Evaluation of three German enhanced diatomaceous earth formulations for the management of two major storage pests in Ghana

In Ghana major stored product insect pests of maize and rice are controlled by the use of synthetic insecticides which are very expensive for farmers, might affect worker safety if not properly applied due to lack of technical know-how. Moreover, its use might eventually lead to some toxic residues in the end product for human consumption. In an attempt to look for alternatives to synthetic insecticides to control storage pest of cereals in Ghana in general, three improved diatomaceous earths (DEs), InsectoSec®, Diatomeenerde Probe-A and Fossil Shield® 90.0 were tested in the laboratory against Sitophilus zeamais Motschulsky (Coleoptera: Dryophthoridae) and Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) from Ghana. Application rates on stored maize or rice were 500, 1000, 2000 and 3000 ppm. Adult mortality was recorded after 32 days and, progeny production after 6 weeks. InsectoSec® was most toxic against the adults of S. zeamais followed by Fossil Shield and Diatomeenerde Probe-A. For the progeny production InsectoSec® and Diatomeenerde suppressed S. zeamais on maize better than Fossil Shield®. In contrast, Fossil Shield® and InsectoSec® were better compared to Diatomeenerde in suppressing progeny production of T. castaneum. There was no significant difference in mortality among the highest dosages of the three DE's against S. zeamais and T. castaneum up to the 14th day, while InsectoSec® and Fossil Shield® were more effective than Diatomeenerde at the lower dosages. Mortality of the adult beetles was dose-dependent. The LT₅₀ ranged from 9 d to 13 d for T. castaneum exposed to 1.0% InsectoSec® and 1.0% Fossil Shield®, respectively. LT₅₀ of 5 d, 6 d, and 9 d were recorded for S. zeamais exposed to the highest dosage of 3.0% Fossil Shield®, InsectoSec® and Diatomeenerde, respectively. All formulations reduced the progeny emergence compared to the control. The potential of using diatomaceous earth for the bio-rational control of major storage pests in Ghana is discussed.