Pesticides, Poisons and Health Issues

Are Wildlife Living in Pesticide-Sprayed Orchards Healthy?

Christine Bishop

Introduction

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 et al.,1945).

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 studied.

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 1958; Kirketal.,1996).

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 fungicides.

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 feathers.

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.

Laboratory Experiments

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 development.

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 non-sprayed sites.

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 1988-1994.

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 eggs.

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 in songbirds.

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 development.

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 problems.

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.

Conclusions

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.

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Reproduced from the Wood Duck (Hamilton Naturalists Club), May 1999)