Abstract: Genetic studies were carried out on susceptible laboratory strains and field resistant strains of Rhyzopertha dominica and Sitophilus oryzae. Dose-mortality characteristics of susceptible and resistants parents and their F_l hybrids, F₂-backcross progeny and Fa mass cross progeny were assessed in order to determine inheritance character. Results indicated that the reaction of F₁ hybrid to phosphine was closer to its susceptible parent strain; x² analysis of the responses observed of F₁-backcross and F₂ progeny rejected the null hypothesis of monogenic inheritance for resistance. The inheritance of phosphine resistance in the two species was more complex and the resistance appears to be controlled by one or more autosomal factors but the major gene involved are incompletely recessive. Degrees of dominate (D) are-0.768 for R.Dorninica and-0.348 for S. aryzae.

Key words: Rhyzopertha dominica——Sitophilus oryzae——phosphine—— insecticide resistance genetics