According to the Food and Agriculture Organization of the United Nations, more than 2.75 million metric tons of pesticides were used worldwide in 2015 with a significant proportion of these chemicals used for insect control. The dangers of various insecticides and their misapplication have been a topic of interest since Rachel Carson wrote Silent Spring about DDT in 1962.
Although reportedly safer insecticides are currently in use, their effects are not always immediately apparent. For example, the widely used compounds malathion, diazinon, and chlorpyrifos were developed in the 1950s and 60s and have recently been shown to be toxic to salmon and endanger organisms that eat salmon (Hotakainen 2018). Chlorpyrifos has also been in the news due to the EPA’s decision in March 2017 that the insecticide should not be banned despite an earlier EPA report that said that the chemical could be harmful to humans. Such reports and consumer concern drive researchers to find alternative solutions to insect control.
A promising control method is the use of a bacteria-derived protein to protect plants from insect attack and damage. Bacillus thuringiensis (Bt) is a soil bacterium that produces insecticidal crystal proteins which bind to receptors in the insect’s gut. These receptors are not found in vertebrates including humans; therefore, these organisms are not harmed. Application of Bt crystal proteins to crop plants has been used in organic farming for more than 50 years. Different types of crystal proteins exist and can provide protection against one or more target insect species. An alternative to external application of Bt crystal proteins is genetic engineering of the crop plant to produce the protein itself using Bt crystal protein (cry) genes. Bt crops were first developed in 1996 and are now widely used in many parts of the world.
Work in our lab was aimed at determining if the expression of a Bt cry gene in tomato could provide control of the leaf miner Tuta absoluta. This insect was initially only a threat to crops in South America but within the past decade it has spread to Europe and Africa where it has earned the nickname ‘tomato Ebola.’ Control of this pest is especially difficult in developing countries which may not have access to insecticides or may not be able to afford the repeated sprays that are needed to eliminate leaf miner. Indeed alternatives to chemical formulations such as camel urine are being tested in parts of Africa for leaf miner control.
In our research, the cry1Ac gene was introduced into tomato plants. The transgenic plants were then examined for their response to leaf miner infection. Up to 100% of leaf miner larvae died after feeding on leaves producing crystal proteins. Moreover, gallery formation by the insect was reduced by 57 to 100%, ensuring that the leaves suffered limited damage and that marketable fruits could be produced. These results indicate that, if adopted, Bt tomato could reduce the use of insecticides for the control of leaf miner and potentially other insects.
These findings are described in the article entitled Cry1Ac-mediated resistance to tomato leaf miner (Tuta absoluta) in tomato, published in the journal Plant Cell Tissue and Organ Culture. This work was led by Hatice Şelale and Anne Frary et al. from the Izmir Institute of Technology. This project was also funded by the Izmir Institute of Technology.