Kenneth M. Smith 181 



The larvae of the third generation have usually pupated by the end 

 of September or the beginning of October though in late seasons they 

 may continue to feed till the end of the latter month. 



The third generation thus winter as puparia and the adult flies 

 emerge in the following spring. 



Taking forty days as a fair estimate of the duration of the life-cycle 

 from egg to adult, the following table gives an idea of the approximate 

 times of appearance of the generations. 



/May 28th > Eggs deposited by flies emerged from 



j overwintering puparia 



i June 1st > Larvae of 1st generation hatch 



Ist Generation 4 | 



I June 19th > Larvae of 1st generation pupate 



I 

 'July 8th > Adult flies of 1st generation emerge 



I Approximate Time for Maturation of Flies = 7 days. 

 ( Jiily 15th >- Eggs deposited by 1st generation adults 



I 



July 18th > 2nd generation larvae hatch 



2nd Generation i \ 



I Aug. 5th > 2nd generation larvae pupate 



I ^ 



■ Aug. 24th > 2nd generation adults emerge 



j Maturation Period — 7 days. 

 /Sept. 1st > Eggs deposited by 2nd generation adults 



„ , p , . J Sept. 4th > 3rd generation larvae hatch 



i 



Sept. 22nd > 3rd generation larvae pupate and 



^ hibernate 



It should be understood that this table is entirely artificial and does 

 not attempt to do more than give approximate dates for the various 

 appearances. It should also be made clear that the generations are not 

 sharply divided off as they appear in the diagram. Some first generation 

 adults may still be emerging at the same time as the second generation 

 adults; and first and second or second and third generation larvae are 

 often found together. 



Habits. Food Plants. The food consists mainly of the onion; the 

 maggots, however, occasionally attack leeks and shallots and have been 

 recorded as feeding upon tulip bulbs and lettuce. Under experimental (i) 

 conditions the larvae have been induced to complete their development 

 in fresh manure and also in radishes. 



Injuries Produced. The worst damage to the onion occurs in the 

 spring when the plant is still a seedling. Owing to the smaU size of the 

 onion and the large numbers of maggots produced, the young plants are 

 devoured wholesale, the larvae migrating from onion to onion, leaving 

 nothing but the green portion above ground. As the onion increases in 

 ize, symptoms of attack are yellowing and wilting of the tops which 



