Microstructure of the prothoracic mycangia in the ambrosia beetle Platypus koryoensis (Coleoptera: Curculionidae: Platypodinae)

Abstract

Platypus koryoensis (Murayama) (Coleoptera: Curculionidae: Platypodinae) is a minute ambrosia beetle that can cause significant damage to live oak trees ( Quercus mongolica) along with its symbiotic pathogenic fungus ( Raffaelea sp.). Although both sexes of the beetle have a number of cuticular depressions for carrying microorganisms, only the females have mycangia that are typical in size on the pronotum. The mycangial cavities are filled with a mass of amorphous substances including yeast-like spores. In addition, mycangial cavities are equipped with cuticular pores which release substances to support symbiotic microorganisms during storage. Small depressions of both sexes can be subdivided into two clusters according to their relative sizes and locations. Although they have a typical cuticular peg (basiconic sensillum), they also share a common morphological characteristic with the typical mycangium of female: a round outlet and an invaginated reservoir containing a mass of secretory substances. Accordingly, our fine structural data suggest that both the female mycangia and the clusters of small cuticular depressions in both sexes also have a mycangial function in common regardless of their relative size and location.