Location: Chemistry ResearchTitle: Resistance monitoring of Heliothis virescens to pyramided cotton varieties with a hydrateable, artificial cotton leaf bioassay Author
|Cabrera Cordon, Ana|
Submitted to: Crop Protection Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/9/2011
Publication Date: 7/1/2011
Citation: Cabrera Cordon, A.R., Kreschmar, J.V., Bacheler, J.S., Burrack, H., Sorenson, C.E., Michael, R.R. 2011. Resistance monitoring of Heliothis virescens to pyramided cotton varieties with a hydrateable, artificial cotton leaf bioassay. Crop Protection Journal. 30:1196-1201. Interpretive Summary: Tobacco budworm is an important pest of cotton and other crops. The growth of transgenic cotton expressing a toxin from the bacteria Bacillus thuringiensis (Bt) has helped manage this pest. However, there is need to monitor populations of tobacco budworm in Bt-cotton fields to prevent or delay the development of resistance. Scientists at CMAVE and North Carolina State University developed a bioassay to monitor Bt-resistance in tobacco budworms using two Bt-cotton varieties (Bollgard II and WideStrike). They found that the leaf extracts from Bt-cotton leaves can be used to rehydrate an artificial diet, which served as food for newly hatched tobacco budworm larvae, and that the number of fecal pellets produced by the larvae after 24 h was an indication of susceptibility or resistance to Bt-cotton. This is important because cotton growers have a new monitoring tool they can use in the field to diagnose, prevent and/or manage resistance of this cotton pest.
Technical Abstract: Proof of concept was demonstrated for a practical, off the shelf bioassay to monitor for tobacco budworm resistance to pyramided Bt cotton using plant eluants. The bioassay was based on a previously described feeding disruption test using hydrateable artificial diet containing a blue indicator dye, a diagnostic dose of insecticide, and novel assay architecture. Using neonate larvae from a Bt-susceptible, laboratory reared tobacco budworm strain, a diagnostic dose for Bollgard II and WideStrike cotton was obtained that limited neonate blue fecal production to 0-2 pellets in 24 h (Bt-resistant larvae produced >2 fecal pellets). The bioassay was tested with three different field populations of tobacco budworm collected from tobacco in central North Carolina (USA) and shown to accurately diagnose susceptibility to Bt. The diagnostic doses were also successfully evaluated with two Bt-resistant, laboratory reared tobacco budworm strains. Shelf-life studies showed the assay could be stored for at least 6 months at room temperature (longer storage times were not studied). The application of the bioassay as an easy to use monitoring tool is discussed.