HERBIVORE ADAPTATIONS TO A LOW-NUTRIENT FOOD - WEED BIOLOGICAL-CONTROL SPECIALIST SPODOPTERA-PECTINICORNIS (LEPIDOPTERA, NOCTUIDAE) FED THEFLOATING AQUATIC PLANT PISTIA-STRATIOTES

Performance of the specialist herbivore Spodoptera pectinicornis (Hamp son) was studied when fed the floating aquatic plant waterlettuce, Pis tia stratiotes L. (Araceae). Plants were either collected from 6 popul ations in southern Florida or from plants grown with low or high ferti lizer levels. Consumption of leaves with increasing toughness resulted in increased larval mortality (>80%); most mortality occurred during the first 2 instars. Larvae compensated for low-nitrogen leaves by inc reasing fresh weight consumption 3-fold. Both developmental lime and b iomass gain were effected by the source of the plants but these perfor mance parameters were not directly related to either leaf toughness or nitrogen levels. These results are useful in understanding the adapta tions arid limitations of specialist herbivores to low-nutrient foods. Additionally, they assist in the selection of suitable release sites for this weed biological control agent. Finally, they improve our mass -rearing techniques for augmentative releases of this biological contr ol species.