Effect of environmental humidity on red flour beetle, Tribolium castaneum (Herbst), developmental rate when fed dried distillers grains with solubles

Dried Distillers Grains with Solubles (DDGS), co-product of corn-ethanol production and raw ingredient being used in feed industry, is expected to double produces in close future. However, no information is available on the vulnerability of DDGS to insect infestation; information which is critical to understanding the growth potential of insects and determining best ways to store DDGS. It is recommended that relative humidity be maintained less than 50-60% at 20-30°C for safe storage of DDGS to prevent decreasing in flowability as a result of increase in the equilibrium moisture content of the DDGS. The objectives of this study were first, to determine the influence of environmental humidity on the developmental rate of red flour beetle, Tribolium castaneum (Herbst), feeding on DDGS at 30 and 50% r.h. and second, to determine the effect of particle size of DDGS on red flour beetle larval development. Larval development was faster when feeding on DDGS samples P₃-B₁ (25.50±0.37)_, P₃-B₂ (26.79±0.39)_, and P₃-B₃ (31.27±0.61) at 50% r.h. compare to 30% r.h. (44.62±0.66, 49.63±1.52, and 45.77±1.58 respectively). At 30% r.h. red flour beetle larvae also grow faster on ground DDGS samples P₃-B₁ (30.96±0.38)_, P₃-B₂ (32.19±0.6)_, and P₃-B₃ (33.48±0.47) compare to the same original (unground) samples. These results indicate that the current recommendation of a maximum storage r.h. of 50-60% will result in greater vulnerability to red flour beetle infestation due to shorter developmental times for all DDGS samples compared to development at 30% r.h. Thus, storing raw DDGS at 30% r.h. and unground with a mixture of larger particle sizes, is recommended to reduce vulnerability to red flour beetle.