Resistance and Its Management to Microbial and Insect Growth Regulator Larvicides in Mosquitoes

Mosquito larvicides derived from microbial organisms and insect growth regulators have been increasingly used to control mosquito larvae worldwide. Their relative target specif‐ icity, nontarget safety, and environmentally friendly profile have been well documented. The current chapter was intended to review and analyze the relevant information regard‐ ing resistance development and resistance management tactics. Bacillus thuringiensis isra‐ elensis de Bajac (B.t.i.) is a quick-acting and highly target-specific biopesticide against mosquitoes, blackflies, and other nematoceran species. Resistance development toward intact complementary toxin complex of B.t.i. was rare; however, low to high levels of re‐ sistance to individual toxins have occurred in laboratory mosquito populations. The tox‐ ins from bacterium Bacillus sphaericus Neide (recently renamed Lysinibacillus sphaericus Meyer and Neide) is another highly active larvicide against mosquitoes, toward which low to high levels of resistance have occurred in both laboratory and field mosquito pop‐ ulations. 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 resist‐ ance management strategies have been well developed and implemented. Spinosad de‐ rived from Saccharopolyspora spinosa Mertz and Yao has been recently used for mosquito control; high levels of resistance and cross-resistance have occurred in laboratory mosqui‐ to populations and no management tactics have ever been developed. Methoprene has been used to control mosquitoes for decades, and 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 at‐ tention has been paid to the resistance management in mosquitoes to other insect growth regulators such as pyriproxyfen and diflubenzuron. The prevention of resistance and re‐ storation of susceptibility in mosquitoes to these biorational larvicides are crucial to the success of sustainable integrated mosquito management.