a1 Research Division, MAF, PO Box 24, Lincoln, Canterbury, New Zealand
a2 Department of Entomology, Lincoln College, Canterbury, New Zealand
a3 Invermay Agricultural Research Centre, MAF, Private Bag, Mosgiel, New Zealand
Sitona discoideus Gylh., an introduced pest of lucerne in New Zealand, exhibits univoltine, aestivatory seasonality in Canterbury and Otago, with each generation appearing in late December. Some two weeks after the December emergence of adults, flights to aestivation sites commenced. These sites were commonly remote from the lucerne stands and included such places as under stones or at the base of trees, fence posts, etc. At the commencement of aestivation, the indirect flight muscles atrophied rapidly, only to redevelop some 6–8 weeks later when autumnal post-aestivatory return flights to lucerne began. During the winter, S. discoideus fed on lucerne foliage and became reproductively mature. By October, age-related adult mortality had begun, and for about two weeks in December no adult weevils were present at all in one Canterbury site. In Otago, there was a distinct generation overlap of 2–3 weeks. The eclosion of new generation weevils was closely synchronised; it is suggested that this may have been the product of differential egg development and egg-laying temperature thresholds and a high fourth instar and pupal develoment threshold. Synchronised emergence of adults tended to accentuate the problem of defoliation caused by their feeding.
(Received October 31 1983)