Low Altitude Flight of Oscinella frit L. (Diptera: Chloropidae)

Abstract

The distribution of Oscinella frit was studied by means of suction traps over fallow, grass and oats at heights of 1 cm to 32 m above the crop, in 1961 and 1962. The effect upon this distribution of generation, sex, time of day and time of year was determined. The effectof climate and population on the numbers flyingwas measured as were the factos determining the height of flight at low altitudes. Aerial density of frit fly over fallow and over oats in the overwintering and panicle generation is uniform up to 2.5 m. Over grass at all times, over oats in the tiller generation, and possibly over fallow in the overwintering generation, there is a dense additional layer of insects from the top of the vegetation up to 0.5 m with regularly diminishing density. From 2.5 m up to 32 m density diminishes regularly, so that at 2.5 m frit flies enter the general aerial circulation. Males and females are similarly, but not identically, distributed. Only rate of emergence consistently affects the number in flight. Flight periodicity is partly determined by rates of eclosion and teneral development. Increase in wind speed, rain and the number emergins all tend to lower the mean height of flight. Increase in wind speeds tends, if anything, to increase the number of frit flies in flight. Panicle generation flies migrate immediately, and rapidly from the crop. Tiller generation flies fly over the crop for about 60 times as long as panicle generation flies. This is probably the post-migration flight of immigrants.