Phoretic dispersal of armored scale crawlers (Hemiptera: Diaspididae)

Dispersal and colonization of new areas by armored scale insects is achieved by mobile first-instar nymphs, called crawlers. Few studies have considered the actual mechanisms by which crawlers disperse, and although crawlers are capable of actively wandering over short distances (generally < 1 m), their dispersal over longer distances has been thought to be wind-mediated. Here, we present evidence of a more important means of dispersal over longer distances (>1 m). We first confirmed that crawlers of four species of Diaspididae (Abgrallaspis aguacatae Evans, Watson & Miller, Hemiberlesia lataniae (Signoret), Aspidiotus nerii Bouché) and Diaspidiotus perniciosus (Comstock) have four hairs on the end of each of their legs, and that each of these hairs ends in a suction cup-like structure, reminiscent of the attachment structures possessed by phoretic mites. Crawlers of A. nerii use these structures to attach themselves to different insect species and can effectively be moved phoretically by these insects. Crawlers can remain attached to flying insects for considerable periods of time. Evidence for phoresy in the field will be presented and its implications for phytosanitary rules will be discussed.