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.     

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.     

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.     

Field and electroantennogram responses to sex pheromone optical isomers by monophagous jack pine sawflies (Hymenoptera: Diprionidae)

Several species of monophagous jack pine sawflies (Hymenoptera: Diprionidae) were tested in the field and by electroantennograms (EAG) for activity toward the optical isomers of a pine sawfly sex pheromone, the acetate and propionate esters of 3,7-dimethylpentadecan-2-ol.Neodiprion rugifrons andNeodiprion dubiosus were attracted to a mixture of the propionate esters of the 2S,3R,7R and 2S,3R,7S isomers, whereasNeodiprion swainei was attracted to the 2S,3S,7S propionate isomer. Samples containing the 2S,3R,7S propionate isomer elicited the strongest EAG responses in these three species andNeodiprion nigroscutum. The 2S,3S,7S propionate isomer was equally active (EAG) in the case ofN. swainei.     

Plant-Derived Semiochemicals as Contact Host Location Stimuli for a Parasitoid of Leafminers

We elucidated the source of chemical cues in a system where the host is concealed and the parasitoid has no direct contact with the host larvae or its frass. Behavioral bioassays with Pholetesor bicolor, a larval parasitoid of the apple leafminer, Phyllonorycter pomonella, showed that the herbivore-damaged leaf epidermis (mine) elicited ovipositional probing of parasitoid females. Probing on larvae or frass was seldom observed. Hexane extracts of mines elicited the same ovipositional probing behavior while no response was observed with hexane extracts of larvae or frass or with methanol and diethyl ether extracts. In addition, gas chromatographic analyses showed qualitatively and quantitatively different profiles of these three components of the host-plant complex. By far the highest quantities and also the highest number of compounds was recovered from mine extracts. Identified compounds in the mine included six alkanes (n-C ₂₇ to n-C ₃₃) and squalene (C₃₀H₅₀). A synthetic blend of the seven compounds was slightly less active in biotests than the equivalent natural blend, as shown by a time delay in female response. We conclude that this leafminer parasitoid does not rely on host-derived kairomones but instead uses plant-derived semiochemicals for host location and ovipositional probing behavior.     

Olfactory sensitivity of two sympatric species of rice leaf folders (Lepidoptera: Pyralidae) to plant volatiles

Electroantennograms (EAGs) were recorded from male and female moths of two sympatric leaf folder species,Cnaphalocrocis medinalis (Gue-née) andMarasmia patnalis Bradley (Lepidoptera: Pyralidae) to 91 volatile chemicals of plant origin. Responses of both leaf folder species were similar to all compounds except to three monoterpenes--myrcene, menthone, and isomenthone- and two sesquiterpenes-cis-nerolidol and isophytol. Response ofM. patnalis, an oligophagous leaf folder, to these compounds was higher compared with that of polyphagousC. medinalis. EAG responses of males to saturated and unsaturated aliphatic aldehydes were significantly higher than those of conspecific females in both species. A higher response ofC. medinalis males also was observed for 1-nonanol, 3-nonen-2-one, andtrans, trans-2,6-dimethyl-2,4,6-octatriene. In contrast, females of both species responded more to monoterpenes, borneol, isoborneol, and fenchyl alchohol. Response ofC. medinalis female was higher for terpinen-4-ol, carveol, dihydrocarveol, (–)-myrtenal, and perillaldehyde. In both species and sexes, high EAG responses were recorded for compounds of the green leaf odor complex. EAG responses to nonanal and hexanal were maximum among the aliphatic aldehydes while 1-hexanol elicited the highest response among the alcohols tested. EAG responses to terpene compounds-citronellal,-terpineol, and (–)-myrtenal-were equal to the response to 1-hexanol. While all compounds tested elicited a negative potential, thymol and carvacrol elicited a positive EAG potential. The EAG data are discussed with regard     

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).     

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.     

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.     

Oviposition attractants and repellents of mosquitoes

Infusions of various organic materials have been known to modify ovipositional behavior of gravid female mosquitoes. Previously, we found that an infusion of Purina Laboratory Chow elicited negative ovipositional behavior inCulex pipiens quinquefasciatus Say andCulex tarsalis Coquillett. In the present chemical studies, the Purina Laboratory Chow infusion, fermented for 10 days, was distilled to give an active distillate which, upon ether extraction, gave an active ether extract. Fractionation of the ether extract yielded an active acidic fraction and inactive nonacidic fraction. Gas Chromatographie analysis on Porapak R and AT-1200-H₃PO₄ columns of the acidic fraction showed the presence of acetic, propionic, isobutyric, butyric, isovaleric, and caproic acids. In bioassay tests, these lower aliphatic carboxylic acids, individually and in combination, exhibited ovipositional repellency against the two species of mosquitoes at the concentration of 6 × 10^–2%. At this concentration, butyric acid caused 100% mortality in first-instar larvae ofC. p. quinquefasciatus. Gravid female mosquitoes might have acquired, through evolutional adaptation, the ability of avoiding ovipositing in unsuitable sites in which toxic compounds might be detrimental to the survival and development of their offspring.Diptera: Culicidae.     

Identification of host fruit volatiles from domestic apple (Malus domestica), native black hawthorn (Crataegus douglasii) and introduced ornamental hawthorn (C. monogyna) attractive to Rhagoletis pomonella flies from the western United States

The apple maggot fly, Rhagoletis pomonella, infests apple (Malus domestica) and hawthorn species (most notably the downy hawthorn, Crataegus mollis) in the eastern USA. Evidence suggests that the fly was introduced into the western USA sometime in the last 60 years. In addition to apple, R. pomonella also infests two species of hawthorns in the western USA as major hosts: the native black hawthorn (C. douglasii) and the introduced ornamental English hawthorn, C. monogyna. Apple and downy hawthorn-origin flies in the eastern USA use volatile blends emitted from the surface of their respective ripening fruit to find and discriminate among host trees. To test whether the same is true for western flies, we used coupled gas chromatography and electroantennographic detection (GC-EAD) and developed a 7-component apple fruit blend for western apple-origin flies, an 8-component black hawthorn fruit blend for flies infesting C. douglasii, and a 9-component ornamental hawthorn blend for flies from C. monogyna. Crataegus douglasii and C. monogyna-origin flies showed similar levels of upwind directed flight to their respective natal synthetic fruit blends in flight tunnel assays compared to whole fruit adsorbent extracts, indicating that the blends contain all the behaviorally relevant fruit volatiles to induce maximal response levels. The black and ornamental hawthorn blends shared four compounds in common including 3-methylbutan-1-ol, which appears to be a key volatile for R. pomonella populations in the eastern, southern, and western USA that show a preference for fruit from different Crataegus species. However, the blends also differed from one another and from domesticated apple in several respects that make it possible that western R. pomonella flies behaviorally discriminate among fruit volatiles and form ecologically differentiated host races, as is the case for eastern apple and hawthorn flies.     

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 major component of male-produced aggregation pheromone of larger grain borer,Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae)

Male beetles of the larger grain borer,Prostephanus truncatus Horn (Coleoptera: Bostrichidae) were shown to produce material causing an electroantennographic (EAG) response from both male and female beetles. Volatiles from mixed sex cultures were collected on Porapak Q and fractionated by liquid chromatography (LC) with gradient elution. The total volatiles and the fractions were analyzed by gas chromatography (GC) linked to EAG, and two compounds eluting in the same LC fraction elicited EAG responses from male and female beetles. These were assumed to be components of the male-produced aggregation pheromone. Amounts of these compounds obtained were very low and less than 10^–3 times the amounts of the aggregation pheromone components produced by the related species,Rhyzopertha dominica, under similar conditions. The most abundant of these EAG-active compounds was identified as 1-methyiethyl (2E)-2-methyl-2-pentenoate by comparison of its GC retention times and mass spectrum with those of synthetic analogs. The synthetic compound elicited electrophysiological and behavioral responses in both male and female beetles significantly greater than those to structural analogs. This compound is attractive toP. truncatus beetles in the field, and has been given the trivial name of trunc-call 1.     

Identification of the antibiotic phomalactone from the entomopathogenic fungusHirsutella thompsonii var.synnematosa

Dichloromethane extracts of culture broth from three strains of the entomopathogenic fungusHirsutella thompsonii var.synnematosa were toxic to two species of tephritid fruit fly and inhibited conidial germination in vitro in several other entomopathogenic fungi includingBeauveria bassiana, Tolypocladium spp., andMetarhizium anisopliae. A major metabolite, toxic to apple maggot,Rhagoletis pomonella, and inhibitory to conidial germination inB. bassiana, was isolated and identified as the antibiotic (+)-phomalactone, 6-(1-propenyl)-5,-6-dihydro-5-hydroxypyran-2-one. This is the first biologically active compound of low molecular weight isolated from the genusHirsutella.Mention of a commercial or proprietary product does not constitute an endorsement by the USDA.     

Identification of host fruit volatiles from hawthorn (Crataegus spp.) attractive to hawthorn-origin Rhagoletis pomonella flies

Solid-phase microextraction (SPME) and gas chromatography coupled with electroantennographic detection (GC-EAD) were used to identify volatile compounds from hawthorn fruit (Crataegus spp.) acting as behavioral attractants for hawthorn-infesting Rhagoletis pomonella flies. Consistent EAD activity was obtained for six chemicals: ethyl acetate (94.3%), 3-methylbutan- 1-ol (4.0%), isoamyl acetate (1.5%), 4,8-dimethyl-1,3(E),7-nonatriene (0.07%), butyl hexanoate (0.01%), and dihydro--ionone (0.10%). In a flight-tunnel bioassay, there was a dose-related increase in the percentage of flies flying upwind to the six-component mixture. Hawthorn-origin flies also made equivalent levels of upwind flight with the synthetic blend and an adsorbent extract of volatiles collected from whole fruit, each containing the same amount of the 3-methylbutan-1-ol compound. Significantly lower levels of upwind flight occurred to a previously identified volatile blend of ester compounds that attracts R. pomonella flies infesting domestic apples, compared with the hawthorn volatile mix. Selected subtraction assays showed further that the four-component mixture of 3-methylbutan-1-ol, 4,8-dimethyl-1,3(E),7-nonatriene, butyl hexanoate, and dihydro--ionone also elicited levels of upwind flight equivalent to the six-component mix. Removal of 3-methylbutan-1-ol from the four-component blend resulted in complete loss of upwind flight behavior. Removal of dihydro- -ionone, 4,8-dimethyl-1,3(E),7-nonatriene, or butyl hexanoate from the four-component mixture resulted in significant decreases in the mean number of upwind flights compared to the four- or six-component mixtures.     

Electrophysiological and field activity of halogenated analogs of (E,E)-8,10-dodecadien-1-ol,the main pheromone component,in codling moth (Cydia pomonella L.)

Pest monitoring and control of the codling moth,Cydia pomonella L., have been developed using the main pheromone component of this species, (E,E)-8,10-dodecadienol (codlemone). However, the activity of codlemone is not satisfactory for pest control by mating disruption. Thus, we have synthesized halogenated analogs of codlemone to see if they could be used as new agents for pest control of the codling moth. Their biological activity was measured by electrophysiological techniques. In EAG screening, codlemone was the most active compound. F(10,11)-codlemone [(E,E)-10,11-difluoro-8,10-dodecadienol] and Cl-codlemone [(E,E)-11-chloro-8,10-undecadienol] elicited significant EAG responses, F(10,11)-codlemone triggering responses not significantly different from responses to codlemone. EAG cross-adaptation experiments and single sensillum recordings revealed that these compounds were detected by the same receptor neuron type as codlemone. No competitive inhibition with codlemone was observed from nonactive compounds. In field trapping, F(10,11)-codlemone and Cl-codlemone were more attractive to male codling moths than codlemone itself. Possible explanations of this activity are discussed.     

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.     

Factors influencing release of hostmarking pheromone byRhagoletis pomonella flies

The effect of fly or fruit treatments on quality and/or quantity of host-marking pheromone (HMP) trail substance released by apple maggot flies (Rhagoletis pomonella) following oviposition was evaluated. Among flies, considerable variation existed in the amount of HMP substance deposited, but overall, the amount of substance released on successively offered fruit (over a day or a week) did not change appreciably. Fly diet did not influence pheromone activity. Older flies (28 days) or smaller flies released less or less active HMP trail substance than younger flies (14 days) or larger flies. Females deposited a similar amount of trail substance on large (18–19 mm diam.) or HMP-marked fruit as on small (12–13 mm) or unmarked fruit. Starvation reduced the amount of measurable trail substance deposited but resulted in a more active HMP deposition. Discrepancy between trail measurement and behavioral bioassay results for the starvation treatment indicated that trail measurement results may be misleading under conditions that reduce gut contents of the fly.     

Patterns of Oviposition Stimulants for Carrot Fly in Leaves of Various Host Plants

Undamaged leaves of 12 host-plant species differing widely in acceptability to ovipositing carrot flies were extracted with a microwave-assisted method with hexane as solvent. The highly stimulatory diethyl ether fraction obtained by separation on a silica gel column was semiquantitatively analyzed by GC-MS for previously identified oviposition stimulants of the carrot fly (phenylpropenes, fluranocoumarins, polyacetylenes). Various plant species exhibited widely differing profiles of these compounds. In choice assays, moderate numbers of eggs were deposited underneath surrogate leaves sprayed with fractions that contained high amounts of just one type of compound and low amounts of the other two types. Only fractions with medium to high levels of at least two compound classes elicited strong ovipositional responses (e.g., phenylpropenes and polyacetylenes in Daucus carota, furanocoumarins and polyacetylenes in Heracleum sphondylium and Conium maculatum). None of the examined plants contained high quantities of all three compound classes. The contents of the stimulants seemed to account in a synergistic manner for the variation in activity of the diethyl ether fraction. However, they could not explain adequately the observed preference hierarchy of the carrot fly for the host-plant species.     

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.).