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Pesticide Toxicology Laboratory

ISU Entomology / Pesticide Toxicology Laboratory / Impact of Cry3A-intoxicated Leptinotarsa decemlineata (Coleoptera: Chrysomelidae) and pollen on consumption, development, and fecundity of Coleomegilla maculata (Coleoptera: Coccinellidae)

Impact of Cry3A-intoxicated Leptinotarsa decemlineata (Coleoptera: Chrysomelidae) and pollen on consumption, development, and fecundity of Coleomegilla maculata (Coleoptera: Coccinellidae)

Authors: Riddick, E.W., Barbosa, P.
Journal, Volume, Year: Annals of the Entomological Society of America, volume 91(3):303-307, 1998
Summary

Colorado potato beetles were reared on transgenic (Cry 3A) or non-transgenic potato and used in feeding experiments with lady beetles. In studies with just the neonates of CPB, the Bt leaf was toxic to 98% of the larvae after 48 hours of feeding. Larvae fed for 24 hours were used in the trophic studies. The consumption experiments showed that less CPB (by weight) was consumed by C. mac. in the Bt-fed treatments than in the non-Bt fed treatments. However, this was probably due to lower weight of Bt fed CPB. When the C. mac. larvae were given the same initial mass of prey, this difference was negated. In the development studies, 2nd instar C. mac were fed CPB neonates (Bt fed or non-Bt fed) and development to pupae and adulthood was recorded. Twice as many larvae reached adulthood in the Bt free treatment, but this difference was not significant. A comparison was also made between feeding the C. mac. larvae a diet of Bt-fed CPB and bee pollen, or pollen alone. The CPB + pollen treatment developed significantly better. Finally, no effects on fecundity were seen in the experiments.

Comments

A worse case situation might have been better estimated if a later instar CPB were used as they would be more resistant to the effects of the Bt and possibly able to carry more toxin. This would only work if the C. mac. larvae were able to consume the larger CPB larvae. This study was not very consistent in using the same life stage of C. mac. In fact, within a single experiment the instar used was not always the same. In the development study there was a trend toward an adverse effect of the Bt-fed prey, but there was not a significant result. A repetition with a larger number of replicates would be advisable. Also, the experiment examining development on a diet of Bt fed CPB + pollen or pollen alone should have included a treatment of non-Bt fed CPB + pollen.