Larvae of the Mexicanbean beetle,Epilachna varivestisMulsant, grew larger when fed on soybean foliage fumigated for 24 h with SO, at concentrations of 131 to 1,834μg m−3than when fed on nonfumigated leaves. Relative weight gain was not linear against SO2concentration in the range sampled; it was greatest when leaves were fumigated with ca. 786μg m−3and less pronounced at either higher or lower concentrations. Smaller relative weight gains, also having a maximum at a concentration of approximately 786μg m−3, were found when larvae were reared on foliage allowed 24 h in which to recover from fumigation. No effect on growth was observed when plants were fumigated with 65μg m−3, indicating a threshold for effect between 65 and 131μg m−3under the conditions of these tests. Change in the plant induced by fumigation, as indicated by growth response of the insects, was rapid, occurring in less than 6 h when plants were fumigated at a concentration of 1,310μg m−3; recovery of the plant from an exposure was slow relative to response time.