No abstract

A 2.2-kb full length cDNA containing an ORF encoding a putative acetylcholinesterase (AChE) precursor of 673 amino acid residues was obtained by a combined degenerate PCR and RACE strategy from an organophosphate-susceptible Bactrocera oleae strain. A comparison of cDNA sequences of individual insects from susceptible and resistant strains, coupled with an enzyme inhibition assay with omethoate, indicated a novel glycine-serine substitution (G488S), at an amino acid residue which is highly conserved across species (G396 of Torpedocalifornica AChE), as a likely cause of AChE insensitivity. This mutation was also associated with a 35-40% reduction in AChE catalytic efficiency. The I199V substitution, which confers low levels of resistance in Drosophila, was also present in B. oleae (I214V) and in combination with G488S produced up to a 16-fold decrease in insecticide sensitivity. This is the first agricultural pest where resistance has been associated with an alteration in AChE, which arises from point mutations located within the active site gorge of the enzyme.

No abstract

SUMMARYIn colonies of the olive fruit fly Dacus oleae maintained on an artificial substrate, an allele of the ADH locus whose frequency in natural populations is about 1 per cent increases in frequency to about 40 per cent within 6 generations of artificial rearing; the allele most common in natural populations suffers a compensatory decrease from 65 per cent to 30 per cent; a third allele is only slightly affected. This rapid genetic change coincides with an initial negative population growth rate followed by gradually increasing rates, an indication that the selection associated with this change has a toll on the colony's growth. Estimation of relative fitnesses shows that under artificial rearing, heterozygotes are on avera twenty times as fit as homozygotes. These are probably the largest selection differentials reported for allozymes, and are comparable only to differentials for tolerance to heavy metals in plants. The hypothesis of linkages of the ADH alleles with other genetic elements (e.g., chromosomal inversions), which are the targets of selection, cannot be excluded. The study demonstrates the types of selection pressures that may operate on newly established colonies of "domesticated" insects and the genetic changes that may result from them.

The rate of allelism of lethals on the O chromosome of Drosophila subobscura in two natural populations and the interpopulation allelism rate are 0.0062, 0.0025 and 0.0058 respectively. They do not differ statistically. It is concluded that the natural populations studied have practically an infinite size. This conclusion is corroborated by ecological data on density and dispersion, and partly by data based on the temporal method. The allelism rate of genes producing male and female sterility was also studied. From the study of the allelism rate for lethal and sterility genes the number of such genes on the O chromosome ofD. subobscura was inferred.