Control of the Life Cycle in a Univoltine Antlion, Myrmeleon bore (Neuroptera)

The larvae of Myrmeleon bore occur on dunes. Most of them reach the cocoon stage within one year after hatching. Developmental rate varies among individuals depending on prey consumption, but adult emergence is concentrated in midsummer. We examined the basis of this periodicity by rearing the third (last) instar larvae with various feeding intervals either under uncontrolled temperature and natural daylength ("natural TD") or 25℃ and LD 16 : 8 ("controlled TD"). All the larvae at controlled TD formed a cocoon, whereas some larvae at low food levels under natural TD did not form a cocoon and entered a second hibernation. Third instar larvae reared at short-days less than LD 13.5 : 10.5 were suppressed to form a cocoon. Larvae supplied with small amounts of prey formed smaller cocoons late in the season, but the duration of the cocoon stage was shorter due to the increased sand temperature and to a physiological factor related to pupal size. As a result, a longer duration of the third instar was followed by a shorter duration of the cocoon stage. We conclude that synchronous adult emergence in this antlion species is caused by the combination of such factors as feeding rate, photoperiod and temperature.