INSECTA 481 



A complete analysis of the environmental conditions governing the 

 onset of sexual phases after a period of parthenogenetic reproduction 

 is yet to be made. Food, temperature and light seem to be important, 

 and of these a reduction of the last mentioned factor seems to be 

 associated with the production of sexual winged individuals. 



Though the order contains insects for the most part harmful to 

 man and his property, a few are useful in that they yield the dyestuffs 

 Kermes (females of Kermes ilicis) and Cochineal {Dactylopius coccus) ^ 

 and the resin stick-lac {Tachardia lacca). The usually harmful plant- 

 sucking habit is being put to good use in Queensland where the 

 coccid bug, Dactylopius tomentosus, is employed against the prickly 

 pear cactus with considerable success. 



Order EPHEMEROPTERA (Mayflies) 



Vestigial mouth parts reduced from the biting type; wings mem- 

 branous with a reticulate vena- 

 tion ; the hinder pair small ; caudal 

 filament and cerci very long (Fig. 

 332). The nymphs are aquatic and 

 an active winged stage known as 

 the subimago occurs before the 

 last moult yields the adult. 



The eggs are laid in water, 

 either scattered over the surface 

 or attached to stones, etc., by the 

 female, which enters the water 

 for the purpose. 



The nymphs at first possess no 

 gills but subsequent instars bear 

 on the abdomen movable tracheal 

 gills (Fig. 333), which may be 

 branched or lamellate, exposed or 

 protected in a branchial chamber. 

 The body form^varies with the 

 habits. Thus inhabitants of fast- 

 flowing streams have flattened 

 bodies with legs provided with 

 strong clinging claws, e.g. Ecdyo- 

 nurus. Those which live in clear 

 still water have a stream-lined 

 form for rapid movement, e.g. 

 Chloeofi, while burrowing types 

 have fossorial legs, e.g. Ephemera, 

 and are often provided with protective gill opercula, e.g. Caenis. The 



Fig. 332. Ephemera vidgata. 

 From Imms. 



