Larval Performance in Relation to Labile Oviposition Preference of Crocidolomia pavonana [F.] (Lepidoptera: Pyralidae) Among Phenological Stages of Cabbage

Crocidolomia pavonana ( binotalis) [F.] demonstrates oviposition peaks in the Þeld that we believe to be correlated with host plant phenology. In previous two-choice laboratory experiments, we found the highest relative proportion of oviposition on cabbage to correspond either to plant growth stages 7Ð8 wk or 9Ð11 wk old, depending on the alternate host plant with which it was presented. In cabbage-only trials, leaves from 7to 8-wk-old plants were preferred. Inconsistency in preference led to the question of whether oviposition on either cabbage growth stage would confer adaptive advantages in offspring performance. We simulated oviposition on four phenological stages of cabbage in two ways. In a study of complete immature development, growth rate, pupal weight, and survivorship were measured. We also compared food utilization efÞciency during the fourth larval instar by analyzing growth rate, efÞciency of biomass accumulation, and frass production by analysis of covariance (ANCOVA). For both experiments, cabbage plants of deÞned phenological stages were designated at the time of oviposition, and larvae were fed from these as plants continued to grow throughout larval development. Our data indicate adaptive advantages in larval growth rate and food conversion efÞciency to oviposition on cabbage at 7Ð8 wk from planting. Oviposition on later cabbage growth stages resulted in comparatively poor larval performance. Possible explanations for C. pavonana oviposition behavior in light of these results are discussed.