Strategies for Resistance Management

Resistance to pesticides has evolved in more than 500 species of insect pests and more than 70 species of weeds (1 , 2 ). It was once believed by some that resistance would be unlikely for biopesticides because they were natural, already exposed to eons of evolution, and of short persistence However, because of the pervasiveness of resistance to other pesticides, few entomologists have ever agreed with that view. In the case of Bacillus thuringiensis (Bt), the most commercially important biopesticide currently, the myth of invincibility was challenged in 1985 with the relatively easy selection in the laboratory of resistance in the Indian meal moth (Plodia interpunctella , a pest of stored grain) (3 ) and was truly demolished starting in 1990 by the appearance of resistance in the diamondback moth (Plutella xylostella , a pest of cabbage and other cole crops) in Hawaii, Asia, the continental United States, and Central America from the use of Bt sprays (4 –8 ). Subsequent laboratory experiments have selected resistance in several other species (7 ). Resistance has also been selected to Bacillus subtihs, a biocontrol agent of a fungal disease of plants (9 ).