An investigation of the distribution during winter of the white clover seed weevil, Apion dichroum Bedel (Gol. Curculionidae).
The following is based almost entirely on the author's summary of this account of investigations carried out in south-eastern England during the winter of 1963-64 on the migration and winter distribution of Apion dichroum Bedel, which attacks the developing seeds of white clover (Trifolium re pens). It was found that A. dichroum, like other species of the genus, migrates in autumn from the clover fields in which it breeds to woodlands where it overwinters in leaf litter. Migration takes place in August and September, shortly after the adults have emerged. Litter from hazel [Corylus avellana] and beech litter collected under yew were more densely populated than beech litter collected away from yew or than mixed litter from ash and sycamore, but the reasons for this are not known. The minimum temperature in woodland leaf litter during the winter was 5.5°C. [9.9°F.] above that in short grass. From the results of laboratory studies on the cold-hardiness of A. dichroum, it is concluded that, if the insects did not migrate from fields of mixed white clover and rye grass [Lolium perenne], which in south-eastern England are grazed by sheep in winter and in consequence provide little shelter, many of them would be killed in some years by low temperature.