The dynamics of ovarian maturation and oocyte resorption in the Queensland fruit fly, Dacus tryoni, in daily‐rhythmic and constant temperature regimes

Abstract

The rate of oocyte development in constant regimes corresponded to the rates predicted by Pritchard's (1970) relationship which indicates that the lower temperature threshold is 13.5dgC. Rates in fluctuating regimes indicated that development occurs at certain temperatures below the constant threshold if these are alternated with higher temperatures on a daily basis In certain fluctuating regimes, oocyte development occurred at a rate in excess of 3.5% per day and maturation proceeded to completion. In such regimes resorption occurred only if egg laying was prevented; when this happened the terminal oocytes usually remained intact and the penultimate ones were resorbed. In other fluctuating regimes, oocyte development proceeded at a rate of less than 3.5% per day and no maturation was achieved because the most advanced oocytes were resorbed‐either before or during the vitellogenic phase. The 3.5% threshold corresponds to a value of 2 day‐degrees per day (2DDPD) above 13.5d̀C. Resorption, but no development, was observed in partly mature flies around O DDPD, whereas neither occurred in a still colder regime. These results are shown to be in accord with Fletcher's (1975) field data which are also used to discuss the significance of resorption. Finally, the DDPD relationship is used to define those daily temperature profiles which may permit maturation in the field.

Crop responses to climatic variation

“…Crop modelling can predict the timing of stages when crops are sensitive to threshold temperatures; experimental studies can provide the quantitative responses that will permit the modelling effort to progress. In this endeavour, plant scientists could be guided by their zoological colleagues who have very carefully characterized the temperature limits of a range of physiological processes (figure 6; Meats & Khoo 1976, quoted in Cossins & Bowler (1987). There is a need for equivalent information for the major food crops.…”

The ecology of Bactrocera tryoni (Diptera: Tephritidae): what do we know to assist pest management?

“…The eggs of B. tryoni are smaller than those of the closely related B. jarvisi and B. tryoni lays them in smaller batch numbers, giving it a competitive advantage in locating and exploiting patches of fruit under field conditions (Fitt, 1990a). Cool winter temperatures trigger resorption of the contents of developing follicles (Fletcher, 1975(Fletcher, , 1986Meats & Khoo, 1976), thereby reducing the potential number of eggs available for oviposition.…”

THE INFLUENCE OF AGE, AMBIENT TEMPERATURE, THERMAL HISTORY AND MATING HISTORY ON MATING FREQUENCY IN MALES OF THE QUEENSLAND FRUIT FLY, DACUS TRYONI

“…Perhaps there may be little or no advantage in acclimation with respect to mating frequency or threshold. Meats & Khoo (1976) point out that in spring the mean dusk temperature of their study area rises by around 0.6 ~ per week and that it can be expected to be just above mating threshold at the time the insects are expected to become mature. Dusk temperatures will inevitably fluctuate from day to day about the mean.…”

“…Males and females were segregated when 5--7 days old. Ovarian development was monitored throughout the maturation period by checking sample batches of flies (Meats & Khoo, 1976). The mean torpor threshold of flies reared by the above procedure was 3.2 ~ .…”

“…Sexually mature insects are present in the field during spring, summer and autumn (Fletcher, 1975). There can be occasions, however, in spring and autumn when dusk temperatures are near to the lower threshold for mating but when insects can also be expected to be mature (Meats & Khoo, 1976). Meats & Fay (1976) considered that it was possible that cold-acclimation with respect to mating threshold may occur so that the number of occasions that mating was possible would be increased or that mating frequency in the range of temperatures just above the threshold would be increased.…”