Effect of Bt cotton expressing Cry1Ac and Cry2Ab, non-Bt cotton and starvation on survival and development of Trichoplusia ni (Lepidoptera: Noctuidae)

Authors: LI, Y. - TAES, WESLACO, TX; Greenberg, Shoil; LIU, T. - TAES, WESLACO, TX

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/13/2006
Publication Date: 4/23/2007
Citation: Li, Y.X., Greenberg, S.M., Liu, T.X. 2007. Effect of Bt cotton expressing Cry1Ac and Cry2Ab, non-Bt cotton and starvation on survival and development of Trichoplusia ni (Lepidoptera: Noctuidae). Pest Management Science. 63:476-482.

Interpretive Summary: Cabbage looper, as a secondary cotton pest, may likely become a major pest because the cotton boll weevil eradication program is currently in action, and natural enemies in cotton are under high adverse pressure from multiple applications of insecticides to control the boll weevil. Growers are aware, that in this case, the risk of secondary pest outbreaks will be increased and Bt cotton has proven to be a useful tool for controlling caterpillar pests, and augments activity of beneficial insects. Bt cotton, especially under the boll weevil eradication program, provides management options that have positive environmental, social, and economic outcomes. Understanding the effects of Bt cotton on cabbaged looper and other pests is certainly essential for developing appropriate strategies to prevent resistance.

Technical Abstract: Effects of Bollgard II cotton containing two Bacillus thuringensis va. kurstaki (Bt) toxin proteins (Cry1Ac and Cry2Ab), non-Bt cotton ('DPL 491') or no-food (starvation) on cabbage looper, Trichoplusia ni (Hubner), were determined in the laboratory. Our results show that the first four larval instars were instantly killed when they fed on the terminal leaves of Bt cotton plants at 50 days after planting (DAP). However, 51.3% of the fifth instars that fed on 50-DAP Bt cotton leaves pupated and 87.1% of the pupae successfully developed into adults. Of the starved fifth instars, 5l.6% pupated and 88.l% of the pupae developed to adults. The pupae that developed from the starved larvae and those fed on Bt cotton were significantly smaller, being 73.2% and 89.7% of the weight of the pupae that developed from the larvae that fed on non-Bt cotton leaves. Leaves of the 120-DAP Bt cotton were less toxic to T. ni larvae. When first instars were continuously fed on 120-DAP Bt cotton leaves, 75.9, 60.6, 56.4 and 38.4% of larvae survived to second, third, fourth, and fifth instars, respectively, and 20.9% pupated and 17.9% of the pupae successfully became adults. However, it took the surviving first instars 37.l d to become adults, which was 7.2 and 8.9 d longer than those fed on 50-and 120-DAP non-Bt cottons, respectively. Pupae that developed from larvae fed on 120-DAP Bt cotton were only 50.9 and 52.6% of the weights of those developed from larvae fed on 50- and 120-DAP non-Bt cottons, respectively. Non-Bt cottons, both 50-DAP and 120-DAP, did not exhibit significant effects on larval survival and development except that the pupae in the 50-DAP non-Bt cotton treatment took significantly longer to develop than those in the 120-DAP non-Bt cotton treatment.