AND OTHER INJURIOUS INSECTS OF I907 AND I908. 



133 



From Pegomya puparia gathered May 9th Dillon reared two Pseudoeu- 

 coila adults, one emerging August 17th, and the other September 2nd. A 

 third specimen was reared August 24th from puparia gathered the 14th of 

 May. The accompanying table shows dates of emergence of both Pegomya 

 and Pseudoeucoila. The figures represent the actual number of specimens 

 reared for five days of each month. The collections of puparia were 

 made in the spring, so that the table represents only one brood of either 

 species. The earlier dates for both insects are emergence from cages 

 in the heated insectary room, and for that reason would be ahead of 

 the time that the fly and parasites appear outside. It will be noticed that 

 the cabbage flies appeared first, followed about two weeks later by Pseu- 

 doeucoila. The largest number of flies of the first brood emerged from 

 May ISth to May 30th, while the greater number of Pseudoeucoil-a emerged 

 from June 1st to June 25th. The intervening time between the emergence 

 of the two insects is sufficiently long for the flies to deposit their eggs, 

 and the young hatch and become partly grown before Pseudoeucoila ap- 

 pears. 



A total of 209 Pegomya of the first brood emerged during the season, 

 and 121 of the Pseudoeucoila. Some of the puparia did not give forth either 

 flies or parasites, and we have no definite record of these. Adding these 

 two figures gives 330 puparia, and taking the percentage of Pseudoeucoila 

 from this total gives 36.6% or nearly 37%. If those puparia from which 

 nothing emerged had been counted doubtless the percentage would be 

 somewhat lower. 



Number of Broods. It is probable that the number of broods corre- 

 spond closely with those of Pegomyia. No attempt was made to breed the 

 parasite on maggots, and so we have no accurate data on that point. 



With the above facts before us it is easy to construct a diagram which 

 hows at a glance when the cabbage maggot fly was most abundant, how 

 its parasite approached it in numbers, and how the latter follows in its 



s 

 near 



appearance that of its host. These data are of value to planters as show- 

 ing approximately at what dates in ordinary seasons the fly is to be looked 



for in greatest numbers. 



