Control of diapause and supercooling by the retrocerebral complex inPyrrhocoris apterus

Effects of external (photoperiod, temperature) and internal (retrocerebral complex, diapause condition) factors on supercooling were studied inPyrrhocoris apterus (L.) (Heteroptera: Pyrrhocoridae) adults. An increase in supercooling capacity is associated with the induction of diapause by short-day photoperiod or cardiacallatectomy of long-day non-diapause insects in spite of a high temperature of 26°C. The induction of diapause is a prerequisite for a further increase in supercooling capacity by cold acclimation. Post-diapause adults show low values of the supercooling point also in late January or early February, although their developmental potential is fully restored. Evidently the ability to supercool associated with diapause induction is maintained by a low ambient temperature in spite of diapause termination. The supercooling point increases rapidly when these adults are transferred to a high temperature of 26°C and cold re-acclimation is then no longer possible. The inhibition of morphogenesis (maturation of gonads) by cardiacallatectomy does not prevent the supercooling point from increasing in post-diapause adults at the high temperature.