Water loss and mortality of adult cowpea weevils (Coleoptera : Bruchidae) exposed to desiccants and desiccating environments

Water relations and desiccation tolerance of adult cowpea weevils, Callosob ruchus maculatus (F.),were examined in response to exposure to desiccants a nd desiccating environments. Cuticular permeability was similar for both se xes (approximate to 5.3 mu g cm(-2) h(-1) torr(-1)) and was comparable with other xerically adapted arthropods. At 30 degrees C and 0% RH, percentage of initial mass lost as well as percentage of total body water lost increas ed curvilinearly with time of desiccation for both sexes. All desiccant and insecticide dust formulations were toxic to cowpea weevils. LT50 values ra nged from approximate to 11 min for male beetles exposed to DeltaDust (0.05 % [AI] deltamethrin) to approximate to 597 min for female beetles exposed t o pine ash. Continuous exposure to any of the formulations resulted in 100% mortality within 24 h. Exposure to any dust formulation resulted in increa sed water loss by adult cowpea weevils. Continuous exposure to Eaten's KIO system (diatomaceous earth) resulted in an 88.7% increase in cuticular perm eability of male beetles; exposure to DriDie (silica gel) resulted in an 1, 660% increase in cuticular permeability for female beetles. Pine ash increa sed cuticular permeability approximate to 150% and approximate to 320% for adult male and female beetles, respectively; similar to the effects of Delt aDust. Exposure to any of the dust formulations tested in this study result ed in significant increases in adult cowpea weevil cutaneous water loss and mortality.