Risk to Pollinators from the Use of Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 224

The main pathway for secondary exposure is transfer of residues in pollen or
nectar into the hive or nest. With CPY, the amount of pesticide in pollen or nectar is
limited to what was present on these materials in the treated area of the crop during
application, since CPY is non-systemic and is not redistributed within the plant.
Some plant species have flowers that provide pollen or nectar for several days after
opening and these would present the highest potential for oral exposure. Secondary
oral exposure from pollen is not limited to sublethal doses since foragers carry
pollen externally and have the potential to bring back to the nest pollen containing
lethal pesticide concentrations without being impaired. This is not likely with prop-
olis, nectar, or water, which are carried internally. Direct transfer of residues from
propolis to larvae is highly unlikely, but some hive adults can subsequently be
exposed when manipulating propolis in the hive.
Potential exposure to contaminated food in the hive depends on the type and
amount of food consumed by the various life stages and castes of bees. While pollen
likely represents the highest risk of oral exposure, there is a decline in concentration
as pollen is processed and used as food in the hive (DeGrandi-Hoffman et al. 2013 ).
Exposure via royal jelly is expected to be minimal because of the large K OW of CPY
(Mackay et al. 2014 ). In field-cage enclosed colonies fed almond pollen, collected
from foraging bees in an orchard, the mean concentrations of CPY in bee bread and
nurse bees were 32 and 8.3% of that found in the pollen, respectively, and no resi-
dues were detected in royal jelly or developing queen bees (DeGrandi-Hoffman
et al. 2013 ). The results in this study show a reduction of at least 1,000-fold between
concentrations of CPY in pollen and those in royal jelly and queen larvae. This
shows isolation of the queen and larvae from exposure to CPY resulting from the
social behavior of the colony, offers significant protection against potential toxicity
of CPY.
As mentioned, amounts of CPY in nectar returned to a hive are expected to be
less than in pollen since nectaries are less exposed than anthers (Willmer 2011 ), but
this is still a pathway for secondary exposure. Nectar is dehydrated and digested by
honey bees to make honey, which is the main source of carbohydrate for the hive.
Mature honey in honey comb is capped with wax for later use, alone or mixed with
stored pollen to make “bee bread”, which is the major protein source for the colony
(Winston 1987 ). Nectar can be consumed directly and is transferred between adult
worker bees as food and when communicating forage sources (Butler 1975 ; Gary
1975 ). Potential secondary contact exposure of eggs and oral- and contact-exposure
of larvae during the first 3 d of development is limited to residues released into royal
jelly by nurse bees or transfer of material from beeswax. As noted above, this route
is minimal for CPY. Older larvae can receive nectar, but only small amounts of pol-
len, and no food is offered to pupae. Larval queen bees are fed royal jelly continu-
ally and food is left in the capped cell for consumption during the pupal stage
(Butler 1975 ; Dietz 1975 ). Even after emergence as an adult, the queen depends on
nurse bees for food and water. This increases the isolation of the queen from expo-
sure to toxicants in the nectar and pollen and exposure via royal jelly is considered
to be less than for other food sources in the hive (USEPA 2012 ). Overall, in honey
bees, greater amounts of pollen are consumed by nurse bees and, to a lesser extent,