Bio-insecticidal effectiveness of three formulations of diatomaceous earths against Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae) in stored cowpea

Three diatomaceous earths (DEs), InsectoSec (R), Diatomeenerde Probe-A and Fossil Shield (R) 90.0, were tested in the laboratory against Callosobruchus maculatus (Coleoptera: Chrysomelidae) from Ghana. Application rates on stored cowpea were 0.05%, 0.1%, 0.2% and 0.3% wt/wt. Adult mortality was recorded after 13-16 d, progeny production after 6 weeks. InsectoSec (R) was most effective towards adults, followed by Fossil Shield and finally Diatomeenerde. The highest dosages of the three DEs showed no difference in effectiveness on the 14th day, while InsectoSec (R) and Fossil Shield (R) were more effective than Diatomeenerde at the lower dosages. For InsectoSec (R), the LD50 and LD90 values were 1.1% and 31.8% wt/wt, respectively, whereas Fossil Shield (R) recorded LD50 and LD90 of 1.0% wt/w and 13.2% wt/wt, respectively. Grain treated with InsectoSec, Fossil Shield and Diatomeenerde recorded less than 4%, 4% and 11% of C. maculatus progeny of the untreated control, respectively; dosage had no effect on the number of progeny. The potential of using diatomaceous earth to control C. maculatus and other major storage pests in Ghana is discussed.