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The nontarget eVects of three plant growth stimulants (gibberellic acid, Siapton and triacontanol) and two plant growth retardants (chlormequat chloride and mepiquat chloride) on the survivorship and developmental parameters of Spilarctia obliqua Walker (Lepidoptera: Arctiidae) were studied. For each compound, various concentrations (0.125£, 0.25£, 0.5£, £ , 2£ and 4£; £ = labeled dose) bracketing the labeled dose were prepared by serial dilution and mixed with an artiWcial diet for the insect. Gibberellic acid caused an increase in the larval period at £ ¡ 4£, but no marked diVerence was observed in the pupal period or in larval survival at any concentration. Siapton induced a signiWcant increase in larval period at the two highest doses but caused signiWcant reduction in pest survival at £ ¡ 4£. Interestingly, triacontanol induced a signiWcant reduction in pest survivorship at almost all doses. The LC 50 for triacontanol was 0.206% and LT 50 was 266.5 hours at the labeled dose. However, triacontanol did not cause any signiWcant diVerence in larval or pupal periods at any dose tested. Chlormequat chloride and mepiquat chloride caused signiWcant reduction of larval survivorship at concentrations higher than the labeled doses, and no eVect on the larval period. Intriguingly, a signiWcant reduction in pupal period was observed with chlormequat chloride at £ and 0.25£. Based on the marked eVect of triacontanol on pest survivorship, this study suggests incorporating triacontanol in integrated pest management modules for S. obliqua. Caution in the use of gibberellic acid and Siapton for pest infestations is also indicated.