Zanthoxylum plants (Rutaceae) have drawn attention because they contain insecticidal principles against insects. An assessment was made of the insecticidal and acetylcholinesterase (AChE) inhibitory activities of Zanthoxylum piperitum steam distillate and Zanthoxylum armatum seed oil, their 28 constituents, and eight structurally related compounds against female stable fly, Stomoxys calcitrans (L.). Results were compared with those of two organophosphorus insecticides chlorpyrifos and dichlorvos. Potent fumigant toxicity was observed with cuminaldehyde, thymol, (1S)-(-)-verbenone, (-)-myrtenal, carvacrol, (S)-(Z)-verbenol, Zanthoxylum piperitum steam distillate, cuminyl alcohol, Zanthoxylum armatum seed oil, piperitone, (-)-(Z)-myrtanol, and citronellal (LC50, 0.075-0.456 microg/cm3). However, they were five orders of magnitude less toxic than either chlorpyrifos or dichlorvos. An in vitro bioassay using female fly heads indicates that strong AChE inhibition was produced by citronellyl acetate, alpha-pinene, thymol, carvacrol, and alpha-terpineol (1.20-2.73 mM), but no direct correlation between fly toxicity and AChE inhibition by the test compounds was observed. Structure-activity relationships indicate that structural characteristics, such as carbon skeleton, degrees of saturation and types of functional groups, and vapor pressure parameter, appear to play a role in determining toxicities of the test monoterpenoids to stable flies. Global efforts to reduce the level of highly toxic synthetic insecticides in the agricultural environment justify further studies on Z. piperitum and Z. armatum oil-derived materials as potential insecticides for the control of stable fly populations.