• Looking for Functional Non-Target Differences Between Transgenic and Conventional Cottons: Implications for Biological Control

      Naranjo, Steven E.; Ellsworth, Peter C.; USDA-ARS, Western Cotton Research Laboratory, Phoenix, AZ; University of Arizona, Maricopa, AZ (College of Agriculture, University of Arizona (Tucson, AZ), 2002-06)
      Evaluations of the non-target effects of transgenic cotton, modified to express the insecticidal proteins of Bacillus thuringiensis (Bt), have been underway in Arizona since 1999. Here we provide a preliminary report of replicated field studies conducted from 1999 to 2001 to examine comparative affects of Bt cotton on natural enemy abundance, overall arthropod diversity, and natural enemy function. Analyses completed to date indicate that natural enemy abundance and overall arthropod diversity are affected by use of additional insecticides for other pests, but not directly by transgenic cottons in comparison with non-transgenic cottons. Further studies suggest that natural enemy function, measured as rates of predation and parasitism on two key pests (Pectinophora gossypiella (Saunders) and Bemisia tabaci (Gennadius)) of cotton in the western U.S., is unaffected in Bt cotton. Our preliminary results suggest that use of transgenic cotton may not have any unintended effects and represents an extremely selective pest control method that could facilitate the broader use of biological control and IPM in an agricultural system long dominated by the use of broad-spectrum insecticides.
    • Transgenic Comparisons of Pink Bollworm Efficacy and Response to Heat Stress

      Ellsworth, Peter C.; Moser, Hal; Henneberry, Tom; Majeau, Ghislane; Subramani, Jay; Maricopa Agricultural Center & Department of Entomology, University of Arizona, Maricopa, AZ; USDA-ARS, Western Cotton Research Laboratory (College of Agriculture, University of Arizona (Tucson, AZ), 2002-06)
      Fifteen lines from 3 different cotton families were compared. Each family had a conventional, non-transgenic standard, as well as 4 other transgenic lines. In some cases, near isogenic lines were available that theoretically only vary from their sibling lines in the presence or absence of one or more transgenes. Each Bt line was evaluated for this trait’s efficacy in controlling pink bollworm under high pressure, artificial infestations. Various agronomic properties were measured including yield, micronaire, ginning properties, and fiber quality. Heat tolerance, a key goal for Arizona adapted varieties, was also evaluated using a flower rating system. The Cry1Ac gene performed flawlessly in preventing PBW larval development when expressed alone (Bollgard®) or in combination with Cry2Ab (Bollgard II®) (i.e., 100% effective, 0 large larvae from 30185 PBW entry holes). In all cases where large larvae were found in Bollgard or Bollgard II plots, the plants bearing the infested bolls were not expressing the Cry1Ac toxin. Thus, those few times when larvae were found, it was due to contaminants in the seed supply. The novel Cry2Ab only expressing plants, produced for non-commercial testing purposes, were also very effective in controlling PBW large larval development; however, control was less than the Cry1Ac-expressing lines (99.622%, 3 large larvae from 4436 entry holes). The ramifications of this are discussed. In terms of agronomic performance, the transgenic lines performed similarly within families and usually not different from the conventional standards. In some cases, statistically different results were found; however, in all but a few cases, performance parameters were superior in the transgenic lines when compared to the conventional standard. Even so, there are instances where characteristics of the transgenic line were inferior to the conventional standard, especially in some fiber properties. Heat tolerance was again similar throughout 2 of the cotton families (SG125 and DP50). However, for the DP5415 family, 3 of the 4 transgenic lines outperformed the conventional standard. More testing under more environmental conditions is warranted before firm conclusions are drawn.