LD50's of emamectin benzoate, chlorpyrifos and methomyl to a field collected sample of a population of the beet armyworm, Spodoptera exigua (Hubner), were significantly lower after six or seven generations of selection than the first two generations. This is inbreeding depression. This beet armyworm population was highly resistant to methomyl (LD50 was >100mg/larva), intermediate in response to chlorpyrifos (LD50 >6mg/larva) but susceptible to emamectin benzoate (LD50 was <0.04 mg/larva) in generation 1-2. In generations 3 and 4 LD50's of seven and four groups of pairs showed a 4191 difference for emamectin benzoate. LD50's showed 3 and 8 fold differences for chlorpyrifos and methomyl, respectively. LD50's for DOW-Zeneca strain were 0.48, 0.064 and 5.18 mg/larva for chlorpyrifos, emamectin benzoate and methomyl, respectively.