The long-term effects of methoxyfenozide on the longevity and reproductive processes of beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), adults were assessed after exposure by ingestion. Methoxyfenozide significantly reduced adult male longevity compared with females by 1.1 and 1.5 d at 75 and 150 mg (AI) /liter, respectively. Fecundity decreased by >60% with both concentrations at 72 and 96 h after treatment, but at 48 h, no significant effect was observed. The carbohydrate, protein, and lipid content in the eggs were determined as representatives of the biochemical effects of methoxyfenozide associated with the disruption of reproductive processes. The content of carbohydrates in the eggs laid 48 h at treatment was similar to that of controls, but it increased by ≈1.5 and 2-fold in eggs laid after 72 and 96 h, respectively, compared with controls (15 µ g per egg). Protein content was reduced ′2.5 and ′3-fold for each treatment concentration, respectively, compared with the controls (25 and 23 µg per egg for 75 and 150 mg [AI] /liter, respectively) in eggs collected 72 and 96 h after treatment. Lipid content significantly decreased by ≈1.6-fold in both treatment concentrations in eggs collected at 48 and 96 h after treatment compared with the controls (24 and 21 µg per egg for 48 and 96, respectively), but it was similar to controls (=19 µg per egg) at 72 h (≈15 µg per egg) for both concentrations. The biochemical effects of methoxyfenozide on S. exigua egg formation detected in this work are consistent with the reduction in fertility observed, as reported previously.