Exposure-related effects of formulated Pseudomonas fluorescens strain CL145A to glochidia from seven unionid mussel species

The study was completed to evaluate the exposure-related effects of a biopesticide for dreissenid mussel (Dreissena polymorpha, zebra mussel and Dreissena rostriformis bugensis, quagga mussel) control on glochidia from unionid mussels endemic to the Great Lakes and Upper Mississippi River Basins. The commercially prepared biopesticide was either a spray-dried powder (SDP) or freeze-dried powder (FDP) formulation of Pseudomonas fluorescens, strain CL145A. Glochidia of the unionid mussel species Lampsilis cardium, Lampsilis siliquoidea,Lampsilis higginsii, Ligumia recta, Obovaria olivaria, and Actinonaias ligamentina were exposed to SDP-formulated P. fluorescens andLampsilis cardium and Megalonaias nervosa were exposed to FDP-formulated P. fluorescens.

All exposures were static, 24 hours in duration, and included six treatment groups. The treatment groups included (1) an untreated control, (2) a positive control which received a nominal target active ingredient (AI) concentration of 300 milligrams per liter (mg/L) of heat-deactivated test article, and (3) treatments that received nominal target AI concentrations of 50, 100, 200, and 300 mg/L of test article. All treatment concentrations are reported based on active ingredient.

Glochidia viability was reduced in two of the six species exposed to 50 mg/L SDP and in four of the six species exposed to 100 mg/L SDP when compared to untreated control groups at 6, 12, and 24 hours. Regardless of sample time, concentrations of 200 and 300 mg/L of SDP and 300 mg/L of heat-deactivated SDP (positive control) substantially reduced glochidia viability in all species except, L. higginsii. Glochidia viability was only reduced for L. cardium exposed to FDP at concentrations ≥ 200 mg/L. After 24 hours of FDP exposure, differences in glochidia viability were only detected in M. nervosa that were exposed to 300 mg/L of heat-deactivated SDP. However, given the low viability in the control group, the results for M. nervosa should be interpreted with caution.