Effects of cadmium on two biocontrol insects and their host weeds

Cd added to the nutrient solution at 1 mg·L−1 significantly reduced growth of alligatorweed and purple nutsedge. Both plant species increased about threefold in Cd content when exposed to the added Cd over the 3 to 4 wk periods. A significant difference existed between the two insect species in their response to Cd; the alligatorweed flea beetle was very sensitive to Cd levels in the alligatorweed and the nutsedge moth was virtually unaffected by the levels in the purple nutsedge and diet. These results implied that the alligatorweed/alligatorweed flea beetle system might serve as a sensitive bioassay for heavy metal pollution in sewage effluent, particularly since alligatorweed has been considered as a potential biological filter for effluent (Wolvertonet al. 1975). Other trace elements may be involved in the biogeography of plants and insects and would merit investigation.