REPRODUCTION 105 



destroy the tissues of their maternal host and ultimately escape 

 through the body-wall. 



There are a few insects which are functional 'hermaphrodites'. 

 The best known example is the Californian race of the Coccid 

 Icerya purchasi, the fluted scale. The gonads produce both sperm and 

 oocytes. Most of the eggs are fertilized by sperm from the same in- 

 dividual, but these hermaphrodite females may copulate with the 

 rare males. 



'Parthenogenesis' on the other hand is widespread among insects. 

 Many species, for example many grasshoppers, and some Lepidop- 

 tera, can occasionally develop from eggs which escape fertilization. 

 Others, such as the familiar stick insect Carausius morosus, are con- 

 stantly parthenogenetic ; males of this species are exceedingly rare. 

 Another classic example is the honey-bee, in which the queen can 

 control the escape of sperm from the spermatheca and can thus 

 ensure whether fertilized eggs, which develop into workers or queens, 

 or unfertilized eggs, which become drones, are produced. We have 

 already referred to the familiar example of the Aphids which give 

 rise to a series of parthenogenetic viviparous generations of females 

 throughout the summer months and then, under the influence of the 

 shortened day-length in autumn, undergo a polymorphic change (p. 

 93) and produce sexual forms, males and oviparous females which 

 lay a small number of fertilized winter eggs. 



BIBLIOGRAPHY 



bonhag, p. f. Ann. Rev. Entom., 3, (1958), 137-160 (ovarian structure and 



vitellogenesis: review) 

 jacobson, m. and beroza, m. Science, 140, (1963), 1367-1373 (chemical 



attractants in insects: review) 

 wiGGLESWORTH, v. b. Adv. Insect Physiol, 2, (1964), 243-332 (hormones 



and reproduction : review) 

 The Principles of Insect Physiology, 6th Edn., Methuen, London, 1965, 



629-684 (reproduction, sex determination, etc.) 

 wilde, J. de, Physiology of Insecta I (Morris Rockstein, Ed.) Academic 



Press, New York, 1964, 9-90 (reproduction) 



