Genetic studies of a predominant ladybird beetle species Epilachna vigintioctopunctata Auctt. (Coleoptera: Coccinellidae) of Bangladesh were conducted to evaluate oviposition period, egg-laying, egg-hatch, incubation period, larval and pupal durations, adult emergence, female ratio and longevity of the male and females. Polygenic inheritance of spot patterns of the beetle suggested a dominance relationship of 12 >28 >20 spots. Cross-matings between beetles from Rajshahi, Khulna and Sylhet regions showed no incompatibility. Cytogenetics revealed 2n=18 chromosomes, and the mean total length of the beetle genome was around 32µm. LC50 values of the aqueous leaf extracts of three plant species Ricinus communis L., Calotropis procera (Ait.), and Datura metel L. against the 3rd instar larvae of the beetle were 18.40mL/250mL, 23.70mL/250mL and 29.61mL250mL, respectively. The plant extracts had highly significant effects on egg-laying, egg-hatch and larval duration (P<0.001), and number of pupae and adult emergence (P<0.05). These findings would help understand the genetics of this important phytophagous ladybird beetle species of the country.