AMADIN · Adaptation, migration and diversity in populations of Tribolium castaneum, a pest insect

Final Activity Report Summary - AMADIN (Adaptation, migration and diversity in populations of Tribolium castaneum, a pest insect)

Our research project addresses an important issue in population genetics, namely, the antagonistic effects of natural selection and migration on evolutionary processes in species with population structure. Adaptation to the local environment is a fundamental process in pesticide resistance acquisition by pest species, but migration between fragmented populations may slow down this process. Therefore, our project explored the interactions between gene flow, population demography and genetic differentiation in strains of a model pest insect, the red flour beetle, Tribolium castaneum. The red flour beetle is a widely-distributed pest of stored products of economical importance and it is well known for the ability to rapidly develop tolerance to chemicals. We investigated evolution of resistance to pirimiphos-methyl, an organophosphorous insecticide with neurotoxic action commonly applied to control T. castaneum infestations. A genetically variable laboratory stock population was established from a wild sample (2006, Bloomington, Indiana, US). The controlled environment setup for the selection experiment consisted of 48 populations/lines of beetles kept in separate vials and periodically exposed to different levels of pesticide exposure and migration between the vials. Every generation of the beetles was tested for levels of susceptibility to the insecticide. After 8 generations animals from the selected lines were significantly more resistant to pirimiphos-methyl than the control lines. They were also heavier, which might potentially explain their lower susceptibility to the insecticide, because with increased body mass the dose of toxin received per unit of body mass gets smaller. We did not find differences in development time or fecundity between the selected and control lines. There was no effect of migration rate on the level of susceptibility to insecticide in the final generation, showing that at the rates tested, gene flow did not affect the speed of resistance development. Neutral genetic markers (microsatellites) were used to examine genetic divergence between strains and genetic diversity within strains. The allele frequencies for 12 microsatellites were determined for the sample of 36 individuals from the base population and from each selection line in the final generation. We compared the frequency changes among the experimental lines at different selection regimes, as well as with the stock population, in order to reveal the causes and mechanisms of loss of the genetic diversity. The preliminary results suggest that significant loss of genetic variation occurred in all selection lines relatively to the stock culture, but it seems that more variation was lost from the lines where beetles were exposed to insecticide and where the gene flow was absent. The main project was expanded into four new lines of research: 1) Development of efficient DNA extraction method for small insects; 2) Development of molecular markers for sex identification in T. castaneum; 3) Comparison of genetic diversity of laboratory and wild strains of T. castaneum; and 4) Characterisation of delayed toxicity of pirimiphos-methyl. All new objectives were succesfully achieved and provided valuable contributions for fields of ecological genetics and ecotoxicology. The major objective of the main project was to provide further training for the fellow so that she will develop herself and fulfill her potential as an independent researcher, and this was fully accomplished. The fellow have gained advanced professional experience in several areas of biological science, project management and communication skills. The most important scientific achievement was to show that increased resistance to toxic exposure can evolve via increase in the body size. We also found that migration did not slow down the evolution of insecticide resistance in the laboratory populations of T. castaneum.

Data: CORDIS, © European Union