Some California Mosquito Abatement districts use golden Bear Oil, or GB-1111, extensively as a larvicide. About 300,000 gallons were used throughout California in 1995, and its use has been recommended for use on federal National Wildlife Refuges as a component of an integrated pest control formula for mosquito suppression.  GB-1111 is a petroleum product that is used as a last-resort larvicide when larvae pupate before the site can be treated via other methods.  Other larvicides are ineffective once the larvae have pupated. The oil works by forming a barrier at the air-water interface that suffocates air-breathing insects such as mosquito pupae.  GB-1111 may affect natural predators of mosquitoes such as predatory beetles and others. Proper diet to sustain proper body temperature is critical during the first few weeks of development of many water birds. Aquatic invertebrates comprise 100 to 50 percent of the diets of young ducklings from age day 1 to day 25. Any impediment to sufficient foraging probably results in loss of fitness and increased mortality especially during the first few weeks of development.  Mosquito larvae can comprise a large part of the diet of developing ducklings; without this component, the remaining prey become much more important.  Human resource managers are confronted with controlling mosquitoes for both nuisance and health concerns, while wildlife managers face the dilemma of an impaired food base for fish and wildlife and potentially toxic effects of chemical mosquito controls.

Field and laboratory studies were conducted to determine the effects of the mosquito larvicide California Golden Bear Oil (GB-1111) on duckling survival, target and non-target avian invertebrate prey, and avian embryo development. The purpose of this study was to evaluate the effects of GB-1111 on:  (1) survival of reared mallard (Anas platyrhynchos) ducklings held under field conditions, (2) productivity and survival of aquatic invertebrate prey organisms of migratory birds, and (3) eggs of mallards, bobwhite quail (Colinus virginianus), and red-winged blackbirds (Agelaius phoeniceus).

Field studies on designated natural ponds located in salt marshes in south San Francisco Bay indicated that GB-1111 had an initial significant impact on potential avian prey that dissipated rapidly 3-days post spray.  Over spray, spray drift or treatment of more extensive areas would likely delay recovery of non-target prey.  Mallard ducklings held on the ponds over the course of 8 days showed no significant effects of weight loss due to prey depletion. However some initial effects of exposure to GB-1111 were noted, i.e., matting of feathers and possible mild hypothermia.  Recommended maximum field application rates were determined to be harmless to developing embryos, but reduced hatching success and subsequently mortality of mallards, red-winged blackbirds, and bobwhites was significant at 3 or 10 times the maximum rate. Malformations, edema, and liver EROD in mallards and bobwhites also occurred at 10 times the recommended application rate of GB-1111.  These results signify the importance of avoiding application of GB-1111 during colder times of the spring season, and care in avoiding spray drift, over spray, or overlap spraying of this larvicide.

Learn More by Reading the Full Report: Miles A.K., Lawler S.P., Hoffman D.J., Albers P.H., Melancon M.J., Dritz D., Spring S., and Buscemi D.M., Effects of California Gold Bear Oil (larvicide) on Duckling Survival, Avian Embryo Formation and Invertebrate Prey in South San Francisco Bay, USGS, Western Ecological Research Center, Davis, CA. 1999.

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