Differential Performance of Beet Armyworm and Cabbage Looper (Lepidoptera: Noctuidae) Larvae on Selected Apium graveolens Cultivars

Three Apium graveolens (L.) varieties and cultivars within varieties were evaluated for host plant suitability to two polyphagous lepidopteran herbivores: the beet armyworm, Spodoptera exigua (Hiibner), and the cabbage looper, Trichoplusia ni (Hiibner). Overall, there were no significant differences in survivorship, developmental time, and pupal weight of S. exigua or T. ni reared on the two varieties A. graveo/ens var. dulce and A. graveolens var. rapaceum. Intravarietal differences did exist between cultivars of A. graveolens var. rapaceum; S. exigua reared on 'Kockanski' had a significantly lower mean survivorship to pupation (27.5 versus 82.5%), a significantly longer mean time to pupation (18.5 versus 13.7 d), and a significantly lower mean pupal weight (37.6 versus 75.0 mg) than S. exigua reared on 'PI 223333', a different cultivar of A. graveolens var. rapaceum. In contrast to the response of S. exigua, there were no significant differences in the life history variables among T. ni reared on the same cultivars of A. graveolens var. rapaceum. Quantitative nutritional analysis showed that the differential response of S. exigua and T. ni to the two A. graveolens var. rapaceum cultivars was caused by inability of S. exigua to compensate for reduced efficiencies of conversion of 'Kockanski' to larval biomass. Variation in total nitrogen contents were not responsible for the observed variation in compensatory abilities.