Todd J. Severson — Page 2

USGS2015

Efficacy of Pseudomonas fluorescens strain CL145A spray dried powder for controlling zebra mussels adhering to native unionid mussels within field enclosures

The efficacy of a commercially prepared spray dried powder (SDP) formulation of Pseudomonas fluorescens (strain CL145A) was evaluated for removing zebra mussels ( Dreissena polymorpha ) adhering to a population of unionid mussels in Lake Darling (Alexandria, Minnesota). Two groups of unionid mussels were used in the study. Unionid mussels were collected near the test area, weighed, photographed, individually tagged, and randomly allocated to one of nine test enclosures in equal proportions and then divided into two groups. The first group of unionid mussels (Group 1, n = 5 per test enclosure) were indiscriminately selected from each test enclosure and used to estimate the number of zebra mussels adhering to unionid mussels prior to exposure. The second group of unionid mussels (Group 2, n = 22 per test enclosure) were used to evaluate the efficacy of SDP for removal of adhering zebra mussels. Both Group 1 and Group 2 mussels were used to evaluate the effects of SDP exposure on unionid mussel survival. Treatment was assigned to each test enclosure by using a randomized block design. The three treatment groups were tested in triplicate and included an untreated control group and groups that received a single application of 50 or 100 milligrams per liter (mg/L) of SDP based on active ingredient. All treatment concentrations are reported as active ingredient of SDP. Test enclosures were removed at the 8-hour exposure termination. Both Group 1 and Group 2 mussels remained in their assigned exposure location during the postexposure holding period. The number of zebra mussels adhering to Group 2 mussels (live and dead) was assessed 18 to 20 days postexposure in addition to assessing the survival of Group 1 and Group 2 unionid mussels. SDP, administered as a single treatment, significantly ( p < 0.01) reduced the number of adhering zebra mussels when compared to the untreated controls. The number of zebra mussels adhering to unionid mussels (Group 2) was reduced 53 percent in the 50-mg/L treatment group and 68 percent in the 100-mg/L treatment group. The number of adhering zebra mussels did not differ ( p = 0.79) between the 50- and 100-mg/L treatment groups after exposure. When standardized to the amount of SDP applied per square meter, each gram (g) of SDP applied in the 50-mg/L treatment reduced the number of adhering zebra mussel 59.8 percent more than the 100-mg/L treatment group. Group 1 mussel survival did not differ between treatment groups ( p > 0.05); however, a difference was detected ( p < 0.01) in the survival of Group 2 mussels. The survival of Group 2 mussels did not differ ( p > 0.23) between control and treated groups. A difference in Group 2 mussel survival was detected ( p = 0.03; odds ratio [OR] = 0.290) between the 50- and 100-mg/L treatment groups (that is, the survival was highest in the 50-mg/L treatment group and lowest in the 100-mg/L treatment group), however, the biological significance of the difference is indeterminate.

Minnesota↗

USGS2015

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 and Lampsilis 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.

Open-File Report↗