Spectral specificity for targeted flight in the black bean aphid, Aphis fabae

Abstract

Two behavioural phases can be recognized in Aphis fabae flying in an automated flight chamber: the migratory (distance) flight phase is characterized by a persistent upward flight to an overhead white light, while the attacking (alighting) phase is a period during which a small, green-illuminated target proves repeatedly more attractive than the overhead light. In summer migrants, a negligible or very short migratory flight precedes the attacking phase. Autumn migrants, on the other hand, undertake a long-lasting migratory flight during which they are completely unresponsive to targets illuminated by monochromatic light in the visible (human) region of the spectrum (wavelengths 448–638 nm). Autumn migrants in migratory flight, and both forms during the attacking phase show a significant response to targets illuminated with white (tungsten) light and ultraviolet (λmax 360 nm). Experimental protocols involving spectral efficiency and sensitivity measurements in the visible region of the spectrum during the atacking phase reveal target attraction to wavelengths between about 500 and 600 nm with peak specificity in the green region (530–560 nm). Both summer and autumn forms behave similarly and targets illuminated with infrared (wavelengths >700 nm) were always ignored. The results are discussed with reference to the location of host plants and the disparity presented by a visual system which appears to be spectrally optimised for the detection of vegetation but which is known to produce a greater attraction for yellow than plant-green.