The ecology of a natural population of Queensland fruit fly, Dacus tryoni III. The maturation of female flies in relation to temperature

Abstract

The relationship between temperature and speed of ovarian maturation in D. tryoni has been investigated in the laboratory, in field cages, and in natural populations, the time required for 50 % of the females to develop mature eggs (TM,,) being used as the basis for comparison. When measurements were made at a series of constant temperatures, rate of maturation increased in a sigmoid manner with increasing temperature up to about 26T, but decreased at higher temperatures. In females held in laboratory cages, speed of ovarian maturation was increased (a) when males were present, and (b) when density was increased. These observations were important when results obtained in the laboratory were used to estimate maturation times of populations in the field. The usefulness of various methods of estimating maturation times in natural populations was judged by measuring speeds of maturation of populations held in large field cages and comparing them with theoretical estimates. A detailed method, by which the amount of development completed each hour under field conditions was estimated from data on the percentage development per hour obtained at a series of constant temperatures in the laboratory, gave quite good estimates, but a number of factors have to be taken into account when transferring data from the laboratory to the field. The method of "temperature summation" was completely inadequate, but a simple method relating TM,, observed in field cages to mean temperature was as good in practice as the detailed method. In natural and field-caged populations in the vicinity of Sydney, N.S.W., maturation of ovaries proceeded very slowly after April through the winter months, but the rate increased rapidly with the higher temperatures of August and September. The shortest time recorded for maturation of 50% of the females in field-caged populations was about 14 days during midsummer, although some individuals matured in half of this time. As in the laboratory, the time required for maturation increased when high temperatures (above 26°C) were frequent.