Larval Conditioning and Aging of Sand Fly Rearing Medium Affect Oviposition Site Selection in Phlebotomus papatasi (Diptera: Psychodidae) Sand Flies

Sand fly larvae develop in sheltered humid habitats containing decaying organic matter on which they feed. Previously, we showed that gravid females of Phlebotomus papatasi Scopoli (Diptera: Psychodidae) are attracted to and stimulated to lay eggs on larval rearing medium containing larvae. That study, however, did not control for the possible effect of medium aging. Our goal in this study was to evaluate the effect of larval substrate conditioning on attraction and oviposition responses of Ph. papatasi sand flies while controlling for the effect of substrate aging. Initially, we confirmed that the pretreatment fresh larval food sources (to be used as larval conditioned and unconditioned media) did not differ with respect to their effect on attraction and oviposition responses. The larval conditioned medium was produced by rearing larvae to the second/third-instar stage over 3 wk using the same larval food source. To produce larval unconditioned medium, the same amount of fresh larval food was added to a control rearing cup that did not contain larvae but was aged under identical time and conditions. Two-choice bioassays were conducted to evaluate gravid female’s attraction and oviposition response to larval conditioned and unconditioned media. We found that gravid females were significantly attracted (P < 0.05) to larval conditioned medium when compared with unconditioned medium under the same amount of time and conditions. However, no such difference was found with respect to oviposition response. Both attraction and oviposition responses were significantly increased for larval conditioned and unconditioned media in comparison to the initial fresh larval food source.

Olfactory Microhabitat Selection in Leptopilina Heterotoma (Thomson) (Hym.: Eucoilidae), a Parasitoid of Drosophilidae

Leptopilina heterotoma (Thomson) and Asobara tabida (Nees), solitary endoparasitoids of frugivorous Drosophila larvae, are assumed to be competitors. Olfactometer experiments showed, however, that the species differ in their preference for microhabitat odours. Whereas A. tabida prefers a fresh fermenting sugar/yeast medium, L. heterotoma prefers this medium in a later stage of decay. These results are confirmed by field observations. This temporal separation between the species, which is not complete because some multiparasitism does occur, may be one of the factors to their coexistence. Odour preference in L. heterotoma is not modified by larval conditioning, but conditioning of the adults significantly influenced their odour response. The ecological significance of such learning is discussed. It is argued that even though such behavioural flexibility may enhance foraging efficiency when resources are unpredictable, it may also influence the amount of competition between the two parasitoid species.