TEMPERATURE-DEPENDENT MODELS TO PREDICT REGIONAL DIFFERENCES IN CORN-ROOTWORM (COLEOPTERA, CHRYSOMELIDAE) PHENOLOGY

Western corn rootworms, Diabrotica virgifera virgifera LeConte, only r ecently have become a serious corn pest in New York and other states i n the Northeast. Because soil conditions, topography, and climate diff er from the Midwest cent belt, questions arose as to the validity of p reviously published phenology models. Our study evaluated larval occur rence and adult emergence of western and northern corn rootworm, D. ba rberi Smith & Lawrence, in 11 fields in central New York during 1991 ( 2 fields), 1992 (3 fields), and 1993 (6 fields). Logistic regression m odels predicted cumulative occurrence/emergence from Julian date or de gree-day accumulations calculated from either soil (base 11 degrees C) or air temperatures. Air temperature degree-days were calculated for minimum thresholds ranging from 1-16 degrees C. Additional threshold a ccumulations were determined by varying the maximum developmental thre shold from 1 degrees C above the lower threshold to 30 degrees C. Mini mum thresholds in the latter series of calculations were set equal to 4, 6, 9, and 11 degrees C. Julian date was a relatively poor predictor of all immature and adult stages. However, accuracy of air temperatur e models was dependent on choice of thresholds. The best fitting air t emperature models either used minimum developmental thresholds near 6 degrees C for immature stages and 1-2 degrees C for adult emergence or calculated degree-days using a minimum threshold of 11 degrees C and a maximum threshold of 18 degrees C. Both soil and air temperature mod els indicated regional differences in immature development and adult e mergence. Although site-specific models gave the best prediction of we stern corn rootworm adult emergence, adult emergence at New York and I llinois sites could be predicted by adjusting daily air temperature de gree-days by the expected accumulations from 1 January to 30 September .