Among disease carriers, mosquitoes are recognized as one of the most important vectors of human diseases. They are capable of transmitting serious, possibly even fatal diseases, such as mosquito-borne encephalitis, dengue, yellow fever, filariasis, and malaria. Transmission of disease occurs when an infected mosquito takes a blood meal. Even though uninfected mosquitoes do not transmit diseases, their bites can result in allergic reactions, which can produce significant discomfort and itching. Each type of disease is transmitted by different species of mosquito. Anopheline mosquito is the main malaria vector. Encephalitis is carried by Culex spp., while dengue and yellow fever are transmitted by Aedes spp. The reason why each species carries different diseases might be because of molecular incompatibilities between the mosquito and the disease agent.
Each year, approximately 300 million people in the developing countries are affected by malaria and over 2 million are killed. Dengue and encephalitis also affect thousands of people in urban areas. There is a close relationship between disease outbreak and the number of mosquito carriers in the area. In other words, the distributionof the disease is mainly determined by the distribution of each mosquito species. Therefore, to reduce the risk of disease, the mosquito population has to be controlled.
The most widely used biological agents for controlling mosquito larvae are Bacillus thuringiensis subsp. israelensis (Bti), and Bacillus sphaericus (Bs). These bacteria produce proteinaceous toxins that specifically kill certain species of mosquito larvae. The toxin is formed as a "crystal" in the bacterial cells. After ingestion by the mosquito larvae, the toxins are dissolved as a protoxin and activated by the larva proteases. The "active form" of the toxin will then bind to the midgut membrane and destroy the midgut cells, leading to starvation and death of the larvae. However, application of both bacteria is limited by the "longevity" of these biocontrol agents. The degradation of microbial proteins in the field is also a main limitation. In addition, toxin resistance has been observed in Culex spp. when B. sphaericus was used. It is thought that the use of a single protein toxin for a long time contributed to the emergence of resistance. Therefore, application of bacteria containing various proteins might be a more effective "broad-range biopesticide" and could overcome the resistance in the mosquito larvae.
The main objective of our group is to improve efficacy and safety of microbial agents for controlling mosquitoes and major insect pests.