374 INSECT PESTS OF FARM, GARDEN AND ORCHARD 



The young nymphs resemble the adults in shape, but are at 

 first almost transparent in color and then a greenish-yellow. 

 They are frequently found feeding in small groups. Both the 

 young and adults have a pair of sharp spines at the tip of the 

 abdomen which they use to drive away enemies by striking them 

 quickly right and left. Two or three days after birth the skin is 

 shed and another molt occurs five or six days later. With the 

 third stage the wing-pads appear. This stage lasts four days, 

 and during it the insects take no food and remain almost quiet, 

 moving with difficulty. On onions the nymphs have been found 

 mostly on the bulbs in the loose soil. With the next molt, the 

 insect becomes mature and winged. Thus, the total life cycle 

 as observed by Professor Quaintance in Florida is about sixteen 

 days. In Russia Dr. Lindeman found that a generation required 

 forty-seven days. "In Florida there are probably no distinct 

 broods, as all stages may be found at the same time. Allowing 

 for the life cycle at sixteen days, a large number of broods could 

 occur during the year, but unfavorable conditions keep them 

 reduced, except during the spring and perhaps early summer (the 

 worst injury occurring in May and June), so that it will prob- 

 ably not happen that they will develop throughout a year accord- 

 ing to their capabilities." 



Control. The best methods of control, according to Dr. 

 Chittenden, include clean farming and crop rotation as pre- 

 ventive measures and spraying with nicotine sulphate as a direct 

 method of killing the thrips. High pressure should be used in 

 spraying and the spray should be directed downward so that it 

 will be forced into the crevices between the leaves or stems, in 

 which the thrips conceal themselves. 



The Imported Onion-maggot * 



The common white maggot which bores into the roots and 

 bulbs, causing them to wilt and decay, is probably the most 

 important insect pest of the onion. The present species is by far 

 the most commonly injurious and is termed " imported" because 

 it was early known as a pest in Europe and was imported into 

 this country probably in colonial times. 



* Pegomyia ceparum Bouche. Family Anthomyiidce. See same references 

 as for cabbage-maggot. 



