Ronald J. Prokopy

Associative learning in egglaying site selection by apple maggot flies.

Evidence is presented demonstrating that associative learning during oviposition in Crataegus or apple hosts can significantly influence the propensity of apple maggot flies to accept or reject these hosts in future encounters. The data suggest that within resource patches of a given host type there may be an enhancement of foraging efficiency.

Sex differences in movement between natural feeding and mating sites and tradeoffs between food consumption, mating success and predator evasion in Mediterranean fruit flies (diptera : tephritidae)

SummarySystematic quantitative observations of the location and diel pattern of adult Mediterranean fruit fly, Ceratitis capitata (Wiedemann), activities were carried out in an orange grove and surroundings on the island of Chios in Greece. Natural fly foods were assessed for their contribution to fly longevity, fecundity and fertility. There were diel shifts in male and female location. Females required a substantial and varied diet to realize peak fecundity. This diet was acquired away from the primary host, orange. Foraging for food throughout most of the day on fig and non-host foliage (including feeding on bird droppings) as well as on fig fruit and grapes, females dispersed and fed more than males. A diet of grapes alone did not support any fecundity, contributing only to longevity. A diet of figs alone, on the other hand, sustained both longevity and egg production. Bird feces alone supported neither egg production nor longevity. However, when added to a diet of figs, bird feces significantly increased fly fecundity. Throughout most of the day, males aggregated in leks within the inner canopy of the primary host, orange. The arrival here during the warmest hours of the day of receptive females, followed by pair formation, reinforced the lek mating system on host foliage. In the afternoon, females shifted to orange fruit where they suffered from high predation mortality while ovipositing. Soon after, males also shifted to orange fruit, where they attempted matings with non-receptive ovipositing females. Male feeding on fig fruit occurred late in the day, a time when they were least likely to find a mate. Male survival did not differ between the natural diets. Tradeoffs between food consumption, mating success and predator evasion are discussed for each sex and related to fruit fly mating systems.

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.

Intraspecific competition in the tephritid fruit fly Rhagoletis pomonella

At densities found in nature, competition among larvae of the frugivorous fruit fly Rhagoletis pomonella (Diptera: Tephritidae) was pronounced. In fruits of Crataegus mollis, a small native host of the fly, survivorship dropped sharply when > 1 larva developed per fruit. Multiple infestation also caused decreased size of pupae, which resulted in pro- longed maturation of females and lower daily fecundity. Our findings suggest that inter- ference competition occurs among rival R. pomonella larvae within the same fruit and that older larvae may be competitively dominant. In most instances, when 2 d separated the introduction of two larvae into unpicked fruits of Crataegus oxyacantha, a very small ornamental hawthorn, the first larva pupated while the subsequent larva failed to complete development. Rhagoletis pomonella marks its oviposition site with a contact pheromone. The amount of pheromone deposited following a single egg-laying in C. mollis fruit was sufficient to deter most females from laying more eggs. By avoiding marked fruits in which a larva is already developing, a female may conserve eggs and add measurably to her fitness. Because most C. mollis fruits can support more larvae to puparium formation than they actually do, it appears that the strategy of host marking by females and monopolization of fruit by larvae may leave some fruit resources unexploited.

Behavioral evidence for host races in Rhagoletis pomonella flies

SummaryOne of the most controversial putative cases of host race formation in insects is that of the apple maggot fly, Rhagoletis pomonella (Diptera: Tephritidae). A principal cause of the controversy is lack of relevant data. In laboratory and field enclosure experiments, we compared the host acceptance behavior of sympatric populations of flies originating from naturally infested hawthorn (the native host) and apple (an introduced host) in Amherst, Massachusetts or East Lansing, Michigan. In general, hawthorn fruit were accepted for ovipositional attempts nearly equally by apple and hawthorn origin females, whereas apples were accepted much more often by apple than hawthorn origin females. Similarly, males of apple and hawthorn origin exhibited about equal duration of residence on hawthorn fruits as sites at which to acquire potential mates, while males of apple origin tended to reside substantially longer than males of hawthorn origin on apples. Irrespective of fly origin, both sexes always responded more positively to hawthorn fruit than to apples. Because all flies assayed were naive (ruling out effects of prior host experience of adults) and because tests revealed no influence of pre-imaginal fruit exposure on pattern of host fruit acceptance by females, the combined evidence suggests the phenotypic differences we observed in host response pattern between hawthorn and apple origin flies may have an underlying genetic basis. Further tests showed that while larval progeny of flies of each origin survived better in naturally growing hawthorn fruit than in naturally growing apples, there was no differential effect of fly origin on larval survival ability in either host. We discuss our findings in relation to restriction in gene flow between sympatric populations of R. pomonella and in relation to current models of host shifts in insects.

Foraging Behaviour of Rhagoletis pomonella, a Parasite of Hawthorn (Crataegus viridis), in Nature

(4) Flies never or rarely oviposited in non-host and marked fruit respectively, and in both cases emigrated from trees harbouring those fruit soon after examining the fruit. (5) Flies exhibited success-motivated search following discovery of and oviposition in uninfested, unmarked fruit. (6) Flies visited more fruit, oviposited more often and remained longer in trees harbouring high v. low densities of fruit clusters. (7) Flies emigrated sooner after the last egg they laid on trees harbouring high, v. low, densities of fruit clusters (Giving Up Time shorter). (8) Rhagoletis pomonella foraging behaviour is discussed in relation to current foraging theory.

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. 0.7μg/hr (close to the natural release rate of a ripe apple) and ca. 500μg/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 insects 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.

VISUAL GENERALIST WITH VISUAL SPECIALIST PHYTOPHAGOUS INSECTS: HOST SELECTION BEHAVIOUR AND APPLICATION TO MANAGEMENT

Our findings suggest that Hoplocampa testudinea adults (apparently monophagous) and Rhagoletis pomonella flies (oligophagous) are more specific in orientation to hue and/or form of feeding, mating, or oviposition sites on a common host (apple) than are Lygus lineolaris adults (polyphagous) on apple. We speculate that subject to varying influence by host plant chemical stimuli, many monophagous – oligophagous insects may tend to be visual specialists in comparison with polyphagous insects, especially those polyphagous species whose preferred feeding, mating, or oviposition sites within an individual plant are of diverse physical characteristics. They may tend more toward being visual generalists. Visual traps incorporating the synthetic equivalents of comparatively specific host plant visual stimuli should prove useful in monitoring and possibly even directly controlling a number of monophagous‐oligophagous insects on crops.

Mite predator responses to prey and predator-emitted stimuli

We found that the searching behavior of two acarine predators,Amblyseius fallacis andPhytoseiulus macropilis, for prey,Tetranychus urticae, is affected by the following stimuli: (1) prey silk and associated feces, whose combined physical and chemical properties elicit reduction in the rate of predator movements and longer halts; (2) kairomone extracted from prey silk and associated feces, which, upon contact, elicits frequent predator return to prey-inhabited locales; and (3) predator-emitted marking pheromone, which elicits shorter duration of search in presearched prey locales. We also found that treatment of filter paper with prey kairomone or silk enhanced predator location of prey eggs, leading us to speculate that application of synthetic prey kairomone could be useful in pest management programs.