Functions of Egg-Coating Substances Secreted by Female Accessory Glands in Alderflies, Fishflies and Dobsonflies (Megaloptera)

SIMPLE SUMMARY: Egg masses of the insect order Megaloptera are coated with female accessory gland substances and are diverse in shape, color, and surface structure. Female alderflies (family Sialidae) and fishflies (family Corydalidae, subfamily Chauliodinae) lay eggs in a single layer on the substrate (although the eggs are occasionally multi-layered in the fishfly genus Nigronia), and the accessory gland substances are usually brown. In contrast, dobsonflies (Corydalidae, Corydalinae) lay a multi-layered hemispherical egg mass, and the accessory gland substances differ in color and chemical properties among genera and species. Egg masses of the dobsonfly genus Protohermes are coated with a sticky substance, while those of other dobsonflies are covered with hardened white powders, both of which contribute to the prevention of egg desiccation. The accessory gland substances of most species of Megaloptera also function to protect eggs from attack by oophagous predators, such as ladybird beetles and ants. The information on the parasitoids of Megaloptera egg masses are also discussed based on the present and previously reported observations. ABSTRACT: Eggs of insects are immobile and must endure harsh environmental conditions (e.g., low temperatures in winter and aridity in summer) and avoid attack by egg-eating predators, egg parasites, and microbes. Females of Megaloptera lay their eggs as a single- or multi-layered egg mass, which is coated with chemical substances secreted from the female reproductive accessory glands. In this study, we observed the egg masses laid by females of two species of Sialidae (alderflies), nine species of Chauliodinae (fishflies), and 23 species of Corydalinae (dobsonflies) belonging to the order Megaloptera and examined the functions of accessory gland substances coating the laid eggs. The female accessory gland is a single tube in alderflies and fishflies but a paired pouch in dobsonflies. The amount and color of the gland substances differ greatly among species. These substances prevent egg desiccation, inhibit egg feeding by ladybird beetles, and repel ants. Most characteristics of the egg mass structures and the effectiveness of accessory gland substances reflect the phylogeny of Megaloptera, although some differ among closely related taxa.