Preliminary investigation on the damage assessment and control of Bostrychoplites Cornutus (Olivier, 1790) on dried cassava chips
EN Nwankwo, NJ Okonkwo, IB Osondu, Ogbonna Confidence U
Preliminary investigation on the damage assessment and control of Bostrychoplites cornutus (Oliver, 1790) (Coleoptera: Bostrichidae: Bostrichinae) was carried out after a preliminary market survey revealed it to be the most abundant and damaging of all the insect pests of dried cassava chips and tubers in Main market, Enugu, Enugu State, Nigeria. The result of the insect morphometrics showed that it has a body size of 8mm by 3mm with a horn-bearing prothoracic neck shield of 3mm in length and a body weight of 30mg. Using two processed cassava varieties, TMS 0581 and TME 419 of 10% and 8% moisture content respectively under an ambient mean temperature of 28.5 ºC and mean relative humidity of 78.5%, the biology of the bostrichid and its damage on the cassava varieties were studied. Within the 30 days of the study, no new larvae or adult emerged and the cassava varieties were moderately damage, with a visual scale damage of 7.0% and 7.2% respectively. In addition, the percentage frass recorded on the two cassava varieties were 2.3% and 3.3% respectively while the percentage weight losses were 3.6% and 4.8% respectively. Statistical analysis showed significant differences (P< 0.05, P = 0.035) between the varieties. The study on the susceptibility of the bostrichid using residual treatment of deltamethrin 12.5 EC showed that it is resistant to deltamethrin as up to 50% mean mortality was not obtained until 72 hours of exposure. The probit graph of the mortality showed the LD50 was 194.36ul/ml whiles the LT50 was 100 hours. From the study, it is suggested that the source of the bostrichid be traced; its life cycle re-studied and several pesticides tested against it to halt its invasion into the cassava production industry.