Development of a strategy for selective collection of a parasitoid attacking one member of a large herbivore guild.

Selectively collecting a single natural enemy species that parasitizes one member of a guild of herbivores that attack the same host plants can be a challenging problem during development of biological control programs. We present here a successful strategy for the collection of a strain of the egg parasitoid Avetianella longoi Siscaro (Hymenoptera: Encyrtidae), that parasitizes eggs of the longhorned borer Phoracantha recurva Newman (Coleoptera: Cerambycidae). This cerambycid is one member of a large guild of woodborers that simultaneously infest dying and fallen Eucalyptus in Australia, and it has become a major pest of Eucalyptus in many areas of the world where Eucalyptus has been introduced. Adult P. recurva of both sexes were caged on freshly cut Eucalyptus logs, and the resulting egg masses were marked and then left exposed to natural parasitization in the field. Parasitized egg masses were then harvested and held in the laboratory until adult parasitoids emerged. Parasitoids were identified as A. longoi by morphological comparisons with reference specimens, and with molecular markers. This strain of A. longoi readily accepted and had high survival rates in eggs of P. recurva. In contrast, the strain of A. longoi that has been used for biological control of P. semipunctata in California since the 1990s strongly prefers eggs of eucalyptus longhorned borer, Phoracantha semipunctata (F.) (Coleoptera: Cerambycidae), and has relatively low rates of survival to adulthood in eggs of P. recurva. The causes of these behavioral and physiological differences between the two strains are not yet known.