Effect of Sitophilus zeamaisMotsch. (Coleoptera: Curculionidae) Infestation on Tryptophan Content of Stored Quality Protein on Maize Varieties.

Abstract

The effect of Sitophilus zeamais infestation on tryptophan content was evaluated on ten (10) maize varieties, comprising nine Quality Protein Maize (QPM) varieties and one non-QPM which served as check. One hundred grammes of each maize variety were infested with ten pairs of newly emerged S. zeamais in separate kilner jars. The number of F, and F2 progeny, percentage damage, percentage weight loss and effect of kernel hardness were evaluated for each maize variety. The tryptophan content of the maize varieties were determined before and after infestation with S. zeamais to determine the amount of losses incurred as a result of feeding by S. zeamais .The result showed that at 45 days after infestation with S. zeamais, FLINT-Q (24.63) was relatively the most susceptible variety with the highest mean number of F1 progeny while SAMMAZ 17 (12.63) had the least amongst the QPM varieties. At 90 days after infestation with S. zeamais, DENT-Q (51.63) had the highest mean number of F2 progeny whereas SAMMAZ 17 (19.25) had the least. The highest mean number of damaged grains with emergent holes were observed in FLINT-Q (36.50) followed by DENT-Q (34.88). The highest weight loss was also observed in FLINT-Q (7.78) followed by DENT-Q (7.59). A maximum reduction in tryptophan as a result of feeding by S. zeamais was found in FLINT-Q (42.86 %) which decreased from an initial value of 0.07 % to 0.04 % at 12 weeks of storage. Minimum reductions in tryptophan (11.11 %) amongst the QPM varieties were observed in SAMMAZ 17 which decreased from 0.09 % to 0.08 %. The results on the determination of grain hardness showed that SAMMAZ 17 appeared to be relatively harder than all the .other QPM varieties. It can therefore be concluded that SAMMAZ 17 variety with relatively hard kernel is the most tolerant variety to S. zeamais infestation which can be stored for 90 days with minimum insect infestation and reduction in tryptophan content.