Abstract
To study the potential for the emergence of resistance in Aedes aegypti populations, a wild colony was subjected to selective pressure with Cry11Aa, one of four endotoxins that compose the Bacillus thuringiensis serovar israelensis toxin. This bacterium is the base component of the most important biopesticide used in the control of mosquitoes worldwide. After 54 generations of selection, significant resistance levels were observed. At the beginning of the selection experiment, the half lethal concentration was 26.3 ng/mL and had risen to 345.6 ng/mL by generation 54. The highest rate of resistance, 13.1, was detected in the 54th generation. Because digestive proteases play a key role in the processing and activation of B. thuringiensis toxin, we analysed the involvement of insect gut proteases in resistance to the Cry11Aa B. thuringiensis serovar israelensis toxin. The protease activity from larval gut extracts from the Cry11Aa resistant population was lower than that of the B. thuringiensisserovar israelensis susceptible colony. We suggest that differences in protoxin proteolysis could contribute to the resistance of this Ae. aegypti colony.
Highlights
Due to the increased resistance of mosquitoes to chemical pesticides and the risks these chemicals pose to humans and the environment, insect control using bacteria, such as Bacillus sphaericus and Bacillus thuringiensis serovar israelensis, has increased in various regions of the world over the last three decades, with a market growth prediction of up to 20% of the world’s pesticide use by 2020 (Whalon & Wingerd 2003, Kumar et al 2008)
An important concern raised against this approach is the high risk of the development of resistance by the target insects as resistance to individual B. thuringiensis serovar israelensis toxins has been observed in laboratory colonies of Cx. quinquefasciatus
In one selection experiment in which individual toxins or combinations of toxins from B. thuringiensis serovar israelensis were used on laboratory colonies of Cx. quinquefasciatus, Georghiou and Wirth (1997) observed that lower levels of resistance occurred when all the toxins were used in combination
Summary
Due to the increased resistance of mosquitoes to chemical pesticides and the risks these chemicals pose to humans and the environment, insect control using bacteria, such as Bacillus sphaericus and Bacillus thuringiensis serovar israelensis, has increased in various regions of the world over the last three decades, with a market growth prediction of up to 20% of the world’s pesticide use by 2020 (Whalon & Wingerd 2003, Kumar et al 2008). The use of insecticides based on B. sphaericus toxins have achieved moderate commercial success in developed countries, but their high cost discourages their use in many developing countries Their long-term use in Culex quinquefasciatus and Culex pipiens control programs underway in France, India, Brazil and China has resulted in resistance in the mosquito populations (Sinègre et al 1994, Rao et al 1995, SilvaFilha et al 1995, Yuan et al 2000, Nielsen-Leroux et al 2002). An important concern raised against this approach is the high risk of the development of resistance by the target insects as resistance to individual B. thuringiensis serovar israelensis toxins has been observed in laboratory colonies of Cx. quinquefasciatus. Ae. aegypti resistance to Cry11A toxin Gloria Cadavid-Restrepo et al 75 the cadherin gene In addition to this polymorphism, the under-expression of this gene was observed. We suggest that differences in the proteolytic activity of mosquito larvae midgut enzymes could be responsible for the resistance we observed in this Ae. aegypti colony
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