1922 ENTOMOLOGICAL SOCIETY. 51 



perio'd of incubation was 5.5 days: in 1919 3.8 days: in 1920 6 days; arid in 

 1921 5.7 days. Under normal conditions nearly all eggs hatch inside of a 

 week. 



Sunlight and dryness of the soil or surroundings are destructive to eggs, 

 approximately 90 per cent, of eggs under these conditions failing to hatch. Shade 

 and moisture are favorable to them. 



The number of broods a year has not been worked out, but we have been 

 able to trace three and believe there may be a fourth, because third brood adults 

 normally begin to emerge by at least the middle of August and as flies continue 

 to emerge throughout most of September and are some years common to the 

 1st of October or later., there is very little doubt that some of these will be 

 fourth brood. As implied above adults of all three broods may be present to- 

 gether in August and September. 



It is interesting to learn that no brood, not even the first, is a full one; for 

 a small percentage, some years about 4%, of the overwintering puparia fail to 

 produce adults that year and pass through a second winter before doing so. 

 Strange to say these adults in our test were not among the earliest to emerge the 

 second year, the first of them coining out the first week in June, and the last the 

 last week. Professor Brittain tells me he, too, has found that there is a two- 

 year life cycle for a few individuals. 



The exemption, with a few exceptions, of late crops of cabbage and cauli- 

 flower from serious injury wotdd appear to be due to — first, the greatly increased 

 number and activity of predaceous enemies, chiefly rove beetles, ground beetles 

 and a large red mite, which destroy the eggs or larva? or both; second, to the 

 greater dryness and heat of the soil which lessens the percentage of eggs hatching; 

 and third probably, as Schoene suggested, to the harder texture of the root 

 tissues themselves at this season of the year. 



Prolonged wet, cold weather when adults are about to emerge seems to lessen 

 greatly the number that do so ; for instance in 1919, May was very wet and cold 

 and only 21.9% of the overwintering puparia produced adults, compared with an 

 average of 85% the other three years. 



Very hot weather seems also to have a great effect upon puparia. Last 

 July was exceptionally hot, especially the first half of it, and from the middle 

 of the month to the end of our work — October 1st — scarcely a fly emerged, radishes 

 being 100% clean. Other years flies were present all through this period and 

 radishes always somewhat wormy. 



Control Measures 



(1) Cabbage and Cauliflower: — From all over Canada and from New York, 

 New Jersey and Indiana reports of excellent success from the use of corrosive 

 sublimate have been received. I need not give figures to prove this but simply 

 state that careful treatment will give from 80% to 100% control even in the 

 worst years. Moreover, growers will use this treatment where they woidd not 

 use tarred felt-paper discs. 



Number of treatments: One, well-timed, will give fair results; two, well- 

 timed, are better and are all that should be necessary, but if the timing, especially 

 of the first application, is not well chosen three will be desirable. , 



Length of interval between treatments: On, the average, one : week . seems 

 about right. It should not be longer, a day .less would not, as a rule decrease 

 its value much, and sometimes would even increase it, = 



