362 



PROTECTION AGAINST INSECTS. 



arise of parthenogenetic insects. The last generation in 

 autumn is winged and produces $ and ? ; from the latter 

 eggs are produced and hibernate. Besides this dimorphism, 

 in the genus Chermes the insects migrate from one species of 

 plant to another in order to change their food. By piercing 

 plants or sucking them, they produce galls and other mal- 

 formations, on leaves, needles, buds, 

 flowers, etc., especially on broad- 

 leaved plants. Most species are 

 monophagous, almost every species 

 of plant having its peculiar plant- 

 lice. Most plant-lice produce honey- 

 dew from leaves, this being their 

 excrement. 



In Chermes, there are three 

 different imagos : winged partheno- 

 genetic ? , wingless parthenogenetic 

 ? , and wingless sexual imagos of 

 both sexes. 



The wingless parthenogenetic ? , 

 stem-mother orfundatrix, hibernates 

 alone on spruce buds. After three 

 moultings in the spring, she sucks 

 the opening buds, lays a number of 

 eggs and dies near them. The 

 sucking of the mother causes a gall 

 to form, and from the eggs, very 

 shortly, wingless lice arise, which 

 force their way deeper into the 



gall, which therefore increases in size, chambers being 

 formed round the lice. The latter, after 3 moultings, acquire 

 rudimentary wings, and, opening the gall-covering, come out 

 as nymphs on the needles. After another moulting they 

 acquire wings. 



Then some of the winged lice remain on the tree, and lay 

 eggs from which the hibernating parthenogenetic J'nudntri.r 

 arises. She continues to act as already described and corre- 

 sponding broods arise for several years. 



The other winged lice leave the spruce for other conifers, 



Fig. 188. Gall of Chermes 

 abietis, L., on a spruce-twig. 

 (Natural size.") 



