Oecologia (Berl) (1981) 48:183 185 Oecologia 9 Springer-Verlag 1981 House-Dust Community (Fungi, Mites) in Different Climatic Regions * G. Rijckaert**, J.E.M.H. van Bronswijk and H.F. Linskens Dept. of Botany, Section Experimental Ecology, Catholic University, Nijmegen, and Dept. of Dermatology, Section Minibiology, State University, Utrecht, The Netherlands Summary. House-dust flora and fauna were compared in the maritime cool temperate climate (in three degrees of continenta- lity), the mediterranean warm temperate climate, the arctic cli- mate and the tropical climate. An inverse relationship exists between continentality of the temperate climate and the numbers of arthropods and fungi (mesophilic as well as xerophilic) in the dust of the houses. The numbers of arthropods and fungi were lowest in mediter- ranean and arctic climates, most likely because of the limiting effect of the drier indoor climate. Fungi are more tolerant of dry conditions than house-dust inhabiting mites. Generally the highest numbers of fungal diaspores and arthropods were found in the tropics, where, however, the lowest number of positive samples was also found, especially for the species of the Aspergil- lus glaucus group and for Wallemia sebi. Maritime cool temperate climate showed the highest numbers of positive samples for fungi and mites. In general, a relationship exists between relative humidity and the density of fungal diaspores and arthropods. Introduction The concept of a house-dust ecosystem was first developed by Bronswijk (1972) to describe and cover that community present in the dust of Western European houses. The dominant organ- isms in this ecosystem are pyroglyphid mites and xerophilic fungi (Lustgraaf 1978; Spieksma 1967). Houses in the cool temperate climate are obviously a border- line habitat so far as humidity is concerned, especially for pyro- glyphid mites (Bronswijk in press; Lustgraaf 1978). A drier in- door climate is to be expected in very cold climates (such as that of the arctic) and in fairly dry climates (such as the dry variants of the mediterranean climate). In houses in these climatic regions, pyroglyphid mites are expected to be almost absent. On the other hand, in the wet tropical climates, mites could have a better chance of flourishing as compared to the cool temperate climate, unless they are beaten out competitively by other house- dust inhabiting arthropods. The same pattern can be expected for the xerophilic fungi. In a cool temperate climate, winter becomes colder and the indoor climate drier the more continental the climate is. Theoreti- cally, an inverse relationship is to be expected between continen- * Supported by grants no. 294 and 78.30 of the Dutch Asthma Foun- dation ** Botanie I, Toernooiveld, 6525 ED Nijmegen, The Netherlands tality and numbers of mites and fungal diaspores present in house dust. Thanks to the cooperation of scientists visiting countries in different continents we were able to compare the mite fauna and fungal flora in the dust from different types of climates, in order to test the above mentioned hypotheses. Material and Methods Samples were collected from localities in the following climatic regions [classification and description according to Bucknell (1967)]: - Maritime cool temperate climate (Ca): 1 5 months below 6.1 ~ C; rain in all seasons, with a possible maximum in winter. Three degrees of continentality: Amsterdam (NL): 5 samples; Nijmegen (NL) : 5 samples and M6nchengladbach (FRG) : 5 samples ; all samples were collected in July 1979. - Mediterranean warm temperate climate (B1): all months above 6.I ~ C but some below 17.8 ~ C; rain in winter. Samples were collected from: Ankara, Nevsehir, Konya, Bursa and Izmir (Turkey) in July i978 and from Mardin, Kahta, Altinbasak and Istanbui (Turkey) in April 1979. - Maritime tropical climate (A2): no month below 17.8 ~ C; no dry season. Samples were collected from: Botucatu, Valinhos and Sgo Paulo (Brazil) in January 1978 and from Nampala, Raselma and Lere (Mali) in September 1979. - Continental tropical climate (A3): no month below 17.8 ~ C; rain in summer. Samples were collected from: Manaus (Brazil) in January 1978 and from Bamako (Mali) in October 1979. - Arctic climate (E): less than 3 months above 6.1 ~ C. Two sam- ples were collected from Holsteinsborg (Greenland) in March 1978. Fungi could only be isolated from the larger sample. Unfortunately it was not possible to collect all the samples at the height of the mite and fungal season. Therefore, it was only possible to detect very large differences among the house-dust communities in the different climatic regions. However, the comparisons within the maritime cool temperate climate were more subtle since here it was possible to collect all samples in the same month. July is one of the known peak months in temperate climates (Bronswijk in press ; Lustgraaf 1978). Most of the house-dust samples were taken by means of a vacuum cleaner. In Mali, parts of the upper layer of the sandy floor were collected with a scoop. With both methods, only part of the fauna is sampled and the large house-dust inhabiting species are missed. In addition, the method used in Mali tends to lower the diversity found in the samples. For the arthropodal analysis 2 x 0.5 g dust was examined by means of the flotation method of Bronswijk (in press). The number of fungal diaspores was determined by means of the dilution plate method of Lustgraaf (1978). In all cases but one 0.02 g fine dust was used for the analysis. Only 0.015 g fine dust was used in the sample of Kahta (Turkey) because of the small amount of dust collected. The samples 0029-8549/81/0048/0183/$01.00