Dawn and Dusk Flight of Drosophila subobscura Collin

Abstract

FEW records exist of insects with two peaks of activity in 24 hr. Of the many identified species attracted to a light in four years of continuous trapping, only one, a moth Pterophorus monodactylus, was caught at two separate times each night¹. Aphis fabae has a double peak of emigrant flight from its secondary host, and this is the result of a complex chain of moulting rhythms, weather influences and flight behaviour². A fall has been observed in the number of Simulium venustum in the air when evaporation-rate was high, leaving density maxima at 09.00 and 18.00 hr.³. Several species of Drosophilidae have been caught at bait traps with maximum numbers at dusk and dawn both in Europe and America^4–6; but many factors, including humidity, will affect the area of influence of these traps and hence the number of insects caught and possibly their time of arrival.