Environmental Engineering Reference
In-Depth Information
exposed when collecting these materials and building nest cells, and immature stages
developing in these cells may also be exposed. When caged adult alfalfa leafcutting
bees, M. rotundata , were exposed to alfalfa plants sprayed with CPY (Lorsban 4E,
2.5 kg ha −1 ), significant mortality was observed. The population of males was
reduced by approximately 90% after only 2 d, and the population of females was
reduced by 30% relative to the controls. No significant additional mortality of
female M. rotundata was observed after the first 4-5 d of exposure (Gregory et al.
1992 ). It was suggested that male M. rotundata were more sensitive to CPY due to
their reduced metabolic capacity and smaller surface area to volume ratio compared
to females.
Studies to evaluate the toxicity of CPY to three species of bees have been con-
ducted (Lunden et al. 1986 ). Field applications of 1.12 kg ha −1 , followed by 24-h
continuous exposure to the treated foliage in small cages was lethally toxic to adult
honey bees, alfalfa leafcutting bees ( M. rotundata ), and alkali bees ( Nomia melande-
ria Cock.) for 5-7 d, whereas a rate of 0.56 kg ha −1 was toxic for 4-6 d. In field tests
on several crops, mortality was observed with application of CPY and reduced for-
aging was observed for 1-7 d (Lunden et al. 1986 ).
Effects on NTA as a surrogate for non - Apis bees . Tier-2 tests with surrogate NTA
species on a natural substrate such as foliage are more realistic than Tier-1 tests that
utilize glass plates (Candolfi et al. 2001 ), but are still conservative because the test
organisms are constrained on or near the treated surface. As with the Tier-1 assess-
ment, no contact toxicity data were found for the recommended wasp species
A. rhopalosiphi . There were data for B. hebetor (Ahmed and Ahmad 2006 ) exposed
to CPY via leaves of cotton, but unfortunately the method of treatment, dipping the
leaves in an aqueous solution, did not allow the deposition on the surface of the leaf
to be calculated, making the data unusable in this risk assessment.
4.3
Tier-3 Field Tests
Several field studies have been conducted to examine the effects on honey bees of
applications of CYP to agricultural crops. These effects are summarized in Table 9
and are described in more detail below. The applications made in these field studies
did not follow current label restrictions, which prohibit application when bees are
actively foraging. The results from application during bloom in a number of crops
under various exposure scenarios suggests that CPY remains lethal to honey bees
for 1-2 d after application on open flowers and may reduce foraging for several
days thereafter.
Dursban was sprayed by helicopter on unreplicated 16-A (approx. 6.5 ha) blooming
alfalfa fields that contained 1-3 honey bee colonies A −1 (Atkins et al. 1973 ). When
applied at night at the highest rate of 1.12 kg ha −1 , Dursban killed an average of 365
bees per colony for 1 d and depressed bee visitation for approximately 3 d. Because
honeybee colonies typically contain 30-60 thousand bees in midsummer when
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