Herbivore host specialization includes changes in behavior, driven by locally induced adaptations to specific plants. These adaptations often result in sexual isolation that can be gauged through detection of reduced gene flow between host associated populations. Hypothetically, reduced gene flow can be mediated both by differential response to specific plant kairomones and by the influence of larval diet on some adult traits such as pheromone composition. These hypotheses could serve as a model to explain rapid radiation of phytophagous tephritid fruit flies, a group that includes several complexes of cryptic species. The South American Fruit Fly Anastrepha fraterculus (Wiedemann) is a complex of at least seven cryptic species among which pheromone mediated sexual isolation resulted in rapid differentiation. Cryptic species also exhibit differences in host affiliation. In search of a model explaining rapid radiation in this group, we studied host plant chemical composition and genetic structure of three host associated sympatric populations of A. fraterculus. Chemical composition among host plant fruit varied widely both for nutrient and potentially toxic secondary metabolite content. Adaptation to plant chemistry appears to have produced population differentiation. We found host mediated differentiation to be stronger between populations exploiting sympatric synchronic hosts differing in chemical composition, than between populations that exploit hosts that fruit in succession. Gene flow among such host associated populations was extremely low. We propose as a working hypothesis for future research, that for those differences to persist over time, isolating mechanisms such as male produced sex pheromones and female preferences resulting from adaptation to different larval diets should evolve.

We compared the host-searching and oviposition behaviors of two Neotropical figitid parasitoids (Hymenoptera) that exploit the same resource: ripe fruit infested by fruit fly larvae (Tephritidae) that have fallen to the ground. Sexually mature Aganaspis pelleranoi (Brèthes) and Odontosema anastrephae Borgmeier females were exposed individually, under no choice conditions, to four types of fruit: 1) Clean, intact guavas, Psidium guajava L. (no fruit fly larvae, no perforations); 2) clean, with artificial perforations; 3) artificially infested (with larvae), no perforations; 4) infested with artificial perforations. A behavioral transition matrix and sequence diagram of the following behaviors was constructed: walking on fruit, detection of larvae via the antennae, tarsi or aculeus, fruit perforation and penetration, and oviposition. Overall, we found that infested fruit (intact and with artificial perforations) elicited the most activity in the females of both species and that A. pelleranoi females exhibited a significantly more diverse behavioral repertoire (i.e., more transitions) and were significantly more active than O. anastrephae females. Females of both species penetrated the fruit in search of larvae by biting through the epi-and mesocarp, but O. anastrephae remained inside for significantly longer periods (up to eight hours). A. pelleranoi females used both their antennae and tarsi to detect larvae but the use of these structures varied depending on context:

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