- Email: [email protected]
Mass-length and mass-volume relationships of larvae ofBradysia paupera (Diptera: Sciaridae) in laboratory cultures
Eur. J. Soil Biol. 36 (2000) 127−133 © 2000 Éditions scientifiques et médicales Elsevier SAS. All rights reserved S1164556300010554/FLA
Mass-length and mass-volume relationships of larvae of Bradysia paupera (Diptera: Sciaridae) in laboratory cultures Matty P. Berg*§ Swedish University of Agricultural Sciences, Department of Ecology and Environmental Research, P.O. Box 7072, 750 07 Uppsala, Sweden
Received 7 February 2000; accepted 7 September 2000
Abstract − General relationships between body fresh and dry weights, and body length and volume are derived for a dipteran larva, Bradysia paupera. Adult midges were placed in containers with substrate consisting of a mixture of peat and ground beans. From these stock cultures, gravid females were released in containers with agar and a thin layer of ground grass powder, on which the larvae were cultured. A brief description of the life history of B. paupera is given. The body sizes of living larvae were measured on moist plaster of Paris immediately after which the larvae were weighed individually. The relationships of body mass versus size were based on logarithms of mass (M) and size (X, either length or volume) that allows the conversion of a power equation (M = a × Xb) to a linear regression. The derived regression equations that relate body size indices to body mass had a high predictive capacity (r ranged from 0.934 to 0.991). Body volume, the integration of two size measurements (length and width), gave the most accurate estimation of body mass (length vs. fresh mass r = 0.977, volume vs. fresh mass r = 0.991; length vs. dry mass r = 0.934, volume vs. dry mass r = 0.958). Both size indices gave a more accurate estimation of the fresh mass than of the dry mass of the larvae. Differences between the predictive capacity of the size-mass regression equations are explained in the light of larval behaviour and compared with regression equations obtained from literature. © 2000 Éditions scientifiques et médicales Elsevier SAS Diptera / Sciaridae / Bradysia paupera / life history / biomass / mass / length
1. INTRODUCTION The larvae of terrestrial Diptera play an important role in the ecology of soils of forests, meadows and agricultural fields. They provide food for a variety of soil arthropods [16, 21, 25], ground-foraging birds [9, 10], and small ground-dwelling mammals [8]. Dipteran larvae consume microorganisms [33, 34]; they frequently infest mushrooms where they may be of economic importance [5], and feed on roots and stem tissue [6, 35]. Furthermore, they are of importance in litter, dung and wood decomposition and nutrient cycling of ecosystems [13, 18].
* Correspondence and reprints. E-mail address: [email protected] (M.P. Berg). § Present address: Vrije Universiteit, Institute of Ecological Science, Department of Animal Ecology, De Boelelaan 1087, 1081 HV Amsterdam, the Netherlands.
To be able to quantify the contribution of larvae of terrestrial Diptera to different ecological processes, it is necessary to estimate the biomass of larvae present within an ecosystem. Numerous studies have estimated the density of terrestrial Diptera larvae inhabiting different habitats, but rather few have attempted to quantify the biomass represented by this component of the ecosystem (e.g. [2, 20, 28, 31]). In many cases, the estimation of biomass of small living soil animals, such as the larvae of midges and flies, presents problems. The weighing procedure is difficult due to the rapid desiccation of the specimens, especially of the first instars, or is at least time-consuming and tedious. Therefore, unless special microbalances which prevent desiccation are available, estimating biomass values using indirect calculations can be used. Traditionally, allometric indices or other measurements have been used to estimate biomass. One indirect estimate of biomass is obtained by the relationship between a linear measure of body size and the individual weight, expressed in terms of fresh or dry
128
M.P. Berg / Eur. J. Soil Biol. 36 (2000) 127–133
mass. For many taxa of small terrestrial animals, linear multiple regressions relating the logarithm of body mass to the logarithm of body length, width or volume, have been established: e.g. Enchytraeidae [1] oribatid Acari [26], Collembola [30], Gastropoda [15], and epigeic arthropod predators [7, 17, 19, 24]. In experiments on the influence of dipteran larvae on ecosystem processes, absolute biomass estimations are necessary but difficult to obtain. Weighing individual larvae to establish body mass is no option due to fast desiccation, and instead their biomass has to be estimated using allometric indices. Generalized body length-dry mass relationships have been established for Sciaridae [2, 20]. Both these authors have extracted Sciaridae larvae, a mixture of several species, directly from calcareous old beech forests soils in central Germany. It is not known: i) if these allometric indices are valid for populations of Sciaridae larvae consisting of one species only; ii) if allometric indices based on body length-dry mass relationships are more precise than indices based on body length-fresh mass or body volume-body mass relationships; or iii) if allometric indices based on field extracted larvae differ from indices based on laboratory cultured larvae. In this paper body mass-length and body mass-volume regression equations for Bradysia paupera larvae are derived.
2. MATERIALS AND METHODS Adults of the species Bradysia paupera Tuomikoski, 1960, were caught in June with an exhauster from the leaves of cucumber plants and the surrounding soil in a greenhouse near Uppsala, Sweden. Adult midges were identified using the key of Tuomikoski [38]. Schematic drawings of the larva and pupa of Bradysia spp. are given in Smith [35] and black and white plates of the larva can be found in Binns [4]. The midges were stock cultured in containers, diameter 8.8 cm, height 14 cm. Ten pairs of adult midges were released per container. The bottom of the container was covered with a 3.5-cm thick layer of a peat/bean mixture. Dry brown beans were put in water and allowed to swell for 24 h. After that, 100 g moist beans were ground (Braun, MX 32) with 500 mL water and added to 2 L sieved (16-mesh) dry peat. Additional water was added (approximately 150 mL) to get a moist mixture (water content around 75 %) and the substrate was thoroughly mixed. The substrate was kept in a refrigerator (4 °C) till further need. Substrate (50 g) was added to each container and firmly packed at the bottom with a spoon. The lids of the containers had a hole (diameter 4 mm) in the middle covered with fine gauze (200 µm) for ventilation. A small quantity of honey was smeared on the inside of the lids serving as food for the midges. Addition of honey doubled the average life span of an
adult midge from 3 to 7 d at 20 °C. The containers were held in a dark climate room at a temperature of 20 °C at a 70 % relative humidity. Several generations of midges were cultured. From the stock culture described above one adult female and two males were placed in a container (diameter 8.8 cm, height 8 cm). Its bottom was covered with a 1-cm thick layer of water agar (2 % solution of non-nutritive bacto-agar, autoclaved for 20 min at 120 °C). On top of the agar 0.5 g dry ground grass powder was spread out to form a very thin layer. Grass was sampled in summer, dried at 50 °C, grinded (mill type ZM1, 1-mm sieve, Retsch Gmbh, Germany) and autoclaved for 20 min at 120 °C. A drawing of the container is given in Persson et al. [29]. The hatching larvae fed on the grass powder and on the fungi emerging on the substrate. The larvae were sampled from the cultures with increasing time intervals, ranging from 1 d to 2 weeks after emerging from the eggs, to sample the full range of the larval stages. Individual larvae were carefully picked up with a needle and placed on moist plaster of Paris (mixed with black pigment). They were deprived of food for 2 d to empty their gut. The body length (magnification 12×) and body width (measured in the mid-part of the body, magnification 25×) of a larva was measured with a graduated eyepiece (0.01 mm) in dorsal view when crawling on the plaster of Paris. Both measures were taken when a moving larva was fully stretched, corresponding to the maximum length and minimum width of the body. Then the larva was put into an aluminium cup (diameter 5 mm, height 7 mm) and weighed immediately on a microbalance (Cahn, type C-33) to the nearest µg. To determine dry biomass, all measured specimens were freeze-dried under vacuum for 7 d at –30 °C (Edwards high vacuum Ltd, model EF2), stored in an desiccator for 3 d, and weighed to the nearest µg. Body volume was calculated by multiplying body length with the surface of the body cross section assuming that cross sections of sciarid larva are circular. This assumption seems only to be justified when the larva is fully stretched, otherwise the cross section has an oval shape. The body mass and body length and volume data were subjected to a power function according to the formula
M=a×X
b
where M is either fresh mass or dry mass (in mg), and X either body length (L, in mm) or body volume (V, in mm3). Logarithmic transformations of these power functions results in linear functions (log M = log a + b × log X). The logarithmic transformations of body length, volume and mass were used for the graphic illustration of mass-length and mass-volume relationships. Linear regressions between body lengthmass and body volume-mass, after logarithmic transformation, were calculated. Differences between cor-
M.P. Berg / Eur. J. Soil Biol. 36 (2000) 127–133
relation coefficients were analysed using the test of homogeneity among two correlation coefficients ([36], p. 589). Statistical analysis of the data was carried out using Systat for Macintosh (version 5.2).
129
larval period ranged from 11 to 17 d, on average 14 d, and ended with the transformation of the 4th instar larvae into pupae. The duration of the pupal stage was about 4.5 d (range: 4–15 d). In total, new adults emerged 27 d after the first eggs were laid (range: 22–32 d).
3. RESULTS 3.1. The life history of Bradysia paupera
3.2. The length-mass and volume-mass relationships
The life history of B. paupera is alike for both the peat/bean mixture and the non-nutritive bacto-agar covered with a thin layer of ground grass powder. Longevity, at 20 °C, of newly emerged females varied from 4 to 7 d. The males emerged 2 to 4 d before the females and their longevity was 1 to 2 d shorter than that of the females. Mating usually took place during the first 24 h after emergence of the female and oviposition occurred 1 or 2 d later. On average 94 eggs (range: 42–154 eggs) were laid, deposited in one to six clusters. The larvae hatched approximately 6.5 d (range: 4–9 d) after oviposition. The length of the
The log-log plots of the body length-mass and body volume-mass relationships are given in figure 1. The data were fitted by different power functions and the linear regressions of the parameters, based upon the logarithmic transformation of the power functions for the valid ranges, are given in table I. Fresh body mass ranged from 0.011 to 2.238 mg and dry fresh mass and from 0.009 to 0.537 mg. Body volume gives a significantly better fit of the power function through the data than body length both for fresh mass (test of homogeneity among correlation coefficients: t = 6.181 (P < 0.01)) and for dry mass (t = 2.897 (P < 0.01)).
Figure 1. Log-log linear regression of body length (mm) to fresh mass (mg) (top left) and to dry mass (mg) (top right) and linear regression of body volume (mm3) to fresh mass (bottom left) and to dry mass (bottom right).
130
M.P. Berg / Eur. J. Soil Biol. 36 (2000) 127–133
Table I. Regression coefficients (a, b) and correlation coefficient (r) in the linear regression of body length (mm) to fresh mass and dry mass (mg) and in the linear regression of body volume (mm3) to fresh mass and dry mass (mg). The range in minimum and maximum body length (first two) or body volume (last two) for which the regressions are valid are given.
Sample size
Length vs. fresh mass Length vs. dry mass Volume vs. fresh mass Volume vs. dry mass
345 300 345 300
Range
1.122–7.079 1.202–7.079 0.022–4.467 0.040–4.467
This indicates that the introduction of a second body size measurement, i.e. body width used to calculate the surface of the body cross section, lead to a better estimate of body mass (table I: correlation coefficients for length vs. fresh mass r = 0.977, volume vs. fresh mass r = 0.991; length vs. dry mass r = 0.934, volume vs. dry mass r = 0.958). Body length and volume gave a more accurate estimate of fresh mass than of dry mass of the larvae (fresh mass t = 7.241 (P < 0.01); dry mass t = 10.648 (P < 0.01)). For the relationship between log volume vs. log dry mass there seems to exist two clouds of data points (figure 1). The smallest individuals appear to be relatively lighter than larger ones. This is however an artefact due to the faster desiccation of the smallest individuals.
4. DISCUSSION 4.1. The life history of Bradysia paupera The life cycle of Bradysia paupera is typical of the development of many sciarid species. The number of eggs deposited (mean 94 eggs) fall within the range reported for other fungus midges: e.g. around 32 eggs are deposited by B. brunnipes in deciduous litter [32], about 59 eggs by Lycoriella auripila [5], and 60–70 eggs by B. praecox in mushroom beds [37], while an average of 287 eggs were found in the ovaries of single females of B. confinis from a deciduous forest [11]. The lengths of the successive developmental stages, i.e. egg (mean 6.5 d), larvae (mean 14 d), and pupa (mean 4.5 d) of B. paupera are all similar to other Sciaridae, like B. impatiens (reared on non-nutritive bacto-agar with grass powder added) [22], L. auripila (compost in mushroom beds) [3], and Corynoptera sp. (peat/beans mixtures) when accounting for the difference in temperature at which the cultures were kept [14]. Furthermore, the average life-span of adult midges (5.5 d) is comparable to the life-span of e.g. B. impatiens [23, 39], L. auripila [3] and L. mali [27], while the length of one complete life cycle (mean 27 d) corresponds to the range reported for various fungus midges [11].
Regression coefficients a
b
1.1836 –2.5495 2.7667 –0.9955
2.5659 2.5127 1.0211 0.9808
Correlation coefficient
0.9771 0.9336 0.9914 0.9582
The observed time of development confirms that the substrate used to culture B. paupera fulfils the nutritive requirements of the larvae. No differences in average length of the life cycle was found between the peat/ bean mixture and the non-nutritive agar/grass powder. According to Binns [4, 5], Kennedy [23], and Deleporte [12], substrate composition may strongly affect the average time of development. Edible substrate that encourage the development of moulds, ascomycetes, basidiomycetes and myxomycetes, their primary food source, is optimal for the growth of the larvae. The types of substrate used in the present study were similar in that respect which explains the resemblance in time of development. However, the established time of development for B. paupera may not be more than a first indication when dissimilar substrate types, substrate additives are used to culture the species or when food availability is suboptimal.
4.2. The length-mass and volume-mass relationships The present work gives regression equations, which relate body mass of living larvae to body length or volume. The predictive capacity of the regression of body size vs. mass based on a single size measurement, i.e. length, is high. When two size parameters, i.e. length and width, are considered, the correlation coefficient is even more significant. Body size measurements were taken from forward moving larvae when the body was fully stretched. The maximum length of the body depends to a high degree on the speed of movement. A fast crawling larva is more stretched, resulting in a larger length and a smaller width. Body volume indices compensate better for differences in degree of body stretching by integrating length and width measurements. In elongated animals, and for taxonomic groups with species that differ greatly in body morphology, volume indices may be preferred over length indices to estimate body mass, although the predictive capacity of regression between body length vs. mass is high. The disadvantage of indices based on body volume estimates is that it is more laborious.
M.P. Berg / Eur. J. Soil Biol. 36 (2000) 127–133
Body volume was estimated assuming that cross sections of Diptera larvae are circular and have an equal radius over the full length of the body. The first assumption seems to be satisfied, but the larval body tapers at both ends when fully stretched. Body volume might, therefore, be somewhat overestimated as the mid section of a larva has a slightly broader radius than the terminal sections. Abrahamsen [1] showed for fixed enchytraeids that the accuracy of the volume estimates increased with increasing number of intervals into which the worms were divided and width was measured. However, multiple time measurements on crawling Sciaridae larva are very laborious. The regression equations were more accurate for fresh mass than for dry mass which might be explained by the consumption of moist plaster of Paris by some larvae during the period of starvation. In these specimens the gut, normally filled with liquid mixed with food particles, contained in part some plaster of Paris. Water-saturated plaster of Paris contains 65 % water and when the animals are dried that water is lost. The remaining dry plaster of Paris in the gut may account for the larger variance in dry mass per unit of body length or volume compared to fresh mass. The body form of B. paupera is typical of almost all other Sciaridae and Mycetophilidae larvae. Moreover, the established regression equations should be applicable, as a first approximation, to larvae of some nematoceran Diptera belonging to the families Chironomidae (terrestrial), Anisopodidae, Thaumaleidae and Ceratopogonidae with a similar body form as Sciaridae. However, the equations might not be appropriate to estimate mass of Bradysia larva feeding under different conditions or of species of Diptera with a substantial different body form. Petersen [30] has shown that Collembola kept in microcosms and supplied with ad libitum food were heavier than specimens extracted from field samples, probably due to better nutritional conditions in the microcosms. This resulted in steeper slopes of the regression lines for the cultured specimens.
4.3. Comparison of allometric indices In figure 2, the log-log body length to dry mass regression equation is plotted together with two published equations [2, 20]. The regression equation for body length to mass obtained in this study is similar to that of Altmüller [2]. All three regression equations have comparable slopes (2.513, 2.313, and 2.420 for this study, [2], and [20], respectively), but the equation published by Hövemeyer [20] has a much lower intercept. Fresh body mass of larvae in this study ranged from 0.011 to 2.2380 mg, which is higher than the range in fresh body mass given by Altmüller [2] (range in body mass: ± 0.012–0.950 mg). Both ranges in body masses are much higher than that by Hövemeyer [20] (range in body mass: 0.016–0.044 mg). According to figure 2, the body mass of larvae used by Hövemeyer is four times lower than recorded in the
131
Figure 2. Fitted log-log linear regressions of body length (mm) to dry mass (mg). The plotted log-log linear regressions of Altmüller and Hövemeyer are recalculated from the published information by the authors.
present study. Differences in food or habitat, geographical origin of the larvae, or method of weighing the larvae cannot explain this discrepancy; these factors were similar in both published studies. For instance, parameter a in the linear regression is influenced by the body composition of the larvae. Laboratory cultured larvae might contain a higher fat content than field collected larvae. Nevertheless, the linear regressions obtained in this study (cultured animals) and that of Altmüller (field-collected animals) are similar. A difference in body stretching of larvae might occur due to the opposed methods used on extracted larvae to measure body length (life specimens in the present study vs. flotated, and probably dead, specimens in the published studies). The maximum body length of larvae in the present study was 7.0 mm, while in the two other studies maximum lengths of 9.0 mm are reported. This cannot account for the observed differences in body mass between Altmüller [2] and Hövemeyer [20], since they used the same extraction method. Despite this unexplained variance in body mass, the almost identical slopes of the regression equations given in figure 2 indicate that when body length increases, body mass increases proportionally when larvae cultured in the laboratory are compared to larvae obtained directly from the field. However, small variations in biomass can strongly bias studies in which biomass is the main variable, such as those focused on resource distribution among species and importance of organisms in nutrient fluxes, and that careless application of size-mass equations can produce misleading results [19]. If accurate estimates of biomass are required and individual species are involved, the actual establishment of size-mass relationships for new species or taxonomic groups is preferable.
132
M.P. Berg / Eur. J. Soil Biol. 36 (2000) 127–133
Acknowledgements. Sven Hellqvist is kindly acknowledged for his advice on how to culture Sciaridae and Simone Deleporte for additional information. Lena Gäredal was so kind as to give permission to sample adult midges in the greenhouse of the Horticultural Research Station. Tryggve Persson, Janne Bengtsson and two anonymous referees are thanked for their positive criticism on an earlier version of the manuscript. Financial support was provided by the Netherlands Organization for Scientific Research (NWO) and the Swedish Natural Sciences Research Council (NFR).
[13]
[14]
[15]
[16]
REFERENCES [17] [1] Abrahamsen G., Studies on body-volume, bodysurface area, density and live weight of Enchytraeidae (Oligochaeta), Pedobiologia 13 (1973) 6–15. [2] Altmüller R., Untersuchungen über den Energieumsatz von Dipterenpopulationen im Buchenwald (Luzulo-Fagetum), Pedobiologia 19 (1979) 245–278. [3] Binns E.S., Laboratory rearing, biology and chemical control of the mushroom sciarid Lycoriella auripila (Diptera: Lycoriidae), Ann. Appl. Biol. 78 (1973) 119–126. [4] Binns E.S., Mushroom mycelium and compost substrates in relation to the survival of the larva of the sciarid Lycoriella auripila, Ann. Appl. Biol. 80 (1975) 1–15. [5] Binns E.S., Field and laboratory observations on the substrates of the mushroom fungus gnat Lycoriella auripila (Diptera: Sciaridae), Ann. Appl. Biol. 96 (1980) 143–152. [6] Binns E.S., Fungus midges (Diptera: Mycetophilidae/ Sciaridae) and the role of mycophagy in soil: a review, Rev. Écol. Biol. Sol. 18 (1981) 77–90. [7] Ciborowsky J.J.H., A simple volumetric instrument to estimate biomass of fluid-preserved invertebrates, Can. Entomol. 115 (1983) 427–430. [8] Corbet G.B., Southern H.N., The Handbook of British Mammals, Blackwell Scientific Publications, Oxford, 1977. [9] Cramp S., Handbook of the Birds of Europe, the Middle East, and North Africa, Volume V: Tyrant Flycatchers to Thrushes, Oxford University Press, Oxford, 1987. [10] Cramp S., Handbook of the Birds of Europe, the Middle East, and North Africa, Volume VII: Crows to Finches, Oxford University Press, Oxford, 1991. [11] Deleporte S., Biologie et écologie du Diptère Sciaridae Bradysia confinis (Winn., Frey) d’une litière de feuilles (Bretagne intérieure), Rev. Écol. Biol. Sol. 23 (1986) 39–76. [12] Deleporte S., Étude expérimentale de l’ajustement entre le cycle de Bradysia confinis (Diptera: Scia-
[18]
[19]
[20]
[21]
[22]
[23]
[24]
[25] [26]
[27]
[28]
ridae) et l’évolution du substrat trophique (litière de feuilles): importance des microorganismes, Acta Oecol. Gen. 9 (1988) 13–35. Deleporte S., Charrier M., Comparison of digestive carbohydrases between two forest sciarid (Diptera: Sciaridae) larvae in relation to their ecology, Pedobiologia 40 (1996) 193–200. Gillespie D.R., A simple rearing method for fungus midges Corynoptera sp. (Diptera: Sciaridae) with notes on life history, J. Entomol. Soc. B. C. 83 (1986) 45–48. Hawkins J.W., Lankester M.W., Lautenschlager R.A., Bell F.W., Length-biomass and energy relationships of terrestrial gastropods in northern forest ecosystems, Can. J. Zool. 75 (1997) 501–505. Hengeveld R., Polyphagy, oligophagy and food specialization in ground beetles (Coleoptera, Carabidae), Neth. J. Zool. 30 (1980) 564–584. Henschel J.R., Stumpf H., Mahsberg D., Mass-length relationships of spiders and harvestmen (Araneae and Opiliones), Rev. Suisse Zool. vol. hors-série (1996) 265–268. Hessel E.D., Wicklow D.T., Decomposition of rabbit feces: role of the sciarid fly Lycoriella mali (Diptera: Sciaridae) in energy transformations, Can. Entomol. 111 (1979) 213–217. Hódar J.A., The use of regression equations for estimation of arthropod biomass in ecological studies, Acta Oecol. 17 (1996) 421–433. Hövemeyer K., Die Dipterengemeinschaft eines Buchenwaldes auf Kalkgestein: Produktion an Imagines, Abundanz und räumliche Verteilung insbesondere der Larven, Pedobiologia 26 (1984) 1–15. Karg W., Raubmilben, Acari (Acarina); Milben Parasitiformes (Anactinochaeta) Cohors Gamasina Leach. Die Tierwelt Deutschlands 59, Gustav Fisher Verlag, Jena, 1993. Kennedy M.K., A culture method for Bradysia impatiens (Diptera: Sciaridae), Ann. Entomol. Soc. Am. 66 (1973) 1163–1164. Kennedy M.K., Survival and development of Bradysia impatiens (Diptera: Sciaridae) on fungal and non-fungal food sources, Ann. Entomol. Soc. Am. 67 (1974) 745–749. Lang A., Krooss S., Stumpf H., Mass-length relationships of epigeal arthropod predators in arable land (Araneae, Chilopoda, Coleoptera), Pedobiologia 41 (1997) 327–333. Lewis J.G.E., The Biology of Centipedes, Cambridge University Press, Cambridge, 1981. Luxton M., Studies on the oribatid mites of a Danish beech wood soil. II. Biomass, calorimetry, and respirometry, Pedobiologia 15 (1975) 161–200. MacDonald A.J., Biology and behavior of a mushroom infesting sciarid Lycoriella mali Fitch, Ph.D. thesis, Pennsylvania State University, 1972. Persson T., Lohm U., Energetical significance of the Annelids and Arthropods in a Swedish grassland soil, Ecol. Bull. 23 (1977) 1–211.
M.P. Berg / Eur. J. Soil Biol. 36 (2000) 127–133 [29] Persson T., Lundkvist H., Wirén A., Hyvönen R., Wessén B., Effects of acidification and liming on carbon and nitrogen mineralization and soil organisms in mor humus, Water Air Soil Poll. 45 (1989) 77–96. [30] Petersen H., Estimation of dry weight, fresh weight, and calorific content of various Collembolan species, Pedobiologia 15 (1975) 222–243. [31] Petersen P., Luxton M., A comparative analysis of soil fauna populations and their role in decomposition processes, Oikos 39 (1982) 288–388. [32] Pobozsny M., Bradysia brunnipes (Meigen, 1804) (Diptera: Sciaridae) und ihre Bedeutung für die Streuzersetzung, Acta Zool. Acad. Sci. Hung. 22 (1976) 139–143. [33] Russel-Smith A., A study of fungus flies (Diptera: Mycetophilidae) in beech woodland, Ecol. Entomol. 4 (1979) 355–364.
133
[34] Shaw P.J.A., Fungi, fungivores and fungal food webs, in: Carrol G.C., Wicklow D.T. (Eds.), The Fungal Community, M. Dekker, New York, 1992, pp. 295–310. [35] Smith K.G.V., An Introduction to the Immature Stages of British Flies. Handbooks for the Identification of British Insects, vol. 10, part 14, Royal Entomological Society of London, London, 1989. [36] Sokal R.S., Rohlf F.J., Biometry, Freeman and Company, New York, 1981. [37] Symes C.B., Insect pests of mushrooms, Fruit Grow 51 (1921) 142–145. [38] Tuomikoski R., Zur kenntnis der sciariden (Dipt.) Finnlands, Ann. Zool. Soc. ‘Vanamo’ 21 (1960) 1–164. [39] Wilkinson J.D., Daugherty D.M., Comparative development of Bradysia impatiens (Diptera: Sciaridae) under constant and variable temperatures, Ann. Entomol. Soc. Am. 63 (1970) 1079–1083.
Mass-length and mass-volume relationships of larvae of Bradysia paupera (Diptera: Sciaridae) in laboratory cultures Matty P. Berg*§ Swedish University of Agricultural Sciences, Department of Ecology and Environmental Research, P.O. Box 7072, 750 07 Uppsala, Sweden
Received 7 February 2000; accepted 7 September 2000
Abstract − General relationships between body fresh and dry weights, and body length and volume are derived for a dipteran larva, Bradysia paupera. Adult midges were placed in containers with substrate consisting of a mixture of peat and ground beans. From these stock cultures, gravid females were released in containers with agar and a thin layer of ground grass powder, on which the larvae were cultured. A brief description of the life history of B. paupera is given. The body sizes of living larvae were measured on moist plaster of Paris immediately after which the larvae were weighed individually. The relationships of body mass versus size were based on logarithms of mass (M) and size (X, either length or volume) that allows the conversion of a power equation (M = a × Xb) to a linear regression. The derived regression equations that relate body size indices to body mass had a high predictive capacity (r ranged from 0.934 to 0.991). Body volume, the integration of two size measurements (length and width), gave the most accurate estimation of body mass (length vs. fresh mass r = 0.977, volume vs. fresh mass r = 0.991; length vs. dry mass r = 0.934, volume vs. dry mass r = 0.958). Both size indices gave a more accurate estimation of the fresh mass than of the dry mass of the larvae. Differences between the predictive capacity of the size-mass regression equations are explained in the light of larval behaviour and compared with regression equations obtained from literature. © 2000 Éditions scientifiques et médicales Elsevier SAS Diptera / Sciaridae / Bradysia paupera / life history / biomass / mass / length
1. INTRODUCTION The larvae of terrestrial Diptera play an important role in the ecology of soils of forests, meadows and agricultural fields. They provide food for a variety of soil arthropods [16, 21, 25], ground-foraging birds [9, 10], and small ground-dwelling mammals [8]. Dipteran larvae consume microorganisms [33, 34]; they frequently infest mushrooms where they may be of economic importance [5], and feed on roots and stem tissue [6, 35]. Furthermore, they are of importance in litter, dung and wood decomposition and nutrient cycling of ecosystems [13, 18].
* Correspondence and reprints. E-mail address: [email protected] (M.P. Berg). § Present address: Vrije Universiteit, Institute of Ecological Science, Department of Animal Ecology, De Boelelaan 1087, 1081 HV Amsterdam, the Netherlands.
To be able to quantify the contribution of larvae of terrestrial Diptera to different ecological processes, it is necessary to estimate the biomass of larvae present within an ecosystem. Numerous studies have estimated the density of terrestrial Diptera larvae inhabiting different habitats, but rather few have attempted to quantify the biomass represented by this component of the ecosystem (e.g. [2, 20, 28, 31]). In many cases, the estimation of biomass of small living soil animals, such as the larvae of midges and flies, presents problems. The weighing procedure is difficult due to the rapid desiccation of the specimens, especially of the first instars, or is at least time-consuming and tedious. Therefore, unless special microbalances which prevent desiccation are available, estimating biomass values using indirect calculations can be used. Traditionally, allometric indices or other measurements have been used to estimate biomass. One indirect estimate of biomass is obtained by the relationship between a linear measure of body size and the individual weight, expressed in terms of fresh or dry
128
M.P. Berg / Eur. J. Soil Biol. 36 (2000) 127–133
mass. For many taxa of small terrestrial animals, linear multiple regressions relating the logarithm of body mass to the logarithm of body length, width or volume, have been established: e.g. Enchytraeidae [1] oribatid Acari [26], Collembola [30], Gastropoda [15], and epigeic arthropod predators [7, 17, 19, 24]. In experiments on the influence of dipteran larvae on ecosystem processes, absolute biomass estimations are necessary but difficult to obtain. Weighing individual larvae to establish body mass is no option due to fast desiccation, and instead their biomass has to be estimated using allometric indices. Generalized body length-dry mass relationships have been established for Sciaridae [2, 20]. Both these authors have extracted Sciaridae larvae, a mixture of several species, directly from calcareous old beech forests soils in central Germany. It is not known: i) if these allometric indices are valid for populations of Sciaridae larvae consisting of one species only; ii) if allometric indices based on body length-dry mass relationships are more precise than indices based on body length-fresh mass or body volume-body mass relationships; or iii) if allometric indices based on field extracted larvae differ from indices based on laboratory cultured larvae. In this paper body mass-length and body mass-volume regression equations for Bradysia paupera larvae are derived.
2. MATERIALS AND METHODS Adults of the species Bradysia paupera Tuomikoski, 1960, were caught in June with an exhauster from the leaves of cucumber plants and the surrounding soil in a greenhouse near Uppsala, Sweden. Adult midges were identified using the key of Tuomikoski [38]. Schematic drawings of the larva and pupa of Bradysia spp. are given in Smith [35] and black and white plates of the larva can be found in Binns [4]. The midges were stock cultured in containers, diameter 8.8 cm, height 14 cm. Ten pairs of adult midges were released per container. The bottom of the container was covered with a 3.5-cm thick layer of a peat/bean mixture. Dry brown beans were put in water and allowed to swell for 24 h. After that, 100 g moist beans were ground (Braun, MX 32) with 500 mL water and added to 2 L sieved (16-mesh) dry peat. Additional water was added (approximately 150 mL) to get a moist mixture (water content around 75 %) and the substrate was thoroughly mixed. The substrate was kept in a refrigerator (4 °C) till further need. Substrate (50 g) was added to each container and firmly packed at the bottom with a spoon. The lids of the containers had a hole (diameter 4 mm) in the middle covered with fine gauze (200 µm) for ventilation. A small quantity of honey was smeared on the inside of the lids serving as food for the midges. Addition of honey doubled the average life span of an
adult midge from 3 to 7 d at 20 °C. The containers were held in a dark climate room at a temperature of 20 °C at a 70 % relative humidity. Several generations of midges were cultured. From the stock culture described above one adult female and two males were placed in a container (diameter 8.8 cm, height 8 cm). Its bottom was covered with a 1-cm thick layer of water agar (2 % solution of non-nutritive bacto-agar, autoclaved for 20 min at 120 °C). On top of the agar 0.5 g dry ground grass powder was spread out to form a very thin layer. Grass was sampled in summer, dried at 50 °C, grinded (mill type ZM1, 1-mm sieve, Retsch Gmbh, Germany) and autoclaved for 20 min at 120 °C. A drawing of the container is given in Persson et al. [29]. The hatching larvae fed on the grass powder and on the fungi emerging on the substrate. The larvae were sampled from the cultures with increasing time intervals, ranging from 1 d to 2 weeks after emerging from the eggs, to sample the full range of the larval stages. Individual larvae were carefully picked up with a needle and placed on moist plaster of Paris (mixed with black pigment). They were deprived of food for 2 d to empty their gut. The body length (magnification 12×) and body width (measured in the mid-part of the body, magnification 25×) of a larva was measured with a graduated eyepiece (0.01 mm) in dorsal view when crawling on the plaster of Paris. Both measures were taken when a moving larva was fully stretched, corresponding to the maximum length and minimum width of the body. Then the larva was put into an aluminium cup (diameter 5 mm, height 7 mm) and weighed immediately on a microbalance (Cahn, type C-33) to the nearest µg. To determine dry biomass, all measured specimens were freeze-dried under vacuum for 7 d at –30 °C (Edwards high vacuum Ltd, model EF2), stored in an desiccator for 3 d, and weighed to the nearest µg. Body volume was calculated by multiplying body length with the surface of the body cross section assuming that cross sections of sciarid larva are circular. This assumption seems only to be justified when the larva is fully stretched, otherwise the cross section has an oval shape. The body mass and body length and volume data were subjected to a power function according to the formula
M=a×X
b
where M is either fresh mass or dry mass (in mg), and X either body length (L, in mm) or body volume (V, in mm3). Logarithmic transformations of these power functions results in linear functions (log M = log a + b × log X). The logarithmic transformations of body length, volume and mass were used for the graphic illustration of mass-length and mass-volume relationships. Linear regressions between body lengthmass and body volume-mass, after logarithmic transformation, were calculated. Differences between cor-
M.P. Berg / Eur. J. Soil Biol. 36 (2000) 127–133
relation coefficients were analysed using the test of homogeneity among two correlation coefficients ([36], p. 589). Statistical analysis of the data was carried out using Systat for Macintosh (version 5.2).
129
larval period ranged from 11 to 17 d, on average 14 d, and ended with the transformation of the 4th instar larvae into pupae. The duration of the pupal stage was about 4.5 d (range: 4–15 d). In total, new adults emerged 27 d after the first eggs were laid (range: 22–32 d).
3. RESULTS 3.1. The life history of Bradysia paupera
3.2. The length-mass and volume-mass relationships
The life history of B. paupera is alike for both the peat/bean mixture and the non-nutritive bacto-agar covered with a thin layer of ground grass powder. Longevity, at 20 °C, of newly emerged females varied from 4 to 7 d. The males emerged 2 to 4 d before the females and their longevity was 1 to 2 d shorter than that of the females. Mating usually took place during the first 24 h after emergence of the female and oviposition occurred 1 or 2 d later. On average 94 eggs (range: 42–154 eggs) were laid, deposited in one to six clusters. The larvae hatched approximately 6.5 d (range: 4–9 d) after oviposition. The length of the
The log-log plots of the body length-mass and body volume-mass relationships are given in figure 1. The data were fitted by different power functions and the linear regressions of the parameters, based upon the logarithmic transformation of the power functions for the valid ranges, are given in table I. Fresh body mass ranged from 0.011 to 2.238 mg and dry fresh mass and from 0.009 to 0.537 mg. Body volume gives a significantly better fit of the power function through the data than body length both for fresh mass (test of homogeneity among correlation coefficients: t = 6.181 (P < 0.01)) and for dry mass (t = 2.897 (P < 0.01)).
Figure 1. Log-log linear regression of body length (mm) to fresh mass (mg) (top left) and to dry mass (mg) (top right) and linear regression of body volume (mm3) to fresh mass (bottom left) and to dry mass (bottom right).
130
M.P. Berg / Eur. J. Soil Biol. 36 (2000) 127–133
Table I. Regression coefficients (a, b) and correlation coefficient (r) in the linear regression of body length (mm) to fresh mass and dry mass (mg) and in the linear regression of body volume (mm3) to fresh mass and dry mass (mg). The range in minimum and maximum body length (first two) or body volume (last two) for which the regressions are valid are given.
Sample size
Length vs. fresh mass Length vs. dry mass Volume vs. fresh mass Volume vs. dry mass
345 300 345 300
Range
1.122–7.079 1.202–7.079 0.022–4.467 0.040–4.467
This indicates that the introduction of a second body size measurement, i.e. body width used to calculate the surface of the body cross section, lead to a better estimate of body mass (table I: correlation coefficients for length vs. fresh mass r = 0.977, volume vs. fresh mass r = 0.991; length vs. dry mass r = 0.934, volume vs. dry mass r = 0.958). Body length and volume gave a more accurate estimate of fresh mass than of dry mass of the larvae (fresh mass t = 7.241 (P < 0.01); dry mass t = 10.648 (P < 0.01)). For the relationship between log volume vs. log dry mass there seems to exist two clouds of data points (figure 1). The smallest individuals appear to be relatively lighter than larger ones. This is however an artefact due to the faster desiccation of the smallest individuals.
4. DISCUSSION 4.1. The life history of Bradysia paupera The life cycle of Bradysia paupera is typical of the development of many sciarid species. The number of eggs deposited (mean 94 eggs) fall within the range reported for other fungus midges: e.g. around 32 eggs are deposited by B. brunnipes in deciduous litter [32], about 59 eggs by Lycoriella auripila [5], and 60–70 eggs by B. praecox in mushroom beds [37], while an average of 287 eggs were found in the ovaries of single females of B. confinis from a deciduous forest [11]. The lengths of the successive developmental stages, i.e. egg (mean 6.5 d), larvae (mean 14 d), and pupa (mean 4.5 d) of B. paupera are all similar to other Sciaridae, like B. impatiens (reared on non-nutritive bacto-agar with grass powder added) [22], L. auripila (compost in mushroom beds) [3], and Corynoptera sp. (peat/beans mixtures) when accounting for the difference in temperature at which the cultures were kept [14]. Furthermore, the average life-span of adult midges (5.5 d) is comparable to the life-span of e.g. B. impatiens [23, 39], L. auripila [3] and L. mali [27], while the length of one complete life cycle (mean 27 d) corresponds to the range reported for various fungus midges [11].
Regression coefficients a
b
1.1836 –2.5495 2.7667 –0.9955
2.5659 2.5127 1.0211 0.9808
Correlation coefficient
0.9771 0.9336 0.9914 0.9582
The observed time of development confirms that the substrate used to culture B. paupera fulfils the nutritive requirements of the larvae. No differences in average length of the life cycle was found between the peat/ bean mixture and the non-nutritive agar/grass powder. According to Binns [4, 5], Kennedy [23], and Deleporte [12], substrate composition may strongly affect the average time of development. Edible substrate that encourage the development of moulds, ascomycetes, basidiomycetes and myxomycetes, their primary food source, is optimal for the growth of the larvae. The types of substrate used in the present study were similar in that respect which explains the resemblance in time of development. However, the established time of development for B. paupera may not be more than a first indication when dissimilar substrate types, substrate additives are used to culture the species or when food availability is suboptimal.
4.2. The length-mass and volume-mass relationships The present work gives regression equations, which relate body mass of living larvae to body length or volume. The predictive capacity of the regression of body size vs. mass based on a single size measurement, i.e. length, is high. When two size parameters, i.e. length and width, are considered, the correlation coefficient is even more significant. Body size measurements were taken from forward moving larvae when the body was fully stretched. The maximum length of the body depends to a high degree on the speed of movement. A fast crawling larva is more stretched, resulting in a larger length and a smaller width. Body volume indices compensate better for differences in degree of body stretching by integrating length and width measurements. In elongated animals, and for taxonomic groups with species that differ greatly in body morphology, volume indices may be preferred over length indices to estimate body mass, although the predictive capacity of regression between body length vs. mass is high. The disadvantage of indices based on body volume estimates is that it is more laborious.
M.P. Berg / Eur. J. Soil Biol. 36 (2000) 127–133
Body volume was estimated assuming that cross sections of Diptera larvae are circular and have an equal radius over the full length of the body. The first assumption seems to be satisfied, but the larval body tapers at both ends when fully stretched. Body volume might, therefore, be somewhat overestimated as the mid section of a larva has a slightly broader radius than the terminal sections. Abrahamsen [1] showed for fixed enchytraeids that the accuracy of the volume estimates increased with increasing number of intervals into which the worms were divided and width was measured. However, multiple time measurements on crawling Sciaridae larva are very laborious. The regression equations were more accurate for fresh mass than for dry mass which might be explained by the consumption of moist plaster of Paris by some larvae during the period of starvation. In these specimens the gut, normally filled with liquid mixed with food particles, contained in part some plaster of Paris. Water-saturated plaster of Paris contains 65 % water and when the animals are dried that water is lost. The remaining dry plaster of Paris in the gut may account for the larger variance in dry mass per unit of body length or volume compared to fresh mass. The body form of B. paupera is typical of almost all other Sciaridae and Mycetophilidae larvae. Moreover, the established regression equations should be applicable, as a first approximation, to larvae of some nematoceran Diptera belonging to the families Chironomidae (terrestrial), Anisopodidae, Thaumaleidae and Ceratopogonidae with a similar body form as Sciaridae. However, the equations might not be appropriate to estimate mass of Bradysia larva feeding under different conditions or of species of Diptera with a substantial different body form. Petersen [30] has shown that Collembola kept in microcosms and supplied with ad libitum food were heavier than specimens extracted from field samples, probably due to better nutritional conditions in the microcosms. This resulted in steeper slopes of the regression lines for the cultured specimens.
4.3. Comparison of allometric indices In figure 2, the log-log body length to dry mass regression equation is plotted together with two published equations [2, 20]. The regression equation for body length to mass obtained in this study is similar to that of Altmüller [2]. All three regression equations have comparable slopes (2.513, 2.313, and 2.420 for this study, [2], and [20], respectively), but the equation published by Hövemeyer [20] has a much lower intercept. Fresh body mass of larvae in this study ranged from 0.011 to 2.2380 mg, which is higher than the range in fresh body mass given by Altmüller [2] (range in body mass: ± 0.012–0.950 mg). Both ranges in body masses are much higher than that by Hövemeyer [20] (range in body mass: 0.016–0.044 mg). According to figure 2, the body mass of larvae used by Hövemeyer is four times lower than recorded in the
131
Figure 2. Fitted log-log linear regressions of body length (mm) to dry mass (mg). The plotted log-log linear regressions of Altmüller and Hövemeyer are recalculated from the published information by the authors.
present study. Differences in food or habitat, geographical origin of the larvae, or method of weighing the larvae cannot explain this discrepancy; these factors were similar in both published studies. For instance, parameter a in the linear regression is influenced by the body composition of the larvae. Laboratory cultured larvae might contain a higher fat content than field collected larvae. Nevertheless, the linear regressions obtained in this study (cultured animals) and that of Altmüller (field-collected animals) are similar. A difference in body stretching of larvae might occur due to the opposed methods used on extracted larvae to measure body length (life specimens in the present study vs. flotated, and probably dead, specimens in the published studies). The maximum body length of larvae in the present study was 7.0 mm, while in the two other studies maximum lengths of 9.0 mm are reported. This cannot account for the observed differences in body mass between Altmüller [2] and Hövemeyer [20], since they used the same extraction method. Despite this unexplained variance in body mass, the almost identical slopes of the regression equations given in figure 2 indicate that when body length increases, body mass increases proportionally when larvae cultured in the laboratory are compared to larvae obtained directly from the field. However, small variations in biomass can strongly bias studies in which biomass is the main variable, such as those focused on resource distribution among species and importance of organisms in nutrient fluxes, and that careless application of size-mass equations can produce misleading results [19]. If accurate estimates of biomass are required and individual species are involved, the actual establishment of size-mass relationships for new species or taxonomic groups is preferable.
132
M.P. Berg / Eur. J. Soil Biol. 36 (2000) 127–133
Acknowledgements. Sven Hellqvist is kindly acknowledged for his advice on how to culture Sciaridae and Simone Deleporte for additional information. Lena Gäredal was so kind as to give permission to sample adult midges in the greenhouse of the Horticultural Research Station. Tryggve Persson, Janne Bengtsson and two anonymous referees are thanked for their positive criticism on an earlier version of the manuscript. Financial support was provided by the Netherlands Organization for Scientific Research (NWO) and the Swedish Natural Sciences Research Council (NFR).
[13]
[14]
[15]
[16]
REFERENCES [17] [1] Abrahamsen G., Studies on body-volume, bodysurface area, density and live weight of Enchytraeidae (Oligochaeta), Pedobiologia 13 (1973) 6–15. [2] Altmüller R., Untersuchungen über den Energieumsatz von Dipterenpopulationen im Buchenwald (Luzulo-Fagetum), Pedobiologia 19 (1979) 245–278. [3] Binns E.S., Laboratory rearing, biology and chemical control of the mushroom sciarid Lycoriella auripila (Diptera: Lycoriidae), Ann. Appl. Biol. 78 (1973) 119–126. [4] Binns E.S., Mushroom mycelium and compost substrates in relation to the survival of the larva of the sciarid Lycoriella auripila, Ann. Appl. Biol. 80 (1975) 1–15. [5] Binns E.S., Field and laboratory observations on the substrates of the mushroom fungus gnat Lycoriella auripila (Diptera: Sciaridae), Ann. Appl. Biol. 96 (1980) 143–152. [6] Binns E.S., Fungus midges (Diptera: Mycetophilidae/ Sciaridae) and the role of mycophagy in soil: a review, Rev. Écol. Biol. Sol. 18 (1981) 77–90. [7] Ciborowsky J.J.H., A simple volumetric instrument to estimate biomass of fluid-preserved invertebrates, Can. Entomol. 115 (1983) 427–430. [8] Corbet G.B., Southern H.N., The Handbook of British Mammals, Blackwell Scientific Publications, Oxford, 1977. [9] Cramp S., Handbook of the Birds of Europe, the Middle East, and North Africa, Volume V: Tyrant Flycatchers to Thrushes, Oxford University Press, Oxford, 1987. [10] Cramp S., Handbook of the Birds of Europe, the Middle East, and North Africa, Volume VII: Crows to Finches, Oxford University Press, Oxford, 1991. [11] Deleporte S., Biologie et écologie du Diptère Sciaridae Bradysia confinis (Winn., Frey) d’une litière de feuilles (Bretagne intérieure), Rev. Écol. Biol. Sol. 23 (1986) 39–76. [12] Deleporte S., Étude expérimentale de l’ajustement entre le cycle de Bradysia confinis (Diptera: Scia-
[18]
[19]
[20]
[21]
[22]
[23]
[24]
[25] [26]
[27]
[28]
ridae) et l’évolution du substrat trophique (litière de feuilles): importance des microorganismes, Acta Oecol. Gen. 9 (1988) 13–35. Deleporte S., Charrier M., Comparison of digestive carbohydrases between two forest sciarid (Diptera: Sciaridae) larvae in relation to their ecology, Pedobiologia 40 (1996) 193–200. Gillespie D.R., A simple rearing method for fungus midges Corynoptera sp. (Diptera: Sciaridae) with notes on life history, J. Entomol. Soc. B. C. 83 (1986) 45–48. Hawkins J.W., Lankester M.W., Lautenschlager R.A., Bell F.W., Length-biomass and energy relationships of terrestrial gastropods in northern forest ecosystems, Can. J. Zool. 75 (1997) 501–505. Hengeveld R., Polyphagy, oligophagy and food specialization in ground beetles (Coleoptera, Carabidae), Neth. J. Zool. 30 (1980) 564–584. Henschel J.R., Stumpf H., Mahsberg D., Mass-length relationships of spiders and harvestmen (Araneae and Opiliones), Rev. Suisse Zool. vol. hors-série (1996) 265–268. Hessel E.D., Wicklow D.T., Decomposition of rabbit feces: role of the sciarid fly Lycoriella mali (Diptera: Sciaridae) in energy transformations, Can. Entomol. 111 (1979) 213–217. Hódar J.A., The use of regression equations for estimation of arthropod biomass in ecological studies, Acta Oecol. 17 (1996) 421–433. Hövemeyer K., Die Dipterengemeinschaft eines Buchenwaldes auf Kalkgestein: Produktion an Imagines, Abundanz und räumliche Verteilung insbesondere der Larven, Pedobiologia 26 (1984) 1–15. Karg W., Raubmilben, Acari (Acarina); Milben Parasitiformes (Anactinochaeta) Cohors Gamasina Leach. Die Tierwelt Deutschlands 59, Gustav Fisher Verlag, Jena, 1993. Kennedy M.K., A culture method for Bradysia impatiens (Diptera: Sciaridae), Ann. Entomol. Soc. Am. 66 (1973) 1163–1164. Kennedy M.K., Survival and development of Bradysia impatiens (Diptera: Sciaridae) on fungal and non-fungal food sources, Ann. Entomol. Soc. Am. 67 (1974) 745–749. Lang A., Krooss S., Stumpf H., Mass-length relationships of epigeal arthropod predators in arable land (Araneae, Chilopoda, Coleoptera), Pedobiologia 41 (1997) 327–333. Lewis J.G.E., The Biology of Centipedes, Cambridge University Press, Cambridge, 1981. Luxton M., Studies on the oribatid mites of a Danish beech wood soil. II. Biomass, calorimetry, and respirometry, Pedobiologia 15 (1975) 161–200. MacDonald A.J., Biology and behavior of a mushroom infesting sciarid Lycoriella mali Fitch, Ph.D. thesis, Pennsylvania State University, 1972. Persson T., Lohm U., Energetical significance of the Annelids and Arthropods in a Swedish grassland soil, Ecol. Bull. 23 (1977) 1–211.
M.P. Berg / Eur. J. Soil Biol. 36 (2000) 127–133 [29] Persson T., Lundkvist H., Wirén A., Hyvönen R., Wessén B., Effects of acidification and liming on carbon and nitrogen mineralization and soil organisms in mor humus, Water Air Soil Poll. 45 (1989) 77–96. [30] Petersen H., Estimation of dry weight, fresh weight, and calorific content of various Collembolan species, Pedobiologia 15 (1975) 222–243. [31] Petersen P., Luxton M., A comparative analysis of soil fauna populations and their role in decomposition processes, Oikos 39 (1982) 288–388. [32] Pobozsny M., Bradysia brunnipes (Meigen, 1804) (Diptera: Sciaridae) und ihre Bedeutung für die Streuzersetzung, Acta Zool. Acad. Sci. Hung. 22 (1976) 139–143. [33] Russel-Smith A., A study of fungus flies (Diptera: Mycetophilidae) in beech woodland, Ecol. Entomol. 4 (1979) 355–364.
133
[34] Shaw P.J.A., Fungi, fungivores and fungal food webs, in: Carrol G.C., Wicklow D.T. (Eds.), The Fungal Community, M. Dekker, New York, 1992, pp. 295–310. [35] Smith K.G.V., An Introduction to the Immature Stages of British Flies. Handbooks for the Identification of British Insects, vol. 10, part 14, Royal Entomological Society of London, London, 1989. [36] Sokal R.S., Rohlf F.J., Biometry, Freeman and Company, New York, 1981. [37] Symes C.B., Insect pests of mushrooms, Fruit Grow 51 (1921) 142–145. [38] Tuomikoski R., Zur kenntnis der sciariden (Dipt.) Finnlands, Ann. Zool. Soc. ‘Vanamo’ 21 (1960) 1–164. [39] Wilkinson J.D., Daugherty D.M., Comparative development of Bradysia impatiens (Diptera: Sciaridae) under constant and variable temperatures, Ann. Entomol. Soc. Am. 63 (1970) 1079–1083.