Residual activity of oviposition-deterring pheromone inRhagoletis pomonella (Diptera: Tephritidae) and female response to infested fruit

Under dry conditions, oviposition-deterring pheromone (ODP) of the apple maggot fly (Rhagoletis pomonella Walsh) on host fruit proved deterrent to ovipositing females for at least three weeks, with a half-life of ca. 11 days. There was no difference in decline of residual activity under lab vs. field conditions or between fly-deposited ODP vs. an application of a water extract of ODP. A decline in pheromone activity resulted from exposure to both natural and simulated rainfall. For natural rainfall, greatest losses (50– 61%) in activity resulted from high-intensity rains, with substantially less activity lost (13–35%) following light or moderate intensity rains.R. pomonella females discriminated against fruit without ODP but with conspecific larvae. Discrimination against infested fruit was manifested within fewer days following infestation of small fruit (9 mm diam.) as compared to larger fruit (15 mm diam.).     

Oviposition deterring pheromone inAnastrepha fraterculus flies

Anastrepha fraterculus (Wiedemann) females were found to deposit a water-soluble, durable, oviposition-deterring pheromone during ovipositor dragging on fruit after egg-laying. We present evidence that the occurrence of pheromone deposition after egg-laying, the amount deposited, and departure from the fruit without additional egg-laying after pheromone deposition are flexible traits inA. fraterculus, varying in expression according to fruit size and other factors. UnlikeRhagoletis, A. fraterculus males were not arrested by the pheromone.     

Oviposition-deterring pheromone ofRhagoletis pomonella

We found that after the parasitoidOpius lectus has arrived on a fruit infested by eggs or early-instar larvae of its tephritid hostRhagoletis pomonella, the following stimuli act to retain it and elicit antennal tapping and oviposition probes: unidentified fruit chemical components; characteristic fruit shape, size and color; andR. pomonella oviposition-deterring pheromone. This is the first demonstration of an oviposition-deterring pheromone in a phytophagous insect serving as a kairomone to one of its parasitoids.O. alloeus, a parasitoid of lateinstar larvae ofR. pomonella, was not influenced by the pheromone. Possible use of the pheromone for management ofO. lectus in a multifacetedR. pomonella suppression program is discussed.     

Host odor and visual stimulus interaction during intratree host finding behavior ofRhagoletis pomonella flies

Responses ofRhagoletis pomonella (Walsh) (Diptera: Tephritidae) flies to host fruit visual stimuli (apples or models of apples) and chemical stimuli (synthetic apple volatile blend) were studied in semidwarf field-caged apple trees. Three different fruit or model densities (1, 4, or 16 fruit or models/ tree) and two odor release rates [ca. 0.7g/hr (close to the natural release rate of a ripe apple) and ca. 500g/hr (amount of odor released by commercially sold apple maggot traps)] were tested. Individually released flies were followed as they moved within a tree for a maximum of 20 min. We recorded three-dimensional search paths followed by foraging flies and computed such variables as total relative distance traveled before alighting on a fruit or model, track length between individual alightment sites, and directness of flight to fruits or models. Effect of odor on propensity to alight on fruit or models and host-searching behavior prior to alighting on fruit or on models varied according to fruit or model color and density. If the fruit visual stimulus was strong (e.g., red color), odor did not increase the probability of finding fruit or fruit models. As the visual stimulus became progressively weaker (red to green to clear), odor (irrespective of concentration) appeared to aid flies during the fruit-finding process. As density of fruit or models increased, the probability of flies finding a fruit or model also increased (e.g., 50% of flies found a red fruit model at 1 model/tree while 90% found a red model at 16 models/tree; 4% of flies found a clear model with odor at 1 model/tree while 35% found a clear model with odor at 16 models/tree). Findings reported elsewhere indicate thatR. pomonella flies are able to discover a point source of odor (an odor-bearing tree in a patch of trees) by flying upwind (in the tree patch) in response to intermittent exposure to odor. Findings here indicate that after arrival on a host tree (point source), flies discover individual apparent and abundant host fruit on the basis of vision. If fruit are less apparent or scarce, odor appears to interact with vision during the fruit-finding process.     

Phytochemical basis of learning inRhagoletis pomonella and other herbivorous insects

Examples of phytochemically-based learning of host preference in herbivorous insects are reviewed in the context of traditionally important issues: the number and kinds of chemicals involved; which sensory modalities are affected; whether peripheral or central nervous processing is altered; and whether learning is associative or not. A fifth issue addressed here— whether experience enhances a feeding or ovipositing insect's propensity to accept familiar chemical stimuli or to reject novel chemical stimuli-has been ignored in previous studies. Following the review, evidence is presented indicating that female apple maggot flies (Ragoletis pomonella) learn to reject both novel physical and novel chemical stimuli.     

Distance of response to host tree models by female apple maggot flies,Rhagoletis pomonella (Walsh) (Diptera: Tephritidae): Interaction of visual and olfactory stimuli

Mature female apple maggot flies,Rhagoletis pomonella (Walsh), were released individually onto a single potted, fruitless hawthorne tree in the center of an open field. The tree was surrounded by four 1-m² plywood host tree models painted green or white, with or without synthetic host fruit odor (butyl hexanoate), and placed at one of several distances from the release tree. Each fly was permitted to forage freely on the release tree for up to 1 hr, or until it left the tree. Flies left the tree significantly sooner when green models with host fruit were present at 0.5, 1.5, or 2.5 m distance from the release tree than when these models were placed at a greater distance (4.5 m) from the release tree or when no models were present. Flies responded detectably to 1-m² models without odor up to a maximum distance of 1.5 m. These results suggest that female apple maggot flies did not detect green 1-m² models with odor 4.5 m away or models without odor 2.5 m or more away. Flies responded to white models with and without odor to a much lesser extent, both in terms of response distance and flight to and alightment upon models. Increasing model size to 2 m² increased the distance to 2.5 m at which flies responded to green models without odor. Decreasing model size to 0.5 m² reduced fly responsiveness to green or white models. The presence of host fruit odor alone, without the visual stimulus of a green model, did not influence residence time on the release tree.     

Host marking pheromone ofRhagoletis cerasi: Foraging behavior in response to synthetic pheromonal isomers

We studied the foraging behavior ofRhagoletis cerasi females in trees treated with synthetic cherry fruit fly host marking pheromone (HMP) under seminatural conditions (potted trees enclosed in a screen cage). Results show that synthetic HMP (particularly the 8RS-@#@ 15R isomer configuration (racemic mixture)) was highly effective in eliciting behavioral responses similar to those reported in studies using natural HMP. Flies exposed to synthetic pheromone exhibited short tree residence times (i.e., emigrated faster), increased flight frequency rates (measured as number of alightings per/minute), higher irritation indices while on a tree or a fruit, and oviposited fewer eggs per fruit visit than flies exposed to clean trees and fruit (not treated with synthetic HMP). Furthermore, we provide evidence showing that when flies were continuously exposed to an HMP-saturated environment, they exhibited an increased tendency to lay eggs in marked fruit.     

Variation in host fruit volatiles attractive to apple maggot fly,Rhagoletis pomonella

We conducted a comparative study of volatiles produced by wholeCrataegus hawthorn fruit and four cultivars of apple (Royal Red Delicious, Red Astrachan, McIntosh, and Wealthy) and determined quantitative and qualitative changes of volatiles associated with fruit ripening. Within the approximate range of the GLC fraction known to elicit behavioral activity in the apple maggot fly,Rhagoletis pomonella (Walsh) (Diptera: Tephritidae), 52 esters were identified.     

Deterrence of repeated oviposition by fruit-marking pheromone inCeratitis capitata (Diptera: Tephritidae)

During ovipositor dragging on the fruit surface following egg laying in hawthorne fruit,Ceratitis capitata (Wiedemann) females deposit an unidentified pheromone that deters repeated oviposition attempts in that fruit. The pheromone proved water soluble and, when collected and sprayed in aqueous solution onto uninfested fruits in laboratory cages, effectively deterred boring attempts byC. capitata females of wild origin for at least 6 days (termination of test). A laboratory population ofC. capitata cultured on artificial media for more than 200 generations deposited pheromone that proved equally as deterrent to wild fly oviposition as pheromone from wild flies. However, lab fly oviposition was not effectively deterred by the presence of pheromone. The ecological significance of the pheromone is discussed.     

Biology of pheromone release by male caribbean fruit flies,Anastrepha suspensa (Diptera: Tephritidae)

Males of the Caribbean fruit fly,Anastrepha suspensa (Loew), typically form leks and attract females by releasing a multicomponent volatile pheromone. Previous reports have identified two nine-carbon alcohols, three lactones, a sesquiterpene, and a monoterpene in the volatiles. The present report is a study of the physiology of male pheromone release and of ecological and social interactions that influence pheromone release by laboratoryreared flies. Volatiles released by males were trapped on Tenax, eluted, separated, and quantitatively measured by gas chromatography. Experiments showed that the volatiles were primarily released from mouth and anus. Sealing the anal opening or the mouth with melted beeswax resulted in up to 40% or greater reduction in most components, and sealing both mouth and anus further reduced release of volatiles, but some volatiles are possibly still released directly from the cuticle. An anal pouch of everted tissue played a major role as a large evaporative surface for release of some of the volatile components. Male flies entrained to a 1410 light-dark cycle showed a peak release of volatiles at 11–12 hr into the photophase, but smaller quantities of the same volatiles were released over a broad period during the daylight hours. Laboratory-reared males peaked in pheromone release at 7–10 days and production and release continued through 35 days of age. Single males released significantly more of all components measured than did groups of males. The reduction by aggregations of males may be related to lekking behavior in this fruit fly. The pheromone probably serves to attract females to a lek site, but additional parameters are likely to enter into the choice of male made by the arriving female.This is University of Florida Agricultural Experiment Station Journal Series No. 9589.     

Attraction of female mediterranean fruit flies to the five major components of male-produced pheromone in a laboratory flight tunnel

Attraction and pheromonal activity of five major identified components of the male-produced sex pheromone of the Mediterranean fruit flyCeratitis capitata to virgin laboratory-reared females was assessed in a laboratory flight tunnel. Dual-choice competitive assays were run to establish a baseline response of virgin females to live male pheromone, individual components, and an ensemble of all five compounds alone (air control) and competitively against one another. Approximately 50% of the females released in the tunnel were captured on leaf models emitting pheromonal odors from five live males. Over 37% of released females responded to an ensemble of five major identified components presented in individual capillaries. Response of females to individual components was less than 10%. Competitive assays showed the live male-produced pheromone to be more attractive than either the five major component ensemble (FMCE) or individual components. Further research is likely to identify other male-produced compounds with pheromonal activity that could improve development of a pheromone-based trap for monitoring Mediterranean fruit fly populations.     

Behavioral responses of female Mexican fruit flies,Anastrepha ludens,to components of male-produced sex pheromone

The behavioral responses of virgin female Mexican fruit flies elicited by components and combinations of the components of male-produced pheromone were measured in a laboratory wind-tunnel bioassay where test chemicals were applied to the undersides of some leaves on a treated tree but to none of the leaves of a control tree. Only treatments containing at least (Z)-3-nonenol and/or (Z,Z)-3,6-nonadienol in combination with (S,S)-(–)-epianastrephin elicited strong behavioral responses. Responses included attraction to the vicinity of the pheromone but not to point sources, increased searching rate, changes in searching strategy, and agonism. The results support a model of pheromone-component function in which components act as a unit to stimulate all behaviors of the pheromone-mediated behavioral repertoire.Diptera: Tephritidae.     

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.     

Differences among sibling speciesRhagoletis mendax andR. pomonella (diptera: ephritidae) in their antennal sensitivity to host fruit compounds

Prior electrophoretic and morphological studies have identified two closely related, economically important tephritid flies,R. mendax (Curran) andR. pomonella (Walsh), which infest the fruits of ericaceous and rosaceous plants, respectively. Further studies also have shown consistent differences among these species in their ovipositional preferences for apples and highbush blueberries and have determined that their ovipositional behavior is elicited by extracts obtained from these fruits. In this paper we report the results of an experiment that tested whether these species show distinct electroantennogram (EAG) responses to a large array of compounds present in gas chromatograph-fractionated pentane extracts of apples and highbush blueberries.R. mendax andR. pomonella flies were found to have significant differences in their antennal sensitivity to 11 blueberry and nine apple extract peaks, which correspond to 24.4% of all blueberry and 25.0% of all apple peaks that elicited a measurable EAG response from either species. Interspecific differences in peripheral sensitivity were more pronounced for blueberry than apple extract;R. pomonella flies were most sensitive to blueberry compounds with low retention times, whereasR. mendax flies responded to blueberry compounds with a broader range of retention times. Both species were most sensitive to apple peaks with high retention times. The retention times of most apple and blueberry peaks that elicited EAG responses fromR. mendax andR. pomonella flies were different from the retention times of seven attractant fruit esters that were previously identified by Fein et al. (1982). The identification of these unknown apple and blueberry compounds could lead to the discovery of new chemical cues that mediate the host-plant preferences of these sibling species.     

Identification of apple volatiles attractive to the apple maggot,Rhagoletis pomonella

Apple volatiles from whole Red Delicious and Red Astrachan apples were found to be attractive to sexually mature apple maggot flies,Rhagoletis pomonella (Walsh), in wind tunnel bioassays. Extracted volatiles elicited directed upwind movement towards the source and significantly increased the number of male and female flies arriving at the source. A behaviorally active fraction was obtained from crude extract by gas-liquid chromatography and assayed in two types of wind tunnels and by electroantennography. The major components in this fraction, identified by chemical derivatization reactions and GLC-mass spectrometry, were hexyl acetate, (E)-2-hexen-1-yl acetate, butyl 2-methylbutanoate, propyl hexanoate, hexyl propanoate, butyl hexanoate, and hexyl butanoate in a 352 81252810 ratio. Synthetics of the identified compounds and the natural extract elicited similar behavioral and EAG responses. None of the synthetics or natural components elicited full activity when presented alone.Diptera: Tephritidae.Research support by USDA/SEA/FR, Special Cooperative Agreement No. 58-32U4-8-24.     

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.     

Biological activity of chemicals identified from extracts and volatiles of maleRhagoletis cerasi

Fractions obtained by chromatographic separation of extracts and volatiles from maleRhagoletis cerasi flies were tested for biological activity on females under laboratory conditions. During the bioassays, the number of incoming flies as well as the time spent by individual flies on the area of stimulus were taken under consideration. Two distinct types of female behavior were observed, i.e., attraction and arrestant behavior. GC-MS analysis of biologically active fractions resulted in tentative identification of 75 compounds. EAG screening for 27 of these compounds was performed, and subsequent laboratory bioassays resulted in the confirmation of arrestant activity for various mixtures of eight fatty acids (octadecanoic, nonadecanoic, eicosatetraenoic, eicosapenaenoic, eicosaenoic, heneicosanoic, docosahexenoic, and docosanoic). Following EAG tests and laboratory bioassays, a possible mode of chemical communication of this species with sex pheromones is proposed.(Diptera: Tephritidae).     

Isolation,identification, and synthesis of male-produced sex pheromone of papaya fruit fly,Toxotrypana curvicauda Gerstaecker (Diptera: Tephritidae)

A male-produced sex pheromone of the papaya fruit fly,Toxotrypana curvicauda Gerstaecker, was isolated from volatiles collected from air passed over calling males and was identified as 2-methyl-6-vinylpyrazine by comparative gas-liquid chromatographic and spectroscopic evidence. Synthetic 2-methyl-6-vinylpyrazine elicited typical pheromonal responses from unmated mature female flies such as walking, running, and flying in an arena bioassay; flying upwind with a zigzag flight pattern; and hovering in the pheromone plume in a wind-tunnel bioassay. These responses were similar quantitatively and qualitatively to responses to naturally occurring pheromone from calling male papaya fruit flies.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.     

Codling moth,Cydia pomonella, (Lepidoptera: Tortricidae): Is its sex pheromone multicomponent?

When the nine identified components in the effluvium of calling female codling moths were compared to pure synthetic (E,E)-8,10-dodecadien-1-ol in flight-tunnel tests, equal responses were obtained over a concentration range of 300-fold. When synthetic (E,E)-8,10-dodecadien-1-ol was compared to extract of female sex pheromone glands by a male wing-flutter bioassay, or in flight-tunnel tests, equal responses were obtained over a concentration range of 1000-fold. The sum total of these and previous studies indicate that the codling moth sex pheromone consists of only one component.     

Intra- and interspecific sex pheromone responses of screwworm and secondary screwworm flies

A laboratory behavioral assay examined intra- and interspecific responses to sex pheromone by screwworms,Cochliomyia hominivorax, and secondary screwworms,C. macellaria, in relation to the duration of colonization ofC. hominivorax test males. Females ofC. macellaria, like those ofC. hominivorax, were found to produce a pheromone that stimulates male copulatory attempts on contact. Newly colonized (<22 generations)C. hominivorax males did not respond toC. macellaria pheromone, indicating that pheromone contributes to reproductive isolation between these two closely related species. Although long-colonized (>200 generations)C. hominivorax males did respond toC. macellaria females or their extract, this behavior was infrequent and significantly less common than intraspecific responses. DeprivingC. macellaria adults of dietary protein did not affect the potency of female extracts, but did reduce male responsiveness to pheromone. These results provided little evidence that colonization reduces the ability ofC. hominivorax males to differentiate betweenC. hominivorax andC. macellaria females using sex pheromones.