244 MANUAL OF VEGETABLE-GARDEN INSECTS 



maggot is largest at the hind end of the body and tapers to a 

 point at the head. Posteriorly the body is obliquely truncate. 

 The flat surface is surrounded by a row of twelve fleshy tubercles, 

 of which the middle lower pair are single-pointed and not two- 

 toothed as in the case of the cabbage root-maggot. In the 

 onion maggot, in addition to the two tubercles just back of the 

 vent, there are two smaller ones on the ventral side just in 

 front of the two large ventral marginal tubercles ; they aid the 

 larva in crawling. 



The maggots become full-grown in two to three weeks in 

 green onions. In second-year onions, they develop more slowly 

 and sometimes require four or five weeks to reach maturity. 

 When full-grown, they transform to pup?e within the hardened 

 larval skin or puparium, generally in the ground surrounding 

 the plant ; sometimes the transformation takes place within 

 the bulb. The puparium resembles a grain of wheat in form, 

 is of a chestnut brown color and about | inch in length. The 

 flies closely resemble those of the cabbage and seed-corn mag- 

 gots but the males may be separated by the characters given 

 in Fig. 26. They emerge from the puparia in about two 

 weeks and lay eggs for another brood. There are at least two 

 or three broods annually. The insect hibernates principally 

 in the form of puparia, but both maggots and flies some- 

 times survive the winter. 



Control. 



The onion maggot has been found rather difficult to control. 

 Carbolic acid emulsion applied as described under cabbage 

 root-maggot, page 33, has been found of some value for killing 

 the eggs and young maggots. Clean cultivation and rotation 

 of crops are widely recommended to prevent maggot attack. 

 Recent experiments in Wisconsin have shown, however, that 

 since the flies require from ten days to two weeks after emer- 

 gence in which to mature their eggs for deposition, the insects 



