The study was conducted as part of our ongoing program to monitor the performance of LARVIN^® brand thiodicarb, Bolstar^® brand sulprofos, Decis^® brand deltamethrin and Sherpa^® brand cypermethrin against tobacco budworm H. virescens larvae collected from different sites in the USA cotton belt.

The 1993 results showed the four insecticides to be highly effective against the larvae obtained from sites in the south-eastern part of the cotton belt. As expected, the four compounds did not perform as well against the larvae collected from sites in the mid-south and the south-western part of the cotton belt. A careful examination of resistance ratios indicated that larvae in mid-south and south-western parts of the belt possessed significantly higher levels of resistance to Sherpa^® and Decis^® than to Larvin^® or Bolstar^®.

The results collected in the last five years illustrated gradual improvement in the toxicity of Larvin^® to the larvae collected from sites in Texas and Louisiana. It showed consistent activity against the larvae collected from sites in North Carolina. We detected a slight difference between the toxicity of Larvin^® to eggs collected from resistant and susceptible tobacco budworm populations. This provides a partial explanation for the consistent performance of Larvin^®.