Further studies on the genetics of the carboxylesterase regulatory system involved in resistance to organophosphorus insecticides in Myzus persicae (Sulzer)

Levels of carboxylesterase activity in F₁ clones of Myzus persicae, obtained by crossing sexuales from a resistant, high esterase clone with those from a susceptible, low esterase clone, fell into two distinct groups intermediate between the levels of carboxylesterase in the parent clones. When sexuales of F₁ clones of the lower of these two intermediate levels of carboxylesterase activity were crossed, segregation ratios in the F₂ generation indicated that this lower intermediate activity level (about 0.4 μmol mg^?1 h^?1). which is about twice the level in susceptible clones, is due to mutation at a single regulatory locus. The results obtained with backcrosses, between sexuales of an F₁ clone having the higher intermediate level of carboxylesterase activity and a parent susceptible, low esterase clone, suggest that a second locus may be involved in the expression of higher levels of esterase activity.