The toxicity of fire ant venom was evaluated under laboratory conditions against Spodoptera litura larvae, a major pest of cruciferous vegetables throughout the Asia-Pacific region. We compared insecticidal activities of venom from Solenopsis geminata, S. invicta (monogyne form) and S. invicta (polygyne form). The Sp. litura larvae were stung by fire ants once in the dorsal thoracic region. A susceptibility assay demonstrated that three kinds of fire ant venom had high insecticidal activities against Sp. litura larvae. Within a few seconds of being stung by the fire ants, the larvae showed significant contractions and paralysis. The mortalities of venom-treated 8-day-old Sp. litura larvae were 100% (S. geminata stung), 96.67% (monogynous S. invicta stung) and 86.67% (polygnyous S. invicta stung) after 24 h. The susceptibilities of Sp. litura to fire ant venom were as follows: S. geminata > S. invicta (monogyne form) > S. invicta (polygyne form), as evidenced by their LT(50) values.