BEHAVIORAL-RESPONSES OF CERATITIS-CAPITATA FLIES TO BAIT SPRAY DROPLETS AND NATURAL FOOD

In studies carried out on field-caged non-fruiting host trees, we examined effects of environmental and adult physiological and experiential state factors on responses of released Mediterranean fruit flies, Ceratitis capitata (Wiedemann), to droplets of proteinaceous bait (PIB-7) with or without 20% insecticide (malathion). We confirmed that fresh PIB-7 is both attractive and phagostimulatory to protein-deprived medflies and found that presence of 20% malathion ultra low volume concentrate (ULVC) in PIB-7 droplets does not significantly repel medflies from approaching droplets but does significantly deter feeding on them. A single relatively fresh deposit of bird feces, an important source of protein for medflies in natural environments, attracted several times more laboratory-cultured and wild medflies than 20 droplets of 80% PIB-7/20% malathion ULVC (about the average number of droplets per m2 of plant canopy in aerial bait spray programs). Attraction to protein was significantly greater among wild medflies deprived of protein continuously from eclosion than among wild medflies that had recent (within 3 days) or continuous access to protein. Attraction to protein increased significantly with increasing age (2, 7 and 12 days) of protein-deprived wild medflies. But we found no significant positive impact of recent brief experience of wild medflies with protein on degree of subsequent attraction to protein. In final experiments that mimicked the size, density and distribution of bait spray droplets on tree foliage typical for an aerial medfly control program, very few (4%) or no released protein-deprived wild medflies found a bait droplet within the 15 min test period even though most found a single deposit of bird feces. We conclude that the effectiveness of aerial bait sprays against medflies might be enhanced substantially (and the proportion of infested area treated with bait spray reduced considerably) by (1) including synthetic equivalents of attractive components of bird feces in the spray mixture, and (2) adjusting spatial and temporal patterns of bait spray applications according to estimates of the composition and abundance of natural medfly food and the age structure of medfly adult populations in infested regions.