Insecticidal activity of some spices against dermestes maculates Degeer (Coleoptera: Dermestidae) larvae on smoked dried Clarias gariepinus.

Abstract

Dermestes maculatus is a major pest of dried catfish (Clarias gariepinus), causing severe post-harvest losses. Conventional control with synthetic insecticides such as dichlorvos raises health and environmental concerns, necessitating safer alternatives. This study evaluated the insecticidal potential of powders and oils of five botanicals, namely: black pepper (Piper guinense), ginger (Zingiber officinale), garlic (Allium sativum), alligator pepper (Aframomum melegueta), and turmeric (Curcuma longa), in the preservation of dried catfish against D. maculatus. The experiment was conducted under ambient laboratory conditions and a completely randomized design (CRD) with treatments comprising the five botanicals in powder and oil forms, dichlorvos, and an untreated control.  The powders, oils, and synthetic insecticide (Dichlorvos) were applied at the rate of 1.0, 2.0, and 3.0g, and the insecticidal activity of oils extracted from selected spices and  Dichlorvos against Dermestes maculatus larvae, tested at concentrations of 0.00, 1.00, 1.50, and 2.00 ml per 25g of disinfected catfish and air dried for 2 hours. Twenty (20) larvae of D. maculatus were introduced into Kilner jars containing fish treated with these powders, oils, Dichlorvos, and untreated fish, which served as a control. Larvae were recorded between 24 to 96 hours. ). Data obtained from mortality counts were analyzed using one-way Analysis of Variance (ANOVA) at a 95% confidence level. Where significant differences (p < 0.05) occurred, means were separated using Duncan’s Multiple Range Test (DMRT). Phytochemical screening identified major bioactive compounds. Essential oils were extracted and analyzed for yield, refractive index, acid value, peroxide value, saponification value, iodine value, and free fatty acid content. Insecticidal assays were performed by treating smoked fish samples with different concentrations of powders and oils, and larval mortality was recorded. The spices oils, black pepper (Piper guinense) and alligator pepper (Aframomum melegueta)  recorded highest mortality (100.00±0.00)  garlic (Allium sativum) (80.00±0.54), ginger (Zingiber officinale) (58.00±1.00),  and turmeric (Curcuma longa), (53.25±1.7), while, the spices powders recorded, black pepper recorded highest mortality (97.50±0.3) followed by pepper alligator (Aframomum melegueta) (92.70±0.50), garlic (71.0.50±0.10), ginger (52.50±045),  and turmeric(43.00±06.0). Black pepper, alligator pepper, and garlic (powder and oils) achieved the highest larval mortality, respectively, comparable to dichlorvos (100% larval mortality). Ginger and turmeric consistently produced the lowest but still significantly higher mortality than the control (P<0.05). Both spices and formulation significantly affected the mortality of D. maculatus (p < 0.05). The study demonstrates that botanical insecticides are promising, eco-friendly, and alternatives to dichlorvos for the protection of dried catfish against D. maculatus.