33^ MAINE AGRICULTURAL EXPERIMENT STATION. I916. 

 LIFE CYCLE OF WOOLLY APHID OF APPLE. 



(Exclusive of root forms.) 



ELM : Primary Host. 



EGGS. 



(Under bark all winter) 



STEM- MOTHER. 



(first generation in leaf. 

 Apterous viviparous females). 



SECOND GENERATION. 



(apterous viviparous females 

 in leaf). 



spring migrants Migrates to apple . 

 (third generation. Alate viviparous). 



Apple : Alternate Host. 



NYMPHS. 



(Hibernating young mi- 

 grating to trunk or 

 branches in early spring') 



SEVERAL GENERATIONS. 



FOURTH GENERATION. 



(apterous viviparous females). 



Migrate to elm 



FIFTH GENERATION. 



(apterous viviparous females). 



FALL MIGRANTS. 



(Alate viviparous 

 parthenogenetic 

 females, mature 

 Aug.-Sept. 



apterous oviparous females sexuparae.) 



AND APTEROUS MALES. 



APTEROUS VIVIPAROUS 

 PART H ENOGENETIC 



females, mature in 

 Aug.-Sept. 



EGGS. 



(under bark all winter). 



HIBERNATING NYMPHS 



(protected during winter 

 about crown of tree). 



