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2,6-dialkylpiperideines found in the venom of <i>Solenopsis</i> (Hymenoptera, Formicidae) fire ants are a range of compounds possessing various biological activities. A series of racemic 2-methyl-6-alkyl-Δ^1,6-piperideines were synthesized for chemical confirmation of the natural products found in fire ant venom, and the evaluation of their biological activity. Synthetic Δ^1,6-piperideines and the natural compounds in the <i>cis</i>-alkaloid fraction of <i>Solenopsis invicta</i> had identical mass spectra and retention times. Their insecticidal activities against the third-instar larvae of cotton bollworm (<i>Helicoverpa armigera</i>) were evaluated by using injection and topical application methods. All three compounds exhibited no lethal effect at concentrations of 0.05–0.4 mol/L by topical treatment, but moderate lethal effect at 0.4 mol/L through injection treatment. Compound <b>6a</b> showed significantly higher activity than the natural insecticide nicotine. The differences in activity among compounds <b>6b</b>, <b>6c</b> and nicotine were not significant. The elongation of the carbon chain at the 6-position of the piperideine ring appears to decrease insecticidal activity.