Are Wildlife Living in
Pesticide-Sprayed Orchards Healthy?
Southern Ontario possesses an unusually temperate climate that provides a
unique habitat for Wildlife and optimum growing conditions for agricultural
crops in Canada. These characteristics promote interactions between a wide
diversity of wildlife and agricultural activities in this zone. The area is the
part of Ontario located along the Lake Ontario shoreline or south of
approximately 43° N latitude (Cadman et al. 1987). It is the transition zone
between two major forest regions: the Eastern Deciduous Forest, which in Canada
is commonly referred to as the Carolinian Zone; and the Great Lakes-St. Lawrence
Forest (Cadman et al. 1987).
In this zone southern Ontario has warmer than average Canadian temperatures
throughout the growing season. There is an ameliorating effect of Lakes Ontario
and Erie on the climate which contributes to the existence of a frost-free
period of 169 days, and mean annual precipitation of 700 mm which are ideal for
tender fruit production (McCuaig and Manning 1982). Consequently, the floral and
faunal assemblage in southern Ontario is diverse and includes many species that
are at or near the northern or southern limits of their geographic range (Heagy
and McHattie, 1995).
Coincidentally these conditions present a valued land resource for
agriculture, especially fruit production, due to the mild climate, and soils
that are mainly class 1 and 2, well-drained and lightly textured (McCuaig and
Manning 1982). Some bird species have thrived in the open landscapes typical of
agricultural areas while other species persist despite the removal of 90% of the
forest cover of southern Ontario for agricultural and urban development (Cadman
et al, 1987; Kirk et al. 1996). Consequently, wildlife that occur in southern
Ontario live in wild remnant and fragmented habitats on or near farms and cities
or in semi-natural areas such as orchards.
Since pesticide use is common in apple orchards in southern Ontario, studies
have been conducted by the Canadian Wildlife Service and the University of
Guelph to determine if pesticides affect the reproduction and health of
songbirds that nest in orchards in southern Ontario.
Historical Pest Control
By 1791, 200,000 inhabitants were established in agricultural settlements
along the Niagara Peninsula in southern Ontario (McCuaig and Manning, 1982). By
the later 1800s, pesticide use on larger orchards was common. “Bordeaux”
mixture, consisting of 0.3 Ibs/10 gallons water each of copper sulfate and lime,
was used as a fungicide for apple scab (Venturia inaequalis) (Beckett,
1913; Emerson et al.,1945).
Two arsenic sprays, Paris green (0.33 lbs/ 50 gallons water) and lead
arsenate (1.5 Ibs/50 gallons water), were used on orchards to control insects,
mainly codling moth (Cydia pomonella) (Emerson et al., 1945). Spray
applications were made from two to seven times per growing season to control the
same pests of concern to apple growers today (Ontario Ministry of Agriculture
and Food, 1994).
By the 1940s, agricultural publications began describing methods by which
these chemicals could be applied efficiently to improve yield and reduce spray
costs (Woodworth and Rawlings,1945). Lead arsenate was still being used but
limesulfur (0.33 gallon/10 gallons water) was beginning to replace Bordeaux
mixture because some apple varieties were tarnished by copper sulfate (Emerson
The Economic Value of Birds
Around the turn of the century, the use of orchards by birds and the economic
value of birds to agriculture and, in particular, to orchards were also being
Beginning in the 1880s, ornithologists in North America were noting the
regular use of orchards by birds and the value of birds, especially woodpeckers,
in the control of codling moth. Downy (Picoides pubescens) and Hairy (Picoides
villosus) woodpeckers consumed the overwintering codling moth larvae (MacLellan
Some birds were also considered pests in orchards and studies on this issue
were also common (Kirk et al., 1996). The study of interactions between orchards
and bird communities was prominent at the turn of the century but declined in
the 1930s and 1940s. This was partly due to the increasing use of pesticides
especially the introduction of DDT and its related compounds in the late 1940s
which appeared to provide efficient and ideal pest control (Kirk et al., 1996).
The extensive use of organochlorine compounds continued in orchards through
to the 1970s, and the value of birds to agriculture was all but forgotten (Kirk
et al., 1996). During this period, the intensity of DDT (9 lbs/acre/year) use in
orchards on the Niagara Peninsula was consistent from the 1950s through the
1960s (Ontario Dept. Agriculture, 1956; 1968).
Pesticide Effects on Birds
By the 1970s, the scientific focus on birds in agricultural areas became the
study of the effects of pesticides on birds. Organochlorine pesticides were
implicated in the death of adult birds and other wildlife as well as embryo
toxicity and eggshell thinning in birds (Newton et al. 1986). Most
organochlorine pesticides (OCs) were banned from use in North America by 1972,
except endosulfan, which remains the only organochlorine compound in use today
in orchards in Canada.
In the latter 1970s and 1980s, chemicals that are less persistent in the
environment than the organochlorine compounds were introduced to control the
major pests of apple development.
Some of the new compounds such as the organophosphorus (OPs) and carbamate
insecticides are immediately toxic to the nervous systems of insects and other
wildlife such as fish, amphibians, birds, and mammals including humans. Other
new compounds such as the synthetic pyrethroids have low toxicity to vertebrates
but are highly toxic to insects and do not persist in the environment.
The difficulty with all of these insecticides from the pest control
perspective is that they are also toxic to the “beneficial” insects that eat
orchard pest insects. To combat other pests, fungicides and miticides have been
developed which have low persistence, and low acute toxicity to vertebrates but
are effective in pest control. Despite the introduction of new chemicals, to
this day, bordeaux mixtures and sulfur are occasionally used in some orchards to
control apple scab.
Pesticides in Ontario Orchards
Apple orchards occupy about 12,565 hectares of land in Ontario (Statistical
Services Unit, 1992). Although there were two organic commercial orchards in
Ontario in recent years, all other orchards use pesticides to control apple
pests. Chemicals are applied on a weekly basis during early April to mid-August
in Ontario. Applications are often made as mixtures of insecticides and
The concern is that due to the continual loss of habitat in urban and rural
areas, agricultural areas with ponds, fence-rows and semi-natural habitats like
orchards will attract more and more wildlife. When pesticides are sprayed,
wildlife are not protected with safety equipment like the human spraying the
pesticide is. Wildlife can be exposed to pesticides through inhalation,
absorption through their skin, on their food, and in birds, when preening their
Pesticide Effects on Wildlife
During the 1990s, Megan Harris of the University of Guelph and myself and
Bill Read of the Canadian Wildlife Service, studied the sublethal effects of
pesticides on birds and amphibians in orchards in the Copetown, Carlisle and
Paris area and in non-sprayed areas including ponds and an old orchard in the
Dundas Valley Conservation Area, and several pastures in the St. George area.
This work was initiated because there weren't any field studies of the
effects on amphibians of pesticides used in orchards. There are a couple of
short-term studies of avian reproduction in wild birds exposed to pesticides in
the United States but CWS felt a longer-term study was necessary and none of the
previous work had been conducted in Canada which has unique climatic conditions.
In general, there is also little understanding of the effects of pesticides
on health and behaviour of wild birds and the impacts on their food resources.
In southern Ontario, casual observations had also revealed 30 species of birds
nesting or feeding in orchards and eight species of amphibians were breeding in
ponds within orchards and this emphasized the potential for pesticide exposure
in many wildlife species.
Field Observations on Amphibians
To test for the effects on amphibians, Megan studied the northern leopard
frog (Rana pipiens) and the green frog (Rana clamitans) (Harris et
al., 1998 a; b). These species were chosen because they seem to represent a
range in sensitivity to environmental change that may exist within the order Anura,
the frogs and toads.
Green frogs often seem unaffected by human activities in rural areas.
Conversely, localized leopard frog populations extinctions in western North
America have been linked to natural chaotic events or human-induced
environmental change, although the specific type of change causing the problem
is unknown (Vial and Saylor, 1993; Green 1997). Adult populations of frogs and
eggs of these species were examined in orchards.
The adult frogs had accumulated residues of persistent chemicals such as DDT,
which was not in current use, and endosulfan, which is still in use. Despite
this and the use of several other pesticides in the orchards during frog
breeding and development, Megan did not find any health problems in the adult
frogs although at two of the orchard sites the animals were smaller in size than
those in ponds in conservation areas.
In laboratory experiments, frog eggs and tadpoles were exposed to a variety
of concentrations of commonly used apple orchard insecticides and fungicides.
The fungicide Dithane DG and the OP insecticide diazinon caused mortality ,
deformities and growth inhibition during early development of green frogs at
concentrations that were environmentally relevant (less than 0.01 parts per
million in water).
Insecticides such as guthion, imidan and a fungicide, nova, were only toxic
to frog development at very high concentrations, the type of concentrations that
would only occur if the pesticide was accidentally oversprayed into a pond or if
water used to fill a sprayer backwashed into the pond.
Frog eggs were also placed in nylon cages and allowed to develop to hatching
in four orchard ponds and four ponds in conservation areas. Poor egg hatching
success and reduced tadpole growth occurred at several orchards, but, there was
no consistent distinction between conservation ponds and orchards.
Increasing development rates in frogs was most closely associated with
increased water temperature suggesting perhaps that any effects of pesticides in
the water could be overcome by certain optimal environmental conditions for
Effects on Songbirds
To test for effects of pesticides on songbirds, Canadian Wildlife Service
chose the tree swallow (Tachycineta bicolor) and the eastern bluebird (Sialia
sialis) to study because these species occasionally nest in natural cavities
within orchards and they readily occupy nest boxes placed in orchards and
The use of nest boxes standardized exposures to pesticides which removed any
effects of nest quality and location. Therefore the study could focus on the
effects of pesticides on the health and reproduction of the birds.
The tree swallow is representative of an aerial insectivore which maintains a
high metabolic rate relative to ground feeding birds (Williams, 1988). The
eastern bluebird is representative of ground foraging birds and produces more
than one brood per year whereas tree swallows in Ontario produce only a single
brood (Robertson et al. 1992; Peck and James 1987a;b).
The study found significant effects of pesticide applications in apple
orchards on reproduction and health in tree swallows and eastern bluebirds.
After organophosphorus and carbamate insecticides were sprayed, both tree
swallows and eastern bluebirds experienced significant depression in
acetyl-cholinesterase, an enzyme essential to nerve impulse transmission
(Burgess et al., 1999).
Both species of birds showed significant declines in reproduction associated
with increasing exposure and toxicity of pesticides applied. In particular, egg
fertility and survival were affected. In all study years during 1988-1994,
reductions in one of either egg fertility or survival of eggs or chicks were
noted. However, while the reductions were statistically significant, the
reproductive rates in sprayed orchards were still at least 76%of that in
non-sprayed sites (Bishop et al., 1998a).
Although the pesticide exposure was similar, tree swallows were more
sensitive than eastern bluebirds to the effects of pesticides applied during
The effects on eastern bluebirds of pesticides used during 1988-1994 may have
been exacerbated by the presence of residues of a metabolite of the banned
organochlorine, DDT. Concentrations of organochlorine pesticides, primarily
breakdown products of DDT, in bluebird eggs were also associated with unhatched
No evidence of eggshell thinning was seen, however DDT can also kill embryos
within the egg while the eggshell appears normal. Despite the numerous
studies on the effects of DDT on birds, most have focused on raptors and members
of the pelican family such as the cormorants and very few have examined effects
This is the first time that increasing concentrations of organochlorine
pesticides in eggs of wild passerines have been reported to correlate with
decreased success of egg hatching (Bishop et al., 1998a).
Of the tree swallow chicks that survive to fledge, the immune and endocrine
systems exhibit significant changes when exposed to typical pesticide exposures
in apple orchards (Bishop et al., 1998 b;c). In sprayed birds, there was a
significantly stimulated immune response. The number of immune cells in blood
plasma that multiplied when exposed to a cell stimulant was higher in sprayed
birds. The thymus, an organ involved in immune cell maturity, showed delayed
Sprayed birds were also anemic compared to birds from non-sprayed sites. It
is difficult to predict the long-term consequences of the stimulated immune
systems in sprayed birds. However, some environmental contaminants that overtly
stimulate the immune system in mammals have induced hypersensitivity and/or
autoimmunity diseases (Waterman et al., 1994) and such an effect may be possible
in tree swallows.
In the endocrine system of 16-day old male tree swallow chicks, the
concentration of a thyroid hormone increased in concentration in the blood as
exposure to mixtures of pesticide sprays increased.
Although a boost in metabolism may appear to be a benefit, the concern is
that this may abnormally increase the metabolic rate of the bird and hence
demand more energy. Also, increasing thyroid hormone activity in one area of the
body may alter other metabolic pathways.
There was also a trend between increasing occurrence of a disrupted cell
population in the testes of the male birds as the number of mixtures of
pesticides sprayed during chick-rearing increased. Correlations between these
responses and spray exposure were found in male chicks suggesting that
developing male tree swallow embryos may be the most sensitive to the effects of
pesticides. This is consistent with other studies that indicate the high
sensitivity of developing male mammals to environmental contamination (Colbom
and Clement 1992).
The study of behaviour of tree swallows exposed to pesticides showed that
there were short-term behavioural effects on the ability of adult birds to
deliver food but no effect on incubating activity. The begging of chicks was
exacerbated in the orchards but this appeared to be associated with chronically
low food availability in the orchards rather than changes in behaviour induced
by pesticide exposure.
Although behavioural changes were found, ultimately, the weights of the
chicks produced in the orchards were unaffected. This is good news because the
weight of tree swallows at fledging is a strong predictor of first year survival
(McCarty , 1995). Taken together, the results of the behaviour study suggests
that effects on reproduction, immune and endocrine systems are probably the
result of direct impacts of pesticides on eggs and chicks rather than an
indirect effect of abnormal behaviour or removal of food resources causing poor
body condition in tree swallows.
Implications of the Studies
The implication of the avian studies is that birds developing in nests in
orchards are at significant risk to their health and survival while in the nest
due to the pesticide exposure. This is consistent with findings in orchards and
songbird reproduction conducted in the United States where northern mockingbird
(Mimus polyglottus), northern cardinal (Cardinalis cardinalis),
and brown thrasher (Toxostoma rufum) showed significantly reduced
reproductive rates as spray exposures increased in pecan orchards in Georgia, (Patnode
and White, 1991).
Similarly, reproduction was lower in American robins (Turdus migratorius)
and mourning doves (Zenaida maricoura) in sprayed orchards as compared to
organic apple orchards in Pennsylvania (Fleutsch and Sparling, 1994).
Impacts of Fungicides
While the organophosphorus and carbamate pesticides present the most acutely
toxic threat to the birds, the fungicides that are sprayed alone or in
combination with these chemicals are actually sprayed more often than the
insecticides and studies suggest that these fungicides can have sublethal health
effects on vertebrates consistent with the effects found in tree swallows.
Unfortunately, there were no orchards in Ontario where fungicides or
insecticides were exclusively applied therefore the individual effect of these
compounds on reproduction, immune and endocrine function could not be derived
from this type of study. Nonetheless, the field approach and its findings
justify the need to identify the chemicals or mixtures of chemicals causing the
If this research had not found any differences between sprayed and
nonsprayed birds, there would be no justification for the expense and time
required for further testing of the effects of individual pesticides and/or the
combined effects of pesticides used in apple orchards.
The results of these studies have implications for amphibian and avian
survival and conservation efforts in Ontario. While Megan found that the
amphibians did relatively well in orchard ponds, typical environmental
concentrations of some pesticides can be toxic and the frog tissues do
accumulate some pesticides used in orchard in their bodies. Under optimal
developmental conditions amphibians can do well in these ponds, but they are not
a good replacement for natural wetlands.
These results reinforce the importance of protecting the water quality of the
ponds from overspraying or allowing pesticide tanks to backwash when they are
being filled into the ponds. Such short term pulses of very high
concentrations of pesticides are very toxic to frogs. Fortunately, farmers are
working with the Ontario Ministry of Agriculture, Food and Rural Affairs, and
Environment Canada to reduce pesticide use, and promote careful use of
pesticides to avoid spills and backwashing sprayer containers into ponds.
The findings for the birds are not as rosy. As birds continue to nest and
feed in sprayed orchards, they will continue to be exposed to a variety of
pesticides. Open cup nesting species would be even more exposed to pesticides
than the cavity nesting birds CWS studied.
Even so, nest boxes are often placed in rural areas to attract eastern
bluebirds due to concern for the status of their populations in the past few
decades (Read and Alvo, 1995). Moreover, species such as tree swallows, house
wrens (Trogolodytes aedon) and black -capped chickadees (Parus
atricapillus) commonly use bluebird nest boxes and, less commonly, other
species such as great crested flycatcher (Myiarchus crinitus), purple
martin (Progne subis) and house finch (Carpodacus mexicanus) also
use nest boxes meant for eastern bluebirds (McNicholletal.1994).
Therefore, songbirds are not only potentially exposed to pesticides when they
nest naturally in agricultural areas but may also be unintentionally exposed by
well-meaning naturalists who often place bluebird box trails in rural areas
where pesticides are used (McNicholletal.1994).
Nevertheless, there is cause for optimism because the chemicals most acutely
and reproductively toxic to birds (OPs and carbamate insecticides) are also the
chemicals farmers are most interested in reducing in use because OPs and
carbamate compounds are very toxic to beneficial insects in orchards. Farmers
are working with the Ministry of Agriculture, Food and Rural Affairs to replace
these pesticides with alternative chemicals and biological control of pests.
Beckett, R.S. 1913. Apple orcharding in Ontario. M.Sc. Thesis.
Dept. Horticulture. Ontario Agricultural College. Gue1ph, ON. 48 pp.
Bishop, C .A. 1998a. The effects of pesticide use in apple
orchard on health and reproduction of cavity-nesting birds. Ph.D. thesis.
McMaster Univ. Harni1ton, Ontario.
Bishop, C.A., Boennans, H.J., Ng, P., Campbell, G.D, Struger,
J. 1998b. Health of tree swallows (Tachycineta bicolor) nesting in
pesticide-sprayed apple orchards in Ontario, Canada I. Immunological parameters.
J. Toxicol. Env. Health, Part A 55.101-129.
Bishop, C.A., Van Der Kraak, G.J., Ng, P., Smits, J.E.G.,
Hontela, A. 1998c. Health of tree swallows (Tachycineta bicolor) nesting in
pesticide-sprayed apple orchards in Ontario, CanadaII. Sex and thyroidhonnone
concentrations and testes development. J. Toxicol. Env. Health, PartA 55.
Burgess, N.M., Hunt, K.A., Bishop, C.A., Weseloh, D. V. 1999.
Cholinesterase inhibition in tree swallows (Tachycineta bicolor)and Eastern
Bluebirds (Sialia sialis) exposed to organophosphate insecticides in Ontario
apple orchards. Environ. Toxicol.Chem.18(4): inpress.
Cadman, M.D., Eagles, P.F.J., Helleiner, F .M. 1987. Atlas of
the breeding birds of Ontario. University of Waterloo Press, Waterloo, ON.
Colbom, T., and Clement, C. 1992, Chemically-induced
alterations in sexual and functional development the wildlife/human connection.
Advances in Modern Environmental Toxicology ed. Mehlman, M.A. Vol. XXI.
Princeton Scientific Publ. Co. Inc. Princeton, NJ . 403 pp.
Harris, M.L., Bishop, C.A., Dixon, D.G., Struger, J., van den
Heuvel, M.R., Van Der Kraak, G.J., Ripley, B., Bogart, J,P. 1998a The functional
integrity of northern leopard frog (Rana pipiens) and green frog (Rana clamitans)
populations in orchard wetlands. I. Genetics, physiology and biochemistry of
breeding adults and young-of-the-year. Environ. Toxicol. Chem. 17(7).1338-1350
Harris, M.L., Bishop, C.A., Struger, J., Ripley, B., Bogart,
J.P. 1998b The functional integrity of northern leopard frog (Rana pipiens ) and
green frog (Rana clarnitans) populations in orchard wetlands. II. Early-life
stage development. Environ. Toxicol.Chem.17(7). 1351-1363
Heagy, A. E. and McHattie, B.J. 1995. Hamilton-Wentworth
Natural Areas Summary Report In: Hamilton-Wentworth Natural Areas Inventory ed.
Heagy, A.E. Hamilton Naturalists' Club. Hamilton, ON; 248 pp.
Emerson, R.A., Howard, R.F" Westgate, V. V.1911. Spraying
as an essential part of profitable apple orcharding. Bull. Agric. Exper.
Station. No. 119. Vol. XXIII. Article IV.
Fleutsch, KM and Sparling, DW 1994. Avian nesting success and
diversity of conventionally and organically managed apple orchard. Environ.
Contam. Toxicol. 13: 1651-1659.
Green, DM. ed. 1997. Amphibian reports from the Canadian
Declining Amphibian Populations Task Force in Herpetological Conservation.
Vol 1. Society for the Study of Amphibians and Reptiles. Saint Louis,MO, USA.
Ginsberg,J.M.andReed,J.P.1954. A survey on DDT accumulation in
soils in relation to difference in crops. J. Econ. Entomol. 47 (3):467474.
Kirk, D.A., Evenden, M.D., Mineau, P. 1996. Past and current
attempts to evaluate the role of birds as predators of insect pests in
temperature agriculture In: Current Ornithology . Vol.13. Chapter5. Eds. Nolan,
V, Jr., Ketterson, E.D. Plenum Press, NY.
MacLellan,C.R.1958.Roleofwoodpeckers in control of the codlin
moth in Nova Scotia. Can. Entomol. 90: 18-22.
McCarty, J.P. 1995. Effects of short-term changes in
environmental conditions on the foraging ecology and reproductive success of
tree swallows, Tachycineta bicolor. PhD. dissertation, Cornell University,
McCuaig, J.D., Manning, E.W, 1982. Agricultural land-use
change in Canada: process and consequences. Lands Directorate, Environment
Canada. Min. Supply and Services, Ottawa, ON. 213 pp.
McNicholl, M.K., Read, W.F., Weseloh, D. V. 1994. Bluebird
nest-box trails in Ontario and their usefulness for bioeffects monitoring of
agricultural chemicals. Canadian Wildlife Service Ontario Region Technical
Report Series No. 202. Environment Canada, Burlington, ON. 82 pp.
Newton, I., Hogan, J.A., Rothery, P. 1986. The role of
different organochlorine compounds in the breeding of British sparrowhawks: J.
Appl. Ecol. 23: 461-478.
Ontario Dept. Agriculture. 1956. Fruit Production Guidelines.
Pub. #360. Toronto, ON. 16 pp.
Ontario Dept. Agriculture. 1968. Fruit Production Guidelines.
Pub. #360.Toronto, ON. 36 pp.
Ontario Ministry of Agriculture and Food. 1994. Fruit
Production Recommendations. Publication 360. Toronto, ON. 95pp.
Patnode, KA, and White, DH. 1991. Effects of pesticides on
songbird productivity in conjunction with pecan cultivation in southern Georgia:
a multiple-exposure experimental design. Environ. Toxicol. Chem.10: 1479-1486.
Peck; G.K. and James, R.D. 1987a. Tree Swallow in: Breeding
birds of Ontario nidiology and distribution Vol 2: passerines. Royal Ontario
Museum, Alger Press, Toronto, Canada. 387pp.
Peck-.G.K. and James R.D. 1987b. Eastern Bluebird in: Breeding
birds of Ontario nidiology and distribution Vol 2: passerines. Royal Ontario
Museum, Alger Press, Toronto, Canada. 387pp.
Read, W.F.andA1vo,R.1995.Statusupdate report on the eastern
bluebird (Sialia sialis). Canadian Wildlife Service. 10pp.
Robertson, R.J., Stutchbury, B.J., Cohen, R.R. (1992) Tree
Swallow In: Birds of North America No. 11 Eds. A. Poole, P. Stettenheim, and F.
Gills. Philadelphia: The Academy of Natural Sciences; Washington, DC: The
American Ornithologists' Union. 27 pp.
Statistical Services Unit. 1992. Agricultural Statistics for
Ontario, 1991. Ontario Ministry of Agriculture and Food: Publication 20, 156pp.
Vial, J., Saylor, L. 1993. The status of amphibian
populations. a compilation and analysis. Working Document 1. World Conservation
Union and Species Survival Commission, Open University, Milton Keynes, UK.
Watertnan, S.J ., Hassan,A.N .E. , and Snyder , C.A. 1994.
Lead alters the immunogenicity of two neural proteins' a potential mechanism for
the progression of lead-induced neurotoxicity . Environ. Health Persp. 102:
Williarns;J.B.1988. Field metabolism of tree swallows during
the breeding season. The Auk 105.706-714.
Woodworth, H.C., Rawlings, C.O. 1945. Studies in economics of
apple orcharding IV. Spray Management. New Hampshire Agricultural Experiment
Station. Station Bulletin 361.
Reproduced from the Wood Duck (Hamilton Naturalists Club), May 1999)