Analysis of Spatial Patterns and Sequential Count Plans for Stalk Borer (Lepidoptera: Noctuidae)

Abstract

Stalk borer larvae, Papaipema nebris (Guenee), were sampled from noncrop, grassy areas and adjacent corn rows to investigate seasonal changes in dispersion and to develop a sampling program for this pest. Regression coefficients for Taylor's power law and Iwao's mean crowding regression indicated an aggregated spatial arrangement for stalk borers in noncrop areas. This aggregated pattern was attributed to the oviposition behavior of stalk borer adults. Although coefficients of Taylor's power law are thought to be species-specific constants, both Taylor's power law and Iwao's mean crowding regression reflected significant changes in dispersion between plants in a row, with dispersion varying from regular to slightly aggregated. We hypothesized that radical changes in behavior, such as movement from grass to corn, may alter spatial distribution. A high correlation between Taylor's power law coefficients, a and b , suggests that a may reflect aggregation rather than being a speciesspecific constant as previously suggested by Taylor. Additional analysis of dispersion between sections of row showed that larvae tended to be aggregated, with clump size a single individual. Single-stage sequential count plans for noncrop areas and two-staged, fixed- k , sequential count plans for corn that are suitable for intensive population research and pest management surveys were developed and discussed.