Differential Response of Cultivar-Morphological Status Combination on Damage Severity of Stored Dates Infested with Oryzaephilus Surinamensis L (Coleoptera: Silvanidae)

Abstract

Three locally sourced date cultivars, Jigawa, Deglet Noor and Mali, were divided into those with and without calyces and infested with 10 pairs of 2-3 days old Oryzaephilus surinamensis to determine their differential response to insect activities and formulate a damage severity scale across 14 weeks. Mean damage severity period (weeks) revealed that date cultivars without calyx significantly (P<0.05) depredated faster than date cultivars with calyx as presence of calyx covering was found to confer protection against infestation and delayed rate of development. Deglet Noor with calyx recorded the longest mean of 11.8 weeks to ferment at damage scale 5, which was statistically different (P<0.05) from Jigawa cultivar without calyx with a mean of 9.0 weeks to reach same damage scale. The result shows significant differences (P<0.05) in the influence of O. surinamensis infestation on stored dates across time where the six date samples recorded varying time periods (weeks) for damage as arranged in decreasing order: Deglet Noor with calyx (DC) > Deglet Noor without calyx (DNC) > Mali with calyx (MC) > Mali without calyx (MNC) > Jigawa with calyx (JC) > Jigawa without calyx (JNC). Thus, the best cultivar-morphological status combination that showed longer quality date storability against O. surinamensis infestation was Deglet Noor cultivar with calyx (DC) while Jigawa cultivar without calyx (JNC) was the least.

Keywords: Oryzaephilus surinamensis, date cultivars, calyx, damage severity scale