Resistance of Dried Chips of Three Yam Cultivars to Damage by Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae)

Abstract

Yam (Dioscorea spp) is one of the most common tuber crops consumed by man due to its nutritional benefits. Yam tubers are often processed into products like Dry Yam Chips (DYC) to minimize postharvest losses. The crop could be processed into other products to reduce perishability and scarcity at certain periods. The insect is mainly controlled with conventional insecticides. However, use of conventional insecticide in preserving DYC is contentious due to concerns about undesirable effects on consumers. This has necessitated the search for safer and more effective control strategies such as resistance traits that is innate. The study was therefore conducted to evaluate the resistance of three yam species (Dioscorea cayenensis, D. rotundata, and D. alata) used in making DYC to infestation and damage by Larger Grain Borer (LGB). Two hundred (200) g of parboiled DYC were weighed into 250 ml Kilner jars and separately infested with twenty adult LGB of 0-5 days old. The treatments were replicated four times and arranged on the experimental table using Completely Randomized Design (CRD). At 90 days post-infestation, the insects were sieved out to separate insects from DYC. Data were collected on weight loss of DYC, damage to DYC, adult mortality of LGB, dust of DYC, and number of emerged LGB. The percentage damage of LGB to DYC of D. alata and D. rotundata was 100.00% and 96.43%, respectively, which were not significantly (p> 0.05) different from each other. The percentage weight loss (70.61) of DYC of D. alata was significantly (p< 0.05) higher than the weight loss in D. cayenensis (28.63) and D. rotundata (46.27). The percent weight loss in the DYC of D. cayenensis was significantly (p< 0.05) lower than the weight loss in DYC of D. alata (70.61) and D. rotundata (46.27). The number of adult LGB (539.80) in the DYC of D. alata was significantly (p < 0.05) higher than the number of the insect in D. cayenensis (117.8) and D. rotundata (216.80). The number of adult mortality of LGB in the DYC of D. alata (38.50) and D. cayenensis (21.12) is comparable, but significantly lower than number of adult mortality of the insect in D. rotundata (41.50) DYC. The number of the insect larvae in DYC of D. cayenensis (4.25) was significantly (p< 0.05) lower than the number of the larvae of LGB in DYC of D. alata (30.00) and D. rotundata (21.00). DYC of D. cayenensis and D. rotundata were moderately resistant to damage by LGB and could be use in preparation of DYC to mitigate damage of LGB to DYC in storage before use.