Jg. Vontas et al., Altered acetylcholinesterase confers organophosphate resistance in the olive fruit fly Bactrocera oleae, PEST BIOCH, 71(2), 2001, pp. 124-132
An organophosphate-resistant strain of the olive fruit fly Bactrocera oleae
, the most important pest for olive orchards worldwide, was obtained by lab
oratory selection with dimethoate. Resistance mechanisms were investigated
in comparison with the colonized parental strain and a field population col
lected from the same area after 12 years of continuous dimethoate-based ins
ecticide pressure. Combined biochemical and bioassay data suggested that, a
lthough esterase and/or glutathione S-transferase metabolic pathways were p
resent and active against dimethoate, they were not selected for and did no
t have a major role in resistance. There was no evidence of increased oxida
se activity in the resistant strains or significant synergism of dimethoate
toxicity by piperonyl butoxide; thus, oxidative metabolism was not a major
component of resistance. An altered acetylcholinesterase (AChE) with poore
r catalytic efficiency for the substrate acetylthiocholine iodide and 5- to
16-fold lower sensitivity to inhibition by omethoate was the major resista
nce mechanism. Dimethoate selected the insensitive AChE allele(s) in the re
sistant insects, which were also insensitive to paraoxon, but the altered A
ChE mechanism conferred negative cross-resistance to the carbamate propoxur
. (C) 2001 Academic Press.