The effects of the particle size of four different feeds on the larval growth of Tenebrio molitor (Coleoptera: Tenebrionidae)

Diet is one of the most important factors affecting the growth and lifecycle of Tenebrio molitor L. The chemical and nutritional properties of the diet of mealworms are well studied whereas its physical properties are almost neglected. This work aims to study the effects of four different particle sizes (0-0.8, 0.8-2, 2-3 and 3-4 mm) of four different feeds (wheat bran, chicken feed pellets, grounded corn kernels and alfalfa dried pellets). Four-week-old larvae were reared on the experimental substrates for four to six weeks depending on the feed. Our results indicate that particle size can significantly influence larval growth and that particles smaller than 2 mm improve larval growth on all feeds except alfalfa pellets. The maximum larval weight was slightly different for wheat bran (12%) when comparing particle sizes smaller than 2 mm with greater than 2 mm but increased up to 70% when corn kernels were used as feed. Significant differences were found between the different feeds for growth rate, larval weight and variability in larval weight. The larvae that reached an average weight of 100 mg the fastest were those reared on wheat bran followed by chicken feed and corn kernels. Larvae reared on alfalfa pellets did not reach an average weight of 60 mg. The variability in larval growth was lowest when fed wheat bran followed by chicken feed and alfalfa pellets, and the highest variability was recorded when fed corn kernels. In conclusion, both the type (wheat bran, chicken feed and corn kernels) and particle size (< 2 mm) of the feed were important determinants of larval growth.