1.3.3 Crawler behaviour and dispersal

Abstract

Many important pest species of Coccoidea have been spread by man through the movement of cuttings, nursery stock and produce, to the extent that they are now virtually cosmopolitan. This chapter describes the natural dispersal mechanisms and crawler behavior. Phoretic transfer of crawlers and gravid females on human clothing, in the hair of mammals and on the plumage of birds is commonly believed to be an important means of dispersal. Studies on species of soft scales, using sticky traps, have shown that crawlers can be dispersed over considerable distances on wind currents. Under alternating light-dark regimes, crawlers of S. oleae emerge from beneath the female at the onset of the light phase in laboratory tests and so would emerge shortly after dawn in the field. Wind tunnel experiments with P. mesembryanthemi, it is reported that the crawlers exhibit take-off behavior but apparently not in another armored scale, the citrus red scale, Aonidiella aurantii and so this behavior may not be present in all species.