Growth and Development of the Biological Control Agent Bagous hydrillae as Influenced by Hydrilla ( Hydrilla verticillata ) Stem Quality

Plant quality of dioecious hydrilla was studied as a factor that may influence larval survival, growth, and development of the biological control agent Bagous hydrillae. Nitrogen content and stem toughness of hydrilla varied among the five sites studied and between summer and fall collections. The nitrogen content of hydrilla collected during summer ranged from 1.2 to 3.6% (dry weight) and during fall from 1.6 to 2.9%. Stem toughness ranged from 487 to 940 g/mm2 during the summer and from 418 to 1442 g/mm2 during the fall. The larvae of this weevil species requiredmore time to complete development when fed hydrilla containing lower levels of nitrogen and tougher stemmed plants. Moreover, pupal and adult fresh weights were also reduced when the larvae were fed the poorer quality plants. Relative growth rates were reduced in larvae fed hydrilla of lower nitrogen level and tougher plants. Hydrilla plant quality constitutes an important factor that may limit the establishment and impact of this potential biological control agent. r 1997 Academic Press