatriene (2) (100), and (2E,4E,6E,8E)-3,5,7-trimethyl-2,4,6,8-decatetraene (3) (3.3). A fourth male-specific compound, (2E,4E,6E,8E)-4,6,8-trimethyl-2,4,6,8-undecatetraene (4) (0.6) was not EAG-active. EAG dose–response studies showed that the antennae were most sensitive to 2 followed by 3 and 1. Synthetic 2, binary blends of 1 and 3, and tertiary blends of 1, 2, and 3 were highly attractive in the field when synergized with fermenting whole-wheat bread dough. In the field, cross-attraction to the C. truncatus pheromone components was observed for Carpophilus lugubris Murray, C. antiquus Melsheimer, and C. brachypterus Say.     

Learning of Herbivore-Induced and Nonspecific Plant Volatiles by a Parasitoid,Cotesia kariyai

Learning of host-induced plant volatiles by Cotesia kariyai females was examined with synthetic chemicals in a wind tunnel. Wasps were preconditioned by exposure to volatiles and feces simultaneously. A blend of four chemicals, geranyl acetate, -caryophyllene, (E)--farnesene, and indole, which are known to be specifically released from plants infested by host larvae Mythimna separata (host-induced blend), elicited a response in naive C. kariyai, but did not enhance the response after conditioning. A blend of five chemicals, (E)-2-hexenal, (Z)-3-hexen-1-ol, (Z)-3-hexen-1-yl acetate, -myrcene, and linalool, which are known to be released not only from plants infested by the host larvae, but also from artificially damaged plants or undamaged ones (unspecific blend), elicited little response in naive wasps, but significantly enhanced the wasps' response after conditioning. With a blend of the above nine chemicals, wasps could learn the blend at lower concentrations than they did in the nonspecific blend. Hence, both the host-induced and nonspecific volatile compounds appear to be important for C. kariyai females to learn the chemical cues in host location.     

Attraction ofCarpophilus Spp. (Coleoptera: Nitidulidae) to volatile compounds present in figs

Various volatile compounds present in ripening figs were attractive toCarpophilus hemipterus, C. mutilatus, C.freemani, andC. lugubris. Field tests demonstrated that traps baited with a mixture of acetaldehyde, ethyl alcohol, and ethyl acetate caught more adultC. hemipterus than those baited with (1) other mixtures involving various combinations of 19 compounds, (2) with 16 single compounds, or (3) with fig paste.This investigation was supported in part by a grant from the California Dried Fig Advisory Board.     

Identification of a New Blend of Apple Volatiles Attractive to the Apple Maggot, Rhagoletis pomonella

Solid-phase microextraction (SPME) and gas chromatography coupled with electroantennographic detection (GC-EAD) were used to identify a new blend of volatiles from apples as the key attractants for the apple maggot fly, Rhagoletis pomonella (Walsh). The new five-component blend contains butyl butanoate (10%), propyl hexanoate (4%), butyl hexanoate (37%), hexyl butanoate (44%), and pentyl hexanoate (5%) compared with a previously reported seven-component mix of hexyl acetate (35%), (E)-2-hexen-1-yl acetate (2%), butyl 2-methylbutanoate (8%), propyl hexanoate (12%), hexyl propanoate (5%), butyl hexanoate (28%), and hexyl butanoate (10%). Volatiles from five different varieties of apple elicited reproducible and high EAD responses from R. pomonella antennae to the same five chemicals. In flight-tunnel choice tests involving red sticky spheres with odor sources, the new five-component blend of apple volatiles showed significantly more activity than the previous seven-component blend or the single compound, butyl hexanoate. In a field trial captures with the new five-component blend were better than with butyl hexanoate, which is currently used with commercial apple maggot monitoring spheres.     

Identification of Host Attractants for the Ethiopian Fruit Fly, <Emphasis Type="Italic">Dacus ciliatus</Emphasis> Loew

The Ethiopian fruit fly, Dacus ciliatus, is an oligophagous pest of cucurbit crops, particularly melons, cucumbers, and marrows (summer squash). The present study aimed to identify host attractants for D. ciliatus and was guided by a behavioral bioassay and an electrophysiological assay. We tested volatile compounds from the fruits of a host plant, ripe and unripe Galia melon, Cucumis melo var. reticulates. Both sexes were attracted to melon volatiles. Those of ripe melon were preferred. Gas chromatography-electroantennographic detection analysis of the behaviorally active ripe melon volatiles consistently showed that 14 compounds elicited similar antennal responses from both sexes. Twelve compounds were identified by gas chromatography-mass spectrometry (GC-MS) using GC-MS libraries, retention indices (RI), and authentic standards. The electrophysiological activities of the compounds that were present at sufficient levels for identification, benzyl acetate, hexanyl acetate, (Z)-3-hexenyl acetate, (Z)-3-octenyl acetate, octanyl acetate, (Z)-3-decenyl acetate, and (E)-β-farnesene, were evaluated at six different dosage levels by using electroantennography (EAG). Benzyl and hexanyl acetates elicited dose responses only in males, while other tested compounds elicited dose responses in both sexes. The strongest responses were observed for doses between 100 ng and 10 μg. The dose response, in terms of attractiveness to synthetic compounds within the active range (as determined by EAG), also was evaluated in the behavioral bioassay. Synthetic acetates were attractive to both sexes when tested individually. Significant attraction was observed when individual compounds were applied in the bioassay arena at doses of 0.5–1 μg/dispenser. Blends of compounds in equal proportions also were attractive to the insects. The most attractive blend was a mixture of four or five identified acetates. The addition of an equal proportion of (E)-β-farnesene to this mixture had a deterrent effect.     

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.     

Interactions between Acetoin,a Plant Volatile,and Pheromone In <Emphasis Type="Italic">Rhynchophorus palmarum</Emphasis>: Behavioral and Olfactory Neuron Responses

Aggregation of Rhynchophorus palmarum weevils on host plants is mediated by a male pheromone (rhynchophorol: R) and host-plant volatiles (PVs) acting in synergy. Synthetic PV blends synergizing pheromone contain acetoin (A) and ethyl acetate (EtAc). R, A, and EtAc are detected by specialized olfactory receptor neurons (ORNs). In addition, particular types of ORNs are tuned to both A and R. To specify the role played by acetoin in pheromone perception, we recorded the responses of ORNs to 100 ng of A or R presented either separately or mixed. Behavioral responses to R, A, and EtAc were studied in a four-armed olfactometer and by field trapping. We screened 59 R-, A-, and AR-tuned ORNs by recording specific responses to odors presented either separately or mixed. Stimulations by blends elicited complex response profiles from the three ORN types: some gave synergistic responses, others were inhibited, and the remainder responded as though both odors were detected independently. Several gave either a weak or no response to a first stimulation by R, but responded clearly to a second stimulation after an intercalary stimulation by A. In the olfactometer, both sexes were more attracted to a blend of A + R (1 + 0.01 ng/sec) than to pure compounds, whereas EtAc did not enhance response to R. Pheromone-baited traps (1 mg/day) containing PV blends (650 mg/day) based on an ethanol/EtAc blend (1:1), plus either 5 or 10% A, or a more complex reference blend, or sugarcane (natural pheromone synergist), caught similar numbers of weevils and about twice as many insects as a control ethanol/EtAc blend. Traps with only pheromone caught about 10 times fewer insects. Behavioral results support the role of acetoin as a pheromone synergist for R. palmarum, and electrophysiological data provide evidence of modulation of peripheral sensory responses to pheromone by acetoin. Sexual dimorphism was observed neither at the ORN nor at the behavioral levels.     

Plant-natural enemy association in tritrophic system,Cotesia rubecula-Pieris rapae-brassicaceae (Cruciferae). III: Collection and identification of plant and frass volatiles

To elucidate the identity of the volatile compounds that could be involved in the searching behavior of the parasitoidCotesia rubecula Marshall (Hymenoptera: Braconidae), the volatiles released by cabbage and frass of Lepidoptera feeding on cabbage were collected and analyzed using a gas chromatograph-mass spectrometer. The volatiles emitted by intact cabbage were -pinene, -pinene, myrcene, 1,8-cineole,n-hexyl acetate,cis-3-hexen-1-yl acetate, and dimethyl trisulfide. Mechanical damage on an intact plant induced the release of two more compounds,trans-2-hexenal and 1-methoxy-3-methylene-2-pentanone. Current feeding by larvae ofPieris rapae L. (Pieridae) induced the plant to release all the compounds released after mechanical damage and additionally 4-methyl-3-pentenal and allyl isothiocyanate. Current feeding by larvae ofPlutella xylostella L. (Plutellidae) induced the plant to release all the compounds present after mechanical damage and additionally allyl isothiocyanate. The volatiles emitted after feeding by the lepidopterans had ceased were the same as those emitted by cabbage damaged by mechanical means. The blend of volatiles emitted by frass was comprised of plant chemicals, mainly sulfur compounds. Frass ofP. rapae emitted allyl isothiocyanate, methyl isothiocyanate, methyl propyl sulfide, dimethyl trisulfide,S-methyl methane thiosulfinate, 4-methyl-3-pentenal,trans-2-hexenal, and 2,3-dihydro-4-methyl furan. Frass ofP. xylostella emitted only dimethyl trisulfide andS-methyl methane thiosulfinate. The blend of volatiles emitted by frass is herbivore-species specific.