Ultrastructural characterization of the scale cover of cryptic Aspidiotus spp. (Hemiptera: Diaspididae) and the ovipositor of their parasitoids

Correctly identifying target insect pests and their natural enemies is important in biological control management programs. In the scale insect outbreak that devastated the coconut industry of the Philippines in 2009, the misidentification of the destructive pest population resulted in an unsuccessful biological control application. The scale cover has been proposed as a diagnostic feature to identify the cryptic Aspidiotus species from one another. Here, we examined the scale cover of three Aspidiotus species at higher magnification using scanning electron microscopy (SEM) to validate the observed difference in scale cover characteristics reported in previous literature. SEM observations revealed that the cryptic species A. destructor and A. rigidus scale covers are ultrastructurally similar, having irregularly arranged and highly agglutinated wax ribbons, whereas A. nerii has highly agglutinated wax ribbons arranged in an overlapping concentric pattern. Additionally, a comparative observation of the ovipositor of the hymenopteran parasitoids directly associated with the two cryptic Aspidiotus species, A. rigidus and A. destructor, was done to provide structural evidence that links ovipositor structure to host specificity. The structure of the ovipositor tip of the hymenopteran parasitoids directly associated with the two Aspidiotus species examined under SEM is congruent with their mode of parasitization.