The relationship between water quality, watermilfoil frequency, and weevildistribution in the state of Washington

During the summer of 1997, we surveyed 50 waterbodies in Washington State t o determine the distribution of the aquatic weevil Euhrychiopsis lecontei D ietz. We collected data on water quality and the frequency of occurrence of water-milfoil species within selected watermilfoil beds to compare the wat erbodies and determine if they were related to the distribution of E. lecon tei. We found E. lecontei in 14 waterbodies, most of which were in eastern Washington. Only one lake with weevils was located in western Washington. W eevils were associated with both Eurasian (Myriophyllum spicatum L.) and no rthern watermilfoil (M. sibiricum K). Waterbodies with E. lecontei had sign ificantly higher (P < 0.05) pH (8.7 +/- 0.2) (mean +/- 2SE), specific condu ctance (0.3 +/- 0.08 mS cm(-1)) and total alkalinity (132.4 +/- 30.8 mg CaC O3 L-1). We also found that weevil presence was related to surface water te mperature and waterbody location (chi (2)(2) = 24.3, P less than or equal t o 0.001) and of all the models tested, this model provided the best fit (Ho smer-Lemeshow goodness-of-fit chi (8)(2) = 4.0, P = 0.9). Our results sugge st that in Washington in waterbodies with pH greater than or equal to8.2 an d specific conductance greater than or equal to0.2 mS cm(-1). Furthermore, weevil distribution appears to be correlated with waterbody location (easte rn versus western Washington) and surface water temperature.