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Studies in the Distribution of Insects by Aerial Currents

J. A. Freeman
Journal of Animal Ecology
Vol. 14, No. 2 (Nov., 1945), pp. 128-154
DOI: 10.2307/1389
Stable URL: http://www.jstor.org/stable/1389
Page Count: 27
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Studies in the Distribution of Insects by Aerial Currents
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Abstract

1. The insect aerial population above an area of agricultural land in Lincolnshire was sampled at heights of 10, 177 and 277 ft., over a front of 4400 ft., by nets flown from the masts of a beam wireless station. 2. The population consists mainly of small weak-flying insects of high buoyancy drifted involuntarily by the wind. Diptera were most numerous near the ground, Hemiptera were dominant above 100 ft., and Aphididae was the most numerous family at all heights. Over half the total number of insects collected were of the species Brevicoryne brassicae, Sciara spp., Pterodela pedicularia, Oscinis spp., Aphidius sp. and Leptocera sp. Those species of insects which were confined to ground-level occurred less frequently than those taken at all heights. 3. The insect species collected may be classified into `aerial' and `terrestrial' forms according to their vertical distribution, and lists are given of typical species and families in these groups. 4. It was found that the local vegetation determined the general character of the aerial fauna, which showed significant changes from month to month. These changes were generally uniform over the whole front, whether broad or narrow, indicating considerable insect activity over an extensive area, although unevenness occurred, especially at ground-level, owing to the close proximity of breeding places to particular nets. 5. The greatest numbers and variety of insects occurred in May, June and September, times of activity in mating and dispersal. Maximum numbers of most groups occurred at relative humidities below 59%, wind velocities of 12 m.p.h. and below and at temperatures in excess of 64 degrees F., the latter factor exercising most control. 6. The biological and economic aspects of wind dispersal are discussed particularly in relation to the results of this work in emphasizing the importance of moderate winds and wind drift rather than that of hurricanes and storms. Reference is made to the occurrence of agricultural pest species in the collections.

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