Exploitation of seed hardness, as a mechanism of host plant resistance, could be a useful component of the integrated control of Callosobruchus maculatus (F.) (Coleoptera: Bruchidae). However, traditional methods of measuring larval development period using bioassays do not provide any information on larval feeding activity within seeds. To overcome this difficulty, a biomonitor was used to investigate feeding in seeds of Vigna spp. of different hardness. Larval weight and activity counts were lower in the hard seeded types. Larvae feeding in soft seeds increased their activity with each stadium, with each stadium separated by periods of inactivity. Conversely, for larvae in hard seeds, activity in the second stadium was prolonged and almost indistinguishable from the third and fourth stadia. It is suggested that associations between seed hardness and bruchid development be investigated as contributors to a better understanding of the mechanisms of host plant resistance.
biomonitor, Callosobruchus maculatus, Vigna, seed hardness, host plant resistance