74 MANUAL OF VEGETABLE-GARDEN INSECTS 



two generations of the pea aphis may develop annually in Vir- 

 ginia. In Indiana breeding experiments have shown that 

 counting from the last-born, thirteen generations are produced 

 annually. The insect hibernates on clover either as mature 

 viviparous females, winged or wingless, or in the cooler part of 

 its range in the egg stage. Males and egg-laying females are 

 produced late in the fall only. The male is usually winged, is 

 considerably smaller than the viviparous female and has darker 

 markings on the head, thorax and abdomen. Only a few 

 wingless males have been observed. The egg-laying female is 

 wingless, and much smaller than the wingless viviparous form 

 which it resembles closely in color. The hind tibifc are con- 

 siderably thickened basally and bear numerous sensoria. The 

 winter eggs are usually found on red or crimson clover. The 

 egg is about A inch in length, elliptical oval in outline and 

 pale when first laid, changing to jet black. 



The pea aphis is subject to the attacks of several parasitic and 

 predaceous insects and particularly to a fungous disease that often 

 destroys a large proportion of the lice. These natural enemies 

 are most effective during the warmer part of the season and 

 often nearly exterminate the lice locally on certain food plants. 



Means of control. 



As the pea aphis lives over winter and begins breeding in 

 the spring on clover, especially on crimson clover, the presence 

 of these crops in the near vicinity of fields of early peas is a 

 menace to the latter. In such cases, when crimson clover is 

 being grown for green-manure and is seen to be infested, it 

 should be plowed under before the migration of the lice to peas 

 takes place, without waiting for it to reach its full growth. 

 The ground should then be harrowed and rolled. In cases in 

 which the clover is grown for hay, it might be well to sacrifice 

 this crop in order to save the peas. Experience has shown that 

 peas grown in rows about thirty inches apart are, as a rule. 



