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Mosquito monitoring in the Subarctic

August 18, 2010 - 16:39 -- Lena Hulden

This season I have together with my husband been monitoring bloodsucking insects at the reindeer research station in Kaamanen, Lapland Finland (69˚ N lat.). The station is about 150 km from Barents Sea and the snow smelts in late May. The ground is frozen from October/November until May/June and the depth of the frost is 80 cm. The staff at the station is really friendly and helpful.

The area has a history of malaria. There were still epidemics of vivax malaria in Murmansk in the 1920s.

The monitoring is done with MosquitoMagnet because light traps don’t work. The sun stays above the horizon from the 22nd of May until the 24th of July. After that it is still quite light for the end of the summer. The sun does not rise between the 30th of November and the 12th of January.

As far as I know this is the first time CO2 and octenol is used for the whole season in these conditions and the result is fascinating. In the last few days of May, beginning of June we got ca 300 Anopheles per “night”. Then we got sporadically a few. The material from July is still waiting in the freezer. The mosquito populations are huge, everything did not get room into the MosquitoMagnet. We calculated that there is not room for more than 20 000 mosquitoes in the net. We are going back up north on Friday to check on the traps. We are also waiting for the new generation to hatch and hope to collect some samples before they go into hibernation.

Basically we sort the material into Culicidae with Anopheles separate, Simulidae and Culicoides, (Ceratopogonidae). Anopheles “maculipennis” is previously known from the monastery of Boris Gleb in Russia. Of course it is not maculipennis s.s., only messeae and beklemishevi is known from the area. The sample was taken when the area was still a part of Finland and long before beklemishevi was described.

The monitoring will continue until the permanent snow cover in October. Although we have not yet analysed the material, some speculation can be made.

1. The phenology of Anopheles is more flexible than we thought. The adult females hibernate, often in human shelters and lay eggs in spring when the ice has melted. The development of the larvae takes place during the summer. The sporadic findings of adult in late June could indicate that we might have hibernating larvae after a cold summer. In theory the larvae drop to the bottom of the lake and hibernate. The lake near the reindeer station is so deep that the ice will not deepfreeze all the way to the bottom and the larvae will survive. A. claviger hibernates as larvae in the South of Finland. A “flexible” phenology with extra hibernations means that meteorological data cannot be used to predict future mosquito populations.
2. Anopheles messeae is not very sensitive to cold. We got it flying around +5˚ C and a colleague has found it active on snow. Previously mosquitoes have been thought to stop flying in temperatures under +8˚ C.