The insecticidal potential of two inert dusts, zeolite (ZE) and kaolin (KA), and carbon dioxide (CA) and their
binary combinations was evaluated against Callosobruchus maculatus (F.) and C. chinensis L. (Coleoptera:
Chrysomelidae: Bruchinae). The inert dusts were applied on cowpea seeds at 100, 500 and 1000 mg/kg, and CA
was tested at 10 and 20% for 12 h. The adult mortality was counted after 1, 3 and 7 days of treatment, and
progeny production and weight loss of cowpea seeds were examined after 60 days. The adult mortality of both
insect species exposed to cowpeas treated with individual and binary treatments increased with the increase of
concentration and exposure time. In general, the adult mortality was higher in binary treatments than individual
treatments. The full adult mortality (100.0%) was observed in combined treatment (ZE (1000 mg/kg) + CA
(20%)) after 1 and 3 days in the case of C. chinensis and after 3 days in the case of C. maculatus. Similarly, the
combined treatments of CA (20%) with three rates of ZE (100, 500 and 1000 mg/kg), and CA (20%) with three
rates of KA (100, 500 and 1000 mg/kg) induced 100% mortality of both insect species after 7 days except for CA
(20%) + KA (100 mg/kg) against C. chinensis. Progeny of C. maculatus and C. chinensis was significantly reduced
in individual and binary treatments compared with untreated cowpea seeds. The highest application rates of the
binary mixtures of inert dusts with CA induced strong progeny reduction and complete protection of cowpea
seeds against damage caused by both insect species for 60 days. Our results indicated that the binary treatments
of inert dusts (ZE and KA), with CA seems to be a promising alternative to synthetic insecticides for the control of
bruchid insects on stored legumes. |
