STRATEGIES OF EMERGENCE IN THE CHESTNUT WEEVIL CURCULIO-ELEPHAS (COLEOPTERA, CURCULIONIDAE)

In the chestnut weevil Curculio elephas, adult emergences spread over 3 or 4 years due to prolonged larval diapause in some individuals. Wee vils with an extended diapause emerge, on the average, 1-10 days befor e those with simple diapause, but whatever the age of insects, emergen ces occur always from mid-August to early October. When the summer is dry, some adults cannot emerge because of the hardness of the soil. Em ergence sucess of adults is smaller in females than in males. The resu lt is that the sex ratio is female-biased before emergence and male-bi ased after. Summer drought cannot be predicted by the chestnut weevil, and when the soil is dry 27-78% of females cannot emerge and do not r eproduce. The year after a summer drought, many reproducing females ma y emerge from larvae with prolonged diapause. These results suggest an evolutionary influence on the variability in diapause duration. Compu ter simulations and observations do not support the hypothesis that th e main cause of variation in diapause length is the existence of sever al distinct genotypes within populations. On the contrary, our data st rengthen the hypothesis for coin-flipping plasticity discussed in a pr evious paper.