Biotype variation in Tribolium castaneum (Herbst.) from Mali.

Geographical strains of Tribolium castaneum (Herbst.) (Tenebrionidae) and Rhyzopertha dominica (Fab.) (Bostrychidae) were collected in different geographical locations in Mali and were tested for differences in various biological parameters. In the preliminary investigations, strains of both species were found to be significantly different in their capacity to damage grain, in their capacity to tolerate pesticides, and in some life-history traits, and these strains were designated as biotypes. There was no evidence of correlation between the fitness of strains and their resistance status, ie no evidence of a 'cost' of resistance. After the preliminary investigations, two biotypes of T. castaneum were retained for the detailed studies. Differences between strains in their ability to damage grain were found to be related to their productivity but not to their metabolic rate, which was determined by measuring their oxygen consumption. The significant difference in body weight found between strains provided an explanation for the significant difference found in oxygen consumption. Significant differences between strains were also found in productivity. Using the techniques of quantitative genetics, significant heritability of body weight was found within one strain of Tribolium castaneum. A selection experiment, with two selection regimes based on culture interval, was designed to identify possible genetic trade-offs that might be maintaining genetic variability in components of fitness. Selection using different culture intervals did not affect developmental period, productivity or body weight. There was no evidence of genetic trade-offs between any of these life-history traits.