Polyphenic wax production in Abacarus hystrix(Acari: Eriophyidae), and implications for migratory fitness

Abstract. . Wax production in the grass-feeding eriophyid Abacarus hystrix (Nalepa) is seasonally variable; enlarged lateral and dorsal bands of wax filaments develop in adults of summer generations. Wax filaments increase the total surface area of summer-generation mites, without a concomitant increase in cuticular surface-to-volume ratio. Genetic and environmental interactions in changes in the rate of wax production were examined. High temperatures, but not changes in photoperiod, were found to stimulate increased rates of wax production. The degree of wax filamentation was independent of the genetic origin of mites, hence filaments are polyphenic, rather than polymorphic, in origin. The role of wax filaments in the regulation of water-loss and in drag maximization were experimentally investigated. The relative survival of waxed and unwaxed mites was compared at various temperature and humidity combinations, and the influence of wax filaments on surface drag was assessed by comparing the slopes of regression lines of cuticular surface area relative to terminal velocity of waxed and unwaxed mites. Significantly greater survival times in waxed compared to unwaxed mites at low relative humidities suggest mat wax filaments have a function in the regulation of water-loss. Significantly lower mean terminal velocities in waxed mites indicated that total drag relative to cuticular surface area was greater in waxed than unwaxed mites, probably as a result of increased skin friction generated by wax filaments. The increased non-cuticular surface area created by wax filaments may be advantageous during summer-migrations of A.hystrix by increasing wind shear stress on the mites at the leaf margin, enhancing buoyancy while air-borne and reducing the rate of desiccation-induced mortality.