CHEMICALLY AND PHOTOPERIODICALLY INDUCED DIAPAUSE DEVELOPMENT IN THE EUROPEAN CORN BORER, OSTRINIA NUBILALIS

¹ Department of Entomology, University of Wisconsin, Madison 6, Wisconsin

1. Diapause development in European corn borer larvae is rate-controlled by photoperiod. The rate of diapause development under conditions of continuous light or long-day photoperiods is approximately 5 times that occurring under a short-day photoperiod.

2. The rate of diapause development under conditions of continuous darkness depends upon the rate established by the photoperiods to which the larvae were exposed before being placed in the dark. Diapause larvae transferred from a short-day photoperiod into darkness continue to develop at the short-day rate. Conversely, diapause larvae exposed to about 10 days of long-day photoperiod continue to undergo diapause development at the long-day rate when transferred to dark conditions.

3. Although the rate of diapause development may be changed by changes in the photoperiod, diapause development is not reversible. Diapause development summates during the period of diapause.

4. Attempts to accelerate diapause development experimentally through increasing the water content of the larvae, or by the administration of chemical nervous system stimulants were uniformly unsuccessful.

5. Diapause development was experimentally accelerated by the administration of massive doses of ammonium acetate or other ammonium compounds. This finding indicates a probable similarity between larval and embryonic diapause development.

6. The ammonium ion effect did not obviate the role of photoperiod. The rate of diapause development was strongly influenced by photoperiod among larvae that had been treated with ammonium ions. The rate of diapause development observed in the presence of both ammonium ions and long-day photoperiods greatly surpassed the rates observed among larvae exposed to either factor alone.