Effect of diet on body size and survival of omnivorous crickets

Omnivory is a feeding habit in which animals prey on organisms from two or more trophic levels. Omnivorous species play important roles in predator–prey interactions, food web dynamics, and ecosystem functions. Although cricket species have been considered omnivores, quantified investigations of their feeding habits have not been carried out. Therefore, we compared the developmental time, body size and mortality rate of the band-legged ground cricket, Dianemobius nigrofasciatus (Matsumura) (Orthoptera: Trigonidiidae) reared on diets meant for carnivores and herbivores. Furthermore, to examine whether the crickets can balance their nutritional conditions through their food choices, we set up two additional diet treatments, which comprised diets for carnivores and herbivores provided simultaneously or by rotation. The mortality rate of the carnivore diet treatment was higher than that of the other diet treatments. This result suggests that D. nigrofasciatus is a “herbivore” that also obtains nutrients from resources other than plant materials. Although developmental time did not significantly differ among the dietary treatments, the body size of the crickets that were provided both diets simultaneously was significantly larger than that of the crickets provided with only the diets for either carnivores or herbivores. These results suggest that an appropriate amount of carnivorous feeding is advantageous for the development of the cricket, and indicates that crickets can balance nutrition on their own.