Efficacy of Nigeria-derived diatomaceous earth, botanical insecticides, and riverbed sand against Sitophilus oryzae (Coleoptera: Curculionidae) and Rhyzopertha dominica (Coleoptera: Bostrichidae)

Efficacy of Nigeria-Derived Diatomaceous Earth, Botanical Insecticides, and Riverbed Sand against Sitophilus oryzae (Coleoptera: Curculionidae) and Rhyzopertha dominica (Coleoptera: Bostrichidae) on Wheat.

Grace O. Otitodun,^1,2 George P. Opit,¹ and Ego U. Okonkwo²

¹Dept. of Entomology and Plant Pathology, Oklahoma State University, 127 Noble Research Center, Stillwater, Oklahoma 74078-3033, USA

²Nigerian Stored Products Research Institute, Headquarters, Km 3, Asa Dam Road, P.M.B. 1489, Ilorin, Kwara State, Nigeria.

Abstract

Nigeria's insect-related post-harvest food losses are estimated at 30%. Since the 1950s, insect control has been by use of synthetic insecticides which resulted in resistant insects and accidental poisonings and deaths. Consequently, the Government of Nigeria banned all powdery contact insecticides and gas emitting tablets in 2008. Locally available inexpensive and safe alternatives such as botanicals and diatomaceous earths (DEs) are needed. Our objective was to investigate the efficacies of Pepperfruit (Dennettia tripetala), African Brown Pepper (Piper guineense), Bularafa DE, and Riverbed Sand against Sitophilus oryzae (rice weevil) and Rhyzopertha dominica (lesser grain borer) on wheat. Botanical insecticides were applied at a dose rate of 60 g/ kg and DE or Riverbed Sand at a rate of 1 g/kg. Adult insect mortality and progeny production suppression were assessed after 14 and 56 d, respectively. Botanical insecticides alone and in combination with Bularafa DE were effective against R. dominica and S. oryzae and resulted in 100% mortality and total progeny suppression. Bularafa DE caused 69 and 98% mortality of R. dominica and S. oryzae, respectively; and suppressed progeny production by 80 and 88%, respectively. Riverbed sand caused 12 and 8% mortality, respectively; and suppressed progeny production of both species by 13%. D. tripetala, P. guineense, and Bularafa DE have potential for use as inexpensive, safe, and locally available grain protectants in Nigeria. For now, we suggest that these be used for the treatment of seed grain only pending toxicological tests to determine their suitability for treating grain for food and feed.

Keywords: Dennettia tripetala, Piper guineense, rice weevil, lesser grain borer, stored-product pests