Biology and Host Relations of Avetianella longoi (Hymenoptera: Encyrtidae), an Egg Parasitoid of the Eucalyptus Longhorned Borer (Coleoptera: Cerambycidae)

Abstract

Avetianella longoi Siscaro, an egg parasitoid of the eucalyptus longhorned borer, Phoracantha semipunctata (F.), was recently introduced into California. Developmental and reproductive biology of the parasitoid, including host selection, and its potential as a biological control agent of the borer were evaluated in the laboratory. These studies demonstrated that A. longoi required ≈16 d to develop from egg to adult: at 25°C, longevity of adults averaged 26 d, and fecundity was ≈200 eggs per female. Oviposition rate was ≈10 eggs per day for young females (1–10 d old), but fell to half that number in older females (>20 d old). Younger females tended to produce primarily female progeny, whereas the progeny sex ratio of older females was male biased. Young female A. longoi preferred newly laid P. semipunctata eggs for oviposition and these eggs yielded nearly equal numbers of male and female parasitoids. However, adult females oviposited in older host eggs if no alternatives were available, resulting in a female-biased sex ratio. Because of its relatively high fecundity and its ability to use host eggs of a range of ages, A. longoi seems to have good potential as a biological control agent. In addition, A. longoi can complete 6 generations for each beetle generation, allowing parasitoid populations to expand rapidly. These biological characteristics may allow the parasitoid population to respond numerically to outbreaks of P. semipunctata. By killing the eggs of the borer, A. longoi reduces the number of beetle larvae attempting to colonize the host tree, thus improving the chances that the tree will survive borer attack.