Test insect and essential oils: C. maculatus from the groceries of Shaheb Bazar, Rajshahi. The cowpea, Vigna unguiculata (L.) Walp. seeds were used as food medium throughout the experiments. The essential oils, cardamom, cinnamon and clove were purchased as pure oil (India) from an essential oil shop. The oils were further dehydrated in a vacuum rotary evaporator. The oils were then collected in sealed glass containers and refrigerated in the dark at 4°C until they are used. Toxicity tests with single dose: Residual film method (Busvine, 1971) was used to test the mortality of the adult C. maculatus. Technical grade of Pirimiphos-methyl (0-2-(diethylamino)-6- methylpyrimidin-4-yl) 0,0-dimethyl phosphorothioate (C.A.) 0-[2-(diethylamino)-6-methyl-4-pyrimidinyl] 0, 0-dimethyl phosphorothioate) was used as insecticide, collected from ACI Limited. The insecticide was diluted in acetone and different doses were prepared. At first an ad-hoc experiment was made. After having a clear picture about mortality of beetles, the final experiments were set up. The doses used for pirimiphos methyl were 0.047, 0.037, 0.028, 0.019 and 0.009 μg cm-2, whereas the doses of cardamom, cinnamon and clove oils were 56.586, 47.155, 37.724, 28.293 and 18.862 μg cm-2, 37.724, 31.436, 25.149, 18.862 and 12.575 μg cm-2, and 47.155, 39.296, 31.436, 23.575 and 15.718 μg cm-2 respectively. One ml of liquid from each dose was dropped on petri dishes (90 mm) separately, covering uniformly the whole area of the petri dish. They were then kept open for sometimes to dry-up. Four plastic rings (30 mm) were placed inside a petri dish and 10 adult beetles were released within each ring. The rings within the petri dish were served as replications. The doses were calculated by measuring the actual amount of active ingredient (μg) present in one ml of the solvent divided by the surface area of the petri dish. One batch of control was maintained in which only acetone was applied for each strains, respectively. Toxicity tests with combined doses: Pirimiphosmethyl was combined in mass ratios (1:1, 1:2, 1:5, 1:10 and 1:20) with the essential oils used and applied on C. maculatus adults. The doses of pirimiphis-methyl and cardamom oil in mass ratios were 0.051, 0.041, 0.031, 0.021 and 0.011 μg cm- 2 for 1:1 ratio; 0.099, 0.079, 0.059, 0.039 and 0.019μg cm-2 for 1.2 ratio; 1.202, 0.962, 0.721, 0.481 and 0.240 μg cm-2 for 1:5 ratio; 1.587, 1.270, 0.952, 0.634 and 0.317 μg cm-2 for 1:10 ratio and 0.790, 0.632, 0.474, 0.316 and 0.158 μg cm-2 μg cm-2 for 1:20 ratio. In case of pirimiphos and cinnamon oil the combined doses were 0.130, 0.104, 0.078, 0.052 and 0.026 μg cm-2 for 1:1 ratio; 0.247, 0.198, 0.148, 0.099 and 0.049 μg cm- 2 for 1.2 ratio; 10.601, 0.481, 0.361, 0.240 and 0.120 μg cm-2 for 1:5 ratio; 10.798, 0.638, 0.479, 0.317 and 0.159 μg cm-2 for 1:10 ratio and 0.790, 0.632, 0.474, 0.316 and 0.164μg cm-2 for 1:20 ratio. The doses of pirimiphos-methyl and clove oil in mass ratios were 0.108, 0.086, 0.065, 0.043 and 0.022 μg cm-2 for 1:1 ratio; 0.206, 0.165, 0.123, 0.082 and 0.041 μg cm-2 for 1.2 ratio; 0.250, 0.200, 0.150, 0.100 and 0.050 μg cm-2 for 1:5 ratio; 1.588, 1.270, 0.953, 0.635 and 0.317 μg cm-2 for 1:10 ratio and 2.369, 1.896, 1.422, 0.948 and 0.474 μg cm-2 for 1:20 ratio. Analysis of Data: The mortality of adult beetles was recorded after 24h of treatment. Corrected mortality percentage was calculated using Abbott’s formula (Abbott, 1925); probit analysis was done using a software developed in the Department of Agricultural and Environmental Science, University of Newcastle upon Tyne, UK. If the probability was greater than 5% an automatic correction of heterogeneity was introduced. Cotoxicity coefficient was calculated.