Fruit-Fly Outbreaks in Adelaide, Sa, From 1948-49 to 1986-87 .1. Demarcation, Frequency and Temporal Patterns of Outbreaks

Abstract

South Australia, and particularly metropolitan Adelaide, can be invaded each summer by either of two pestilent species of fruit fly, namely Dacus tryoni, the Queensland fruit fly, and Ceratitis capitata, the Mediterranean fruit fly. Since 1946-47 a campaign has been conducted to eradicate outbreaks of either species whenever they occur. This paper is the first of a series which examines the efficacy of the eradication program up to 1986-87 by attempting to test the hypothesis that there is (or has been) an association between outbreaks in successive years. The data suggest that there was a change in the pattern of outbreaks of both species after 1970-71, outbreaks becoming more frequent and each species being more abundant each year. The change may have coincided with a change in eradication procedures. For both species of flies, the abundances in successive years were significantly correlated negatively. Two hypotheses are proposed to explain the negative correlations. One, called the carry-over hypothesis, postulates the presence of a low, persistent population some of whose local populations or patches take 2 years, on average, to increase to the level at which they are noticed and eradication procedure taken against them. The second, called the repeated introduction hypothesis, proposes that the population is not persistent and that all outbreaks are due to new introductions and are eradicated whenever they occur. These two hypotheses and the efficacy of the eradication campaign are briefly discussed. The two hypotheses are discussed in detail in later papers.