Abstract
AbstractTwo Apium graveolens var. rapaceum (L.) cultivars that differ in their suitability for the survival and growth of Spodoptera exigua (Hübner) and Trichoplusia ni (Hübner) were used to examine the effect of genetic and seasonal environmental variation in host plant suitability on the efficacy of Bacillus thuringiensis subsp. kurstaki (Berliner). The effects of host plant genotype and B. thuringiensis were generally independent, so that B. thuringiensis efficacy was greatest on the resistant host plant cultivar. Host plant suitability varied within growing season for both insect species but, while host plant suitability decreased with increasing plant age for T. ni, the response of S. exigua to plant age was not as clear. Within season variation in host plant suitability affected B. thuringiensis efficacy and the interaction between B. thuringiensis and host plant cultivar for S. exigua but not for T. ni. Soluble protein and Folin‐Denis phenolic concentrations of host plant tissue were not correlated with changes in host plant suitability to either insect species.
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