イエシロアリの営巣実態調査(1)(シロアリ)

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When termite damage has been discovered, the best thing to do is locate the nests, i. e. the termites' breeding source, and destroy them completely. Locating the nests is, however, no easy task; as a matter of fact, investigative date on termite nesting behavior, that is, on the places where termites are liable to nest, is still scanty. Therefore, the further investigation of termite damaged buildings for the purpose of learning more about the general destructive tendencies of termites and their nesting behavior would be useful for the future detection of termite nests and their ultimate control. The present paper summarizes the results of an analysis of the field data on twenty-six termite nests discovered in buildings of the Japanese National Railway's Moji Railway Operating Division between June 1963 and February 1967, and on six nests found in or under old pine stumps in the pine forests of Nijinomatsubara Park, Higashikaratsu and Uminonakamichi, Fukuoka. The data submitted to analysis are those on the damage caused by Formosan termites, whose nests were located by either detection or excavation; data concerning the termites whose nests could not be located, or whose damage was negligible, have been omitted. The results of the analysis can be summarized as follows: 1) The number of objects attacked by termites whose nests were dug up or detected was 26; two of which were concrete block buildings and the rest all wooden ones. 2) In 7 out of 26 cases, the nests were found within the building, and in the remaining cases, they were located in pieces of wood or trees around the damaged building. Thus, we can conclude that it is essential not only to protect the building itself from termites, but also render the surroundings of the building unfavourable for nest building. 3) Old sleepers utilized in wooden fences, retaining stakes and coal storage offered the material for termite nesting in 10 out of 26 cases. This was followed by telephone poles (5) ; standing trees or stumps (3); walls, floors or concrete floors (2 each); and a wooden beam (1). It seems significant that few nests were detected within the buildings. 4) The characteristic feature of the damage found in JNR property was the fact that old sleepers used for wooden fences and other purposes around the stations or buildings proved desirable breeding grounds for termites, and consequently JNR has come to be heavily infested with termites. The use of old sleepers, as they are, should also be avoided, because termites breeding in them will fly out to neighbouring buildings. 5) The ratio of nests built above ground to those below ground level was 5 : 16 thus showing a strong tendency for subterranean nesting. 6) The depths of the underground nests, as measured from the ground surface to the top of the nest, were in the range of 0〜30 cm, and most frequently between 15〜30 cm. 7) Winged adults were observed in the period from early May to the beginning of July, but not in other seasons. From this fact it is surmised that the termites only grow wings several months before the swarming period and never winter with grown wings. It would of course be desirable from the standpoint of termite control to dig up and destroy the termites before the swarming period begins. 8) The water content of soil surrounding a nest in a sandy zone was 3 to 7 % up to 100 cm below ground level, and increased with the depth of the soil. 9) Six nests were found in an approximate layer of humus soil. Water content of the soil around the nests turned out to be 4.3〜55.4 % down to the depth of 100 cm below the surface ; i. e. this value was larger than that of sandy soil and more widely distributed. The soil beneath the nests contained slightly less water than the soil on the sides of the nests ; a characteristic also observed in the case of sandy soil. 10) As for the mechanical composition in the sandy zones, coarse sand predominated, followed by fine sand, clay and silt in that order. 11) As for the soil reaction, the soil of Uminonakamichi exhibits a pH value of 7.9 to 8.2 down to 100 cm below ground level, which shows that it is alkaline. The soil of Nijinomatsubara Park exhibits a pH value of 5.13 to 8.01, which shows that it ranges considerably from feeble acidity to feeble alkalinity. In both districts it was observed that the pH value of the soil tended to rise with increasing depth.
日本家屋害虫学会の論文
1980-12-30

イエシロアリの営巣実態調査(1)(シロアリ)

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