Risk to Pollinators from the Use of Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 244

alfalfa is in bloom, the loss of this many bees is not likely to be significant for the
health of the colony. It is unclear whether reduced visitation was due to mortality of
bees, a repellent effect of the treated foliage, or, if the lack of bees returning to the
hive to communicate the location of the food resource in the treated area lead to a
shift in foraging to areas from which bees did return. Laboratory bioassays with this
field-treated foliage killed 100% of exposed bees for 3 d. Unfortunately the concen-
tration of CPY per unit of surface area was not determined. Results were similar but
less severe at lesser concentrations of Dursban. No dead bees were found at the
colonies when Dursban was applied at 0.28 kg ha −1 in the morning, although visita-
tions on the field were moderately depressed for 2 d. Bioassays of foliage aged for
12 h from this treatment killed 100% of bees, and showed 0-31% kill on foliage
aged 48-96 h (Atkins et al. 1973 ).
A number of field trials examining mortality and visitation to flowers in alfalfa,
raspberry, dandelion, carrot, and corn were reported by Lunden et al. ( 1986 ). In field
tests on alfalfa in Washington State, Lorsban 4E was applied by aircraft at 1.12 kg
CPY ha −1 to several 0.4-0.8 ha plots in the evening (19:00-21:00 h). Each location
contained two honey bee colonies and three nesting boards with alfalfa leafcutting
bees adjacent to the crop. Mortality of honey bees in the treated plots was five-to
eight-fold higher than in controls. A 56-67% reduction in nesting along with reduc-
tions in visits to flowers of up to 100% was reported for alfalfa leafcutting bees. The
authors concluded that “low-range” honey bee kills occurred (100-200 dead bees
per day on an apron in front of a hive), but colonies did not die. Leafcutting bees,
which do not have multiple generations per year, would suffer more. It was also
suggested that application of CPY to blooming alfalfa would seriously reduce seed
set in crops grown for seed. Lorsban 4E applied to single 0.004 ha plots of dandeli-
ons in pear and apple orchards at 1.12 kg CPY ha −1 caused no reductions in the
number of honey bees foraging and no effects on behavior (Lunden et al. 1986 ).
When Lorsban 50 WP (1.68 kg CPY ha −1 ) was applied by ground-sprayer to
raspberry plots in the evening (Lunden et al. 1986 ), bees behaved erratically after
foraging on blossoms 1 d after treatment, in that they would “mill around, land on
leaves and walk in a wobbly fashion”. Visitation to flowers was 40% of that observed
in the control on d-1 and remained reduced for 7 d. Bioassays conducted in cages
with 3-d-old foliage resulted in 70% mortality of honey bees after 24 h. Chlorpyrifos
is no longer registered for use on raspberries.
Lorsban 50 W applied to a single, blooming carrot field (8.1 ha) at 1.12 kg CPY
ha −1 containing adjacent honey bee hives resulted in over 12-fold more dead bees
and reduced foraging on the crop the day after application, and threefold more dead
bees 2 d after application. The actual number of bees lost was considered to be only
a moderate honey bee kill (250-500 dead bees per hive from an Apron type dead
bee trap or 500-950 from a Todd type dead bee trap) based on criteria of Mayer and
Johansen ( 1983 ), and the long-term viability of the hive was not affected (Lunden
et al. 1986 ). In an unreplicated corn field with adjacent honey bee hives, application
of CPY resulted in four-fold more dead bees and 95% reduced foraging on corn
pollen compared to pre-application counts (Lunden et al. 1986 ). It is unclear whether
there was an overall reduction in foraging, or whether bees simply avoided the CPY-
treated plots. Impacts on long-term survival of the hives were not reported.