Respiratory Activity during Development and Diapause of Cephus cinctus (Hymenoptera: Cephidae), with Emphasis on Effect of Temperature1

Abstract

Oxygen uptake of the wheat stem sawfly, Cephus cinctus Norton, was measured during prediapause (just before termination of feeding), diapause, and postdiapause development by means of a recording differential respirometer. During the last few days of larval feeding, oxygen uptake was about 0.75 mm3 per nig live weight per hour at 25°C. Within 3–4 clays after termination of feeding, the O2 uptake declined to 0.03–0.05 mm3, which represented about a 15- to 25-fold decrease in energy expenditure. Diapause was terminated by chilling the larvae at 5–10°C for 90–100 days. Following the chilling period and a transfer to 25°C, the O2 uptake increased about 10-fold within a week, whereupon the larva:pupa molt occurred. Thereafter, O2 consumption continued to increase until adult emergence. Temperatures of 30–°C during early postdiapause development caused a rapid return to the diapause condition. Respiratory analysis revealed that many postdiapause developing larvae exposed to 35°C for 20 hr reverted to the diapause condition within a period of 48 hr. It is postulated that moderate temperatures (15–28°C) promote the release of brain neurosecretion, whereas higher temperatures inactivate or destroy some mechanism involved in hormone transport or release.