Movement of Stalk Borer Larvae (Lepidoptera: Noctuidae) from Noncrop Areas into Corn

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Abstract
Stalk borer, Papaipema nebris Guenée, populations in noncrop, grassy areas and border rows of corn were intensively sampled to investigate movement characteristics of larvae. Plant samples and linear pitfall traps were used to determine population densities and movement patterns. Analysis of data indicated a significant interaction between plant speciesand larval size, with first through fourth instars found most often in grasses. However, the proportion of larvae within broadleaf plants increased sharply for instars five through eight. A decline in stalk borer density in grassy areas was followed by an increase in density in bordering corn rows. Capture of stalk borers in pitfall traps coincided with changes in densities within plant samples. Pitfall traps indicated that moving larvae were mostly fourth through sixth instars. Trap captures also indicated a similarity in movement pattern between years, with first capture at ca. 600 degree-days (DD) and 50% capture ca. 900 DD (base temperature, 5.1°C [accumulated from 1 January]). Little movement was observed after 1,100 DD. Regression equations were derived to predict larval density and percentage damaged plants within the first two corn rows, based on mean stalk borer density in noncrop areas.