Insect attack is a serious agricultural problem leading to yield losses and reduced product quality. Insects can cause damage both in the field and during storage in silos. Each year, insects destroy about 25 percent of food crops worldwide. The larvae of Ostrinia nubilalis, the European corn borer, can destroy up to 20 percent of a maize crop.
European corn borer:A major pest in southern and central Europe. Insect resistant Bt maize is already being grown in Spain, France, Germany, Portugal and the Czech Republic. Western corn rootworm beetles feeding on a maize cob. Certain cultivars of Bt maize are resistant to this serious pest. GM rootworm resistant crops are not approved for cultivation in the European Union but are now being grown in the US.
The “Bt concept” – pest resistant transgenic plantsBacillus thuringiensis, or Bt, is a bacterium that has attracted much attention for its use in pest control. The soil bacterium produces a protein that is toxic to various herbivorous insects. The protein, known asBt toxin, is produced in an inactive, crystalline form.When consumed by insects, the protein is converted to its active, toxic form (delta endotoxin), which in turn destroys the gut of the insect. Bt preparations are commonly used in organic agriculture to control insects, as Bt toxin occurs naturally and is completely safe for humans.More than 100 different variations of Bt toxin have been identified in diverse strains ofBacillus thuringiensis. The different variations have different target insect specificity.
For example, the toxins classified under Cry1a group target Lepidoptera (butterflies), while toxins in the Cry3 group are effective against beetles.Researchers have used genetic engineering to take the bacterial genes needed to produce Bt toxins and introduce them into plants. If plants produce Bt toxin on their own, they can defend themselves against specific types of insects. This means farmers no longer have to use chemical insecticides to control certain insect problems.| Critics claim that in some cases the use of insect resistant crops can harm beneficial insects and other non-target organisms. Extensive ecological impact assessments have been addressing these issues. In the field, no significant adverse effects on non-target wildlife nor long term effects of higher Bt concentrations in soil have yet been observed.
New concepts on the way
Bt crops have been planted commercially for more than eight years. Other naturally occuring insecticidal compounds are now becoming available as alternatives to the Bt approach. Among these are chitinase, lectins, alpha-amylase inhibitors, proteinase inhibitors, and cystatin. Plants genetically modified to express these defense proteins are still in early stages of development.