Relative Susceptibility and Proximate Composition of Some Imported and Local Rice Varieties to Infestation and Damage by <i>Sitophilus oryzae</i> L. (Coleoptera: Curculionidae)

Abstract

Ten rice varieties were assessed for their comparative susceptibility and proximate composition to post harvest infestation and damage by Sitophilus oryzae L. (Coleoptera: Curculionidae). The damage parameters used to compare the susceptibility of the rice varieties to S. oryzae were; percentage mortality 4 weeks after adult insects infestation, number of F1 progeny, percentage grains weight loss and F2 adult emergence. Four weeks post infestation (WPI), almost all the adults introduced to ITA 315 had died (95% mortality rate) which was significantly (P 0.05) in the weight loss of Igbemo, Ofada and Erio varieties. Highest and lowest weight loss was obtained for Isan and ITA 315, at week 8 and 12 respectively. The extent of damage done by the introduced adult S. oryzae were observed to be reduced in ITA 315, Caprice, ITA 257 and Cisadene varieties, as they may have found it hard to puncture into or oviposit in the grains, resulting in reduced weight loss, and low F1 progeny and F2 adult emergence. Grain hardness, moisture content and anti-nutrient compositions of the selected varieties were investigated whether it may be used as indicators of resistance. Only moisture content could be established as an indicator of resistance, as the grain moisture content was significantly positively correlated with both F1 and F2 adult emergence. The imported varieties which recorded higher resistance had lower moisture content compared to the local varieties. Grain hardness and anti-nutrient composition did not affect susceptibility of the rice varieties to infestation and damage of S. oryzae because there was no significant (P>0.05) correlation between the two variables and susceptibility to the weevil.