BIOLOGY AND HOST RELATIONS OF AVETIANELLA-LONGOI (HYMENOPTERA, ENCYRTIDAE), AN EGG PARASITOID OF THE EUCALYPTUS LONGHORNED BORER (COLEOPTERA, CERAMBYCIDAE)

Avetianella longoi Siscaro, an egg parasitoid of the eucalyptus longho rned borer, Phoracantha semipunctata (F.), was recently introduced int o 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 dem onstrated that A. longoi required approximate to 16 d to develop from egg to adult at 25 degrees C, longevity of adults averaged 26 d, and f ecundity was approximate to 200 eggs per female. Oviposition rate was approximate to 10 eggs per day for young females (1-10 d old), but fel l to half that number in older females (>20 d old). Younger females te nded to produce primarily female progeny, whereas the progeny sex rati o of older females was male biased. Young female A. longoi preferred n ewly laid P. semipunctata eggs for oviposition and these eggs yielded nearly equal numbers of male and female parasitoids. However, adult fe males oviposited in older host eggs if no alternatives were available, resulting in a female-biased sex ratio. Because of its relatively hig h fecundity and its ability to use host eggs of a range of ages, A. lo ngoi seems to have good potential as a biological control agent. In ad dition, A. longoi can complete 6 generations for each beetle generatio n, allowing parasitoid populations to expand rapidly. These biological characteristics may allow the parasitoid population to respond numeri cally to outbreaks of P. semipunctata. By killing the eggs of the bore r, A. longoi reduces the number of beetle larvae attempting to coloniz e tile host tree, thus improving the chances that the tree will surviv e borer attack.