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L'ÉVALUATION DE LA DÉGRADATION DE L'ENVIRONNEMENT: QUELQUES LIGNES DIRECTRICES
GÉNÉRALES, VALEUR ET FAISABILITÉ DES ÉTUDES SUR LES INSECTES
Le présent mémoire porte sur l'élaboration de normes scientifiques pertinentes pour la surveillance et l'évaluation de la dégradation de l'environnement. Les insectes sont utiles à maints égards pour ces évaluations, ainsi que le démontrent les exemples cités. Les objectifs de toute étude de ce type devraient être définis par consultation entre toutes les parties intéressées. Il faudrait planifier l'étude complète en définissant les objectifs scientifiques dans un contexte écologique et en faisant examiner les plans par des pairs. Les renseignements recueillis devraient se rapporter à des questions spécifiques concernant l'influence d'une altération donnée sur le système. Les réponses scientifiques devant être les meilleures qu'on puisse recueillir dans l'état actuel des connaissances, il faut donc confier à des spécialistes la conception de l'étude, l'analyse et l'identification des espèces. A cause de leur diversité dans les systèmes naturels et parce qu'ils sont mal connus, les insectes n'ont habituellement pas été identifiés au niveau de l'espèce lors des études de ce type déjà effectuées. À l'heure actuelle toutefois, avec l'aide de spécialistes, on peut ordinairement résoudre les problèmes d'identification; il est normalement indispensable d'identifier les espèces, car elles sont les seules unités taxonomiques qui permettent d'organiser l'information recueillie sur le fonctionnement des systèmes naturels. Certaines recommandations résumant ces conclusions sont présentées dans le présent document.
Problems in the particular case of formal Environmental Impact Assessments have been commented on at length by Beanlands and Duinker (1983), Rosenberg, Resh et al. (1981), Munn (1975), Lash et al. (1974) and others.
This brief indicates that many of the scientific problems in environmental studies of all kinds can be overcome. The brief considers the use of insects in such studies, and demonstrates:
Reasons for dissatisfaction with many studies
Use of insects in monitoring and evaluating environmental disturbance
To offset the problems just outlined and to take advantage of recent advances, some examples of ways in which insects can demonstrate environmental changes are briefly noted. On this basis, general guidelines for studies which appraise the effects of such changes are put forward.
Insects and their relatives comprise three-quarters of all living animal species. In Canada alone there are over 66,000 species of terrestrial arthropods (Danks 1979). Furthermore, this diversity includes many closely related species which may respond uniquely to environmental conditions and disturbances.
Insects have figured in various attempts to measure the results of environmental disturbances such as cultivation, land clearing, forest fires, dam construction, or pipeline construction, and the pollution of habitats by fertilizers, pesticides, nutrient enrichment, sewage disposal, chemical waste disposal, radioactivity and acid rain. However, most of these studies have been completed at a low level of biological resolution, or the projects were chiefly organized by engineers or chemists rather than biologists, and have shown only well-known principles already established for other organisms and in other ways: disturbances lead to community changes; very severe disturbances lead to substantial mortality and usually to reductions in diversity. These conclusions provide no understanding of events, and hence are of illustrative but little predictive value. Examples cited below show several ways in which insects can be used more precisely to detect and interpret the significance of environmental perturbations. Insects are particularly useful in this regard because they possess many readily measurable biological characteristics, and they are ubiquitous and diverse. Moreover, because insects display species specific physiology, behaviour and other traits that are fixed genetically (without much of the lability of response seen in vertebrates, for example), they are especially useful indicators of particular conditions. However, it is precisely the informative diversity of insects that demands careful and detailed work if useful results are to be obtained.
General mortality responses
Laboratory experiments have demonstrated that some species of arthropods are excellent indicators of contamination. For example, mortality of the oribatid mite Humerobates rostrolamellatus is closely correlated with sulphur dioxide concentrations (Andre et al. 1982) and this mite responds more rapidly to air pollution than do most plants.
Other studies in field situations have proved that insects can indicate the severity of pollution. For instance, populations of the species of carabid beetles studied by Freitag et al. (1973) decreased, for example by a factor of more than 4 in Agonum decentis, toward the source of pollution from a pulp mill. Other field studies show that environmental impacts frequently are more subtle, and not all species are affected in the same way, as for various soil mites exposed to pesticides (Smith et al. 1980). Populations of some species may even increase as a result of chemical contaminants. Species of chironomid midges and mayflies are not all necessarily harmed by oil pollution, but each species responds differently (Rosenberg and Wiens 1976, Rosenberg et al. 1980): some species increase in number and others decrease, and changes in abundance of these species could therefore be used to identify small spills or chronic low-level contamination by oil and its derivatives. Similarly, species of Ceraclea caddisflies each change differently in occurrence and abundance in response to environmental deterioration, allowing the different species to be used as indicators of water quality (Resh 1976, Resh and Unzicker, 1975). Susceptibility of soil Collembola to insecticides and fungicides varies widely from one species to another, and varies among fungicide analogs (Tomlin 1975,1977), showing that toxicity data cannot easily be extrapolated from one species to another or between related chemicals. Since the fertility of the soil depends partly on activities of such arthropods (e.g. Biological Survey of Canada 1982), these results suggest ways in which detailed studies of soil arthropods will reveal changes not shown by other, larger, organisms.
The structure of insect communities may also change after pesticide treatments: low numbers of predators after river treatment by methoxychlor led to a preponderance of certain prey species and hence to an unusual community structure (Lehmkuhll 1982). Analogous changes in the natural predator-prey balance were documented much earlier in sprayed apple orchards, forcing a revision of previous practices in the use of chemical pesticides.
Insects can also be used to show long-term effects. In Britain the melanic form of the moth Biston betularia became locally prevalent because on soot-darkened substrates it was less conspicuous than the normal form to bird predators, thereby showing the influence of industrial pollution over many years (Kettlewell 1961, 1973). The sensitivity of insects to changed conditions has also allowed some long-term effects of pesticide application to be recognized. McNeil et al. (1979) discovered that the jack pine sawfly was susceptible to very small doses of fenitrothion (applied against spruce budworm) which had built up in needles of the host plant through repeated annual applications. The same insecticide depressed yields of blueberries for several years because native bee pollinator populations had been decimated; the populations took several years to recover after fenitrothion use was discontinued (Kevan and Laberge 1979, Kevan and Opperman 1980). Aquatic invertebrates provided a better indication of streamwater-quality than did routine chemical monitoring because they exhibited long-term responses to sporadic urban runoff of organic materials and silt (Whiting and Clifford 1983).
On a still longer time scale, historical events such as land clearing have been traced in detail through the analysis of chironomid head capsules preserved in lake sediments (Warwick 1980a). In the Bay of Quinte, Lake Ontario, the chironomid fauna responded to initial colonization of the lake basin by Europeans by developing a composition characteristic of enriched nutrient conditions.Subsequent activities caused massive erosion in the watershed, and mineral sedimentation returned the structure of the fauna to one less characteristic of rich waters. As the erosion stabilized, the suppressed effects of still greater nutrient inputs were realized. Such a history allows prediction of the sort of changes that result from similar environmental disturbances. This is possible both for testing past effects and forecasting expected changes. Insects thus provide several means to evaluate historical and community changes in a broad framework. Especially credible estimates of environmental changes are obtained when information has been integrated over time and space in this way.
Some general principles
Problems with earlier work, and lessons drawn from the examples just cited, suggest ways in which environmental appraisals using insects might best be planned and executed.
Value of information at the species level
For example, interpreting population change requires a knowledge of the ecology of individual species. Whether changes observed are due to life-history events, environmental heterogeneity and dispersion patterns in the population, artifacts of the sampling protocol, or results of the process of concern can only be ascertained by detailed knowledge of the life history and ecology of the species under study.
Each species of insect has much information associated with it. The key to this information is identification to species. A family or generic name is not adequate, because examples can be found in all groups in which species of the same genus or family differ considerably in certain features. Therefore order, family, genus, and subgenus often give little information regarding the range of ecological conditions under which a given species is found. Thus studies based on identifications above the species level often have little value in ecology or the appraisal of disturbance.
Work at the species level was once frequently precluded by taxonomic difficulties. However, with more experienced and more highly trained personnel available and the rather considerable progress in taxonomic and basic ecological work in the last decade (compare references cited in Danks 1979), this is no longer true. Taxonomically, many groups are now feasible subjects for species-level studies, and expertise exists within Canada to provide specific identifications.
In essence, the reason for species level work is that the species is the most universally valid biological currency by which information can be organized. Such information can be cross communicated and developed. Because it is available to other workers, a progressively more comprehensive picture of biota in relation to environmental conditions can be built up. By this means each environmental study can best contribute not only to the case at hand, but also to the future development of environmental appraisals. Such a fund of organized relevant knowledge is based on accurate identifications: voucher specimens of material on which information is based should therefore be preserved.
Need for a broad approach to planning
Consequently, the results (Lehmkuhl 1981) satisfied all parties involved, including the funding agencies, the scientific workers and outside reviewers of the report.
Planning must therefore include the means to conduct the study properly. Careful conduct of the fieldwork, and accurate identification of the insect species collected, can usually be done only by qualified scientists: appropriate personnel should therefore be involved in such studies.
Although decisions based on environmental assessments are influenced by many social and economic factors, usable results from the studies depend critically on good science. This brief suggests that good entomological science for environmental monitoring and evaluation can be assured by accepting the following general principles:
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Beanlands, G. E. and P. N. Duinker. 1983. An ecological framework for environmental impact assessment in Canada. Institute for Resource and Environmental Studies, Dal housie University, Halifax. 132 pp.
Biological Survey of Canada. 1982. Status and research needs of Canadian soil arthropods. Bull. Ent. Soc. Can. 14(1), Suppl. 5 pp.
Danks, H. V. (Ed.). 1979. Canada and its insect fauna. Mem. Ent. Soc. Can. 108. 573 pp.
Freitag, R., L. Hastings, W. R. Mercer and A. Smith. 1973. Ground beetle populations near a Kraft mill. Can. Ent. 105(2): 299-310.
Hamilton, A. L. and O. A. Saether. 1971. The occurrence of characteristic deformities in the chironomid larvae of several Canadian lakes. Can. Ent. 103(3): 363-368.
Kettlewell, H. B. D. 1961. The phenomenon of industrial in Lepidoptera. A. Rev. Ent. 6: 245 262.
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Kevan, P. G. and W. E. LaBerge. 1979. Demise and recovery of native pollinator populations through pesticide use and some economic implications. Proc. IVth Symp. on Pollination. Md. Agric. Exp. Sta. Spec. Misc. Publ. 1: 489-508.
Kevan, P.G. and E.B. Oppermann. 1980. Blueberry production in New Brunswick, Nova Scotia and Maine: a reply to Wood et al. Can. J. Agric. Economics 28(1): 81-84.
Koehn, T. and C. Frank. 1980. Effect of thermal pollution on the hironomid fauna in an urban channel. pp. 187-194 in D.A. Murray (Ed.), Chironomidae. Ecology, systematics, cytology and physiology. Proc. 7th Int. Symp. Chironomidae, Dublin, August 1979. Pergamon Press, Oxford, England.
Lash, T. J. F. et al. 1974. On doing things differently Issues in Canadian Science Policy 1: 9-16. Science Council of Canada, Ottawa.
Lehmkuhl, D. M. 1981. Report on the impact of methoxychlor on non-target organisms in the Saskatchewan River. Appendix 111, 165 pp., in W. W. Sawchyn, Impact of methoxychlor as a blackfly larvicide in the Saskatchewan River. SRC publ. No. C-805-19-E-82.
-----1982. The impact of methoxychlor on non-target organisms in the Saskatchewan River with emphasis on long-term effects and the effectiveness of reduced dosages. Prepared for Saskatchewan Agriculture. 54 pp.
Matthews, W. H. 1975. Objective and subjective judgments in environmental impact analysis. Environ. Conservation 2: 121-131.
McNeil, J. N., R. Greenhalgh, and J. M. McLeod. 1979. Persistence and accumulation of fenithrothion residues in Jack Pine foliage and their effect on the Swaine Jack Pine Sawfly, Neodiprion swainei (Hymenoptera: Diprionidae). Environ. Ent. 8(4): 752-755.
Minshall, G. W., R. W. Peterson, K. W. Cummins, T. L. Bott, J. R. Sedell, C. E. Cushing, and R.L. Vannote. 1983. Interbiome comparisons of stream ecosystem dynamics. Ecol. Monogr. 53(1): 1-25.
Munn, R. E. (Ed.). 1975. Environmental impact assessments: principles and procedures. SCOPE workshop Rep. 5. 160 pp.
Resh, V. H. 1976. Changes in the caddis-fly fauna of Lake Erie, Ohio, and of the Rock River, Illinois, over a fifty year period of environmental deterioration pp. 167-170 in H. Malicky (Ed.), Proc. 1st Int. Symp. on Trichoptera. Lunzam See (Austria), September 16-20, 1974. Dr. W. Junk, The Hague, Netherlands.
Resh, V. H. and T. D. Unzicker. 1975. Water quality monitoring and aquatic organisms: the importance of species identification. J. Water Pollution Contr. Fed. 47: 9-19.
Rosenberg, D. M., V. H. Resh, et al. 1981. Recent trends in environmental impact assessment. Can. J. Fish. Aquat. Sci. 38(5): 591-624.
Rosenberg, D. M. and A. P. Wiens. 1976. Community and species responses of Chironomidae (Diptera) to contamination of fresh waters by crude oil and petroleum products, with special reference to the Trail River, Northwest Territories. J. Fish. Res. Bd. Can. 33(9): 1955- 1963.
Rosenberg, D. M., A. P. Wiens, and J. F. Flannagan. 1980. Effects of crude oil contamination on Ephemeroptera in the Trail River, Northwest Territories. pp. 443-445 in J. F. Flannagan and K. E. Marshall (Eds.), Advances in Ephemeroptera biology. Plenum Press, New York.
Saether, O. A. 1975. Nearctic chironomids as indicators of lake typology. Verh. Int. ver. theor. angew. Limnol. 19: 3127-3133.
-----1979. Chironomid communities as water quality indicators. Holarctic Ecology 2(2): 65-74.
-----1980. The influence of eutrophication on deep lake benthic invertebrate communities. Progr. Water Technol. 12: 161-180.
Smith, T. D., D. K. McE. Kevan, and S. B. Hill. 1980. Effects of six biocides on non-target soil mesoarthropods from pasture on Ste. Rosalie Clay Loam, St. Clet, Quebec. pp. 55-68 in D. L. Dindal (Ed.), Soil biology as related to land use practices. Proc. Vllth Intl. Soil. Zool. Colloquium of the Intl. Soc. Soil Sci. Office of pesticides and toxic substances, Washington, D.C. 880 pp.
Stanford, J. A. and J. U. Ward. 1983. Insect species diversity as a function of environmental variability and disturbance in stream systems. pp. 265-278 in J. R. Barnes and G. W. Minshall (Eds.), Stream Ecology application and testing of general ecological theory. Plenum Press, N.Y.
Symons, P. E. K. 1977. Assessing and predicting effects of the fenitrothion spray program on aquatic fauna. Proc. Symp. on Fenitrothion, the long term effects of its use in forest systems. (Apr. 20-22, 1977), pp. 391-414. N.R.C., Ottawa. Associate Committee on Scientific Criteria for Environmental Quality.
Tomlin, A. D. 1975. Toxicity of soil applications of insecticides to three species of springtails (Collembola) under laboratory conditions. Can. Ent. 107(7): 769-774.
-----1977. Toxicity of soil applications of the fungicide Benomyl and two analogs, to three species of Collembola. Can. Ent. 109(12): 1619-1620.
Warwick, W. F. 1980a. Palaeolimnology of the Bay of Quinte, Lake Ontario: 2800 years of cultural influence. Can. Bull. Fish. Aquat. Sci. 206: 1-117.
-----1980b. Pasqua Lake, southeastern Saskatchewan: a preliminary assessment of trophic status and contamination based on the Chironomidae (Diptera). pp. 255-267 in D.A. Murray (Ed.), Chironomidae. Ecology, systematics, cytology and physiology. Proc. 7th Int. Symp. Chironomidae, Dublin, August 1979. Pergamon Press, Oxford, England.
Wiederholm, T. 1984. Responses of aquatic insects to environmental pollution. pp. 508-557 in V. H. Resh and D. M. Rosenberg (Eds.), The ecology of aquatic insects. Praeger Publishers, New York.
Whiting, E. R. and H. F. Clifford. 1983. Invertebrates and urban runoff in a small northern stream, Edmonton, Alberta, Canada. Hydrobiologia 102(1): 73-80.
This brief prepared by a subcommittee of the Biological Survey: D. M. Lehmkuhl (Chairman), H. V. Danks, V. M. Behan-Pelletier, D. J. Larson, D. M. Rosenberg, I. M. Smith.
Published by The Entomological Society of