Influence of single-species and species-species competitive interactions, in a food limited environment, among certain stored-grain beetles on population size and grain weight losses

Resource competition is a common biotic factor that affects progeny production and population size of stored-grain beetles. Larvae of the external feeding competitors, Tribolium, Oryzaephilus, and Trogoderma have almost identical habits, all developing and feeding outside grains Trogoderma larvae therefore are likely to face the competition of both competitors that share the same habitat, with the possibility of displacement of one or both of these species from the habitat. A series of trials of the single-, two-, and three-species competitive interactions among Trogoderma granarium, Tribolium castaneum, and Oryzaephilus surinamensis beetles were performed in 20g cracked-wheat grains at 30 ± 1 $°C$ and 65 ± 5% r.h. Population sizes of living individuals, total populations (living + dead), and grain losses in all combinations were estimated after 30 and 60 days. This was to understand the role of external competitors in T. granarium establishment and vice versa. The population size of Trogoderma benefited more from coexisting with Oryzaephilus than with Tribolium, whereas that of Oryzaephilus did not benefit from coexisting with either species. Each of Trogoderma and Tribolium inhibited development of Oryzaephilus with more suffering in the treatment containing the two, which eventually led to greater collapse in Oryzaephilus populations. However, path analysis of the population growth rates of each species in pure and mixed infestations indicates coexistence is possible between all species and mixed infestations are more harmful to the grains than pure ones, since there are positive associations among them.