The effect of processing method of cassava chips on the development of Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae)

Abstract

Susceptibility of processed cassava chips to infestation by the Larger Grain Borer, Prostephanus truncatus (Horn) was investigated in the laboratory (25 - 34°C, 61 - 92% r. h and 12 h: 12 h light: dark regime). Chips of two varieties were variously processed by fermentation, parboiling and sun-drying and stored for different periods. About 150, 200 and 300 g of processed cassava chips in Kilner jars were artificially infested with 15 pairs of P. truncatus adults and stored for 49, 59 and 69 days respectively. Significant differences (P < 0.05) were observed in the mean numbers of adults recorded on the processed chips after 49 days of storage. Across varieties, fermented chips recorded the highest number of adults (407.0 ± 53.9), followed by 395.9 ± 34.5 and 351.0 ± 42.1 adults found on plain and sundried chips, respectively. Parboiled chips however supported the lowest number of adults (89.0 ± 16.4). The number of P. truncatus adults increased with increasing storage period on all chips. The overall mean weight loss recorded on plain, sun-dried and fermented chips were 71.5 ± 7.7%, 71.2, 6.7% and 71.7± 8.8% respectively after 69 days of storage by which time most of the chips had disintegrated completely. The lowest amount of loss, 20.9 ± 5.0%, was recorded on parboiled chips. The study showed that the practice of parboiling confers greater protection to cassava chips against infestation and losses due to P. truncatus than the other traditional fermentation and sun-drying methods.