Ultrastructural and chemical studies on waxy secretions and wax-producing structures on the integument of the woolly oak aphid Stegophylla brevirostris Quednau (Hemiptera: Aphididae)

Abstract

The woolly oak aphid (WOA), Stegophylla brevirostris Quednau, is a recently described oak pest in Florida, USA. Colonies of WOA on live-oak trees are distinguished by a thick layer of white filamentous waxy material covering most individuals. Nymphs and apterous adults have several long waxy threads/bundles extending from their head, thorax and especially from their abdomen. We used scanning electron microscopy of ‘naturally waxed’ and ‘dewaxed’ aphids to study the ultrastructure and distribution of wax-producing structures on the cuticle. Two types of ‘wax pores’ and smaller wax ‘pits’ were found clustered in wax pore plates around dorsal setae on the head, thorax and abdomen. The larger, type-1, wax pores produce short or long wax columns with honeycomb interior; the smaller, type-2, wax pores produce short or long hollow wax tubes; whereas wax pits produce the shorter and more loosely net tufts of wax filaments covering most of the body dorsally. Wax columns or tubes produced by clusters of types-1 and 2 wax pores aggregate together forming the longer and thicker wax bundles that extend dorsally and laterally from the cuticle, especially near the posterior end of the abdomen. Type-2 wax pores and wax pits were also found on parts of the legs and antennae. Infrared spectroscopy indicated that wax esters, containing saturated fatty acids and fatty alcohols, are the major constituents of WOA waxy secretions. The possible roles of these secretions, especially in avoiding contamination with honeydew and providing some protection against natural enemies and adverse climatic conditions, are discussed.