PREDICTING MOVEMENT OF STALK BORER (LEPIDOPTERA, NOCTUIDAE) LARVAE INCORN

The stalk borer [Papaipema nebris (Guenee)], is a sporadic, yet seriou s pest of corn, (Zea mays L.), in the midwestern USA, particularly whe re corn fields are adjacent to grassy areas, such as roadside ditches, grass waterways, and terraces. An important management strategy is to apply an insecticide when the larvae move from the initial grass or b roadleaf hosts to corn hosts. After the larvae bore into corn stalks, they are much more difficult to manage. Therefore, predicting the move ment of larvae from weed hosts to corn hosts is crucial. This study wa s conducted to determine probable dates for stalk borer larval movemen t using climatic data from 67 locations across portions of South Dakot a, Nebraska, Kansas, Minnesota, Iowa, Missouri, Wisconsin, Illinois, M ichigan, and Indiana. We also examined the difference in probable date s of larval movement using the entire climate data record (60-90 yr) a s opposed to using the 30-yr climatic normal record (1961-90). The min imum number of degree-days (780 Celsius degree-days 4.4 degrees C base temperature) in which larvae move from initial weed hosts to corn, we re accumulated for each year in the climate record beginning 1 March a nd correlated with calendar dates. The mean date of larval movement in the in the states examined spans approximately 3 weeks, from 2 June i n the southern portions to 23 June in the northern portions. Standard deviations about the mean date of larval movement were 5, 6, and 7 day s in the southern, central, and northern portions, respectively. There was little difference between predicted dates using long-term climati c data compared to those using 30-yr climatic normal data. (C) 1998 El sevier Science Ltd. All rights reserved