Biopesticide value of Uapaca corbisieri and Sterculia oblonga plants against Dermestes maculatus DeGeer (Coleoptera: Dermestidae) infestation in smoked-dried fish Clarias gariepinus Burchell

Fish merchants and consumers face severe deterioration and damage of smoked-dried fish due to Dermestes maculatus (Coleoptera: Dermestidae) infestation. This study evaluates the potential of Sterculia oblonga and Uapaca corbisieri plant powder as natural alternatives to synthetic fumigants for controlling D. maculatus infestation and minimising damage to smoked-dried Clarias gariepinus fish. The powders were separately admixed at concentrations of 5.0, 7.5 and 10.0% w/w per 20 g of dried fish. Results showed that U. corbisieri and S. oblonga powder at different concentrations evoked significant (P<0.05) larval mortality compared to the untreated fish as the concentration increased. Similarly, the application of U. corbisieri powder significantly (P<0.05) inhibited adult emergence compared to the control, whereas adult emergence inhibition rate was non-significant between the samples treated with different concentrations of S. oblonga powder. Feeding activity of D. maculatus larvae on smoked dried fish treated with U. corbisieri was significantly affected compared to S. oblonga powder-treated fish. Untreated fish samples suffered significant weight loss compared with samples treated with plant powders, revealing insecticidal potential of these two plant powders. Their adoption can be encouraged and developed as a biopesticide to reduce the use of synthetic chemicals for the protection of C. gariepinus smoked fish against D. maculatus infestation by some merchants. Further study is recommended to determine the chemical constituents of the plant materials that are responsible for their insecticidal activity. In addition, the toxicity of the plant powder should be evaluated to determine the safe consumption of treated fish.