Fruit fly larval trail acts as a cue in the host location process of the pupal parasitoid Coptera occidentalis

The pupal parasitoid Coptera occidentalis Muesebeck (Hymenoptera: Diapriidae) was reared in the 1970s in California for the biological control of the Walnut husk fly, Rhagoletis completa Cresson (Diptera: Tephritidae) and later introduced into Europe to be used as a biological control agent against fruit flies. Some behavioral aspects relating to the host location process were investigated in the laboratory in order to improve the chance of success in possible biological control programmes. The searching behavior of the female parasitoid was examined in an open arena in order to evaluate the role of larval trails or rotten-fruit trails (walnut) in the host location process. The response of C. occidentalis to four Tephritid hosts was evaluated: the natural host R. completa, the factitious host Ceratitis capitata (Wiedemann) and two fruit flies of economic importance, Rhagoletis cerasi Linnaeus and Bactrocera oleae (Rossi). In order to assess the response of the parasitoid, a number of behavioral parameters were considered, such as: arrestment behavior, resident time, walking distance, linear and angular speed. The larval trails of R. completa, as well as rotten-fruit liquid trails, were clearly detected by C. occidentalis females, even though the species has been reared for more than 80 generations on C. capitata. In addition, bioassays performed with C. capitata larvae showed a good behavioral response of parasitoid females to the larval trails. Finally, R. cerasi and B. oleae larval trails were barely detected in comparison to the traces left by R. completa and C. capitata larvae. The results are discussed in the light of the possible use of C. occidentalis in biological control programmes.