News about studies of arctic insect
News and Notes
Instead of publishing a separate newsletter, therefore, Canadian arctic interests will now be supported by including relevant submissions in this section of the main BSC newsletter. Contributions to Arctic Corner are welcomed by the Editor (see general information).
Arctic Insects, Global Warming and the ITEX
The experiment was initiated by the conclusions of the Global Circulation Models of the time that predicted mean summer temperatures in northern regions would increase by 1.5º to 4.5ºC by the year 2030 (Mitchell et al. 1990). Indeed, these predictions now seem moderate compared to the analyses of current Global Circulation Models (Hengeveld, 2000). Such drastic climate change in so sensitive an area as the high Arctic could have a major impact not only on plant life but also on the arthropod fauna (Strathdee et al. 1993).
The effects of OTCs on insects and on insect/plant interactions have, therefore, been studied within the ITEX context. Insect specimens have been collected from six ecologically distinct plant communities at Alexandra Fiord, a polar oasis on Ellesmere Island in Nunavut. The four main emphases of the program are:]
(1) general collecting of actively flying insects by the use of Malaise flight-intercept traps at two of these sites on the lowlands,
(2) a comparison of the insect fauna within and without (i.e. control) the OTCs using yellow pitfall traps,
(3) since OTCs have physical effects such as excluding flying insects (many of which are known pollinators of arctic flowers), a comparison of the frequency of likely pollinators both within and without the OTCs using yellow pitfall traps, and
(4) an analysis of the direct effects of the OTCs on insect development
and phenology, mainly within the soil micro-arthropods.
Alexandra Fiord is a small (c. 8 km2) lowland valley on the East Coast of Ellesmere Island in Nunavut, a Canadian Territory (78º 53' N; 75º 55' W) (Fig. 1). It is located approximately halfway up the eastern coast of Ellesmere Island near the transition from the exposed bedrock of the Canadian Shield to a younger sequence of sedimentary deposits. The lowland is near the mouth of Alexandra Fiord which deeply dissects the eastern coast of Ellesmere about 70 km south of Sverdrup Pass and 60 km west of Greenland. The Alexandra Fiord Lowland represents a terrestrial arctic oasis that is generally characterized by elevated summer temperatures and higher moisture levels compared to the surrounding “arctic desert”. The lowland’s physiography is largely responsible for the less inclement conditions; it is a periglacial outwash surrounded by steep mountains on all sides except to the north, which borders the sea (Fig. 2). Snow cover on the surrounding scree slopes and glaciers tends to reflect solar radiation into the lowland, increasing its temperature while the surrounding edges act as a wind foil. Water collected from glacial tongues, which spill out of the Ellesmere ice cap, drains through the gently sloping lowland and irrigates it through a network of small channels before flowing into the fiord. The lowland valley has a milder climate than surrounding areas, and is a good example of a high arctic oasis. The mean July temperature is 5.1ºC compared to an average of 4.4ºC for the surrounding “arctic desert” regions (Freedman et al. 1994). In addition to the increased temperatures, the topography of Alexandra Fiord allows a greater availability of moisture within the valley basin. Glacial and niveal runoff provides a source of ground water, which is highly restricted elsewhere in the high arctic. The plant and insect communities are consequently much richer in the Fiord lowland than in adjacent areas. Organisms are limited elsewhere by water and temperature constraints, which are eased somewhat in polar oases (Downes 1964). The climatic effects allow a greater diversity of species as well as a greater productivity to exist on the lowlands. The high relative abundance of organisms found in Alexandra Fiord compared to surrounding areas lends the area to the study of global change scenarios (Danks 1992).
Fig. 2 The lowland with ITEX set-up
Results and Discussion
(1) Malaise Trapping and Diversity
The insect fauna is dominated by the Diptera, especially the Chironomidae, which is not unexpected for the high arctic (Danks 1981). However, there was a surprising abundance of Empididae and Dolichopodidae, which are predators on other insects. The two species of mosquitoes (Aedes impiger and Aedes nigripes), were also seasonally abundant and showed some interesting trends even at the sex level. Males emerged earlier at both sites, but female abundance was much greater at the wet “Sedge Meadow” site later in July - important information for the ITEX workers carrying out their plant growth measurements! The main fungal feeding insects (Sciaridae and Mycetophilidae) were also present in moderate numbers, an observation supported by the number of mushrooms and other fungi collected in the lowlands.
Among the Hymenoptera, the insect parasitoids Ichneumonidae were the most speciose and abundant. Again, this is not unexpected considering the large number of potential hosts in Alexandra Fiord - caterpillars and dipteran larvae. Other authors have also found a very high rate of parasitism (up to 75%) when examining the relationships between the lymantriid caterpillars of Gynaephora groenlandica and G. rossii and their parasitoids, lending support to this observation. Although very few Lepidoptera were ever retrieved from the trap samples, this is more likely due to a factor in the trap design, because numerous butterflies and moths were collected in the attractive yellow pitfall traps in the same localities during the latter half of July. No Coleoptera were collected by the Malaise traps.
(2) Indirect Effects of OTCs.
Dipterans predominate in the samples, both in terms of overall abundance and number of families represented. Few specimens of other major orders are present, except for Lepidoptera. Of the Dipterans, the Muscoidea predominate within the samples. Species in this superfamily are important pollinators since they feed on nectar and have been shown to carry pollen among High Arctic flowers. These results indicate that reduced pollen deposition in some plant taxa and reduced pollinator visits in OTCs have the potential to influence plant species which are highly dependent upon outcrossing for successful seed production.
(3) Direct Effects Of OTCs
Although there is no evidence of significant direct effects of OTC warming on woolly bear caterpillar growth and development, there are some interesting trends that are obvious and should be monitored over successive years into the future. Even small changes in phenology and growth (as measured here) could, when multiplied from year to year, eventually have significant effects on the life cycle of this species.
(4) Soil Micro-Arthropods
A great deal of variability was found within each site, making comparisons among sites difficult. The Willow Site produced a greater number of individuals, both within and without the OTCs. This site was also the only one where Thysanoptera were represented. Without the OTCs, all Thysanoptera found were developmentally immature, while those within the OTCs were mature. Also, within the OTCs, Diptera larvae were conspicuously absent. Oribatids were generally not common, although they were dominant in one sample from within an OTC. Some of the most abundant soil mites identified were: Trichoribates polaris Ceratozetidae immatures, Lugoribates gracilis, Liochthonius sellnicki, Cyta latirostris, Moritzoppia clavigera, Epidamaeus sp. near longitarsalis, and Hermannia scabra. At every site, the most abundant categories included both “other mites” and Collembola sp. 1. Abundance of Thysanoptera, Diptera, predatory mites, and oribatids was relatively low. Collembola sp. 2 was common only in the Willow Site.
The main differences among the samples from within the OTCs were the developmental maturity of the Thysanoptera and the absence of the Diptera. The maturity of Thysanoptera was probably a direct result of the increased temperature. It has been demonstrated that thrips reach maturity faster at a higher temperature. One Finnish thrips, Limnothrips denticornis, when raised at a temperature of 25°C, will reach maturity in half the time required by wild populations. This increased rate of maturation could have an effect on the reproductive abilities of arctic thrips in a warmer climate. In many thrips, the number of eggs laid and generations per annum are dependent on temperature. Furthermore, mites have been shown to be more resistant to climate change than collembolans (Coulsen et al. 1996; Hodkinson et al. 1996). Therefore, if climate change leads to significantly drier conditions in the High Arctic, mites would be expected to become more abundant in the soil.
Brodo, F. 2000. The insects, mites and spiders of Hot Weather Creek, Ellesmere Island, Nunavut. pp. 145-173 in M. Garneau and T.B. Alt. (eds.), Environmental Response to Climate Change in the Canadian High Arctic, Geological Survey of Canada Bulletin 529.
Coulson S.J., I.D. Hodkinson, N.R. Webb, W. Block, J.S. Bale, A.T. Strathdee, M.R. Worland and C. Woolley. 1996. Effects of experimental temperature elevation on high Arctic soil microarthropod populations. Polar Biology 16: 147-153.
Danks, H.V. 1981. Arctic Arthropods: A Review of Systematics and Ecology with Particular Reference to the North American Fauna. Entomological Society of Canada, Ottawa, Ontario. 608 pp.
Danks, H.V. 1992. Arctic insects as indicators of environmental change. Arctic 45: 159-166.
Downes, J.A. 1964. Arctic insects and their environment. Canadian Entomologist 96: 279-307.
Freedman, B., J. Svoboda and G.H.R. Henry. 1994. Alexandra Fiord - an ecological oasis in the polar desert. pp. 1-9 in J. Svoboda and B. Freedman (eds.), Ecology of a Polar Oasis: Alexandra Fiord, Ellesmere Island, Canada. Captus University Publications, Toronto, Ontario.
Hengeveld, H.G. 2000. Projections for Canada’s Climate Future. Climate Change Digest, CCD 00-01. Environment Canada, Ottawa. 27 pp.
Hodkinson I.D., S.J. Coulson, N.R. Webb and W. Block. 1996. Can high Arctic soil microarthropods survive elevated summer temperatures? Functional Ecology 10: 314-321.
Kukal, O. 1990. Energy budget for activity and growth of a high-arctic insect, Gynaephora groenlandica (Wocke) (Lepidoptera: Lymantriidae). pp. 485-510 in C.R. Harrington (ed), Canada’s Missing Dimension: Science and History in the Canadian Arctic Islands, Vol. II. Canadian Museum of Nature, Ottawa, Ontario.
Mitchell, J.F.B., S. Manabe, V. Meleshko and T. Tokioka. 1990. Equilibrium climate change - and its implications for the future. pp. 131-172 in J.T.Houghton, G.J. Jenkins, and J.J. Ephraums (eds.), Climate Change: The IPCC Scientific Assessment. Cambridge University Press, New York.
Oliver, D.R. 1963. Entomological studies in the Lake Hazen area, Ellesmere Island, including lists of species of Arachnida, Collembola and Insecta. Arctic 16: 175-180.
Strathdee, A.T., J.S. Bale, W.C. Block, N.R. Webb, I.D. Hodkinson and S.J. Coulson. 1993. Extreme adaptive life-cycle in a high arctic aphid Acyrthosiphon svalbardicum. Ecological Entomology 18: 254-258.
Svoboda, J. and B. Freedman (eds.). 1994. Ecology of a Polar Oasis: Alexandra Fiord, Ellesmere Island, Canada. Captus University Publications, Toronto, Ontario. 268 pp.
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