Interference of tritrophic (grape × medfly × parasitoid) interactions by mineral and biomaterial films

Fruit fly infestation is one of the main obstacles to the exportation of fresh agricultural produce. Films of mineral particles and biomaterials have the potential to protect fruits against tephritid fruit fly infestation. The present study evaluated the effects of particle films on the tritrophic interactions of grape (Vitis vinifera L.), the fruit fly Ceratitis capitata (Wiedemann) and the parasitoid Diachasmimorpha longicaudata (Ashmead) under semi-field conditions. Grapes were biometrically characterised (i.e. colour, firmness, mass, length and diameter), treated with mineral particles, biomaterials or distilled water (control), and then used in oviposition and parasitism bioassays. In the oviposition bioassay, the treated grapes were exposed to 50 C. capitata pairs in field cages, and after 48 h, the punctures and eggs on each fruit were counted. In the parasitism bioassay, treated grapes were artificially infested with third-instar C. capitata larvae (two per fruit), exposed (2 h) to 50 D. longicaudata pairs in field cages to determine parasitism index, larval and pupal viabilities and number of flies and parasitoids emerged. Treatment with the mineral film affected fruit colour and reduced C. capitata oviposition but failed to significantly affect the parasitism capacity of D. longicaudata. The ability of the parasitoid to locate and parasitise C. capitata larvae in kaolin-coated fruits suggests that kaolin films could be used in conjunction with biological agents to control fruit flies.