The impact of the protein-carbohydrate ratio in animal feed and the initial insect population density on the development of the red flour beetle, Tribolium castaneum

Progeny numbers and life parameters of Tribolium castaneum reared on a range of different animal feeds which varied in their protein-carbohydrate ratios (corn starch; corn feed flour; wheat bran; soybean meal; corn gluten; soy protein concentrate and soy protein isolate), four initial (population) densities (1, 2, 5 and 10 insect pairs) were evaluated. Adult insects were kept for seven days on a range of different diets to feed and oviposit before they were removed. After removing the adults, the emerging progeny were examined. The study found T. castaneum offspring could not develop on a carbohydrate-rich diet (corn starch) and on protein-rich diets (corn gluten, soy protein concentrate and soy protein isolate). Soy isolate showed a high, possibly insecticidal effect on parents. The fastest total development (egg to adult) (23.25–23.88 days, depending on the initial density), the highest offspring number (111.63–324.13) and the highest offspring body mass (1.38–1.73 mg) were recorded in wheat bran, while the slowest egg to adult development (35.13–37.88 days), the lowest offspring number (25–29) and the lowest offspring mass (1.04–1.48 mg) were recorded in soybean meal. The higher initial densities caused the eclosion period to be prolonged, reductions in female productivity and in offspring body mass on all diets. Initial density interacted differently with diet type in terms of offspring number, so as the density rose, the number of offspring in wheat bran and corn feed flour increased, while in soybean meal it remained low at all initial densities. This research gives us a better insight into the development of T. castaneum in animal feed that can help us to improve existing pest management in a way of finding a better solution to store products based on their susceptibility to this storage pest.