Ecdysone and the super tick

Abstract

TICKS and insects develop and grow through intermittent replacement of their integument. This moulting does not occur beyond the adult stage, with the exception of primitive apterygote insects such as silverfish, which continue to moult and grow after they become sexually mature. Moulting ceases to occur in the pterygote adult insect because the glands secreting ecdysone, the hormone required to induce moulting, break down and disappear soon after the insect (and presumably also the tick) becomes adult¹. The adult tissues of both hemimetabolous insects and those with complete metamorphosis continue to respond to ecdysone if exposed to it. There are, however, differences in the responsiveness of different segments of the insects and the resulting ‘super-moulted’ adult insects are usually defective^2–5. We have found that ticks also retain the full potential to moult, grow and reproduce normally as adults if they receive ecdysone. Through successive adult moults ‘super ticks’ are obtained (Fig. 1) which consume very large volumes of blood and produce many more viable eggs than normal ticks.