Attracticidal spheres for controlling apple maggot flies: commercial-orchard trials

Wooden pesticide-treated red spheres and biodegradable sugar/flour pesticide-treated red spheres were compared with wooden sticky-coated red spheres and insecticide sprays for controlling apple maggot flies, Rhagoletis pomonella(Walsh) (Diptera: Tephritidae), in small blocks of apple trees in Massachusetts commercial orchards in 1997, 1998 and 1999. Pesticide-treated spheres received a coating of 70% latex paint, 20% feeding stimulant (sucrose), and 10% formulated insecticide (containing 20% imidacloprid). To replenish sucrose lost during rainfall, wooden spheres were capped with a disc comprised of hardened sucrose that seeped onto the sphere surface, whereas the surface of sugar/flour spheres received sucrose that seeped from the interior. Each year, each of the 24 perimeter trees of each non-sprayed block received a sphere baited with butyl hexanoate (an attractive component of host fruit odor), with the intent of intercepting immigrating flies. Based on captures of flies on unbaited sticky-coated red spheres placed near the center of each block and on periodic samples of fruit for injury, there was a consistent pattern of treatment performance. Each year, sticky-coated spheres were only slightly less effective than two or three sprays of organophosphate insecticide, sugar/flour pesticide-treated spheres were only slightly less effective than sticky spheres, and wooden pesticide-treated spheres were least effective. Versions of pesticide-treated spheres used in 1999 were more durable than those used in previous years, but further improvement is needed before either wooden or sugar/flour pesticide-treated spheres can be recommended for grower use.     

Prior experience affects the visual ability ofRhagoletis pomonella flies (Diptera: Tephritidae) to find host fruit

Females of the apple maggot fly,Rhagoletis pomonella, were allowed for 3 days to alight upon and oviposit in green or red 18- to 20-mm hawthorn host fruit (Crategus mollis) or green or red 45- to 55-mm apple host fruit (Malus pumila) hung from branches of potted host trees in field enclosures. Subsequently, when females were released individually on potted host trees harboring fruit of one of these types, their ability to find fruit of unfamiliar size proved unaffected by prior experience with fruit but their ability to find fruit of unfamiliar color was significantly affected. Specifically, females exposed to red hawthorns or red apples were less able to find green hawthorns or green apples than were females experienced with either of the latter fruit types. Fruit odor was found to have no effect on female ability to find familiar compared with unfamiliar green fruit. In contrast, a difference in size (or surface chemistry) between familiar and unfamiliar fruit but not a difference in fruit color had a significant negative influence on the propensity of alighting females to bore into unfamiliar fruit. Three bouts of experience with alighting upon and ovipositing into fruit over a period of about 1 h had no detectable effect on female ability to find unfamiliar fruit but did reduce propensity to bore into unfamiliar fruit. Our findings are discussed in relation to insect ability to learn visual and chemical stimuli of resources and insect propensity to form host races. We also discuss the potential impact of our findings on nonpesticidal, behavioral methods of managingR. pomonella in commercial apple orchards.     

Learning of apple fruit biotypes by apple maggot flies

Previously, we showed that after a female apple maggot fly, Rhagoletis pomonella,arrives on a host hawthorn or apple fruit, its propensity to accept (bore into) or reject that fruit prior to egg deposition can be modified by previous ovipositional experience with one or the other species and, hence, involves learning. Here, we present both field and laboratory evidence indicating that females also are able to learn characteristics of three different apple biotypes or cultivars: Early Macintosh, Red Delicious, and Golden Delicious. We suspect that females learn to discriminate among these three cultivars on the basis of differences in chemical stimuli among cultivars. The effect of fruit cultivar learning was not as strong as the effect of fruit species learning.     

Parasitism of the apple maggot,Rhagoletis pomonella,infesting hawthorns in Washington

Five species of larval parasitoids were reared fromRhagoletis pomonella (Walsh) infested fruit of hawthorn,Crataegus, collected from several locations in southwest Washington over a four year period. A braconid,Biosteres melleus (Gahan), parasitized larvae infesting fruits of a native hawthorn species,Crataegus douglasii Lindl. Another braconid,Opius downesi Gahan, emerged exclusively fromR. pomonella pupae reared from fruits of an introduced species of hawthorn,Crataegus monogyna Jacq. A pteromalid,Pteromalus sp., and two eulophids,Tetrastichus spp., attackedR. pomonella larvae infesting fruits of both hawthorn species. No parasitoids emerged from a total of 4385 pupae reared from apple. Percent parasitism ofR. pomonella was higher inC. monogyna compared toC. douglasii fruits. The highest average levels of parasitism ofR. pomonella inC. monogyna andC. douglasii fruits were 90% and 23% respectively. The kinds of parasitoids, their relative abundances and timing of parasitization on the two hawthorns was related to differences in fruit ripening patterns and its effect on the development ofR. pomonella on these two hosts. Parasitization ofR. pomonella byTetrastichus spp. is a new host record. The detection of these species andPteromalus sp. in southwest Washington are the first records of ectoparasitoids attacking this tephritid.     

Effects of pyriproxyfen on ovarian development and fecundity ofRhagoletis pomonella flies

Three-day old female apple maggot flies,Rhagoletis pomonella (Walsh), were topically exposed to different doses (0.1, 1, 10, and 100 μg per fly) of a juvenile hormone mimic, pyriproxyfen, in the laboratory. Pyriproxyfen had little lethal effect on females except at the extremely high dose of 100 μg. It also had no significant effect on egg viability of treated females. A non-lethal dose of 1 μg per fly did, however, enhance significantly the fecundity (egg production) as well as the ovarian development (number of eggs in ovaries and length of egg folicles) of treated flies. We conclude that pyriproxyfen could be a useful aid in exploring endocrine regulation of feeding and reproductive physiology behavior inR. pomonella, about which current knowledge is scant.     

Influence of protein hydrolysate baits on oviposition in the apple maggot, Rhagoletis pomonella

Ovipositional responses of apple maggot (AM), Rhagoletis pomonella (Walsh), females were studied in the laboratory on apples (var: Golden Delicious) treated with different rates of four protein hydrolysate baits in choice and no-choice tests. Protein hydrolysate baits at rates of 0.5 and 1% had no significant effect, but oviposition was greatly reduced at higher rates of 5 and 10%. Apple maggot females exposed to apples treated with protein hydrolysate baits at a rate of 10% made 41–71% fewer punctures and laid 41–73% fewer eggs than in untreated control. No oviposition activity was shown on apples treated with 25 and 100% Nulure®. In no-choice tests the AM females laid 75–96% fewer eggs in apples treated with 10 and 25% Nulure compared to controls and no oviposition occurred in apples treated with 100% Nulure. Apple maggot females arrived in similar numbers on apples treated with 10% Nulure and untreated apples, but only 5% of those arriving on Nulure-treated apples showed ovipositor boring with no egg deposition while 60% of females arriving on untreated apples showed ovipositor boring activity and laid an average of 2.5 eggs per apple. In another experiment, individual AM females displayed similar behavioral responses to 10% Nulure-treated apples; none of the 56 females tested on treated apples displayed ovipositor boring activity, but 59% of the females (N=56) tested on untreated apples displayed ovipositor boring within 5 min of their arrival. Ninetyeight percent of AM females stayed and fed on fruit surfaces for 5 min on Nulure-treated apples without ovipositor boring compared to only 2% on untreated apples. Of the females that arrived on untreated apples, 39% flew away within 5 min without ovipositor boring compared to only 2% of those that arrived on Nulure-treated apples. Results of these two behavioral experiments suggest that upon arrival on a protein bait-treated apple, an apparent change of behavior occurs in AM females and instead of attempting to oviposit, they attempt to feed on fruit surfaces resulting in reduced oviposition activity. These results indicate that the feeding and oviposition-related activities of AM females are probably mutually exclusive and that the feeding behavior preempts oviposition activities on host fruits treated with higher rates of protein hydrolysate baits.     

Multiple Mating and Reproductive Success of Male and Female Apple Maggot Flies, Rhagoletis pomonella (Diptera: Tephritidae)

Mature male and female apple maggot flies mated frequently on a field-caged host tree during a 14-day study. Each sex averaged one mating per day (mean of 1.0 ± 0.1), but some females mated up to eight times per day and some males up to six times per day. Reproductive success was estimated based both on observed numbers of matings in the field cage and on previous work relating fecundity and fertility to female mating status. Male and female flies did not differ in mean or variance in reproductive success, indicating that this is a polygamous mating system consisting of both polygyny and polyandry. We discuss the significance of this with regard to the framework of insect mating control and frequency proposed by others. We also discuss behaviors (such as movements, agonistic encounters, occurrences on fruit, and ovipositions) that do and do not show correlations with mating success in apple maggot flies.     

Genetic differentiation in the viability of sibling species of Rhagoletis fruit flies on host plants, and the influence of reduced hybrid viability on reproductive isolation

Prior theoretical studies have analyzed host-associated factors restricting gene flow between phytophagous insect species, and simulated evolutionary changes in components of fitness contributing to the adaptation of species to distinct host plants. However, there is relatively little empirical information on these topics. In this paper we report data on two host-associated sibling species of tephritid fruit flies, Rhagoletis mendax (Curran) and R. pomonella (Walsh) which infest ericaceous and rosaceous host plants, respectively. To test the hypothesis that these species have evolved viability differences on alternate hosts which can contribute to the restriction of gene flow between them, we measured the larval-to-adult viability of R. mendax, R. pomonella and F₁ interspecific hybrid progeny reared on naturally-growing, highbush blueberry (Vaccinium corymbosum L.) and apple (Malus pumila Miller = Pyrus malus L.) plants in the field. Our results indicate that genetic changes associated with the adaptation of these species to distinct host plants could also cause reduced fitness of interspecific hybrids, and thereby restrict interspecific gene flow. Fewer interspecific hybrids survived to adulthood than either R. pomonella progeny reared in apples or R. mendax progeny reared in blueberries. These differences in the viability of progeny from hybrid versus conspecific crosses can substantially restrict gene flow between R. mendax and R. pomonella flies, and may be an important factor influencing their reproductive isolation. Genetic differences among hybrid and conspecific crosses were also detected for the lengths, widths and weights and weights of pupae reared from blueberries and apples. In a second experiment, the ovipositional preferences of R. mendax and R. pomonella flies were recorded on host plants inside a field cage. R. mendax flies had a strong ovipositional preference for blueberries over apples, whereas R. pomonella flies readily oviposited in both host fruits. Other studies have determined that R. pomonella flies also oviposit in the fruits of several other plants which are not hosts under field conditions; this behavior can promote host shifts to new plants by flies with suitable plant-finding and viability traits. Our results support the theoretical assumption that divergence in host-acceptance behaviors and viabilities on host plants are key aspects of evolutionary differentiation among closely-related taxa of phytophagous parasitic insects. We discuss our results in the context of other traits that can restrict gene flow between R. mendax and R. pomonella, and in relation to the findings of other studies on the evolution of host plant use.

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Résumé Bien que des études théoriques aient analysé tant l'influence des éléments de l'adaptabilité sur l'évolution de l'utilisation d'une plante par un insecte phytophage que les caractéristiques de l'hôte limitant le flux génique entre espèces voisines, peu de données concrètes concernent ces aspects.Nos résultats portent sur deux espèces jumelles de téphritides, R. mendax Curran et R. pomonella Walsh qui vivent respectivement sur éricacées et rosacées. Pour vérifier si des différences dans le comportement d'acceptation des hôtes et dans leur survie sur des hôtes alternatifs sont apparues chez ces espèces jumelles, nous avons observé dans la nature le comportement de ponte et la survie des 2 espèces et des F₁ hybrides interspécifiques sur Vaccinium corymbosum L. et Malus pumila Miller = Pyrus mali L. Le pourcentage de pondeuses, le nombre d'ufs pondus par femelle et la survie des larves ont été plus élevés pour R. mendax que pour R. pomonella sur V. corymbosum, tandis que le contraire était observé sur M. pumila. Des différences génétiques ont été observées pour la mortalité avant la nymphose et avant la mue imaginale lors des croisements hybrides et interspécifiques. Les descendants mâles et femelles de R. mendax ont mieux survécu sur V. corymbosum, tandis que la survie de la descendance des croisements entre R. pomonella était la même sur les deux plantes. Un peu plus d'hybrides ont atteint le stade adulte sur pomme que de descendants de croisements intraspécifiques, et la mortalité des descendants de femelles de R. pomonella sur V. corymbosum était plus élevée que celle des femelles de R. mendax. Les différences de survie et de comportement de ponte de R. mendax et de R. pomonella peuvent limiter le flux génique entre les 2 espèces. Des différences génétiques peuvent être observées quant à la taille et au poids des pupes de R. mendax et R. pomonella. Ces résultats confortent l'hypothèse que des divergences évolutives du comportement d'acceptation de l'hôte et de mortalité sur hôtes respectifs sont des facteurs clés séparant des taxa très voisins d'insectes parasites phytophages. La discussion intègre les autres aspects pouvant limiter le flux génique entre R. mendax et R. pomonella et les autres hypothèses sur l'évolution de l'exploitation des plantes hôtes.

     

Are the apple maggot,Rhagoletis pomonella,and blueberry maggot,R. mendax,distinct species? Implications for sympatric speciation

Rhagoletis pomonella (Walsh) and R. mendax (Curran) (Diptera: Tephritidae) are major economic pests of apple and blueberry fruits, respectively, in eastern North America. The taxonomic status of these flies as distinct species has been in dispute because of their close morphological similarity, broadly overlapping geographic distributions and inter-fertility in laboratory crosses. Starch gel electrophoresis of soluble proteins was performed to establish the extent of genetic differentiation and levels of gene flow between blueberry infesting populations of R. mendax and apple and hawthorn infesting populations of R. pomonella. R. mendax and R. pomonella were found to be genetically distinct sibling species as eleven out of total of twenty-nine allozymes surveyed possessed species specific alleles. Data from three sympatric apple and blueberry fly populations in Michigan indicated that these flies do not hybridize in nature and gave no evidence for nuclear gene introgression. Differences in host plant recognition were implicated as important pre-mating barriers to gene flow between R. pomonella and R. mendax; a result supporting a sympatric mode of divergence for these flies.

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Résumé R. pomonella Walsh and R. mendax Curran sont respectivement deux mouches très nuisibles aux pommes et aux myrtilles du N E des USA. La position taxonomique de ces mouches comme espèces distinctes a été longtemps mise en doute par suite de leur grande ressemblance morphologique, de l'important chevauchement de leurs répartitions et de leur interfécondité au laboratoire. L'électophorèse sur gel d'amidon de protéines solubles a été utilisé pour établir l'importance de la différenciation génétique et du flux génique entre R. mendax contaminant des myrtilles et R. pomonella contaminant des pommiers et des aubépines. R. mendax et R. pomonella se sont révélées des espèces jumelles car, à l'exception de 11 alolozymes sur 29, chaque espèce possédait des allèles spécifiques. Les données concernant 3 populations sympatriques de mouches des myrtilles et des pommes du Michigan ont montré que des mouches ne s'hybrident pas dans la nature et n'ont fourni aucune indication sur une introgression de gènes nucléaires. Des différences concernant la découverte de hôtes sont impliquées comme obstacles prézygotiques importants au flux génique entre R. pomonella et R. mendax; ce résultat conforte l'hypothèse d'une divergence sympatrique de ces mouches.

     

Host marking pheromone of Rhagoletis cerasi: field deployment of synthetic pheromone as a novel cherry fruit fly management strategy

We tested the efficacy of synthetic host marking pheromone (HMP) of the European cherry fruit fly (R. cerasi) as a fruit-infestation-reducing-agent in an experimental cherry orchard. Two different pheromone deployment strategies were compared: covering entire tree canopies with synthetic HMP or treating only one half (top to bottom or lower half) of the tree canopy. Pheromone application caused a tenfold reduction in fruit infestation if the entire tree canopy was covered (0.226 vs 0.021 pupae/fruit in untreated and treated trees, respectively). Results show, nevertheless, that a significant reduction in fruit infestation can be achieved by treating only one half of tree canopies (top to bottom) (0.021 vs 0.048 pupae/fruit when comparing totally vs partially treated trees). We conclude that synthetic cherry fruit fly HMP has potential as a fruit fly management tool, especially in cases where organically grown fruit reaches high market values.     

Decay rates of attractive and repellent pheromones in an ant foraging trail network

Pharaoh’s ants (Monomorium pharaonis) use at least three types of foraging trail pheromone: a long-lasting attractive pheromone and two short-lived pheromones, one attractive and one repellent. We measured the decay rates of the behavioural response of ant workers at a trail bifurcation to trail substrate marked with either repellent or attractive short-lived pheromones. Our results show that the repellent pheromone effect lasts more than twice as long as the attractive pheromone effect (78 min versus 33 min). Although the effects of these two pheromones decay at approximately the same rate, the initial effect of the repellent pheromone on branch choice is almost twice that of the attractive pheromone (48% versus 25% above control). We hypothesise that the two pheromones have complementary but distinct roles, with the repellent pheromone specifically directing ants at bifurcations, while the attractive pheromone guides ants along the entire trail. Received 15 November 2007; revised 7 March 2008; accepted 18 March 2008.     

Low genetic variability in a Utah cherry-infesting population of the apple maggot, Rhagoletis pomonella

The apple maggot fly, Rhagoletis pomonella (Walsh), has only recently been found in Utah infesting sour cherry, Prunus cerasus L. An electrophoretic comparison of flies from Utah cherries with flies from Illinois hawthorns, Crataegus mollis (T. & G.) Scheele (a native host within the native range of the fly), show a marked reduction of genetic variability in the Utah sample. This result is indicative of a genetic bottleneck associated with the establishment of the apple maggot population in Utah cherries.

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Résumé R. pomonella (Walsh), est originaire de Crataegus dans l'Amérique du N.E. Il attaque de nombreux autres fruits, y compris les pommes et les cerises aigres (Prunus cerasus). La mouche a été récemment signalée en Utah, à la fois sur cerises et sur Crataegus douglasii. Nous avons comparé les niveaux de variabilité génétique d'une population de l'Utah contaminant les cerises et d'une population de l'Illinois contaminant C. mollis (la population de l'Illinois est représentative des niveaux de variabilité génétique dans l'aire d'origine de la mouche).La variabilité génétique à 17 loci a été évaluée par électrophorèse sur gel d'amidon. 10 de ces loci sont polymorphes dans la population d'Illinois, mais seulement 4 dans la population de l'Utah. Les fréquences alléliques de ces 4 loci de R. pomonella diffèrent significativement en Utah et en Illinois. La population de l'Utah présente nettement moins d'allèles par locus, un plus faible pourcentage de loci polymorphes et une hétérozygotie moyenne plus faible que la population de l'Illinois. Tous ces résultats sont conformes aux conséquences prévisibles d'un goulot d'étranglement.Deux explications existent pour cette perte de variabilité, toutes les deux liées à la combinaison de la faible taille de la population et de la dérive génétique ultérieure. Pour la première, la colonisation du cerisier par les mouches venant de Crataegus peut avoir provoqué un goulot d'étranglement génétique. Au contraire, la réduction de la variabilité peut avoir été la conséquence de la colonisation de l'Utah par R. pomonella. Nous retenons cette dernière comme la cause la plus vraisemblable de la variabilité génétique de la population de R. pomonella contaminant les cerises de l'Utah.

     

On the ecology of Cephalodella

A material consisting of 66 species of Cephalodella (Rotifera), from diverse waters in south and central Sweden, was analyzed to reveal their possible relationships to substrate and habitat. Most species preferred periphytic environments. Most species have a broad ecological range, only a few being bog specialists. An artificial substrate, white cotton, was colonized by several species, even some without eyes.     

Apple maggot fly response to red sphere traps in relation to fly age and experience

Responses of the apple maggot fly,Rhagoletis pomonella (Walsh), to 8 cm red sticky sphere traps, baited with the synthetic fruit odor butyl hexanoate, were investigated in field-caged apple trees containing green or red Gravenstein apples. Trap capture rate and the probability of oviposition in apples before capture generally increased with female age and number of mature eggs in ovaries. Two days of pre-test exposure of mature females to red hawthorns, green Red Delicious apples or green Gravenstein apples had no significant effect on the likelihood of a fly finding a red sphere. However, before capture on a sphere or departing a tree, hawthorn-exposed females found significantly fewer apples and laid significantly fewer eggs than females exposed to Gravenstein apples. Variation in duration of pre-test exposure (1–4 days) of flies to Gravenstein apples had no detectable influence on female response to apples or to a red sphere in a test tree. The relevance of these findings to effectiveness of sphere traps, forR. pomonella control in commercial orchards is discussed.     

Catching Ariadne by her thread: how a parasitoid exploits the herbivore's marking trails to locate its host

Chemical signals that can be associated with the presence of a host insect often work as arrestants in close range host location by parasitoids, leading to longer searching times on patches where such signals are present. Our current view of parasitoid host location is that by prolonging the search times in patches, randomly searching parasitoids enhance their chance of detecting host insects. However, prolonged search times are not necessarily the only modification in parasitoid behaviour. In this study, we examine the exploitation of host-fruit marking pheromone of rose-hip flies, Rhagoletis basiolaOsten-Sacken (Diptera: Tephritidae) by the specialized egg-larval parasitoid Halticoptera rosae Burks (Hymenoptera: Pteromalidae). We provide evidence that the instantaneous probability that a host egg will be located by a searching parasitoid wasp differs markedly between pheromone-marked and unmarked fruits. The arresting response to the marking pheromone, i.e., the prolonged time a wasp is willing to search on marked fruits, can only account for a small fraction of the difference in successful host location on marked and unmarked fruits. We further demonstrate that the time wasps require to locate the host egg is independent of the size of the rose-hip harbouring the fly egg, and thus is independent of the area the wasp potentially has to search. A comparison of our findings with results of different search algorithms for parasitoid wasps suggests that wasps use the fly's pheromone marking trail as a guide way to the fly's oviposition site and thus the host egg.     

Vertical distribution of codling moth adults in pheromone-treated and untreated plots

The vertical distribution of codling moth,Cydia pomonella (L.) within pheromone-treated and untreated apple and pear orchard canopies was determined using tethered virgin females, unbaited sticky traps, and blacklight observation of released moths. Mating of virgin females tethered at various heights in untreated orchard canopies increased with placement height from 1–4 m. Application of pheromone dispensers for mating disruption at 2 and 4 m above the ground greatly decreased mating. Greatest capture of males and females on unbaited sticky traps occurred at mid- and upper-canopy heights. Total capture of males and females in pheromone-treated plots was not statistically different than in untreated plots. The percentage of mated females captured on sticky traps did not vary with trap height or pheromone treatment. Released moths marked with flourescent powder and observed at dark with a blacklight indicated that moths are primarily distributed high in the canopy. However, males shifted to a position lower in the canopy when pheromone dispensers were placed 2.1 m above the ground. Results suggest that pheromone dispensers be placed in the upper canopy for optimal disruption of codling moth mating.     

Egg marking pheromones of anarchistic worker honeybees (Apis mellifera)

In honeybees, worker policing via egg eating enforces functionalworker sterility in colonies with a queen and brood. It is thoughtthat queens mark their eggs with a chemical signal, indicatingthat their eggs are queen-laid. Worker-laid eggs lack this signaland are, therefore, eaten by policing workers. Anarchistic workerhoneybees have been hypothesized to circumvent worker policingby mimicking the queen egg-marking signal. We investigated thisphenomenon by relating chemical profiles of workers and theireggs to egg acceptability. We found that the ability of someworkers (anarchistic workers in queenright colonies and deviantworkers from a queenless colony) to lay more acceptable eggsis due to them producing significant amounts of queen-like estersfrom their Dufour's gland. These esters appear to be transferredto eggs during laying and increase egg survival. However, theseesters cannot be the normal queen egg-marking signal, as theyare generally absent from queen-laid eggs and only increasethe short-term persistence of worker-laid eggs, because only7–30% of anarchistic worker-laid eggs persisted to hatchingversus 91–92% of queen-laid eggs. All workers can producesome esters, but only workers that greatly increase their esterproduction lay more acceptable eggs. The production of estersappears to be a flexible response, as anarchistic workers rearedin queenless colonies did not increase their ester production,while some deviant workers in queenless colonies did increasetheir ester production.     

Oviposition deterring pheromone influences dispersal distance in tephritid fruit flies

We tested the hypothesis that Rhagoletis pomonella females exhibit a greater propensity for engaging in long distance (i.e.1000 m) flight following encounters with egg-infested oviposition-deterring-pheromone (ODP) marked host fruit than similar females that encounter uninfested, clean (i.e. no ODP) fruit. Female flies which were first tethered to flight mills were presented with and permitted to explore (a) ODP-marked or (b) clean fruit and then stimulated to fly. Results showed that females that had encountered a high rate of infested, ODP-marked fruit displayed long distance flight more frequently and flew greater average distances than females that had searched uninfested fruit. We discuss there results in light of contemporary foraging theory.

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Résumé La réponse d'insectes à leurs phéromones de dissuasion (ODP) est examinée généralement à un seul niveau de prospection, c'est-à-dire celui de la ressource individuelle elle-même. Ces marqueurs chimiques peuvent, cependant, fournir aussi des informations au prospecteur sur la disponibilité en ressources, tant au niveau de l'inflorescence qu'au niveau de l'habitat. Une telle information influence vraisemblablement le comportement de prospection à différents niveaux.Dans cette note, nous vérifions l'hypothèse que la rencontre avec des hôtes marqués par ODP influence la tendance de Rhagoletis pomonella (Dipt: Tephrit) à entreprendre des vols importants (c'est-à-dire interhabitats). Nous avons montré dans des expériences de laboratoire que les femelles lors de trois rencontres consécutives avec des fruits marqués par ODP: 1) entreprenaient plus fréquemment (19 cas sur 81 contre 6 sur 81) un vol à longue distance (c'est-à-dire 1000 m) et 2) parcourient des distances moyennes supérieures à celles couvertes par des femelles ayant eu la possibilité de prospecter successivement trois fruits propres (sans ODP).Nous engageons le lecteur à examiner nos résultats d'un point de vue qualitatif. Nous ne pouvons nous attendre à ce qu'un vol à longue distance se produise aussi facilement dans la nature qu'au laboratoire, étant donné le plus grand nombre de variables (par exemple, la taille de l'arbre) qui peuvent y modifier le vol réel.Pour terminer, nous discutons les coûts et bénéfices potentiels qui peuvent résulter de ce comportement.

     

Genetic variation among apple and hawthorn host races of Rhagoletis pomonella across an ecological transition zone in the Mid-Western United States

In previous studies, we have shown that apple and hawthorn populations of Rhagoletis pomonella (Diptera: Tephritidae) represent partially reproductively isolated and genetically differentiated host races; a result consistent with predictions of sympatric speciation models. The geographic pattern of allozyme variation for these flies is complex, however, as inter-host differences are superimposed on latitudinal allele frequency clines within the races. In addition, pronounced allele frequency shifts exist among R. pomonella populations across three major ecological transition zones in the mid-western United States. This suggests that selection related to environmental heterogeneity is responsible for the allele frequency shifts, but does not rule out secondary contact as an alternative possibility. Resolution of this issue is important, because if secondary contact is involved, then we would have to reassess the relationship host race formation has with speciation in the R. pomonella group.Here, we present results from a detailed genetic analysis of fly populations spanning the deciduous/prairie transition zone near the border between the states of Wisconsin and Illinois. Allele frequencies for hawthorn populations within the zone formed spikes, rather than the expected steps, and these frequency peaks correlated with variation in local ambient temperature conditions. Ambient temperature, and not secondary contact, therefore appears to be an important determinant of the shape of R. pomonella allele frequency clines. Allele frequency heterogeneity was also observed among apple populations, but was less pronounced compared to that for hawthorn flies. This suggests that ambient temperature differentially affects the host races, possibly through differences in the fruiting phenologies of apple and hawthorn trees. Several pairs of linked loci displayed concordant allele frequency changes and were in disequilibrium among both apple and hawthorn populations along the Wisconsin/Illinois transect. Although we do not know the reason for the observed pattern of disequilibrium, site to site variation in levels of inter-host migration, coupled with selection, seem the most likely explanations. We conclude by discussing how host specific adaptations, such as those associated with ambient temperature, may interact with host recognition traits to drive the sympatric speciation process for R. pomonella group flies.