The Ecology of a Natural Population of the Queensland Fruit Fly, Dacus Tryoni. Iv. The Immigration and Emigration of Adults.

Abstract

Mark-recapture techniques were used to study the immigration and emigration of adults of the Queensland fruit fly in an isolated orchard at Wilton, N.S.W. During the 1968 season, several thousand mature flies migrated into the orchard during late February and early March; the females in this influx were responsible for laying the majority of eggs which contributed to the next generation. After the fruit disappeared these immigrants left the orchard, but immature flies continued to enter the orchard in smaller numbers until late in the season. In the early part of the season approximately 75% of adults that emerged in the orchard left during their first week. Later in the season, when lack of rain made conditions less favourable, nearly all the flies left the orchard in the first week after emergence. During the 1969 season, when no fruit was present because of a spring drought, fewer mature flies migrated into the orchard in late February and March, even though traps located over a wide area around the orchard indicated that at least as many flies were present in the general area as in 1968. Studies on emigration rates at the orchard were carried out using flies bred from infested fruit collected in neighbouring towns. As in the comparable part of the 1968 season, approximately 75% of the flies left the orchard in the first week after emergence. It is postulated that dispersive movements in D. tryoni can be divided into three main categories: a post-teneral dispersive stage, host seeking, and responses to adversity.