60 MASS. EXPERIMENT STATION BULLETIN 388 



orchards the injury was negUgible, and even in the smaller home orchards which 

 received little attention the pest was not conspicuous. 



This reduction is not believed to be due to any marked increase in energy on 

 the part of the growers or to any improvement in the handling of dropped fruit 

 or other precautionary measures. It is the general belief that adverse weather 

 conditions and especially deficient rainfall at the period of normal emergence 

 of the flies were the chief contributing factors. 



In the emergence cages at Waltham the flies began to appear on June 19 which 

 is the earliest date since the observations were started. Although the cages were 

 operated in the same way as in the previous years, the emergence in the culti- 

 vated cage was greater than usual and that in the sod much smaller than usual. 

 This condition is apparently correlated with the deficiency of soil moisture this 

 year. The emergence record is as follows: 



In Sun — Light Soil 

 Cultivated Sod 



Degree of Emergence: 



First fly June 19 June 24 ' 



25% June 30 July 3 



50% July 7 July 9 



75% July 12 July 15 



100% August 7 July 27 



Number of larvae in 1940 400 400 



Number of flies emerged 1941 207 43 



Percent emergence 51 .75 10.75 



Insecticides for the Control of European Corn Borer. (A. I. Bourne and \V. D. 

 VVhitcomb.) The unsea.sonably warni weather throughout April promoted ab- 

 normally early pupation of the overwintering corn borer larvae. Seasonable 

 weather in May allowed development to progress normally and resulted in a 

 very early emergence of the spring brood of moths. On the other hand most of 

 the growers planted corn at the usual time, with the result that considerable 

 moth emergence took place before corn was above ground or at least when it was 

 too small to be attractive for oviposition. In addition, during much of the time 

 that the moths were present the temperatures at dusk were too low for moth 

 activity. As a result the infestation by first generation larvae was negligible 

 throughout the State. Growers harvested very clean corn even where no control 

 measures were practiced, and in fields which were sprayed or dusted there was 

 slight evidence of the borer. 



In the experimental fields the plots sprayed with derris and Ultrawet showed 

 4 infested ears out of 660, 99.4 percent clean corn, 84.5 percent of which was 

 grade 1 or 2; in other words, 84 percent of the total yield was marketable grade. 

 A fixed-nicotine spray gave 97.1 percent clean corn, 84 percent of which was 

 marketable. In the plots dusted with derris there were 4 infested ears in a total 

 of 652, 99.4 percent clean corn, 90 percent of which was of marketable grade. 

 Dual-fixed nicotine dust gave 98.8 percent clean ears, and 84 percent of the total 

 yield was of marketable grade. The infested ears were so few that the grower 

 made no effort to salvage them. The unsprayed check plots yielded a total 

 of 682 ears, 48 of which were infested. In other words the infestation was so 

 light that 92.9 percent of the yield was free from borers. In the entire field, re- 

 gardless of treatment, only 83 ears out of 3,341 examined weve infested. No 

 attempt was made to spray late corn because of the scarcity of 2d brood larvae. 



The infestation by the first generation of the European corn borer in the ex- 

 perimental planting at Waltham was so light that results of spray applications 



