Risk to Pollinators from the Use of Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 225

by larvae. Larger amounts of nectar or honey are consumed by wax-producing bees,
brood-attending bees, “winter” bees, and foragers, with foragers consuming relatively
large amounts (Rortais et al. 2005 and references therein).
For honeybees, the potential for exposure to CPY can be greater during produc-
tion of bee bread by worker bees than in other activities in the colony. To make bee
bread, workers break newly collected pollen balls deposited by foragers, mix the
pollen with saliva and honey, and pack it into cells with their mandibles and tongue
(Dietz 1975 ). It is possible that the appearance of dead bees in front of a hive fol-
lowing accidental overexposure to pesticides could be the result of these bees being
exposed to a greater dose than the forager bees (Atkins 1975 ).

2.4 Endpoints

Assessment endpoints are explicit measures of the actual environmental value or
entity to be protected (USEPA 1998 ). They are important because they provide
direction and boundaries in the risk assessment for addressing protection goals and
risk management issues of concern. Assessment endpoints were selected a priori
based on likely pathways of pollinator exposure, patterns of use of CPY, and toxic-
ity, as well as their ecological, economic, and societal value. For honey bees, rel-
evant assessment endpoints are colony strength (population size and demographics)
and survival of the colony (persistence), both of which have ecological relevance,
are known to be affected by pesticide use, and are directly relevant to the stated
management goals (Fischer and Moriarty 2011 ; USEPA 2012 ). Productivity of hive
products such as honey was also considered as an assessment endpoint and is
reflected in hive strength. For wild pollinators, species richness and abundance
were considered to be the principle assessment endpoints. In contrast to honey bees,
where the loss of a single forager has little impact on a colony as a reproductive
unit, the loss of an individual bee of a solitary species represents the loss of a
reproductive unit.
Measures of effects are specific parameters that are quantified as indicators of
potential effects of stress that are linked to assessment endpoints (USEPA 1998 ).
These measures are obtained from multiple levels of investigations, including labo-
ratory dosing studies, modeling exercises, controlled field application studies, and
incidents documented in the field. This approach covered all combinations of tox-
icity and exposure. In the laboratory, effects of pesticides on bees are mainly mea-
sured through survivorship after 24-96 h following acute topical or oral exposure,
which is usually expressed as a LD 50 (dose that kills 50% of the test organisms) or
LC 50 (the exposure concentration that kills 50% of test organisms). Acute exposures
are particularly relevant for this risk assessment on pollinators since CPY exerts its
toxic effects rapidly and has a relatively short half-life on vegetation (<1 wk) and
soil surfaces (≈1 wk) (Mackay et al. 2014 ; Racke 1993 ; Solomon et al. 2001 ).
Chronic and sublethal tests can be conducted in the laboratory but there are no
formal guidelines for conducting and interpreting these toxicity tests with pollinators
(Desneux et al. 2007 ; Fischer and Moriarty 2011 ; USEPA 2012 ), and consistent