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 February, '16] SCHOENE: pegomya brassic.E 137 



After this fact had been determined certain simple experiments 

 were initiated, the results of which have shown that this delay or 

 retardation is much more apparent under some conditions than others. 

 These results are stated tersely as follows: First, when the puparia 

 were held at a temperature in which the daily maximum readings aver- 

 aged 78° F. and the minimum readings averaged 56° F., the so-called 

 delay in development was practically absent, only a small percentage 

 of the individuals being affected. Second, when the puparia were 

 held at a high temperature, such as frequently occurs in western 

 New York, a small number completed their development several days 

 sooner than usual, while others remained quiescent and showed no 

 visible development, while the high temperature was maintained. 

 By holding these retarded individuals at a low temperature some were 

 able to finish their development, though manydied. 



This behavior of the species has been interpreted in the same way 

 as that outlined by Osborn^ and Webster- for the Hessian fly, which is, 

 namely, that high temperature or severe drouth causes a retardation 

 of developing larvae and pupae, which lasts until low temperature 

 returns. 



The effect of this retardation behavior on the Hfe-history of the 

 insect in western New York is very apparent by a study of breeding 

 records and observations made during the summer of 1909 and 1911. 

 In 1909 there were three well-marked broods of adults. The first 

 brood emerged during the latter part of May and the first of June; 

 the second brood flies appeared during the latter part of June and 

 continued to emerge through July, and the third brood emerged 

 during the period of August 26 to September 27. These data were 

 secured by covering large numbers of infested plants with cloth screens 

 and capturing the adults as they issued from the soil. However, the 

 adults were abundant everywhere about cabbage fields during the 

 periods mentioned. In 1911 the situation was very different. The 

 first brood of adults emerged as usual. The second brood was marked 

 by the appearance in cages of a few individuals between June 30 and 

 July 6. No adults emerged in the laboratorj^ between this date" and the 

 first of September. During this period adults were very scarce in the 

 field. A few of our first-brood pupae gave out flies between August 31 

 and September 9, but adults were still very scarce in the field and con- 

 tinued so until the 23d of September. However, they were conspic- 

 uous in cabbage fields from the above date until October 8. The 

 third brood appeared so late that many of the adults, eggs and larvae 

 were destroyed by the cold. 



lU. S. Ent. Bui. 16:24. 

 2U. S. Ent. Cir. 70:11. 



