Electrophysiological and Behavioral Responses of the Cabbage Moth to Plant Volatiles

Plant volatiles from cabbage and chrysanthemum were studied as to how they affect behavior of the cabbage moth, Mamestra brassicae (L.). Chemical, electrophysiological, and behavioral techniques were used. The electroantennographic (EAG) evaluation of selected compounds from Brassi-caceae showed that isothiocyanates (NCS) elicited weak responses, and some did not evoke significant EAG responses at all. Green leaf volatiles (GLVs) evoked the strongest responses in both male and female antennae. The capacity of NCS to stimulate upwind flight of mated females was not different at doses of 10^–7, 10^–6, or 10^–5 g when tested in a wind tunnel. At the higher doses, allyl NCS stimulated upwind flight in the females more than the other compounds. Allyl NCS was significantly better than the other compounds at stimulating females to land on targets. Mated females flew upwind and landed on the targets with allyl NCS more often than virgin females and males. With respect to the behavioral activity of GLVs, only (E)-2-hexenal and (Z)-3-hexenyl acetate elicited upwind flight and landing in females. Ten compounds were identified from a chrysanthemum extract by using coupled gas chromatography–electroantennography. Five of these, (Z)-3-hexenyl acetate, 1-8-cineole, -terpinene, chrysanthenone, and camphor, elicited upwind flight of mated females, but only three stimulated landing.     

Behavioral Response of Female Codling Moths, Cydia pomonella, to Apple Volatiles

Apple volatiles stimulated pheromone release, oviposition, and upwind orientation in female codling moths, Cydia pomonella. Green apples increased the percentage of virgin females calling, the duration of female calling, and advanced the onset of egg-laying in gravid females. In a tube olfactometer, both virgin and mated females were more active in the presence of apple volatiles than in clean air. They responded by walking while wing-fanning; mated females showed a stronger attraction response than unmated females.     

Identification of Host Fruit Volatiles from Flowering Dogwood (Cornus florida) Attractive to Dogwood-Origin Rhagoletis pomonella Flies

Solid-phase microextraction and gas chromatography coupled with electroantennographic detection were used to identify volatiles from fruit of flowering dogwood, Cornus florida, as key attractants for Rhagoletis pomonella flies originating from dogwood fruit. A six-component blend containing ethyl acetate (54.9%), 3-methylbutan-1-ol (27.5%), isoamyl acetate (0.9%), dimethyl trisulfide (1.9%), 1-octen-3-ol (9.1%), and -caryophyllene (5.8%) was identified from flowering dogwood fruit that gave consistent EAD activity. In a flight tunnel assay there was no significant difference in the response of individual dogwood flies exhibiting upwind anemotactic flight to volatile extracts from dogwood fruit and the six-component synthetic mixture. Dogwood flies also displayed significantly greater levels of upwind flight to sources with the dogwood volatile blend than with previously identified volatile blends from domestic apple or hawthorn fruit. Selected subtraction assays showed that the three-component mixture of 3-methylbutan-1-ol, 1-octen-3-ol, and -caryophyllene elicited levels of upwind flight to the source equivalent to the six-component mixture. Our study adds to previous ones showing that populations of Rhagoletis pomonella flies infesting apple, hawthorn, and flowering dogwood fruit are attracted to unique mixtures of fruit volatiles, supporting the hypothesis that host fruit odors could be key traits in sympatric host shifts and establishing host fidelity within members of the Rhagoletis pomonella species complex.     

Flight Initiation by Male <Emphasis Type="Italic">Rhodnius prolixus</Emphasis> is Promoted by Female Odors

Several triatomine bug species utilize chemical cues for sexual communication. We tested whether female or male Rhodnius prolixus, a vector of Chagas disease, produce volatile chemicals that elicit flight responses from conspecifics, and then isolated the source of the chemical. Males confronted with an airstream containing female odors showed a significantly greater take-off frequency compared to a blank airstream or an airstream with male odors. In contrast, females exhibited similar take-off frequencies to male or female odor as to a clean airstream. Occlusion of female metasternal glands with paraffin wax resulted in a significant decrease in male take-off frequency compared to that of intact females. Additionally, excised female metasternal glands elicited a similar take-off frequency from males as did intact females, both significantly greater than the take-off frequency to clean air. These results show that R. prolixus females release a pheromone from their metasternal glands that causes upwind flight in conspecific males.     

Chemical Stimuli from Apple Influence the Behavior of Neonate Caterpillars of the Generalist Herbivore, Epiphyas postvittana

When introduced into a wind tunnel with low windspeeds (0.2–0.3 m/sec), neonate E. postvittana larvae were more likely to walk in a downwind rather than upwind direction. This tendency to walk downwind did not change when odors from apple leaves or fruit were introduced into the wind tunnel. In a second assay that measured travel times of larvae as they walked from the center to the edge of filter paper disks, larvae moved more slowly on disks treated with extracts of apple leaves or extracts of apple fruit, but did not slow their movement on disks treated with extracts of a nonhost, Coprosma repens. Analysis of videorecords revealed that larvae on disks treated with a dichloromethane extract of apple leaves took more circuitous routes, walked more slowly, and stopped more frequently than larvae walking on solvent-treated disks. When the dosage of this dichloromethane apple leaf extract was increased or when larvae were held without food prior to testing, differences between travel times on solvent- and extract-treated disks did not increase significantly. The dichloromethane apple leaf extract, when tested in the wind tunnel with low windspeeds, also caused larvae to delay spinning down on a silken thread after reaching the edge of the disk, but had no effect on spin-down times when tested in still-air conditions. Testing of rotary evaporated apple leaf extracts and fractionation of these extracts indicated that a number of both volatile and relatively involatile chemicals contribute to the behavioral responses of E. postvittana larvae.     

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.     

Influence of odor from wood-decaying fungi on host selection behavior of deathwatch beetle,Xestobium rufovillosum

Adult females of Xestobium rufovillosum de Geer demonstrated anemotactic orientation when exposed to an odor plume containing volatiles generated by wood-decaying fungi (Coriolus versicolor, Donkioporia expansa) and decayed oak wood (Quercus petraea, Quercus robur). They did not orient towards undecayed oak wood, beech (Fagus sylvatica), or pine wood (Pinus sylvestris). Although all insects tested showed anemotactic orientation, responses were nonlinear with respect to insect age. Adult females more readily oriented upwind when they were between 10 and 16 days old. Oviposition choice bioassays showed that ovipositing females would preferentially oviposit on extract-treated cellulose paper discs that had been treated with various strains of the wood-decaying fungus, Donkioporia expansa. HPLC-fractionated mycelial extracts were attractive to ovipositing deathwatch beetles, whereas HPLC-fractionated fungal broth extracts were repellent to ovipositing females. The implications of these results are discussed in the context of timber pest management in historically important buildings.     

Effect of Wind Speed on the Pheromone-Mediated Behavior of Sexual Morphs of the Potato Aphid, Macrosiphum euphorbiae (Thomas) Under Laboratory and Field Conditions

The effect of wind on the potato aphid, Macrosiphum euphorbiae, male responsiveness to the sex pheromone, and on the calling behavior of virgin oviparae, was studied under constant wind speeds in the laboratory and in the field. A significant proportion of females called at wind speeds up to 4 m/sec, whereas male flight behavior in clean air was inhibited at velocities > 2 m/sec. However, males continued to walk over the range of wind speeds at which females called. Under constant wind velocities in a wind tunnel, males downwind of calling females oriented on the upwind edge of the release stand, and fewer individuals took flight at low constant wind speeds than in a clean air plume. In all cases, whether calling females were present or not, the males that took flight moved downwind. However, when a bridge was available, a significant proportion of males walked upwind to the pheromone source. The same orientation and walking behaviors were observed when males were placed downwind of calling females under variable wind conditions in the field. However, contrary to the laboratory results, 30% of the males tested flew upwind and landed on the source. A more detailed examination found that males orienting toward a source would walk if wind speeds were high but initiated flight in an “upwind” direction if there was a lull in wind velocity. These findings suggest that for the potato aphid, and probably for many other insect species with weak flight capacity, walking behavior is a significant component of pheromone-mediated mate location. This would permit males to continue foraging for calling females in the vicinity when wind velocities inhibit flight.     

Apple Volatiles Synergize the Response of Codling Moth to Pear Ester

Codling moth, Cydia pomonella L. (Lepidoptera: Tortricidae), is a major cosmopolitan pest of apple and other pome fruits. Ethyl (E,Z)-2,4-decadienoate (pear ester) has been identified as a host-derived kairomone for female and male codling moths. However, pear ester has not performed similarly in different fruit production areas in terms of the relative magnitude of moth catch, especially the proportion of females caught. Our work was undertaken to identify host volatiles from apples, and to investigate whether these volatiles can be used to enhance the efficacy of host kairomone pear ester for monitoring female and male codling moths. Volatiles from immature apple trees were collected in the field using dynamic headspace sampling during the active period of codling moth flight. Using gas chromatography-electroantennogram detector (GC/EAD) analysis, six compounds elicited responses from antennae of females. These compounds were identified by GC/mass spectrometry (MS) and comparisons to authentic standards as nonanal, (E)-4,8-dimethyl-1,3,7-nonatriene, methyl salicylate, decanal, (Z,E)-α-farnesene, and (E,E)-α-farnesene. When the EAD-active compounds were tested individually in the field, no codling moths were caught except for a single male with decanal. However, addition of (E)-4,8-dimethyl-1,3,7-nonatriene, methyl salicylate, decanal, or (E,E)-α-farnesene to pear ester in a binary mixture enhanced the efficacy of pear ester for attracting female codling moths compared to pear ester alone. Addition of the 6-component blend to the pear ester resulted in a significant increase in the number of males attracted, and enhanced the females captured compared to pear ester alone; the number of males and females caught was similar to that with the pear ester plus acetic acid combination lure. Our results demonstrate that it is possible to synergize the response of codling moth to host kairomone by using other host volatiles. The new apple–pear ester host kairomone blend should be helpful for monitoring female codling moth, and may provide the basis for further improvement of codling moth kairomone.     

Interspecific Pheromone Plume Interference Among Sympatric Heliothine Moths: A Wind Tunnel Test Using Live, Calling Females

Three species of North American heliothine moths were used to determine the level at which interspecific female interference of male attraction to conspecific females occurs. We used live calling females of Heliothis virescens, H. subflexa, and Helicoverpa zea, as lures for conspecific males in a wind tunnel, and then placed heterospecific females on either side of the original species such that the plumes of the three females overlapped downwind. In nearly all combinations, in the presence of heterospecific females, fewer males flew upwind and contacted or courted the source than when only conspecific females were used in the same spatial arrangement. Males did not initiate upwind flight to solely heterospecific female arrangements. Our results show that the naturally emitted pheromone plumes from heterospecific females of these three species can interfere with the ability of females to attract conspecific males when multiple females are in close proximity. However, the fact that some males still located their calling, conspecific females attests to the ability of these male moths to discriminate point source odors by processing the conflicting information from interleaved strands of attractive and antagonistic odor filaments on a split-second basis.     

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.     

Flight response ofHeliothis subflexa (Gn.) females (Lepidoptera: Noctuidae) to an attractant from groundcherry,Physalis angulata L.

Mated femaleHeliothis subflexa (Gn.) (HS) moths 1–7 days old responded positively in a Plexiglas flight tunnel to an attractant extracted with methanol from fresh whole-leaf washes of groundcherry,Physalis angulata L. Response to the groundcherry extract, as indicated by plume-tracking (i.e., upwind flight toward the odor source) and contact with the chemical dispenser did not change significantly during the first 5 hr of scotophase. Overall, ca. 50% of the responding moths also landed on the chemical dispenser; ca. 50% of the moths that landed also deposited eggs. There were no significant differences in the behavioral responses of females mating only once and those that had mated two or more times. Virgin females and male moths were significantly less responsive to the groundcherry attractant than mated females. The flight tunnel bioassay described provides an excellent system for evaluating plant allelochemics associated with host-plant selection.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.     

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.     

Flight and landing behavior ofTrypodendron lineatum (Coleoptera: Scolytidae) in response to different semiochemicals

The responses of the striped ambrosia beetle,Trypodendron lineatum (Olivier) (Coleoptera: Scolytidae), to modified drainpipe traps baited with the host attractant ethanol, the aggregation pheromone lineatin, both alone and in combination, were studied in a wind tunnel. Exposure of males to ethanol increased their frequency of steady, upwind flight; however, only lineatin was effective in inducing them to land on and enter the traps. In contrast, exposure of females to either ethanol or lineatin alone resulted in an increased frequency of trap landing and entry. Both compounds released simultaneously did not significantly increase the frequency of trap landing and entry for either sex. These responses are consistent with the life history strategies used by both sexes to seek and colonize suitable host material.     

Responses ton-dipropyl disulfide by ovipositing onion flies: Effects of concentration and site of release

Onion fly females,Delia antiqua (Diptera: Anthomyiidae) laid the most eggs on ovipositional dishes havingn-dipropyl disulfide (Pr₂S₂) release rates of 1–6 ng/sec from polyethylene capsules placed beneath a sand substrate. When dipropyl disulfide was released from the wax coating of surrogate foliage rather than from the substrate, ovipositing females again responded differentially to various concentrations, laying more eggs around stems containing 0.075 and 0.089 mg/stem. Factorial combinations of several concentrations released from surrogate foliage and substrate showed that releases from surrogate foliage stimulated four times more egg-laying than releases from the substrate. Females tended to lay more eggs around surrogate stems having Pr₂S₂ at the base rather than on the upper half of foliage. Observations of individual females performing preovipositional examining behaviors on Pr₂S₂-treated surrogate stems indicated that females tended to land on the upper portions of the foliage, but after landing, spent most of their time examining areas of soil and surrogate within 1 cm of the soil-surrogate foliage interface. Surrogate stems provide a realistic context for investigating effects of plant chemicals on host-acceptance behaviors.Journal article No. 12034 of the Michigan Agricultural Experiment Station.This work was supported by USDA Competitive Grant 5901-0410-9-0229-0.     

Crayfish feeding responses to zebra mussels depend on microorganisms and learning

Three species of crayfish (Orconectes virilis, O. rusticus, andCambarus robustus) were tested for feeding responses to potential food odors from mollusks (either zebra mussels,Dreissena polymorpha, or native gastropods). In all three crayfish species, feeding responses to odor cues were shown only by individuals experienced with feeding on a prey type. Individuals exposed to just the smell of prey organisms did not show feeding responses, indicating the role of associative learning in diet breadth. Establishment of a learned association took more than one feeding experience but once established lasted more than three weeks. When microbial enzymatic degradation of food protein was eliminated, either by UV radiation or microfiltration, feeding responses were eliminated even for crayfish experienced with a prey type.     

Sex pheromone-mediated flight and landing behaviors of the European corn borer,Ostrinia nubilalis (Hübner)

The pheromone-mediated flight and landing behaviors of maleOstrinia nubilalis were studied in a wind tunnel. The pheromone source was placed in the middle of an 18 × 18-cm horizontal surface, and a smaller surface placed 4, 18, or 36 cm downwind. The smaller surface did not appear to affect significantly the flight tracks or position of landing of males on the upwind surface, and it allowed the positions and altitudes of males as they passed over the downwind surface to be estimated. The flight altitude and position of males as they passed over the downwind surface related to where males landed on the upwind surface. Regardless of the downwind position of the downwind surface, most males flew over its center (i.e., in line with the source) and landed in line with the source on the upwind surface. When a small 2.5 × 10-cm vertical object was placed on the upwind surface, just upwind and to one side of the source, males flew over the downwind surface in positions skewed toward the vertical object and in broader distributions than for the comparable situation without an object: males landed on the upwind surface on positions skewed toward, or on, the object and with a broader distribution (laterally). Flight altitude also corresponded with landing position. Thus, when there was no vertical object, most males flew just above the downwind surface and landed on the downwind edge of the upwind surface. In contrast, with the vertical object, males flew significantly higher and tended to land past the downwind edge of the upwind surface. With a taller object (20 cm), males flew even higher, past the downwind edge and most landed on the vertical object. These data show the close relationship between flight and landing behaviors of maleO. nubilalis and suggest that flight maneuvers that determine track and altitude largely govern where a male lands.     

Laboratory Evaluation of Odor Preferences of the Brushtail Possum

The Australian brushtail possum (Trichosurus vulpecula) is the major vertebrate pest in New Zealand. Possums cause significant damage to the country's native and exotic forests and, as a vector of bovine tuberculosis, are a serious threat to the country's meat industry. Strong smelling odors are often used as lures during possum control operations in New Zealand, but little is known about the preferences of possums for these odurs. A test was designed to determine the preferences of captive wild possums for a number of odors commonly used as lures. To assess the effectiveness of the method, the possums were tested for their responses to a familiar food odor (apple) versus no odor. The possums spent significantly more time investigating the apple odor and also sniffed it more often than the no-odor control in the 15-min test period. The same procedure, however, showed that five odors commonly used as lures (almond, cloves, cinnamon, peanut, and orange) were no more preferable than water. Our results suggest that these unfamiliar odors are either equally attractive or unattractive to possums and that odors that are more familiar to these animals may be more appropriate as lures.     

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.     

Antennal responses of the two host races of the larch bud moth,Zeiraphera diniana,to larch and cembran pine volatiles

The larch bud moth (LBM) Zeiraphera diniana Guenée causes defoliation on larch in the Alps at 8- to 10-year intervals, after which populations crash. There are two LBM host races, one on larch and the other on cembran pine. These host races are morphologically indistinguishable as adults but they differ genetically in larval color types. Furthermore, females of each host race produce distinct pheromone blends and show oviposition preferences for their respective hosts. It is not clear to what extent host choice contributes to assortative mating in the LBM. Here, we compare the olfactory sensitivities of the two host races to the odors of fresh foliage of the host plants using the electroantennogram (EAG) technique, and the responses of the two host races to volatiles collected from the two host plants as analyzed by gas-chromatography-linked antennographic detection (GC-EAD). Both sexes of the larch and cembran host races show the same EAG responses to vapors of fresh larch and cembran pine foliage. Fifteen plant volatiles identified as chemostimuli by GC-EAD from larch and cembran pine odors elicited the same antennogram responses from the two host races. However, the GC-EAD analyses indicate that the number and quantity of chemostimuli emanating from each host plant is different. It is, therefore, most probably the array of olfactory receptors responding to the bouquet of volatiles unique to each host plant that underlies the host preferences of the two races. What remains open is the extent to which the similarity of the olfactory systems may contribute to cross-attraction. The fact that LBM individuals with intermediate characteristics between the two host races exist, suggests that olfactory perception does not hinder gene flow and contributes to sustained genetic diversity within the species Z. diniana.