Death by desiccation: Effects of hermetic storage on cowpea bruchids

Abstract

When cowpea grain is stored in airtight containers, destructive populations of the cowpea bruchid (Callosobruchus maculatus) don’t develop even though the grain put into the store is already infested with sufficient C. maculatus to destroy the entire store within a few months. The surprising effectiveness of hermetic storage for preserving grain against insect pests has long been linked with the depletion of oxygen in the hermetic container and with the parallel rise in carbon dioxide. With C. maculatus, low oxygen (hypoxia) leads to cessation of larval feeding activity, whereas elevated levels of carbon dioxide (hypercarbia) have little or no effect on feeding. Cessation of feeding arrests the growth of the insects, which don’t mature and don’t reproduce. As a result, population growth ceases and damaging infestations don’t develop. C. maculatus eggs, larvae, and pupae subjected to hypoxia eventually die after exposures of various duration. The cause of death is desiccation resulting from an inadequate supply of water. We demonstrate that blocking the supply of oxygen interdicts the main supply of water for C. maculatus. This leads to inactivity, cessation of population growth, desiccation and eventual death.