Chapters 1 - U.S. Fish and Wildlife Service

Chapter 5
Methoprene applied at levels recommended on the label are not likely to be toxic to non-target
species. For example, methoprene was found to have an effect on copepods, crabs, and shrimp,
although these effects were generally observed at concentrations higher than those of operational
rates (Bircher and Ruber 1988, Marten et al. 1993, Hershey et al. 1998). According to the latest
USEPA fact sheet for methoprene (USEPA 2001), data generated under laboratory and field
conditions indicate that methoprene mosquito product formulations, including slow release
briquette formulations, have a maximal rate of release of 4 parts per billion (ppb). The typical
amount of methoprene necessary for mosquito control is < 1.0 ppb. The initial concentrations of
Methoprene when applied to aquatic habitats may reach 4 to 10 ppb, but residual concentrations
are approximately 0.2 ppb (Ross et al. 1994). Most non-target organisms support margins of safety
of >200 ppb, therefore, exposure to methoprene would not be expected to reach levels which are
toxic to aquatic non-target species either after acute or chronic exposure. Once methoprene is
released into the aquatic environment, it is non-persistent with a half-life of about 30-40 hours.
The conclusions of a few longer term studies of the effects of Bti and methoprene on the
environment do however indicate that repeated use of these products may have indirect effects
related to disruptions in the invertebrate food web that could affect non-target wetland fauna
(Hershey et al. 1998, Poulin et al. 2010). The general conclusion of these studies is that an
integrated approach to mosquito control is necessary to avoid long term detrimental effects on the
environment that appear to be occurring as a result of the continuous (year after year) application
of these types of pesticides within a given area (Hershey et al. 1998, Walker et al. 2005, Tilquin et
al. 2008, Poulin et al. 2010). To minimize the potential for impacts to fish and other marine
organisms from mosquito control, the OCVCD’s Special Use Permit limits the application of these
products to areas around the perimeter of the salt marsh complex.
Public Use
The current public use program does not include any uses with the potential to impact fish or
marine organisms. Research activities are directed by the Refuge Manager through Special Use
Permits that include project specific conditions to avoid any adverse effects to Refuge resources.
Therefore, no adverse effects to fish or marine organisms would result from the continuation of
these programs.
5.4.1.4 Effects to Terrestrial Invertebrates, Amphibian, and Reptiles
Wildlife and Habitat Management
The Refuge management activities that would continue under Alternative A would have limited
potential for impacts to terrestrial invertebrates, amphibians, or reptiles in part because
population numbers and appropriate habitat to support these organisms is relatively low on the
Refuge. Mechanical removal of invasive vegetation could adversely affect some individuals, but
such losses would be low and therefore not considered significant. In areas that have the potential
to support tiger beetles, habitat disturbance associated with Refuge management is minimized to
the maximum extent practicable. Generally, nonnative plant control and culvert maintenance are
not required in these areas. Other activities such as trash removal, surveys/monitoring, and
predator control when conducted in these areas, are limited to reduce the potential for direct and
indirect impacts to these invertebrates.
Pest Management
Based on available literature, the USEPA has concluded that glyphosate is practically nontoxic to
invertebrates, including honeybees (USEPA 1993). The use of products with the active ingredient
oryzalin is not expected to impact terrestrial invertebrates, amphibians, or reptiles. In addition,
oryzalin is classified as practically nontoxic to honey bees (USEPA 1994). According to the
5-42 Seal Beach National Wildlife Refuge