Two laboratory strains of tobacco budworm (Heliothis virescens, F.) were evaluated for the ability to cause fruiting structure damage on cotton (Gossypium hirsutum, L.) in a small plot field trial during the 1999 growing season. The two colonies are reared under different rearing systems as well as for different intended research purposes. The Dow AgroSciences (DAS) colony (Indianapolis, IN) is reared for the purpose of maintaining consistent year to year laboratory bio-assay evaluations of foliar applied instecticides. Alternately, the colony obtained from the insectary of the Corn/Cotton Host Plant Resistance Research Units, at the U.S.D.A, Agricultural Research Service (A.R.S.) facility at Starkville, MS is reared for the express purpose of artificially infesting field plots in order to evaluate cotton lines for host plant resistance. While there are various housing and minor nutritional differences between the two colonies, a major difference in the two rearing systems is that A.R.S. scientists out-cross their laboratory females with natural population "wild" males on an annual basis in the Fall of each year. The progeny from the cross are then used to begin a new colony and the old colony is discarded. The DAS budworm colony has not been out-crossed to a natural population in over 15 years. Sampling data averaged over 6 weeks showed that the A.R.S. tobacco budworm colony closely exhibited a 2:1 difference over the DAS colony in terms of greater damage and a 3:1 difference in greater larval presence in squares and bolls under field conditions. Seed cotton yield data showed that there was a reduction in yield in the A.R.S. budworm infested plots of 12% from the non-infested control plots and a 15% reduction in yield from the DAS budworm infested plots. There was no difference in yield in the DAS budworm infested plots when compared with the non-infested control plots. The research appears to show that laboratory reared colonies of tobacco budworm used for artificial infestation on cotton can differ in the ability to cause fruit damage under field conditions. Out-crossing a laboratory colony with natural population insects seems to play a major role in enhancing the ability of the progeny to aggressively damage fruit under field conditions when using artificial infestation methods. This in turn may increase the reliability of germplasm screening techniques for host plant resistance, or other pesticide screening research that involve plant/insect interactions.