Dawn and dusk flight of Drosophila subobscura Collin

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 America4–6; 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. RESP-3346