THE REGULATION OF CYCLIC REPRODUCTIVE AND FEEDING ACTIVITY IN THE MILKWEED BUG ONCOPELTUS BY TEMPERATURE AND PHOTOPERIOD

¹ Department of Zoology, University of Iowa, Iowa City, Iowa 52240

1. Mating, feeding, and oviposition cycles were observed in the large milkweed bug, Oncopeltus fasciatus, under four regimens of varying temperatures and 24-hour photoperiods.

2. Mating and feeding activity reached maximum at the end of the light phase while oviposition occurred 8 hours after light on.

3. When placed in continuous light or dark, cyclic activity of all three behaviors persisted for at least one cycle and in the case of oviposition for five cycles. In general, the period of the first one or two cycles for all three activities, in both continuous light and dark, was approximately 21 hours; subsequent cycles, if present, had periods of 24 hours or longer.

4. Photoperiod was found to affect the maximum mating and feeding activity which occurred during the day. Long photoperiods promoted higher levels of mating and feeding than did short photoperiods.

5. The time from eclosion to first mating was photoperiod- as well as temperature-dependent; longer photoperiods and higher temperatures shortened the time to first mating.

6. The interaction of the various cyclic activities was discussed in reference to the ecology of Oncopeltus. The hypothesis was proposed that the occurrence of most mating and feeding in the early evening would allow maximum opportunity for oviposition or migratory flight, which reach peak activity earlier in the day, to occur.

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