Voltinism and its determination in some beetles of cruciferous crops

The influence of some token stimuli (photoperiod, temperature and food) on the annual cycle of univoltine insects ( Ceuthorrhynchus assimilis Payk., C. pleurostigma Marsh., spring and autumn races, and Psylliodes chrysocephala L.) was studied. The reproductive diapause of C. assimilis and the spring race of C. pleurostigma was not affected by the photoperiods studied. In the autumn race of C. pleurostigma and P. chrysocephala , the summer diapause was induced by long days and oviposition in the autumn by short days. The different responses to photoperiod in the 2 races of C. pleurostigma , races which were not geographically isolated, were sufficient to cause their reproductive isolation and so their maintenance. Both races were well synchronized with the annual cycles of their host plants