INDUCTION AND TERMINATION OF PUPAL DIAPAUSE INSARCOPHAGA(DIPTERA: SARCOPHAGIDAE)

Abstract

1. In temperate regions species of Sarcophaga overwinter in pupal diapause. The environmental control of diapause is investigated in Sarcophaga argyrostoma, S. crassipalpis, and three strains of S. bullata. Environmental cues of daylength and temperature, water content of the larval medium, and the sex of the animal determine the induction of diapause. Termination of diapause is temperature dependent.2. Daylength is of primary importance for induction. Diapause is completely averted when adult mothers and larvae are maintained under a long daily photophase or continuous light at 25° C. Short-day exposure of the adults and larvae at 25° induces a high incidence of diapause. However, if short-day is received by only the larvae, diapause is absent, and adult short-day without subsequent larval short-day produces a low diapause incidence. The maximum diapause response is observed when adults are maintained under a short daily photophase at 25°, and larvae are reared at a short daily photophase at 17°.3. Critical daylength for wild populations of S. bullata from Illinois and Missouri is 13½ hours at 25°.4. A decrease in larval temperature from 28° to 17° C increases the incidence of pupal diapause in animals reared at short-day.5. Addition of 10% water to larval medium increases diapause incidence 10%.6. Males enter diapause at a higher rate than females. Sex ratio approaches 1:1 in pupae representing 0 and 100% diapause, but lots showing a partial diapause response have a higher percentage of males than females in diapause.7. Larvae reared under diapause-inducing conditions pupariate over a period of days 3-4 times greater than larvae reared under non-diapause conditions; mean day of pupariation is 4-5days later in diapause batches. The incidence of pupal diapause increases with an increase in the delay of pupariation.8. Photoperiod is ineffective in terminating diapause.9. At constant temperatures the duration of diapause decreases with an increase in temperature. A combination of 17° and 25° provides a shorter diapause than constant exposure to either temperature.10. Significant differences are found in the diapause responses observed with different species of Sarcophaga; wild strains of S. bullata also differ from each other and differ greatly from a lab strain of the same species.