Effects of Variety and Processed Forms of Cassava Chips on the Development Ofprostephanhs Truncates (Horn) (Coleoptera: Bostrchidae) and Araecerus Fasciculatus (Degeer) (Coleoptera Anthribidae)
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Date
2002-11
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University of Ghana
Abstract
Studies were earned out on the effects of variety and processed form of cassava chips on the development of Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) and Araecerus fasciculatus (Degeer) (Coleoptera: Anthribidae). Additionally, changes in the nutrient composition of the chips due to infestation, and the influence of major nutrients on the population parameters of these insects were also studied Statistical analysis of insect preference to the processed chips in a choice test revealed that adults of A. fasciculatus significantly (P<0.05) preferred sun-dried and fermented chips to parboiled
and plain chips. On the other hand, no significant difference (P> 0.05) was observed in the preference of these chips by P. truncatus adults, suggesting that P. truncatus selection of chips occurred mostly by chance. A susceptibility test and adult development at 25-34°C and 61 -92%r h were conducted to
further understand the factors responsible for the differences in the processed chips P. truncatus density increased on fermented chips but this was not significantly different (P>0.05) from the densities recorded on plain and sun-dried chips. However, on parboiled chips low adult densities were recorded and this was significantly different (P< 0.05) from other processed forms Similar studies with A. fasciculatus also revealed the same trend This suggested that in parboiled chips, conditions are less favourable for higher oviposition, larval development and survival of adults and thus constitute a less susceptible form of cassava chips for storage Percentage weight loss due to the two pests in separate studies suggested that P. truncatus caused more damage to the chips compared to A. fasciculatus Weight loss and frass produced by both insects followed almost the same was similar on all the processed form, although A. fasciculatus development was slightly prolonged in sun-dried chips.
Insect infestation caused noticeable changes in the nutrient composition of the cassava chips Starch content decreased in both P. truncatus and A. fasciculatus infested samples. There was an increase in the sugar content of parboiled chips infested by the two insects whereas sugars in plain, sun-dried and fermented chips were reduced Correlation analysis revealed relationships between the nutrient composition of the chips and the population parameters of the insects Significant positive association (r=0.71, P<0.05) was found between starch content and P. truncatus density Alternatively, A. fasciculatus density showed a significantly positive association (r=0.77, P<0.05) with non-reducing sugar and negative association with reducing sugar (r= -0 70, P<0.05). The study has shown the importance of parboiling of cassava as opposed to other processing forms and its effectiveness in conferring protection to chips as a management strategy against losses due to P truncatus and A. fasciculatus Changes in the nutrient contents of cassava due to infestation and the relevance of the significant association of the nutrients and population parameters of the insects are also discussed.