CEREAL PESTS INSECTS 



481 



527. Spring grain louse (Toxoptera graminum, Rond). 

 This insect is sometimes very destructive, but at pe- 

 riods widely separated. In Texas and Oklahoma where it 

 has been a serious pest it is known as the " green bug." 

 It appears on winter wheat in September in the form of 

 wingless females, which are parthenogenetic, and go 

 through several generations quickly (Figs. 151 and 152). 

 They feed generally on the 

 surfaces of the leaf, some- 

 times literally swarming 

 down at the base of the 

 unfolding leaves where they 

 are in a measure protected. 

 According to Webster, a 

 mild winter followed by a 

 cold wet spring is the se- 

 quence of meteorological 

 conditions most likely to 

 induce a serious outbreak of 

 this pest. In the northern 



FIG. 151. Wingless female of the 



states the wingless lemales spring grain louse, 



hatch from the eggs in April, 



passing through many generations until harvest. In the 

 South there are no eggs, the insect reproducing viviparously 

 during the entire year. The winged insect is shown in 

 Fig. 153. There are many natural enemies of the grain 

 louse, including predaceous beetles, flies, and internal 

 parasites. The most important of the latter is Lysiphlebus 

 testaceipes, Cress. These enemies and unfavorable weather 

 conditions are usually sufficient to prevent excessive mul- 

 tiplication of the insect and much devastation. In the 

 case of extensive infestations, there are no practicable 

 remedies. Another species (Macrosiphum granaria, Buck- 

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