Every year million hectares of genetically modified (GM) crops, including varieties of soya, maize, tomatoes, potatoes, cotton, tobacco and oilseed rape, are planted for commercial purposes worldwide.
It is important that any potential negative side effects of GM plants are studied in detail and research in this area has clearly expanded and advanced during recent years.
The research group of the Unit of Applied Ecology and Biological Control of ISE-CNR studied the effect of transgenic maize crops both in the laboratory and in open field in order to show a possible effect of Bt corn on non-target insects.
The resistance of pests to Bacillus thuringiensis was studied in the laboratory on populations of Plodia interpunctella, a species of Lepidoptera which usually attacks maize in granaries. Bioassays were carried out using an isolate of B. thuringiensis subsp. kurstaki (Btk) which is active against Lepidoptera larvae, and the mortality rate of the selected treated populations and of subsequent generations was measured.
The results of the trials showed that after treatment with the isolate Btk P. interpunctella can develop resistance, assessed as an increase in LC50, after just one generation, and that this resistance can actually increase by over five times. These findings confirm reports of other authors on resistance phenomena of populations of P. interpunctella induced by different experimental methods.
Chrysoperla carnea was chosen for the laboratory toxicity tests (Fig. 1) because of its important role in the trophic chain since the larvae of this Neuroptera feed on phytophagous insects. It has been found that Chrysopidae larvae need an intake of sweet liquid in the early stages of life as a source of energy for capturing prey. It is in this stage that the insect is more vulnerable and more liable to interact directly with the transgenic plant. However, it has been observed that the juices of Bt-maize, besides having an unpleasant flavour and being of low toxicity, are difficult for the insect to suck directly since it is unable to penetrate the plant's tissues. Toxicity tests with Bacillus thuringiensis kurstaki have shown that C. carnea is sensitive to the toxin which has effects that are both acute, in terms of mortality, particularly of the youngest larvae, and sublethal, reducing the fecundity of the adult females.
In-field investigations were carried out by comparing 2 varieties of maize, one transgenic (Compa CB), which is resistant to Ostrinia nubilalis and Sesamia nonagrioides, and a corresponding isogenic (Fig. 2), non- transgenic variety (Dracma). Population densities of some groups of arthropods living in the maize fields were counted, including phytophagous insects specific to the crop.
The transgenic maize showed good autoprotective capacity up to flowering, after which considerable infestation by the two target lepidopters occurred. The results, obtained by comparing the number of insects observed and/or captured in the plots of the two varieties, indicate that the transgenic maize has no significant effect on the non- target zoophagous or phytophagous species under consideration.
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