Risk to Pollinators from the Use of Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 252

There are other reasons to expect contaminated dew or wet foliage exposure will
be insignificant to honey bees. All the models used are conservative, since they are
based on the assumption that honey bees will consume 100% of the water they
need from a given water source, whereas in reality they can obtain 7-100% of their
required water from food (USEPA 2012 ). Given the short foliar half-life of CPY
(Williams et al. 2014 ), the peak concentrations associated with the higher RQ val-
ues are present for a short time.
Assessment of aggregate risks to honey bees through semi - field and field tests .
Several studies have investigated the concentrations of CPY on foliage of treated
plants and this material was used in laboratory bioassays with bees (Atkins et al.
1973 ; Lunden et al. 1986 ). Their data generally showed that foliage treated with
CPY at the label rate can remain lethal to honey bees, alfalfa leaf cutting bees, and
alkali bees for several days after application. Residual toxicity was determined by
calculating a RT25 value, which is the residue-degradation time required to bring
bee mortality down to 25% or less (Lunden et al. 1986 ). For CPY, the RT25 was
longer than 72 h. For comparison, an RT25 of 8 h that was suggested as indicative
of a product that poses little risk to bees (Lunden et al. 1986 ). Although this result
from caged bioassays is expected to overestimate uptake of material from the sur-
face and the duration of effects, it corresponds with results of multiple semi-field
and field studies that indicate residual CPY on plant foliage poses a risk to honey
bee survival 1-2 d after application.
With one exception, there are no guidelines for pollinator-safe post-spray periods
for CPY. The exception is citrus crops in California, for which CPY must be applied
from 1 h after sunset until 2 h before sunrise (see Atkins and Kellum 1993 ), giving
a 2-h minimum post-spray interval. Assessments of effects after field applications
indicate that some mortality may occur 1-2 d after application on flowering crops,
and reduced foraging may persist for up to a week, but residues remaining after 7 d
have no impact. Rapid, normal turnover of foragers in honey bees colonies and
availability of alternate foraging sites should buffer out these short-term effects.
There were no reports of adverse effects of CPY on honey bee brood development.
The field tests of Lunden et al. ( 1986 ) indicate that concentrations of CPY on
alfalfa during flowering remain lethal to alfalfa leafcutting bees for at least 1 d after
application, with reduced nesting observed. Because leafcutting bees are univoltine,
Lunden et al. ( 1986 ) suggested applications to blooming alfalfa could have a “sub-
stantial” effect on this pollinator. Current label precautions preclude application
when bees are foraging and are intended to mitigate this risk.
Assessment of risk through exposure to contaminated beeswax . A few studies have
reported contamination of beeswax with CPY. Concentrations in beeswax reported
by Mullin et al. ( 2010 ) were similar to amounts found in pollen. Although there can
be a risk of sublethal effects through this route of exposure for some pesticides, one
study found this was not the case for CPY (Wu et al. 2011 ). No data were available
on the uptake of pesticides into larvae from contaminated wax and this is an area of
uncertainty.