The functional response of Trichogramma fuentesi (Hymenoptera: Trichogrammatidae), an egg parasitoid of Cactoblastis cactorum (Lepidoptera: Pyralidae) in north Florida, USA

The cactus moth, Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae), was successfully introduced from Argentina to Australia to control non-native infestations of prickly pear cactus, Opuntia spp. (Dodd 1940). Unfortunately, the insect was found in the Florida Keys, in 1989 (Dickel 1991) and is considered an important ecological and economical threat to native Opuntia spp. throughout the southern U.S. and in Mexico. Field surveys for natural enemies attacking C. cactorum in North Florida identified the egg parasitoid Trichogramma fuentesi Torre. To assess the potential of T. fuentesi as a biological control agent of C. cactorum, the functional response of the female parasitoid to this host was investigated under laboratory conditions. Mated, one day –old, female T. fuentesi were exposed to various egg densities (10, 20, 40, 60, 80, and 100) of two- day old C. cactorum eggs for 48hr. The total number of parasitized eggs and number of emerged parasitoids (F1 progeny) per host egg was determined. The type of functional response was identified by performing a logistic regression on the proportion of parasitized eggs with host egg density. Egg density had a significant effects on the number of eggs parasitized (F=15.38; df=1, 113, p < 0.001). The relationship of egg density to number of eggs parasitized fit a linear equation (N_e=1.37 + 0.0636N₀). The response of T. fuentesi to C. cactorum egg density was determined to be a Type I functional curve, indicating a lack of host density dependence.