156 - Operational Perspectives of Mosquito Larvicide Resistance Management

Abstract: Mosquito larvicides derived from microbial organisms and insect growth regulators have been increasingly used to control mosquito larvae. Their relative target specificity, non-target safety and environmentally friendly profile have been well documented. Bacillus thuringiensis israelensis (B.t.i.) is a quick and highly target-specific biopesticide against mosquitoes and blackflies, resistance toward intact toxin complex of B.t.i. was rare. The toxins from bacterium Bacillus sphaericus is another highly active larvicide against mosquitoes, toward which low to high levels of resistance have occurred in both laboratory and field mosquito populations. The Cyt1A toxin from B.t.i. and Mtx toxin from certain strains of B. sphaericus are the key components in resistance management to B.t.i. and B. sphaericus. The resistance management strategies have been well developed and implemented for resistance prevention and susceptibility restoration. Spinosad derived from Saccharopolyspora spinosa has been recently used for mosquito control; high levels of resistance have occurred in laboratory mosquito populations, as well as in some local wild populations; no management tactics have ever been developed, although B.t.i. may shed some light on spinosad resistance management. Methoprene have been used to control mosquitoes for about 40 years, low to high levels of resistance have been occasionally reported in both laboratory and field mosquito populations. Studies on mechanism and management of methoprene resistance are quite meager. Very little attention has been paid to the resistance management in mosquitoes to other insect growth regulators such as pyriproxyfen and diflubenzuron. In nature, multiple resistance and cross resistance make resistance management more challenging. The prevention of resistance and restoration of susceptibility in mosquitoes to these biorational larvicides are crucial to the success of sustainable integrated mosquito management. Special consideration must be taken into account in mosquito control operations.