Why were there so many Grain Aphids among the moths in my light trap?

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WHY W E R E THERE SO MANY GRAIN APHIDS AMONG THE MOTHS IN MY LIGHT TRAP? G . D . HEATHCOTE

Research projects, whether undertaken by professional or amateur entomologists, tend to expose more problems than they solve. This is perhaps the charm of research, but it can be very frustrating, especially for the professional; financial restraints always prevent him or her from following up many potentially interesting lines of work because they offer no financial reward for their employers. This article presents some unexpected facts and minor mysteries regarding insect behaviour arising from one such incomplete study. It provides a little in the way of explanation, and shows the danger of assuming that closely related insects must behave in similar ways. We still have a lot to learn about common insects. Many tungsten-lamp traps (Williams, 1948) are operated in England as part of the Rothamsted Insect Survey (Taylor et al., 1981) to determine the numbers of some migratory moths and pest species. The insects caught by these traps (which include many species other than moths) are killed and examined later. Tungsten-lamp traps catch many fewer insects than the mercury vapour lamp traps used by most amateur lepidopterists, who release most of the insects they trap unharmed. I operated one of the Rothamsted light traps at Broom's Barn Experimental Station, Higham, Bury St. Edmunds, from 1968 to 1984. (The details of the moths caught are kept by the Biological Records Centre at Ipswich.) Similar traps were operated at Fiatford Mill (Field Studies Council), at Ipswich in parkland (Miss V. A. Short), although not throughout the whole of this period, and at Santon Downham (Forestry Commission Research Branch). Trap sites in neighbouring counties included Methwold Fen and Monks Wood (Institute of Terrestrial Ecology). There were, in all, about 80 traps throughout England each year, all l-4m from the ground Over short grass and operating from sunset to sunrise. Broadbent (1947) established that aphids are caught throughout the night by Rothamsted light traps in Britain, but he did not establish which species. Most aphids fly between 09.00 and 21.00 h GMT but, using small, low-level suction traps, Eastop (1951) found that up to 12% of the total catch might be Aying between 18.00 and 07.00 h. I wanted to know if the Rothamsted light traps could provide useful information on the time of flight and numbers of aphids which are pests of crops in addition to the valuable data on moths. I therefore removed and identified all the aphids from the Broom's Barn trap each day from 1968 to 1977. In addition, in certain years, I examined the aphids caught in similar traps at Rothamsted Experimental Station, Harpenden, Herts., which is about 80km from Broom's Barn but at much the same latitude. Unfortunately, due to the bulk of insect material involved, it is normally impossible to retain most of the insects caught by the light traps from the Rothamsted Insect Survey; the aphids caught are seldom identified or retained.

Trans. Suffolk Nat. Soc. 23

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