G. S. Tulloch.
Mosquito Investigations In Alaska.
Psyche 41(4):201-210, 1934.

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Mosquito Investigatiom in Alaska
MOSQUITO INVESTIGATIONS IN ALASKA
BY GEORGE S. TULLOCH
Brooklyn College, Brooklyn, N. Y.
During the summer of 1931 the United States Department of Agriculture and the United States Smelting Refining and Mining Company entered into a cooperative agreement in connection with investigations as to the "habits? biology and methods of control of mosquitoes in Alaska". The writer was employed by the United States Smelting Refining and Mining Company to carry on the investigations under the technical direction of F, C. Bishopp of the Bureau of En- tomology. The investigations were carried on in the vicin- ity of Fairbanks, Alaska? with headquarters at the Fair- banks Exploration Company, a subsidiary of the United States Smelting Refining and Mining Company. Labora- tory quarters (Fig. 1) were located at Fox? eleven miles northeast of Fairbanks.
The purpose of the investigations was to determine if practical control methods could be suggested which would reduce the annoyance of mosquitoes to men engaged in gold mining operations. In this region workmen must protect themselves from the attacks of these pests. Nets (Fig. 2) and gloves or similar means of protection (Fig. 3) serve this purpose during the periods in which mosquitoes are abundant. Although mosquito investigations have been carried on in many parts of the world, it is believed that this was the first attempt to study the control of mosquitoes in a practically arctic environment.
The area in which the investigations were carried on lies between 64O-10' and 64'-50' north latitude and between 147'-20' and 147O-20' and 147'-50' west longitude in the Yu- kon-tanana region which forms a part of the central plateau of Alaska. Mr. James Crawford, research engineer of the



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Fig. I. Laboratory Qnarters at Fox, Alaska Fig. 2. Net. med as protection Fig. 3. Use of gloves 8s pro*- against mosquitoa tion against nwsquihes



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19341 Mosquito I~~e,stigat~~ in Aluska 203 Fairbanks Exploration Company, has described the general region as follows :
"The region may be described as a plateau, with bed rock composed predominantly of schists, which has been cut by numerous streams and their tributaries. Comparatively broad unsymmetrical valleys with broad interstream areas am characteristic. Isolated prominenms, locally known as Fig 4.
Characteristic view of country in the regton where mosquito inve&igatims were made
domes, which are composed of igneous rocks and owe their presence ta the resistance of such rocks to weathering, rise above the general level of the neighboring ridges (Fig. 4). The average elevation of the ridges is around 2000 feet above sea level, while that of the valleys varies from 4'70 feet at Fairbanks to 940 feet in the valley of Goldstream at Gilmore."
"The region has been subjected to long continued and inw tricate stream modeling and since it lies outside the area of



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204 Psyche [December
glaciation, its topography is due almost exclusively to stream erosion. A mantle of 'muck', in part decomposed organic material, covers the hillsides and the unconsoligated gravel deposits in the valleys. This mantle is in turn covered by varying thicknesses of moss on the hillside? which is com- bined with bunch grass? locally known as 'niggerheads? in the valleys. Spruce trees grow extensively on the side hill while clumps of birches? willows and alders are found in the valleys. Since the ground is permanently frozen over large areas and during the summer thaws to shallow depths only? the trees are for the most part stunted." "The drainage in the area is controlled by the Tanana, the chief streams being the Chatanika? Goldstream, and the Tanana. Most of the tributaries head at about the same elevation? have about the same grade and carry approxi- mately the same amount of water. The courses of the small tributary streams are well defined and definite throughout their lengths? however, drainage conditions in the flat por- tion of the valleys traversed are poor, due in part to frozen ground and vegetation. In most of the valleys shallow swamps intherspersed with 'niggerheads? stand above the general elevation of the stream. In the broad valleys such as those of the Chatanika and Goldstream? large areas of such swamps are present. * * * *."
The climate of the interior of Alaska is characterized by extremes in temperature and light precipitation. The so- called "interior9' of Alaska is the drainage system of the Yukon River with its tributaries, thle Koyukuk~ Chandalar, Tanana, Kantishna and Porcupine Rivers. This region lies well to the north of the Gulf of Alaska and the Aleutian chain of islands. It is well known that the vicinity of The Alaska Peninsula is a continuous low pressure area and a breeding place for storms. The cyclones and anti-cyclones occurring in this region move eastward across the Gulf and follow several established routes across the United Skates and Southern Canada. The offshoots from these lows rarely affect the climate of the interior? although they



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19341 Mosquito Investigations in Alaska 205 cause storms and precipitation on the southern slopes of the Alaska Range. Occasionally a low pressure area will move through the interior? coming up from the Bering Sea. These give southerly winds throughout the interior. During the summer the heated interior of Alaska is conducive to low pressure areas of slight intensity which? in turn, induce precipitation.
The precipitation over the greater part of the interior is small. Around Fairbanks it averages from 10 to 14 inches. About 25% of this occurs in the form of snow. Normally the wettest months are July and August with June and September following. These four receive over half the year's precipitation. Over a period of 15 years thle records show that the wettest years gave over twice the precipitation of the dry years. This disparity is due largely to the ex- cess of rainfall in the summer months of the wet years and a deficiency of rainfall in dry years rather than marked changes from normal in other months. Around Fairbanks snow is usually gone by the last of April, although an occas- ional fall of snow in May or June is not uncommon. During
the summer months rainfall is sometimes attended by mild thunderstorms and sometimes hail.
The summers of interior Alaska have delightful tempera- ture conditions. They are warm enough for comfort, but are not oppressively hot. The long days and continuous sunshine cause rapid growth of vegetation. The highest
temperature ever recordfed over many years was 100' F. at Fort Yukon in July? 19150 The spring months have the highest percentage of possible sunshine and the late fall and the early winter months the lfeast. Fairbanks averages 17 dear days in April and only 8 in September. Winter tern-
peratures are as low as 75' F.
The situations in which mosquito larv~ were found de- veloping fall into two fairly well defined cat~egories. The
first included those areas in which the water was present during the greater part of the summer while the second included those apeas in which the pools were temporary in



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206 Psyche [December
nature. Prospect shafts and permanent swampy areas are included in the first category while the surface pools found in the moss and in the "niggerheads" are included in the second category.
The larvae found to be peculiar to the permanent breed- ing areas represented two species, Culiseta alaskmis and Culex apicalis. The larvae of the first species appeared dur- ing the latter part of the season having developed from egg's laid by the overwintering females. The larvae of the second species were found earlier in the season, having developed from overwintering eggs. The adults of C. alaskznsis al- though they were present in great numbers during the early part of the season of 1931 did not cause any great annoyance to the workmen.
The following species appear to be represented in the material collected during 1931 :
TABLE I
1. Anopheles maculipennis Meigen
2. Culiseta alasksensis Ludlow
3. Culiseta impatiens Walker
4. Aedes diantasus H. D. and K.
5. Aedes communis Felt and Young
6. Aedes fitchii H. D. and K.
7. Aedes punctor Kirby
8. Aedes aldrichi Dyar
9. Aedes cyclocerculus Dyar
10. Aedes lezwonotips Dyar
11. Aedes W e r Walker
12. Aedes aboriginis Dyar
13. Aedes stimulans Walker
14. Aedes cataphylla Dyar
15. Culex apicalis Adams
16. Eucorethra underwoodii Underwood
17. Chaoborus trivittatus Lo'ew
18. Corethra sp.
Adult
Larva and Adult
Adult
Larva
Larva and Adult
Larva
Larva and Adult
Larva and Adult
Larva
Larva
Larva
Larva and Adult
Larva and Adult
Adult
Larva and Adult
Larva and Adult
Larva
Larva and Adult




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19341 Mosquito Investigations in Alaska 207 The mosquitoes found to be developing in the temporary situations represented several species, many of which were troublesome. The water in these pools resulted from two sources, the more important of these being the melting of the snow. The subsequent accumulation of water in small pools provided excellent breeding places for the development of the larvae from the overwintlering eggs. The second source was not of as much consequence, being the result of the thawing of the frozen ground; the water rising to the surface and forming new pools or adding to the pools which had resulted from the melting of the snow. During some seasons it is possible that the rainfall during- April and May may result in the formation of pools similar to those formed by the melting snow. Such a condition did not exist dur- ing 1931; water from rainfall acted in a contributory ca- pacity, viz., replenished pools so that the water remained long enough to allow larvae to complete their normal de- velopment.
Although the number of species present was rather large only four, A. punctor, A. communis, A. aldrichi and A. stim- ulans were present in large numbers. As far as is known, the life histories of these four specijes are very similar, the general description which follows being equally applicable to all. The eggs are laid in summer on moist or dry ground and remain unhatched until after having been 'exposed to winter cold. Early in the spring when rising temperatures cause the accumulated snow and ice to melt forming- pools on the frozen ground, the eggs hatch and the first stage lar- vse appear. During 1931 some larvae reached maturity early in June, pupation being first noted on June 8. Adults of A. communis, A. punctor, and A. aldrichi appeared about the same time in the middle of June and were present in notice- able numbers throughout the same period (Table 2) during the season. A stirnulam appeared somewhat later and was present in numbers throughout a longer period than the other three. Information pertaining to the distribution and relative abundance of these troublesome species was col-



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208 Psyche [December
lected by the timekeepers at four different stations in the gold dredging area . The method employed was to have each timekeeper make a five minute collection at the same time and the same place each day .
Specimens were sent in for
identification on Saturday of each week . The results from one of these collection points are tabulated below . These results are similar to others collected from other stations except in a few minor details .
TABLE I1
Number of specimens of different species taken in five minute collections on man at Gilmore. Alaska . Aedes Culi- Ano-
No . of corn- Aedes Aedes Aedes seta pheles Un- speci- mu- punc- aid- stim- alaska- rnaculi-iden- Date mens nis tor richi ulans ensis pennis tified* 6-17 .... 20 4
6-18 .... 11 7
6-19 .... 16 5
6-20 .... 3
6-21 .... 30 3 7
6-22 .... 3
6-23 . . . 20
6-24 .... 20 2
6-27 .... 8 1
6-28 .... 15 1
6-29 .... 6
6-30 .... 2
7-2 .... 4
7-3 .... 4
7-6 .... 8
7-7 .... 7
7-8 .... 4
7-16 .... 3
7-18 .... 3
8-11 .... 4
8-12 .... 2
8-13 .... 5
8-14 .... 4
8-15 .... 5
8-16 .... 4
8-17 .... 6
*Specimens damaged during collection .




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19341 Mosquito Investigations in Alaska 209 Although no detailed study of the various natural factors controlling the abundance of mosquitoes was made, the fol- lowing observations were made which indicated that con- siderable numbers of mosquitoes were destroyed by preda- cious insects and other enemies. Larvae of Dytiscid and Hydrophilid beetles were abundant as well as backswim- mers, all of which are known to be efficient enemies of mos- quito larvae. The predacious larvae of three species of mos- quitoes (Table 1) were found in large numbers and birds and amphibians reputed to prey upon the larva or adult mosquito were present also in this region. It was a generally admitted fact that the mining opera- tions themselves have aided in abating the nuisance from mosquitoes. The removal of the surface moss and muck and the dredging operations have reduced the extent of the breeding areas. The removal of brush has reduced the ex- tent of the natural environment preferred by the trouble- some adults and driven them away from the vicinity of the workmen. As a result of these two operations the conditions in certain localized areas have been improved greatly. At the conclusion of the investigation in 1931 specific recom- mendations were made relative to further improving the conditions near the mining operations.
As indicated before the major portion of the breeding during 1931 was in the pools in the moss and the nigger- heads situated in the lower level portions of the valleys, These pools are usually covered partly or entirely with dead grass and moss from the previous year. The presence of this dead vegetation retards the evaporation of water as well as impedes thle drainage. It was recommended that all the dead grass and moss around the operations be removed by burning during the spring of the year. This recommen- dation was prompted by the observation that an area of about one hundred acres which had been fired accidentally contained relatively few pools containing larvae while in the adjacent unburned areas larvae were abundant in the pools. Other recommendations included oiling and draining of



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210 Psyche [December
pools within 500 yards of the operations, the use of copper sulphate as a larvicide and the use of repellants by the work- men. Control work was carried on during 1932 under the di- rection of Mr. J. D. Crawford. In the report at the end of the season, Mr. Crawford recommended that the work be continued during the season of 1933.




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