Risk to Pollinators from the Use of Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 253

5.2 Estimates of Risk to Non-Apis Pollinators

Studies with non - Apis pollinators . No acute direct contact or oral toxicity data
(LD 50 ) based on laboratory tests were reported for non- Apis pollinators. In a green-
house experiment, Gregory et al. ( 1992 ) exposed alfalfa leafcutter bees ( M. rotun-
data ) to CPY-treated alfalfa and found that mortality only occurred during the first
3 d after treatment. This is in agreement with semi-field and field studies with honey
bees (see discussion above). Because females can only construct nests if doses of
CPY on foliage are sublethal, and because the bioavailability of CPY on foliage
drops rapidly, it is expected that few eggs and larvae will be exposed to hazardous
amounts of CPY from nesting materials.
The only semi-field or field study with a non- Apis pollinator was performed by
Gels et al. ( 2002 ). Detrimental effects were seen in bumble bee ( B. impatiens ) colo-
nies exposed for 2 wk to CPY-treated clover. However, bumble bees were confined
within tunnels for the duration of the entire experiment (a worst-case scenario). In
an open system, effects would likely be less severe. Following label precautions to
avoid application when bees are present, mowing flower heads before treatment,
and weed management with herbicides are useful tactics to alleviate such hazards
from applications of CPY (Gels et al. 2002 ).
No studies on the exposure of bee flies, Bombyliidae, and hover flies, Syrphidae,
to CPY were found. Their potential for exposure is dominated by foraging at flow-
ers since they are nonsocial insects that do not build nests, and feed only them-
selves. Honey bee foragers must visit more flowers, and bee behavior while on the
flower leads to a much higher potential for transfer of material. Therefore, the honey
bee may be considered a conservative surrogate for these taxa. Measures that are
taken to protect honey bees are expected to be protective of these pollinators.

Estimated risk to non - Apis pollinators using NTAs as surrogates . Since toxicity data
for CPY in NTAs is limited and the suitability of these small wasps as surrogates for
wild pollinators is questionable (see above), this risk assessment was not conducted.
However, Addison and Barker ( 2006 ) found that although Microctonus hyperodae ,
another parasitic wasp, was initially (1 h post-treatment) highly susceptible to foli-
age treated with CPY, no 24-h mortality was observed with 2-d old foliage at rates
up to 100 g CPY ha −1 . Bioassays such as these, where insects are confined to cages
are conservative, because most flying insect pollinators do not spend much time on
foliage. The risk posed by CPY is still an area of uncertainty because of the lack of
data for non- Apis pollinators.

Estimated risks through exposure to contaminated soil . Although honey bees can be
a good surrogate for many flying insect pollinators, ground nesting bees and mason
bees can experience exposure via soil (Fig. 1 ), which is not encountered by honey
bees. Mason bees collect soil and use it for the construction of nests, and ground-
nesting bees nest below the soil surface. They might dig their own burrows or they
may use existing cavities built by other animals such as mice (Michener 2007 ). CPY
is toxic to soil dwelling insects and is used in the management of soil dwelling pests.
European chafer grubs ( Amphimallon majalis ) and leatherjackets ( Tipula spp.) are
known to have suffered significant mortality at field-relevant CPY soil concentrations