Bacillus thuringiensisBerliner toxicity is a dose-dependent phenomenon, and the dose acquired by an individual is directly related to the quantity of treated food consumed. A bioassay was conducted using twoApium graveolens var. rapaceum(L.) cultivars to determine if theB. thuringiensisdose acquired bySpodoptera exigua(Hübner) (Lepidoptera: Noctuidae) larvae was influenced by host plant-induced variation in consumption rates.S. exiguafed the cultivar more suitable for larval growth and development consumed significantly greater leaf surface areas, survived longer, and grew faster than larvae fed the less suitable cultivar.S. exiguafedB. thuringiensis-treated foliage consumed significantly smaller leaf surface areas, had significantly shorter survival times, and grew slower than larvae fed untreated foliage. When leaf surface area consumption was adjusted to reflect theB. thuringiensisconsumed, larvae fed the more suitable cultivar received significantly higher cumulativeB. thuringiensisdoses, but this difference did not explain the observed differences in insect performance. The fact that larvae fed the more suitable cultivar received a greaterB. thuringiensisdose than larvae fed the less suitable cultivar demonstrates that host plant-induced variation in consumption rates can affect theB. thuringiensisdose a herbivore receives. In this particular case, larvae that received the overall greaterB. thuringiensisdoses performed better than larvae that received the overall lower doses, indicating that other factors associated with the host plant play an important role in mediatingB. thuringiensisefficacy.