Nigerian Stored Products Research Institute (NSPRI) has patented a Diatomaceous Earth, a non-toxic pesticide NSPRIDUST® Patent No. 000744 for storage of grains with Trade Marks Section of the Federal Ministry of Trade and Investment, Abuja, Nigeria. Efficacy of four Nigerian Diatomaceous Earths (DEs): Bularafa, Abakire, Share and Kwami as grain protectants of stored cowpea against cowpea bruchid were compared to a commercial DE Insecto®. The grains were admixed with two varieties of cowpea (Ife brown and IT 98-12 white) separately at 0.1% w/w (1000 ppm). All treatments were infested with 30 unsexed adults of Callosobruchus maculatus (48 h-old). Adult mortality, progeny production, IDK, repellency test and germination of seeds were assessed in NSPRI laboratories in 2016. The Insecto®, Bularafa, Abakire, Share and Kwami caused corrected mortalities of 90, 80, 76, 76 and 43% respectively against adult C. maculatus on Ife brown cowpea while 86, 80,76, 73% and 73% were recorded respectively on IT 98-12 after 72 h exposure. There was F1 progeny suppression. Bularafa was as effective as Insecto®. Results showed that the number of emerged F1 progeny reduced in proportion with increased DE dose rate, but could not prevent progeny production even where complete adult mortality was observed within 5 days. This study showed that progeny suppression is a more important criterion to be considered in efficacy of the DEs on cowpea than adult mortality as the adults are short-lived, do not feed or cause damage but only lay eggs. Repellency showed that test insects avoided treated grains of the two cowpea varieties. There was no significant effect on germination capacity observed in the study.
Key words: Nigerian diatomaceous earth, Callosobruchus maculatus, infestation, stored cowpea.
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