EFFECTS OF PROCESSING AND DRYING METHODS ON SUSCEPTIBILITY OF WHITE YAM CHIPS TO ARAECERUS FASCICULATUS DEGEER INFESTATION.

Abstract

Laboratory studies were conducted on the survival and extent of deterioration of differently dried and processed yam chips caused by Araecerus fasciculatus. The studies were carried out at temperature of 28±2oC and relative humidity of 75±5%. Chips of white yam, Dioscorea rotundata Poir were obtained using different methods as follows: Parboiled sun dried, Parboiled oven-dried, Parboiled solar dried, Non-parboiled sun dried, Non-parboiled oven-dried, and Non-parboiled solar dried. Fifty grammes of each of the dried yam chips were placed in a glass jar and ten unsexed (1-3 day old) adult Araecerus fasciculatus were placed in each separately and stored for 45, 55 and 65 days. The proximate compositions of dried yam chips were also investigated before and after infestation by A. fasciculatus. Statistical analysis of insect survival on the differently dried and processed chips revealed that adults of A. fasciculatus significantly (p< 0.05) survived on parboiled sun dried than non-parboiled chips. In the susceptibility test and insect developmental study conducted, weight losses caused by A. fasciculatus on parboiled and non-parboiled chips in all the drying methods used at 65 days of storage ranged from 10.17±0.27% to 64.12±0.42% respectively. However, non-parboiled chips sustained lower weight loss of 10.17±0.27%. Adult population density was also significantly lower (P<0.05) on non-parboiled oven dried chips (72.75±0.75) compared to parboiled open sun dried chips (118.67±0.91) at 65 days of storage. The developmental period of A. fasciculatus was similar on all the different processed chips, although it was slightly prolonged on non parboiled oven dried chips. Based on the parameters above, parboiled oven-dried and non-parboiled oven-dried yam chips were less damaged by A. fasciculatus than parboiled sun-dried and non-parboiled sun-dried yam chips. Therefore non parboiled yam chips and the use of solar drier are better than sun dried parboiled chips for the production of yam chips that can be stored for 65 days.