The occurrence of pyrethroid resistance in field populations of the tobacco budworm, Heliothis virescens (F.), has been known for several years. Pyrethroid resistance in the mid-south has been verified several times, and development of resistance has been evaluated using a variety of bioassays. Recently, tobacco budworm larvae were collected in cotton in which pyrethroids failed to give control (Delta City, Miss., 1989). Resistance to pyrethroid, carbamate, organophosphate, and formamidine insecticides in this collection was evaluated in laboratory tests for one year. Eggs, adults, and two larval instars were tested. Testing with a residual plant bioassay indicated high levels of resistance to two synthetic pyrethroids and tolerance to a carbamate. Resistance was stable in the laboratory for more than five generations. Resistant neonate larvae were nearly susceptible to rates which indicated resistance when applied to third instars. Some resistance was detected in the eggs. This area was sampled again this past season (1990); pyrethroid resistance was the same as 1989. However, carbamate resistance had increased.

In August, 1990, adult tobacco budworms were collected from cotton in northeast Louisiana at Hebert (Caldwell Parrish) in an area where control problems were occurring. Residual plant bioassays indicated high levels of resistance to synthetic pyrethroids and a carbamate, with increased tolerance to three organophosphates. Two fields sampled in northwest Louisiana at the Red River Research Station (Bossier Parrish) yielded larvae which responded similarly to the Hebert collection. Two additional fields, one at Lake Providence, La., the other at Friar's Point, Miss., also yielded larvae resistant to several classes of insecticides. Cross resistance was also confirmed to thiodicarb and methomyl.

This is the first report of resistance in field Populations of tobacco budworm to the carbamate thiodicarb. The mortality response levels found with the organophosphates sulprofos, profenofos, and acephate are a cause for concern, particularly since tobacco budworm has exhibited resistance to organophosphates in the past.When faced with control failures, alternative classes of insecticides should be used. However, as resistance to additional classes of insecticides increases, fewer options remain available. Increased research on alternative control measures and strategic use of available chemical control measures are needed to effectively maintain commodity profitability.