Comparative studies with Tribolium (Coleoptera, Tenebrionidae) — II: Productivity of T. castaneum (herbst) and T. confusum Duv. on natural, semi-synthetic and synthetic diets

Productivity of T. castaneum and T. confusum has been determined in the following diets: Naylor's synthetic medium; corn supplemented with the amino acids cystine, glutathione, proline and tryptophan in amounts necessary to bring them to the level found in wheat; corn and whole wheat flour without any supplements, and corn and whole wheat flour supplemented with brewer's yeast and vitamins. Relative developmental rates of the two species in these media were also determined by counting the numbers of adults emerging in 14-day periods.

Significant differences in productivity (the number of eggs surviving to the adult stage) have been detected within a species in the different media and between species within a given medium. The Naylor medium is unfavorable for both species, and judging from relative developmental rates less favorable to T. confusum than to T. castaneum.

T. castaneum performs poorest in non-supplemented media, better in media supplemented with vitamins, and the best in media supplemented with yeast. While T. confusum also shows an increased productivity in vitamin- and yeast-supplemented media, this increase is not as marked as in T. castaneum. Considering both the productivity and the developmental rates, it appears that the addition of the four amino acids to corn had a beneficial effect to T. castaneum but not to T. confusum. The two species were most productive in corn plus yeast, but this productivity was not significantly higher than in whole wheat flour plus yeast.

Drawing upon the evidence available in the literature, and the present data, it is concluded that T. confusum is better adapted to utilize a wider variety of foods than T. castaneum and in order to satisfy its greater quantitative requirements for certain nutrients, this species engages in cannibalism more often than T. confusum. The result is that, when the two species are introduced into the same container, i.e. compete for food and space, T. confusum is more often eliminated than T. castaneum.