1909.] 



The Genus Chermes. 



447 



Life History of Chermes abietis Kalt. 



The primary host is the Spruce. There is no intermediate host, 

 and the life cycle is completed on Spruce in one year. There are 

 two alternating generations, with no sexual multiplication ; a wingless 

 generation, corresponding" to the Foundress Generation of the life 

 history given above, alternates with a winged generation correspond- 

 ing to the Migrant Generation. 



The gall on the Spruce— the work of the foundress — resembles that 

 of Chermes viridis Ratz., but is smaller. It is also said to be ripe 

 later, opening at the end of July (the galls of Chermes viridis may be 

 ripe, in the south, in May). 



The life history may be represented graphically thus :— 



Graphic_I illustration of the Life History of Chermes abietis Kalt. 



The galls and the insects of these generations resemble those of the 

 other species so closely, though the insects are yellow rather than green, 

 that Chermes viridis Ratz. and Chermes abietis Kalt. are very difficult 

 to distinguish. 



Exceptionally members of Generation 2 may wander or migrate to 

 conifers other than Spruce, but the eggs, if laid there, are unproductive. 



Life History of Chermes strobilobius Chol. 



The primary host is the Spruce (Picea), the intermediate host is 

 the Larch (Larix), and there are five generations. 



In connection with Generation 4 there is additional complexity 

 inasmuch as this generation in C. strobilobius divides itself into two 

 parallel series. A certain number of the insects of Generation 4 

 become winged adults, and behave just as the sexuparce of Chermes 

 viridis Ratz. Others, however, of the same Generation, do not 

 become winged when adult, but as wingless females remain on the 

 intermediate host; this series is known as the Exile Generation. 

 Ultimately the progeny of the Exiles pass the winter on the inter- 

 mediate host like the larvae of the Colonists of Generation 3, and 

 develop in the following spring into adult Colonists. 



Foundress La.n/(XQ 

 hibernate /qo&-oc} 



Yellow eggs 



