INFLUENCE OF HEAVY METALS AND COWPEA VARIETIES ON DEVELOPMENT OF COWPEA SEED BEETLE CALLOSOBRUCHUS MACULATUS FABRICIUS (COLEOPTERA : CHRYSOMELIDAE).

Abstract

Investigations were conducted on the levels of heavy metals (Cd, Cr, Pb and As) and nutrient elements (Zn, Na, Ca and K) in six cowpea varieties (Oloyin, Drum, Sokoto local, Niger white, Ife brown and Ife bpc). The estimated daily intake levels of the elements in man and effects on the development of Callosobruchus maculatus were assayed. The concentrations of Cd, Cr, Pb, As and Zn in cowpea were determined using atomic absorption spectrophotometry while those of Na, Ca and K were determined by flame photometry. The Estimated Daily Intake (EDI) were computed and compared with the Provisional Tolerable Daily Intake (PTDI) for toxic elements or Dietary Reference Intake (DRI) in case of nutrient elements. The EDI for Cr, Cd, Pb, As, Zn, Na, Ca and K were 8.65μg/day, 2.45 μg/day, 2.01 μg/day, 1.23 μg/day, 2.33 mg/day, 10.40 mg/day, 11.60 mg/day and 51.02 mg/day respectively. Oviposition correlated strongly with hardness (r = -0.896) and moisture content (r = 0.585) of the cowpea varieties. Also, adult emergence and weight loss are negatively correlated with hardness, r = -0.84 and r = -0.73 respectively. The intake levels of toxic elements in the cowpea varieties studied were within the provisional tolerable limits for the elements. In conclusion, the results of this study showed that intake levels of toxic element does not pose any serious health risk to human. Seed hardness strongly inhibits the infestation of Callosobruchus maculatus on cowpea, and moisture contents influence the level of susceptibility of cowpea to bruchid attack.