Studies of Fluctuations in Insect Populations: V. The Leaf-Curling Pear Midge, Dasyneura pyri (Cecidomyidae)

Abstract

This is the fifth of a series of papers describing the fluctuations of insect populations. It deals with Dasyneura pyri Bouche, the leaf-curling pear midge. 2. A short account of the bionomics of this midge is given. 3. The dates of emergence and number of broods obtained from larvae collected in Devon and reared at Harpenden, Hertfordshire, are shown. The constancy with which minor variations caused by differences in weather conditions become levelled out by the end of the year is notable. A limitation of broods by the length of the season in which new growth can be found on pear trees is suggested. 4. The parasite Misocyclops marchali Kieff. is recorded as attacking the second and ensuing broods of the midge but in no case the first brood. This partial adjustment of parasite to midge is interesting. A delayed emergence of the parasites compared with that of the host midge is shown to exist. Both these facts may indicate a recent change of host on the part of the parasite. M. marchali Kieff. is known also to parasitise Dasyneura arabis Barnes and D. ulmariae Bremi. 5. The sex ratio of the various broods is different, as the season advances so the percentage of males increases. This can be explained on the hypothesis that the further developed the eggs are at the time of entry of the sperm the more males result.