Effect of bacillus thuringiensis (bt)–cotton protein endotoxins (cryiac and cry2ab2) on below ground fauna diversity with reference to entomopathogenic nematodes

Abstract

This study was conducted with the aim of determining the impact of genetically modified (GM) cotton on the diversity of below ground fauna. The entomopathogenic nematode, Steinernema karii infectivity to the larvae of the wax moth was also used to determine the effect of Bacillus thuringensis-cotton protein endotoxin on below ground biodiversity. Soils from theconfined field trial area had a diverse fauna that included Hemiptera, Hymenoptera, Coleoptera, spiders, wireworms and chaffer grabs. Cotton containing Bt series, non Bt cotton and kenaf were grown in pots under confined conditions and uprooted at flowering stage. Soils from the rhizosphere (soils that adhered to the roots) were tested for the presence of Bt endotoxin using the Quick Stix Comb strip method and were found to be positive for the endotoxin even within non Bt treatments. Those soils werethen inoculated with S.karii and fifth instar larvae of the wax moth, Galleria mellonella in the laboratory. Cadavers of Galleria larvae were recovered from the soils over a period of 10 days and dissected to confirm the cause of mortality. Data was transformed using SQRX + 1, subjected to Analysis Of Variance (ANOVA) and means separated using LSD. Results from the study showed that there were no significant differences between treatments. Galleria larva mortality due to S. karii infections were 64%, 63%, 61% and 50% for HART89M, sterilized soil, Bt cotton and Isoline treatments respectively. A number of false positives were recorded during the experiment for the Bt toxin implying that further refinement of the Quick Stix comb strip technique is required.