Linda Benedict | 11/19/2004 1:04:54 AM
Stephen Micinski, Donald R. Cook, B. Rogers Leonard, Ralph D. Bagwell, Eugene Burris and Alexander M. Stewart
Resistance monitoring provides a useful tool for detecting changes in the insecticide susceptibility of field populations of insect species from year to year. During the late 1980s and into the 1990s, resistance monitoring of the tobacco budworm provided data for establishing and modifying the tobacco budworm resistance management plan implemented by Arkansas, Louisiana and Mississippi. Resistance monitoring also helps validate whether field control failures are the result of a true decrease in insecticide susceptibility or whether other factors should be examined to determine the cause of unsatisfactory control.
Development of resistance in a key cotton pest to a particular chemical or class of chemicals can threaten the profitability of the industry. This is especially true when other integrated management strategies, including alternative chemicals for that pest, are limited.
In the Mid-South, two of the most devastating cotton pests are the bollworm and tobacco budworm. The pyrethroid insecticides provided the most economical control of these two pests during the 1980s and into the 1990s. In Louisiana, pyrethroid resistance monitoring was initiated in 1986 for the tobacco budworm and in 1988 for the bollworm. Additionally, these two pests were monitored for susceptibility to a non-pyrethroid insecticide, spinosad (Tracer), beginning in 1991 for the tobacco budworm and in 2000 for the bollworm. Spinosad represents a new class of chemicals called naturalytes.
Monitoring involves the collection of male moths with wire cone traps baited with an artificial sex pheromone lure. These traps were located in several parishes across the cotton production regions of the state. Adult male moths collected from these traps were placed in glass vials treated with one of the selected insecticide concentrations or in nontreated control vials. Cypermethrin was one of the earliest pyrethroids used for control of these two cotton pests in Louisiana. Spinosad is one of the most recently registered insecticides for control of these insect pests. Mortality of the moths in both the treated and control vials were determined after 24 hours of exposure. Information presented here is based on seasonal percentage survival of these two cotton insect pests.
Figure 1 shows the percentage survival of the pests in the last 15 years to cypermethrin. Bollworm survival remained relatively constant at a level below 10 percent from 1988 to 1997. During 1998, bollworm survival reached 18 percent and was followed by two years at 16 percent. In 2002, bollworm survival increased to 34 percent.
Tobacco budworm and bollworm survival to spinosad is shown in Figure 2. Tobacco budworm survival in 2002 was extremely high, reaching 52 percent. In 2001, survival was only 11 percent, which was similar to survival observed during the early 1990s. Bollworm survival followed a similar pattern. In general, results were similar to those for tobacco budworm, although overall survival was much lower. The results with spinosad are highly variable and indicate the need to continue to monitor bollworm and tobacco budworm susceptibility to spinosad. At this time, spinosad has never been implicated in any field failures.
Resistance monitoring continues to be an important tool in monitoring the susceptibility of insect populations in the field to various insecticide classes. Monitoring allows entomologists to follow long-term trends in insect susceptibility. It also provides valuable information in determining the possible causes of insecticide field failures when they occur.
Stephen Micinski, Associate Professor, Red River Research Station, Bossier City, La.; Donald R. Cook, Research Associate, Department of Entomology, LSU AgCenter, Baton Rouge, La.; B. Rogers Leonard, Professor, and Ralph D. Bagwell, Associate Professor, Macon Ridge Research Station, Winnsboro, La.; Eugene “Gene” Burris, Northeast Research Station, St. Joseph, La.; and A.M. “Sandy” Stewart, Assistant Professor, Dean Lee Research Station, Alexandria, La.
(This article was published in the 2003 spring issues of Louisiana Agriculture magazine.)