Co-ordination of Successive Activities in an Aphid. Depression of Settling after Flight.

The background to this work on the parthenogenetic winged form of Aphis fabae Scop, is given in two earlier papers (Kennedy & Booth, 1963a, b: referred to hereafter by date only), where it was shown that aphids allowed to fly and alight freely in a laboratory flight chamber become increasingly ready to settle down, feed and larviposit on a leaf the longer they have flown. Flight and settling are the two main activities of these insects and they are nervous antagonists, each a complex of responses which inhibits the other. But the strengthening of the settling responses, following flight, is not in the first place a consequence of some negative feedback weakening flight, for it occurs even when flight is still gaining in strength. This type of coordination of two successive activities was therefore thought to be a central nervous process and named antagonistic induction. Settling responses are in large measure inhibited before flight occurs and totally inhibited when it starts; and afterwards, when the settling responses that have been primed by flight are initiated on an unsuitable leaf, or even on a suitable one if the priming has not been sufficient, they are soon inhibited by flight once again (1963 a, b). This suggested a method of confirming that the co-ordination of flight and settling is a central nervous function, with peripheral feedback having only a reinforcing effect. If so, then it might be possible, by appropriate external stimulation alone, to tip the balance against the excitatory, priming effect of flight on settling and in favour of the inhibitory effect, even to the point of reversing the normal course of events and producing a decrease instead of an increase in settling readiness after flight. This paper gives the evidence obtained on that point.