28 MANUAL OF VEGETABLE-GARDEN INSECTS 



than xV i'^<^*li ii^ len^tli, the head and tliorax are blaek and the 

 abdomen apple-green. 'J'hc legs and antennie are nuieli darker 

 than in the wingless form. Both forms give birth to living 

 young. In the course of its development the aphis passes 

 through four nymphal stages and becomes mature after the 

 fourth molt. This requires from five to twenty-five days for 

 the wingless forms and for the winged forms twelve to sixteen 

 days, depending on the temperature. Rearing from the first 

 born of each generation, thirty-five generations have been 

 secured in one year in Texas. The number of young produced 

 by each female varies considerably, from twenty-five to over 

 one hundred, born over a period of eleven to twenty-seven 

 days. During the summer in Texas, the turnip aphis is not 

 found on cultivated plants, but its wild host plants have not 

 yet been determined. In Indiana it is found abundantly on 

 wild mustard and in Colorado on shepherd's purse. 



Control. 



The turnip aphis can be controlled by thorough spraying 

 with "Black Leaf 40" tobacco extract, f pint in 100 gallons of 

 water to which 4 or 5 pounds of soap have been added. This 

 material will kill all the lice wet by the spray, the great difl[iculty 

 being in hitting them. Spraying should begin early, when the 

 first colonies of lice are found. Good pressure should be used 

 and the spray applied with upturned angle nozzles, so directed 

 as to wet the underside of the leaves. Effective work can 

 also be done by spraying with whale-oil soap or laundry soap, 1 

 pound in 7 gallons of water. 



References 



Tex. Agr. Exp. Sta. Bull. 180. 1915. 

 Ind. Agr. Exp. Sta. Bull. 185. 1916. 



