Abstract
A glass-vial technique was developed to detect permethrin resistance in soybean looper, Pseudoplusia includens (Walker), larvae. Third-, fourth-, fifth-, and sixthinstar soybean loopers from two susceptible (laboratory) and eight field strains were exposed to permethrin using a glass-vial technique to estimate concentration-mortality lines. Probit analysis of results from each field strain indicated that LC5s for third, fourth, and fifth ins tars were not significantly different. Therefore, concentration-mortality lines for each soybean looper strain were estimated by pooling data from these three instars. A discriminating concentration of 0.5μg permethrin per vial was identified for detection of permethrin resistance in field populations of soybean looper larvae. Field strains from cotton-soybean agroecosystems responded similarly and had higher levels of resistance than strains from soybean-com agroecosystems. The reliability of the vial bioassay was confirmed by topical bioassays done on the same populations that had been tested in the vials and a comparison of resistance ratios. Correlation analysis indicated that the vial technique was as reliable as topical bioassays in estimating resistance, although resistance ratios with vials were slightly higher at most locations.
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