INFLUENCE OF CONSANGUINITY ON THE SEX-RATIO AND DIAPAUSE OF DIPRION-PINI L (HYM, DIPRIONIDE) POPULATIONS .1. OBSERVATIONS ON A REARING POPULATION - RELATION WITH THE SEX DETERMINISM AND CONSANGUINITY

Observations made on a rearing population of Diprion pini L. bred sinc e more than 30 generations in photoperiodic and thermic conditions fav ourable to without-diapause development, show that during the first re ared generations sex-ratio evolued rapidly in favour of males while di apause rate highly increased, reaching more than 90% of individuals. T hen diapause rates decreased gradually, after what, stay devinitively to a low level, while males remain much more numerous than females. Th ese observations suggest a high consanguinity in rearing populations a nd that the increasing diapause rates, that are not without analogy wi th diapause variations during outbreaks of natural populations, may be linked with this consanguinity. Initial diapause rate recovery will r esult in the selection realised by the reproduction of the without dia pause individuals only at every generation. The hypothesis is further advanced that the increase in males may result in a sex determinism we ll-known for some Hymenoptera and at least for a Diprionidae that invo lve the production of diploid males favoured by consanguinity. This ph enomenon may be at the origin of observed diapause rate variations. Se veral factors such as insect weight, wing setae number and, in particu lar, the presence of heterozygote males in natural populations corrobo rate the existence of diploid males for D. pini. The existence of gyna ndromorphs in nature as in laboratory populations may also constitute an indicator of the consanguinity. Consanguine crossings realised betw een brother-sister insects through several generations reproduce the p henomena seen in rearing quite faithfully, as much for diapause as sex -ratio.