THE POTENTIAL ROLE OF PHORESY IN THE EVOLUTION OF PARASITISM - RADIOLABELING (TRITIUM) EVIDENCE FROM AN ASTIGMATID MITE

Using tritium as a radiolabel marker of interspecific fluid transfer, we present experimental evidence that the heteromorphic deutonymph of an astigmatid mite (Hemisarcoptes cooremani) acquires materials (at le ast water) directly from the haemolymph of its beetle host (Chilocorus ; cacti). This acquisition is above that obtained from atmospheric vap our. The material acquired from the host is necessary for the completi on of the ontogeny of H. cooremani and is likely procured through the action of the caudal ventral suckers of the heteromorphic deutonymph ( hypopus). On gross morphological criteria, this mite-beetle relationsh ip was previously defined as phoretic (for dispersal). Scanning electr on photomicrographs of the physical relationship between the hypopodes and the beetles shed light on the 'parasitic' nature of the hypopus o f H. cooremani. Our findings are discussed in terms of the evolution o f parasitism from a free-living astigmatid form. This transition into parasitism is facilitated by the heteromorphic hypopus and represents a classic 'wolf-in-sheep's-clothing' strategy. The heteromorph retains the characteristic phoretic morphology while exploiting the host in t ransit.