Survival, Development Rates and Generation Times of the Queensland Fruit Fly, Dacus Tryoni, in a Marginally Favourable Climate: Experiments in Victoria.

Abstract

The abundance of the Queensland fruit fly, Dacus tryoni (Froggatt), is greatest in the tropical-sub- tropical part of its range in Queensland and declines towards its southern extreme in Victoria, where conditions are not very favourable for survival in winter or for a rapid rate of increase in summer. The rate of detection of larval infestations and the level of trap catches of adults indicate that Melbourne (southern Victoria) has had a very low population of D. tryoni each summer for at least 8 years and probably for the last 30 years. Field cage studies in Melbourne, of cohorts started each month as eggs, pupae and teneral adults, indicated that adults emerging from mid-April to mid-May could survive to breed in the following spring. It appears that adults emerging earlier would not survive to produce eggs in spring, and that adults would not be expected to emerge later in autumn because the survival rates of larvae are very low and the survival rate of pupae is zero in winter months. Times taken for cohorts to develop from egg to pupariation, from egg to adult emergence and from egg to adult maturity agreed with the predictions ofthe model of Meats (1981) using temperatures prevailing over the study period. A continuing culture established in a field cage in northern Victoria achieved 3.7 generations in the 1981-82 season. The number and time span of generations also agreed with the predictions ofthe model. It is concluded that a permanent population in Melbourne would have two or sometimes three complete generations per year and never achieve a high density. However, populations in northern Victoria would have three or sometimes four complete generations per year, and relatively high densities may be reached in seasons permitting four generations.