Impact of Cry1AB toxin from transgenic maize (Mon 810) and microbial BT spray (Dipel) on the ecology of a non-target parasitoid, Cotesia marginiventris

Abstract

Cry1Ab toxin derived from Bacillus thuringiensis (Bt) has been used for the control of susceptible lepidopteran species throughout the world. Currently, sprayable Bt formulations and transgenic plants have been used for lepidopteran pest control. As plants and insects are part of a complex multitrophic system, using Bt toxin may also affect non-target organisms and thus pose an environmental risk. This research was conducted under controlled laboratory conditions – first tier lab testing on the second (Spodoptera littoralis) and third trophic levels (Cotesia marginiventris).
Spodoptera littoralis were fed with four different types of maize leaves; non-transgenic isogenic control, transgenic (MON810), and isogenic control plants sprayed with a control spray or Bt spray (Dipel). S. littoralis larvae maintained on non-transgenic maize leaves from day 6 to day 20 were significantly heavier when compared to the other maize treatments. No significant effect of Cry1Ab toxin was observed on the survival and pupation time of S. littoralis larvae. The groups exposed to transgenic maize were shown to have the lowest weight of parasitized S. littoralis larvae at 2 and 5 days after parasitism, and also the lowest weight of parasitoid cocoon.
The behaviour of Cotesia marginiventris with S. littoralis hosts (same age or same size) in no-choice tests was observed. Time taken to the first attack took significantly longer in the same-age host fed either transgenic maize or Bt spray maize when compared to control maize-fed hosts, however this did not differ in the same-size host. Time to cocoon formation and adult emergence was significantly shorter in the same-age larvae fed on non-transgenic maize when compared to other maize-fed hosts. In the parasitoid developed within same-size hosts, no significant differences in the time to cocoon formation and adult emergence were observed. Moreover, the number of parasitoid cocoons and adults were significantly higher in the same-age host fed on non-transgenic maize, while in the same-size hosts showed no significant difference in these numbers. The results would suggest the attack of parasitoid may be due to the size and age of the hosts. To conclude, the low parasitism and non-emergence of parasitoids observed may be due to the decreased quality of hosts that can not provide sufficient nutrients for development of parasitoid larvae. This present study has helped to understand the direct or indirect effects of Cry1Ab on the non-target insects in the tri-trophic systems that could lead to the changes on host-parasitoid population dynamics in the ecosystem. The ecological relevance of the present study is discussed within a wider context of risk assessment in the environment.

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