ANNUAL REPORT, 1938 65 



was the last variety to succumb to blast, remaining upright and comparatively 

 free from thrips when the plants in all other plots were flat. 



Insecticides for the Control of European Corn Borer. (A. I. Bourne.) The 

 weather during the month of April was unusually mild and at the end of the month 

 the season was considerably in advance of normal. May, however, was more 

 nearly normal although there were several periods when the temperature at dusk 

 was unseasonably low and frosts occurred at intervals as late as the last 2 days 

 of the month. Pupation of European corn borer larvae began much earlier than 

 usual. Observations in southern Hampden County showed that on light, earlv 

 soil from 75 to 100 percent pupation had taken place by May 11. Moths from 

 material collected on that date began to emerge on May 16. In heavier soil and in 

 less exposed fields pupation was considerabh' later, and emergence was delayed 

 by the comparatively cooler weather during May. The low temperature at dusk 

 and the frost late in the month retarded the activity of the moths and corres- 

 pondingly prolonged the period of egg laying, while the irregularity in develop- 

 ment in different fields was much greater than normal. Under such conditions 

 accurate timing of the first application of sprays or dusts was particularly difificult. 



Field tests with 3 dusts, dual-fixed nicotine, cube-vatsol, and a commercial 

 rotenone, and with 4 sprays including ground derris, cube, and 2 commercial 

 rotenone sprays, were conducted in a commercial planting in Hampden County. 

 Both sprays and dusts were applied at 5-day intervals from June 10 to June 25, 

 the first application based on the general appearance of the young larvae. 



The infestation throughout the entire planting of several acres was verj' heavy. 

 Unsprayed corn yielded only 25 to 35 percent borer-free ears in the first picking 

 and approximately 16 percent in the second. 



All of the insecticides proved toxic to corn borer larvae and furnished satis- 

 factory protection for the period covered by the schedule. The degree of control 

 was not so high as in previous experiments owing partly to the unusually severe 

 infestation and partly to the comparatively large number of larvae appearing 

 very early as a result of the abnormal season. 



The sprays gave satisfactory protection and the dusts fair commercial control 

 on the basis of the borer-free ears harvested. The real value of the insecticidal 

 treatments, however, is indicated by the relative proportion of the total yield 

 which was of marketable grade. In the dusted plots from 62 to 65 percent of the 

 crop was borer free and 50 to 56 percent was of marketable grade; in the sprayed 

 plots from 75 to 80 percent of the total yield was borer free and 57 to 60 percent 

 marketable; while in the unsprayed plots only 16 percent of the crop was borer 

 free and less than 12 percent of the ears were fit for market. 



The corn in the experimental plots matured very early and the entire crop was 

 harvested by July 19. Because of the heavy infestation of other early corn in 

 the market, the grower found a great demand for his crop and realized a sufficient 

 premium on his borer-free corn to receive from his whole planting a return of 

 approximately 3 to 4 cents per ear. 



Insects Concerned in the Dispersal of Dutch Elm Disease. (W. B. Becker.) 

 Studies on the biology of the native elm bark beetle, Hylurgopinus rufipes, were 

 continued. A progress report on part of the work follows: 



Examination of the contents of some larval galleries of H. rufipes showed that 

 the number of instars varied, as many as eight exuviae being found in one com- 

 pleted gallery. A study of larvae of one generation collected at about weekly 

 intervals from a pile of American elm logs, indicated that five instars was the 

 most common number under the conditions of the experiment. A detailed account 

 of the study will be published. 



