Factors affecting the establishment and survival of Anaitis efformata (Lepidoptera: Geometridae) introduced into Australia for the biological control of St. John's wort, Hypericum perforatum. I. Laboratory experiments.
Abstract
Anaitis efformata [Aplocera efformata], a potential biological control agent for St. John's wort (Hypericum perforatum) in south-eastern Australia, was found to have a thermal tolerance range of 7.5-30°C, with optimal performance of growth, survival and fecundity in the 20-25°C range. An average of about 800 day-degrees>7.5°C was required for one complete generation, although this time could be significantly altered by the quality of larval food. A. efformata should survive and establish in all areas infested with St. John's wort and should complete 2 generations per year in cooler regions and up to 4 generations in warmer regions. Under optimal conditions, the population increase per generation was found to be about 100 times. Females of A. efformata laid their eggs singly or in small clusters mainly in the top part of the host-plant and on the undersides of leaves. Small larvae were relatively immobile, but as they matured they migrated up the stems of St. John's wort and later down again to pupate in the soil. Larval survival was increased by the presence of prostrate basal foliage, which provided food and refuge for larvae dislodged from the upright stems. About 20 larvae, surviving to maturity, are required to defoliate a 1-m length of St. John's wort stem. The placement of synchronized pupae in weed-infested areas appears to be the most efficient method of release of A. efformata for field trials.