Linkage of acetylcholinesterase insensitivity to methyl parathion resistance in Heliothis virescens

A single gene (yes) controls pigmentation of eyes and scales in Heliothis virescens

A yellow-eyed mutant was discovered in a strain of Heliothis virescens, the tobacco budworm, that already exhibited a mutation for yellow scale, y. We investigated the inheritance of these visible mutations as candidate markers for transgenesis. Yellow eye was controlled by a single, recessive, autosomal factor, the same type of inheritance previously known for y. Presence of the recombinant mutants with yellow scales and wild type eyes in test crosses indicated independent segregation of genes for these traits. The recombinant class with wild type scales and yellow eyes was completely absent and there was a corresponding increase of the double mutant parental class having yellow scales and yellow eyes. These results indicated that a single factor for yellow eye also controlled yellow scales independently of y. This gene was named yes, for yellow eye and scale. We hypothesize that yes controls both eye and scale color through a deficiency in transport of pigment precursors in both the ommochrome and melanin pathways. The unlinked gene y likely controls an enzyme affecting the melanin pathway only. Both y and yes segregated independently of AceIn, acetylcholinesterase insensitivity, and sodium channel hscp, which are genes related to insecticide resistance.

The development of genetically inherited resistance to zinc in laboratory-selected generations of the earthworm Eisenia fetida

The capacity of species to adapt both physiologically and genetically to contaminants may allow populations to persist in polluted environments. Such 'adaptation' can have important implications for risk assessment, since it may mean that prediction based on extrapolation of toxicity studies with naïve populations may prove invalid for long-term contaminated sites. To investigate the evolution of zinc resistance in Eisenia fetida, worms from a previously unexposed population (parent) were selected and reared over two generations (F1, F2) while exposed to zinc in the laboratory. Relative sensitivities of unexposed and selected generations were then compared by exposing parent, F1 and F2 individuals to zinc in contact filter papers tests. Calculation of effect concentrations from this work indicated differences in sensitivity to zinc for successive generations, with higher toxicity values (LC(50), LC(90), LC(99)) found for the selected worms. The increases in resistance found for F1 and F2 worms were confirmed in a discriminating dose study. In addition to comparing the sensitivities of the parent, F1 and F2 generations for zinc, toxicity tests were also conducted with copper to assess if there was evidence of cross-resistance between the two metals. Results indicated similar increases in resistance to copper to those found for zinc. Mechanisms underlying the increased metal resistance were studied in toxicokinetic experiments. Results indicated no clear trends between the three generations indicating that physiological responses, other than differences in kinetic parameters, are responsible for the increased resistance found in the selected worms.

Resistance to insecticides in Heliothine Lepidoptera: a global view

The status of resistance to organophosphate, carbamate, cyclodiene and pyrethroid insecticides in the heliothine Lepidoptera is reviewed. In particular, resistance in the tobacco budworm, Heliothis virescens , and the corn earworm, Helicoverpa zea , from the New World, and the cotton bollworm, Helicoverpa armigera , from the Old World, are considered in detail. Particular emphasis has been placed on resistance to the most widely used of these insecticide groups, the pyrethroids. In each case, the incidence and current status of resistance are considered before a detailed view of the mechanisms of resistance is given. Controversial issues regarding the nature of mechanisms of resistance to pyrethroid insecticides are discussed. The implications for resistance management are considered.

A genomic approach to understanding Heliothis and Helicoverpa resistance to chemical and biological insecticides

Genomics is the comparative study of the structure and function of entire genomes. Although the complete sequencing of the genome of any insect pest is far in the future, a genomic approach can be useful in the study of mechanisms of insecticide resistance. We describe this strategy for Heliothis and Helicoverpa , two of the most destructive genera of pest moths (Lepidoptera) worldwide. Genome–wide linkage mapping provides the location of major and minor resistance genes. Positional cloning identifies novel resistance genes, even when the mechanisms are poorly understood, as with resistance to Bacillus thuringiensis toxins. Anchor loci provide the reference points for comparing the genomes and the genetic architecture of resistance mechanisms among related species. Collectively, these tools enable the description of the evolutionary response of related, but independent, genomes to the common selective pressure of insecticides in the environment. They also provide information that is useful for targeted management of specific resistance genes, and may even speed the search for families of novel insecticidal targets in Lepidoptera.