Risk to Pollinators from the Use of Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 241

Table 8 Vitality of bumble bee, B. impatiens , colonies following 2-wk
exposure to dry chlorpyrifos (CPY) on mixed stands of turf and flowering
white clover (adapted from Gels et al. 2002 )
Colony measure Control CPY

Weight (g)
Colony (without hive)

193.4 ± 26.3 107.8 ± 7.2 a

Workers 23.1 ± 4.9 7.5 ± 1.1 a

Queen 0.78 ± 0.05 0.78 ± 0.08

No. in colony
Workers 132.8 ± 19.6 56.8 ± 6.5 a
Honey pots 41.8 ± 12.9 5.5 ± 3.6 a
Brood chambers 56.0 ± 5.1 3.5 ± 1.3 a
a Indicates statistically significant (α = 0.05) based on analysis with four
treatments: control, CPY, carbaryl (not shown) and cyfluthrin (not shown)

lasted the duration of the 4-d post-exposure assessment period. Exposure to older
residues of Dursban resulted in a delayed reduction in forager activity. Since the
effect persisted longer than in any other study, there could have been a repellent
effect from a component of the formulation other than the active ingredient, or the
memory by bees of CPY on foliage might have been a retained behavioral influence
on foraging, possibly involving the level of demand for food in the hives. No effects
on brood development were seen in any treatment (Bakker 2000 ).
In conditions such as those presented in these studies, where bees are confined to
experimental plots with a lack of choice of forage, it appears that CPY is toxic for
the first 24 h post-application but only has sublethal effects such as repellency after
24 h. Repellency is considered a sublethal effect but it may be beneficial and is only
an indirect adverse effect in that it may result in a reduced food supply to the hive.
Avoidance of a pollinator to potentially harmful CPY residues is beneficial.

Toxicity studies with non - Apis pollinators . Acute toxicity data for pesticides and
non- Apis pollinators is far less common than for A. mellifera . No reports of contact
and oral LD 50 values for CPY to Bombus spp. were found. However, a semi-ield
study with B. impatiens Cresson was conducted (Gels et al. 2002 ). Colonies of
B. impatiens confined in field cages were exposed to dried residues of CPY on
weedy turf 24 h after application of Dursban 50 W at 1.12 kg CPY ha −1 . Effects on
colonies were evaluated at 14 d. Adverse effects on vitality of bumble bee colonies
were observed, including fewer worker bees, honey pots (stored food), and brood
chambers in hives from treated plots relative to control plots (Table 8 ). Biomass of
workers and weights of colonies were also reduced, and two of the four colonies had
no live brood or adults. Reduced foraging activity was also recorded when bumble
bee colonies were confined to CPY-treated plots, although endemic bumble bees did
not avoid foraging on CPY-treated flowering white clover intermixed with turf (Gels
et al. 2002 ).
Some species of non- Apis bees can be exposed to residues of CPY on nesting
materials such as foliage or soil collected in or near treated crops. Adults can be