Antagonistic, additive and synergistic interactions in the fumigant toxicity of binary mixes of powders of cloves and citrus fruit peels to adults of Callosobruchus maculatus Fabricius (Coleoptera: Chrysomelidae: Bruchinae)

The study evaluated the fumigant toxicity of cloves (Eugenia aromatica Baill.) and citrus peels (Citrus spp.) powders applied singly and binary combinations (1:1 ratio) to the cowpea storage beetle, Callosobruchus maculatus Fabricius under ambient laboratory conditions (28 ± 4°C and 75 ± 10% rh). The powders (singles and mixtures), placed in empty tea bags, were tested at the dosages of 0.0 (control), 0.5, 1.0 1.5 and 2.0 g/20 g of grain in plastic bottles with airtight lids against freshly emerged adult beetles. Adult mortality was observed 24, 48, and 72 h post fumigation. To determine antagonistic, additive and synergistic interactions, corrected mortality data was used to compute co-toxicity factors. Co-toxicity factor for the binary combinations of powders at different dosages at 24 hours indicated antagonistic interaction, ranging from - 40 to -100. Co-toxicity factor at 48 hours ranged from -30 to -90 indicating mainly antagonistic interaction except for Clove + Tangerine, Clove + Lime and Clove + Grape applied at 2.0 g/20 g of grain with -6.7, 0.0, and 6.6 respectively, indicative of additive interaction. Co-toxicity factor at the 0.5 g/20 g of grain dosage at 72 hours ranged from -53.3 to -56.6 indicating antagonistic interaction; at the 1.0 and 1.5 g/20 g ranged from -20 to 6.7 indicating additive interaction; and at the 2.0 g/20 g was 19.7 for Clove and Sweet orange mixture also indicating additive interaction, but 40, 46.7 and 46.7 for Clove and Grape, Clove and Tangerine, and Clove and Lime mixtures, respectively, indicating synergistic interactions.