Resistance to fenvalerate (Pydrin) and methomyl (Lannate) was linked to crosses of males from a field collected Tifton (T) strain and females of a susceptible (S) reference strain of beet armyworm, Spodoptera exigua (Hubn.). In F1, LD50's of both insecticides from crosses of male T x female S and brother-sister matings of T strain were significantly greater than those from crosses of female T x male S and brother-sister matings of S strain. Results suggest that genetic factors for resistance to these insecticides are present on the Y chromosome of male even though insecticides have completely different modes of action. Backcrosses of either insecticide to either sex of S and T with F1 reciprocal crosses showed variable LD50 values. When T male and T female were paired with either T x S and S x T of F1 generation, LD50's of fenvalerate were similar but brother-sister matings of T showed a non-significant regression. The presence of S strain in the backcrosses maintained a dose-response. For fenvalerate two introductions of S in the backcross generation had LD50's which ranged from 0.12 to 0.41. Where two introductions of T were made LD50's of fenvalerate ranged from 0.34 to 14.33. For methomyl two introductions of S in the backcross generation had an LD50 of 0.72. Where two introductions of T were made LD50's to methomyl ranged from 1.32 to 3.45. An increase in the factors from T strain resulted in generally greater LD50's.