Factors affecting the locomotor and settling responses of alate aphids

Abstract

In suitable environmental conditions for flight, alate aphids typically fly from their parent host plants and they can not normally be brought to settle down on those or other plants until after they have engaged in flight or other activity. In unsuitable flight conditions they remain on the plants but do not respond to them by feeding and reproducing. Aphids alighting on plants after flight normally spend some time wandering and probing and they may settle down. By allowing young alatae of Aphis fabae Scop, short tethered and untethered flights of a minimum of 10–20 seconds and then putting them on a leaf surface, it was possible to induce wandering and probing behaviour. There is evidence that aphids do not normally alight and show this behaviour after being airborne for such a short time, and the behaviour of the aphids in the experiments was probably due to the composite effect of flight and some part of the experimental procedure. Wandering and probing behaviour could also be produced by giving aphids a knockdown dose of CO 2, and by allowing them an extensive period of activity other than flight. The length of time aphids spent wandering on plants before they took off again, and whether or not they settled down to feed and reproduce, was influenced by the length of flight they had engaged in, the nature of the surface they were released on, and the physical environment. Aphids flown for five minutes or less and put on mature host leaves in the light wandered and probed but soon took off again; aphids released on host seedlings or on mature leaves which were then put in darkness, after short flights of a few seconds, and on mature leaves kept in the light after long flights of 30 minutes to 8 hours, frequently settled down to feed and reproduce. The effect of both short and long flights was soon lost and in the absence of strong contralocomotory stimuli such as darkness or a very suitable host, the aphids reverted to typical locomotory behaviour after showing some degree of the settling response (i.e. wandering and probing or settling down for some time). Much of the behaviour of alate aphids can be grouped under two opposing general responses: the locomotor response and the settling response; it is suggested that the stimuli determining the type and strength of response of aphids at any time are principally of the same kinds as those which were shown in the experiments to affect the strength of the settling response.