Ecological, biochemical and insecticidal studies were carried out on the European corn borer in Manitoba during 1965 and 1966. The insect has been found to be established in Manitoba and to occur as far north as Dauphin. In Manitoba it follows a predominantly univoltine pattern of development but a small number of second generation adults were caught during the summer of 1966. Development of overwintered last-instar larvae proceeds in the spring and by July the adults emerge ... Both laboratory and field studies on the effect of temperature on the rate of development of the corn borer were conducted ... A relationship between the presence of glycerol in the hemolymph lymph of last-instar larvae and their ability to withstand exposures to low temperatures was established. A build-up in glycerol and a lowering of the supercooling point coincided with the onset of low winter temperatures. Prepupae, unlike winter larvae, were very susceptible to sub-zero temperatures ... Pupae survived the freeezing process but not prolonged exposure to sub-zero temperatures. The variations with time in undercooling temperature and glycerol concentration of wet-warmed winter larvae were no different from those of dry-warmed winter larvae ... The winter mortality of corn borer larvae for 1965-66 was 12 per cent. Parathion and Sevin were equally effective in controlling corn borer damage in sweet corn. A systemic insecticide NA-10242 was found to be more effective than D.D.T. or Parathion or Sevin in controlling the corn borer.