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A BASIC computer program (DEGDAY) for calculating degree-days on microcomputers is presented. The program calculates heating degree-days with the rectangle, triangle, and sine wave methods and calculates cooling degree days with the sine wave method. Assumptionsand approximations associated with degree-day calculations are noted. In particular, eight factors affecting degree-days are discussed: 1) substrate availability, 2) enzyme availability, 3) approximations in laboratory estimates of development, 4) approximations in calculating the developmental minimum, 5) approximations in calculating a developmental maximum, 6) approximations in using single values for thresholds, 7) thermoregulation, and 8) limitations of temperature data. The various errors arising from these factors are discussed in relationship to error attributable to differences between actual and estimated degree-days.

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The European corn borer, Ostrinia nubilalis (Hu¨ bner), causes economic damage to corn, Zea mays L., throughout the Corn Belt. Because this insect has become the primary target of Bacillus thuringiensis Berliner (Bt) transgenic corn, current efforts addressing the management of O. nubilalis resistance to Bt corn require information on adult European corn borer dispersal and factors affecting its dispersal. In 1998 we conducted markÐreleaseÐrecapture, releaseÐrecapture, and caged-mating studies to directly measure and compare local dispersal patterns of O. nubilalis adults within and proximal to irrigated and non-irrigated cornÞelds. Releases of marked adults were made corresponding to the Þrst and second ßight of O. nubilalis in eastern Nebraska. Adult dispersal was signiÞcantly different between irrigated and non-irrigated cornÞelds. Released adults tended to remain in and near irrigated cornÞelds, but dispersed out of and away from non-irrigated cornÞelds. When released at the edge of the cornÞeld, neither male nor unmated female O. nubilalis displayed an initial tendency to move out of irrigated corn and into the mixed smooth bromegrass (Bromus inermis Leyss) and broadleaf-weed Þeld edge. Mating ef Þciency in a late-season cornÞeld was not signiÞcantly different than in dense foxtail (Setaria spp.