Effect of Bt cotton on important insect pests and their natural enemies
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Date
2017
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Punjab Agricultural University, Ludhiana
Abstract
The studies on the effect of Bt cotton on some important pests and their natural enemies were
conducted at Punjab Agricultural University, Ludhiana during 2015 and 2016. The Cry toxin
concentration estimation at the three trophic levels of Bt cotton plant, prey (Aphis gossypii Glover) and
predators, Cheilomenes sexmaculatus (Fabricius) and Chrysoperla zastrowi sillemi (Esben-Petersen)
revealed maximum Cry1Ac and Cry2Ab concentration in cotton leaves in the treatment of 60 days old
Bt plants and minimum concentration in cotton leaves of 40 days old Bt plants. While, in similar
experiment with Bt cotton leaves, prey (Bemisia tabaci Gennadius) and predators (C. sexmaculatus and
C. z. sillemi), maximum Cry toxins concentration in Bt cotton leaves was observed at 70 days and
minimum concentration in 110 days old Bt plants. In the tritrophic experiment of Bt cotton, aphid and
C. sexmaculatus at second trophic level, we found mean values of 0.24, 0.41µg/g FW of Cry1Ac and
Cry2Ab toxins respectively, in aphids reared on Bt cotton. Whereas, in Bt cotton, whitefly and C.
sexmaculatus tritrophic experiment, 0.31, 0.52 µg/g FW of Cry1Ac and Cry2Ab toxins were detected
in whiteflies. Further, the flow of these toxins in the predator, C. sexmaculatus adults has been
recorded with the values of 0.04, 0.09 µg/g FW of Cry1Ac and 0.07, 0.19 µg/g FW of Cry2Ab toxins
in case of aphid and whitefly feeding. In the tritrophic experiment of Bt cotton, aphid and C. z. sillemi
at second trophic level, mean values of 0.20, 0.38 µg/g FW of Cry1Ac and Cry2Ab toxins respectively,
were recorded in aphids reared on Bt cotton. Whereas, in Bt cotton, whitefly and C. z. sillemi tritrophic
experiment, 0.24, 0.37 µg/g FW of Cry1Ac and Cry2Ab toxins were detected in whiteflies. At the third
trophic level in predator, C. z. sillemi adults, 0.06, 0.07 µg/g FW of Cry1Ac and 0.08, 0.09 µg/g FW of
Cry2Ab toxins were recorded in case of aphid and whitefly feeding.When the Bt toxin reared prey, A.
gossypii and B. tabaci were used in the tritrophic feeding bioassay experiments with C. sexmaculatus
and C. z. sillemi, no significant indirect effects of Cry toxins were observed on the various
developmental and reproductive parameters of both the predators. Though, slightly lower larval
survival, fecundity, adult emergence and longevity were recorded in predators fed with Bt reared prey.
In the abundance and diversity studies in Bt and non-Bt cotton under field conditions, a total of 70 and
73 species of arthropods distributed over 12 orders belonging to 48 and 50 families were found to be
associated with the cotton crop during 2015 and 2016, respectively. Among the different categories of
the pests, four species of target insect pests, nine species of sucking insect pests, 25 species of natural
enemies and 32 and 35 species of non-target insects were recorded from Bt and non-Bt cotton during
two years. BG II cotton did not significantly affect the arthropod abundance, species richness and
diversity indices of arthropods with some exceptions of target insect pests (bollworms) as their
population was negligible in the Bt treatments. The abundance of sucking insect pests was significantly
more in Bt cotton plots during the year 2015 in comparison to 2016. Moreover, arthropod abundance,
species richness and diversity indices were more under unprotected conditions as compared to treated
plots in Bt and non-Bt cotton. On the whole, cultivation of BG II cotton did not pose any adverse effect
on biodiversity including natural enemies found in cotton ecosystem.
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