Flexible schedule in the development of the red flour beetles, (Tribolium castaneum Herbst and T. freemani Hinton) associated with the cannibalism

A number of tenebrionid beetle species are cannibalistic in the larval and adult stages, preying primarily on immobile eggs and pupae. We propose that in response to cannibalism, some beetles have evolved flexibility in the development schedule of larva, delaying pupation in crowded conditions to avoid becoming prey. That is, under crowded conditions, larva of these species should undergo continuous molts producing supernumerary larval instars. We investigated differences between the development schedules of two closely related Tribolium species, T. castaneum and T. freemani, and different strains of T. castaneum (Georgia-1, Goliath, pygmy, small, and pearl) among crowded conditions. We found that T. freemani was highly sensitive to crowded conditions, producing supernumerary larvae and delaying pupation for longer than 3 months, while T. castaneum showed large variations among strains and individuals in crowded conditions. Georgia-1, Goliath, pygmy and small strains showed high individual variations, while a pearl strain (i.e., pu11 transgenic line) is insensitive to crowded conditions, having no supernumerary larval molting.  When T. castaneum (Georgia-1) and T. freemani were compared, interestingly, we found that the frequency of cannibalism was inversely correlated to the frequency of supernumerary molting in crowded condition. An expanded investigation of the inter-strain differences in T. castaneum and their genetic mechanisms is under way to better understand the relationship between developmental flexibility, life history and cannibalistic behavior.