Larval cannibalism and fitness in the stored grain weevils Sitophilus granarius and Sitophilus zeamais

Abstract

Resource limitation is an important determinant of life history and behavior while mediating competition and reproduction among organisms. Discreet and closed systems such as grain kernels and seeds impose drastic restrictions to grain beetles that spend their immature stages within a single kernel selected by their mother. This is the case of internally feeding stored grain beetles, such as the grain weevils. Female egg-laying decisions and larval competition largely determine resource limitation for such insects where clustered egg distribution and contest competition with larval interference and cannibalism take place. As the clustered eggs within a grain lead to larval competition and conspecific weevil larvae face each other off during development allowing the emergence of one or two larvae per kernel, we hypothesized that such competition and consequent cannibalism will have fitness consequences for the competing individuals and their offspring. Thus, larvae of the granary weevil (Sitophilus granarius L.) and the maize weevil (Sitophilus zeamais Motsch.) were subjected to larval competition with cannibalism, and lack of it, to assess the potential fitness consequence of cannibalism on these non-carnivorous pest species of stored grains. Larval cannibalism reduced developmental time of maize weevil, but not of granary weevil. However, such condition led to heavier adult weevils of both species exhibiting higher reproductive output generating more and better quality progeny than non-cannibal weevils. These findings indicate direct nutritional benefits of cannibalism to grain weevils favoring their status of key pest species of stored cereal grains.