Effectiveness of diatomaceous earth combined with chlorfluazuron and hexaflumuron in the control of Callosobruchus maculatus and C. chinensis on stored cowpea seeds

Abstract

The insecticidal potential of diatomaceous earth (DE), two chitin synthesis inhibitors [chlorfluazuron (CH) and hexaflumuron (HE)] and their binary mixtures was tested against Callosobruchus maculatus (F.) and C. chinensis (L.) on cowpea seeds. Diatomaceous earth was assessed at rates of 100, 500 and 1000 mg/kg. The two insecticides (CH and HE) were evaluated at rates of 0.5, 1.0 and 2.0 mg/kg. The mortality of adults was recorded after 7 days, progeny production, seed weight loss and seeds germination were tested after 45 days of treatment. The combined treatments of DE with CH or HE produced higher adult mortality of both insect species than the individual treatments. The maximum adult mortality of C. maculatus (100.0%) and C. chinensis (97.4%) achieved in a binary combination of DE (1000 mg/kg) + CH (2.0 mg/kg) after 7 days of exposure. Likewise, a complete mortality of both insect species was obtained in the mixtures of DE (500 mg/kg) + HE (2.0 mg/kg) and DE (1000 mg/kg) + HE (2.0 mg/kg) after 7 days. Progeny of C. maculatus and C. chinensis was significantly decreased in all tested treatments compared with untreated cowpea seeds. Furthermore, the mixtures of DE (1000 mg/kg) + CH (2.0 mg/kg) and DE (1000 mg/kg) + HE (2.0 mg/kg) induced complete protection of cowpea seeds (weight loss <0.5%) against damage caused by C. maculatus and C. chinensis after 45 days. The results indicate that the combinations of DE with CH or HE at low rates seem to be an effective approach for the control of two bruchids on stored cowpeas.