The work described here is an attempt to assess the effect of insecticides, particularly DDT, on the more prominent elements of the insect fauna of alsike clover Trifolium hybridum L., and on the yield of seed harvested. The decline in legume seed production, over a period of years, in districts which were once major seed producing areas is a familiar story in North America. For instance, Sorenson (1939) records that in 1925 Utah produced nearly 40 per cent of the total alfalfa seed in the United States. Five years later this state produced less than 4 per cent, the drop being largely the result of a decline in yield from an average of 6.4 to 1.2 bushels per acre. A similar history has been experienced in the production of alsike clover seed in Southern Ontario in the last twenty years. Haldimand County once produced heavy and profitable yields of over 5 bushels per acre but now yield is so poor and unprofitable that it is difficult even to find fields left for Experimental work. No doubt many causes are at work in this reduction but there is good reason to believe that the successful establishment oi specific insect pests, as a large and permanent part of the fauna, has been partly responsible in both these cases.

Certain species of Aedes occurring in North America have been considered difficult if not impossible to identify from adult females alone. Five band-legged species, Aedes excrucians (Walker), A. stimulans (Walker), A. fitchii (F. & Y.), A. riparius D. & K., and A. increpitus Dyar, are in this class. They form a compact group, and female specimens have been very difficult to identify with assurance. Matheson (1944) used mesonotal colour and mesepimeral bristling for separating most specimens of these species. To these characters Gjullin (1946) added the colour of the torus and of the palp, but he also was unable to definitely identify some specimens of excrucians and fitchii. Ross (1947) used the characters employed by Matheson to separate stimlans, fitchii, and excrucians, but admitted that the characters are often unsatisfactory.