Factors affecting the distribution and abundance of the southwestern corn borer, Diatraea grandiosella, in the central United States

The primary goal of this research was to examine the characteristics of, and factors determining the northern range limit of the southwestern corn borer (SWCB) in the central United States. The historic range limit was compared to combinations of climatic factors. Although the northwestern range limit was associated with winter temperature isotherms, summer degree-day isolines provided a better fit across the entire northern range limit. Comparison of low temperature mortality measured in the laboratory with temperatures measured in overwintering locations near the northeastern range edge indicated that winters typically are not cold enough there to result in substantial mortality of dry larvae. There was also no evidence that selection for increased cold hardiness had occurred in that region. These data suggest that winter mortality is not a limiting factor in the northeastern part of the range as had previously been assumed. Rather, they suggest that some factor associated with summer temperatures is responsible for the range limit.;Flight curves derived from pheromone trapping, and fall observations of diapausing larvae were compared to temperature and maize phenology data to evaluate potential effects of specific limiting factors. A deficit of degree-days to complete development at the range edge was the most strongly supported of the hypotheses considered. Developmental rates of larvae originating at the range edge were faster than those of larvae near the range center, a result consistent with this hypothesis. Abundance profiles derived from historical survey data and pheromone trapping indicate that where a relatively stable range limit has been reached, it is the result of a steady decline in abundance toward the range edge that is directly associated with a decline in summer degree-days. The current 12 km/yr range extension in southwestern Indiana was documented at a high spatial resolution. Historic records of this exotic species' invasion of the central U.S. suggest that summer degree-days may strongly influence the rate of range extension as well.