ORIGINAL PAPER Efficacy of diatomaceous earth formulations against Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) in Kersting’s groundnut (Macrotyloma geocarpum Harms): influence of dosage rate and relative humidity Benjamin K. Badii • Charles Adarkwah • Daniel Obeng-Ofori • Christian Ulrichs Received: 13 September 2013 / Accepted: 17 December 2013 / Published online: 29 December 2013 Ó Springer-Verlag Berlin Heidelberg 2013 Abstract The pulse beetle, Callosobruchus maculatus F. is a key pest to stored Kersting’s groundnut, Macrotyloma geocarpum Harms. There are many reports evaluating various diatomaceous earths (DEs) against stored product pests, but there is limited information on the efficacy of these materials against C. maculatus and none on Kerstings groundnut. Laboratory experiments were conducted to evaluate the efficacy of the DEs, Diatomenerde, Probe-A, Fossil shield, and Damol-D1 against C. maculatus in seeds of M. geocarpum. Each DE was applied at 0.50, 1.00, 1.50, and 2.00 g kg -1 , and each treatment infested with newly emerged C. maculatus in petri dishes. The set up was maintained at 50 and 80 % RH regimes at ambient tem- perature. Data were collected on adult mortality (at 24 h, 48 h, 7 days, and 14 days), oviposition, and progeny emergence of the beetles, and their effects on weight loss and viability of seeds. Probe-A proved the most effective against the beetle, followed by Damol-D1 and Fossil shield. Adult mortality increased progressively with the increasing dosage of DE and exposure time. Seeds treated at 2.00 or 1.50 g kg -1 recorded significantly lower number of eggs and F1 emergence compared with the lower dos- ages in all DEs. Increased DE concentration consistently decreased seed weight loss due to low beetle infestation, but there was no significant effect on seed viability. DEs were more effective at 50 % RH than at 80 % RH. Probe-A or Damol-D1 applied at 1.50 or 2.00 g kg -1 at 50 % RH is a viable alternative for preventing C. maculatus infestation in stored Kersting’s groundnut. Keywords Diatomaceous earth Á Callosobruchus maculatus Á Macrotyloma geocarpum Á Dosage Á Relative humidity Introduction Kersting’s groundnut, Macrotyloma geocarpum (Harms) Marechal and Baudet, is a subterranean grain legume cul- tivated in the savanna zones of West Africa (Okigbo 1992). In Ghana, the crop is produced along the northern guinea savanna belt (Bayorbor et al. 2010) mainly for its mature bean-like seeds which are of high nutritional and medicinal significance (Obasi and Ezedinma 1991; Obasi and Ag- batse 1994). A major constraint to the postharvest preser- vation of Kersting’s groundnut seeds in the tropics is infestation by the pulse beetle, Callosobruchus maculatus (F.), which is capable of rendering unprotected seeds unviable and unsuitable for utilization as food within few months of storage (Badii et al. 2011). Infestation occurs when female beetle oviposites on the seed coat. The egg hatches into larva which feeds and pupates inside the grain kernel, and eventually emerges as adult through an exit hole. Complete egg–adult development may last between 26 and 37 days depending on the environmental and host conditions (Beck and Blumer 2011). The control of this Communicated by C. G. Athanassiou. B. K. Badii (&) Department of Agronomy, Faculty of Agriculture, University for Development Studies, P.O. Box 1882, Tamale, Ghana e-mail: benbadii@yahoo.com C. Adarkwah Á C. Ulrichs Division of Urban Plant Ecophysiology, Faculty for Agriculture and Horticulture, Humboldt-University of Berlin, Lentzeallee 55/57, 14195 Berlin, Germany D. Obeng-Ofori University of Energy and Natural Resources, P.O. Box 214, Sunyani, Brong-Ahafo, Ghana 123 J Pest Sci (2014) 87:285–294 DOI 10.1007/s10340-013-0548-0