RESUMO
Insects have successfully adapted to most insecticides by becoming resistant to them. This adaptation, of recent origin, has evolved rapidly and independently in a large number of species and is of serious economic and medical importance. The origins of resistance are still obscure, but resistance is assumed to be pre-adaptive, arising through recurrent mutation of existing alleles. However, in at least one well-researched case it probably originated by gene duplication. Resistance can be monofactorial or multifactorial. When several independent mechanisms confer resistance to the same group of insecticides the order in which these mechanisms are selected may reflect their effectiveness in protecting insects from the toxic effects of the different compounds. Our concept of resistance is changing as insects continue to adapt to the insecticide-containing environment. Criteria for defining resistance in both fundamental and practical terms are re-examined here in the light of recent work.
Assuntos
Adaptação Biológica , Insetos/fisiologia , Resistência a Inseticidas , AnimaisRESUMO
The recent allocation of many visible mutants to specific linkage-groups has made possible their use as genetic markers in the study of the inheritance of insecticide resistance. In most organophosphorus-resistant strains, resistance is controlled by a single gene on the V linkage-group responsible for resistance and low ali-esterase activity, but in some strains more than one factor is present. The present work was done to analyse the genetics of resistance to diazinon in a strain (the SKA strain) bred from two diazinon-resistant strains. Crosses between the SKA flies and four susceptible recessive marker strains, each marked on one linkage-group, followed by test-crosses with recessive markers and by bioassays of each cross, have shown that non-recessive factors for resistance to diazinon are present on the IV and V linkage-groups. The SKA strain genetically resembles its parents but differs by being considerably more resistant.