- Email: [email protected]
Reproductive performance of the generalist predator Hypoaspis aculeifer (Acari: Gamasida) when foraging on different invertebrate prey
applied soil ecology 36 (2007) 130–135
available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/apsoil
Reproductive performance of the generalist predator Hypoaspis aculeifer (Acari: Gamasida) when foraging on different invertebrate prey Lars-Henrik Heckmann a,1, Andrea Ruf b, Karin M. Nienstedt c, Paul Henning Krogh a,* a
National Environmental Research Institute, Department of Terrestrial Ecology, Vejlsøvej 25, P.O. Box 314, DK-8600 Silkeborg, Denmark University of Bremen, UFT, Department 10-General and Theoretical Ecology, Leobener Strasse, 28359 Bremen, Germany c Springborn Smithers Laboratories (Europe), Seestrasse 21, Horn 9326, Switzerland b
article info
abstract
Article history:
In this study, we assessed the influence of prey quality and prey biomass during a
Received 5 October 2006
standardized 3-week test on adult survival and reproductive output of the predatory mite
Received in revised form
Hypoaspis aculeifer when fed one of six different diets: springtails (Folsomia candida and
18 January 2007
Folsomia fimetaria), a storage mite (Caloglyphus cf. michaeli), an oligochaete (Enchytraeus
Accepted 19 January 2007
crypticus), a nematode (Turbatrix silusiae), and a 1:1:1 mix of F. candida:F. fimetaria:E. crypticus. Our results revealed that a single prey species may be nutritionally sufficient for a 3-week period, as H. aculeifer performed equally well, or better, on a diet based on a 1:1:1 mix of F.
Keywords:
candida:F. fimetaria:E. crypticus. However, when fed C. cf. michaeli, H. aculeifer had a poor
Predator–prey interactions
reproductive output (<200 juveniles) and a reduced survival (60–70%). Thus, investigators
Prey quality
should validate their choice of prey prior to testing H. aculeifer performance during toxicant
Prey density
exposure. # 2007 Elsevier B.V. All rights reserved.
Survival Non-target arthropods Toxicity test
1.
Introduction
Among the soil mesofauna, predatory mites (Gamasida) play a key role in the soil ecosystem (Larink, 1997), especially in agriculture, where they may have a potential regulatory effect on pest populations, e.g. bulb mites (Lesna et al., 2000). Hypoaspis (Geolaelaps) aculeifer Canestrini (Mesostigmata: Laelapidae) is a good candidate representing the Gamasida as they do not overkill their prey nor exhibit cannibalism, unless during extreme starvation (Usher and Davis, 1983), and the species is easily cultured (Schlosser and Riepert, 1992). European guidelines on risk assessment of pesticides have
recently included H. aculeifer as a test species, but at the same time they have indicated the need for further development of existing protocols (European Commission, 2002; EPPO, 2003). This study is part of the research and development activities of the HASTE (H. aculeifer soil test) working group including European institutions and businesses engaged in developing a standard toxicity test with the predatory mite H. aculeifer (endpoints survival and reproduction). The aim of the HASTE working group is to satisfy the above-mentioned European need for soil toxicity tests. Different important test parameters have been tested, e.g. life stage specific sensitivity (Heckmann et al., 2005), by members of the group. However,
* Corresponding author. Tel.: +45 89201588; fax: +45 89201413. E-mail address: [email protected] (P.H. Krogh). 1 Present address: Environmental Biology, School of Biological Sciences, The University of Reading, Reading RG6 6AJ, UK. 0929-1393/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.apsoil.2007.01.002
131
applied soil ecology 36 (2007) 130–135
the consequences of test parameters, such as prey quality and prey biomass for the performance of H. aculeifer have not been considered. Furthermore, although H. aculeifer is a general predator thriving on a variety of different prey, e.g. collembolans, nematodes and oligochaetes (Sardar and Murphy, 1987), the feasibility of applying monotypic diets, as is the case in a standard toxicity test, needs to be validated. The added prey biomass and the nutritional value of a particular prey is an essential element in a standardised test protocol, as differences in food levels and quality may have a great impact on the susceptibility to toxicants (e.g. Antunes et al., 2004). Our aim was to assess the influence of prey quality and prey biomass during a 3-week test on adult survival and reproductive output of H. aculeifer when fed one of six different diets: springtails Folsomia candida Willem (Collembola: Isotomidae) and F. fimetaria Linnaeus (Collembola: Isotomidae), a storage mite Caloglyphus cf. michaeli Oudemans (Astigmata: Acaridae) (E. Wurst, personal communications), an oligochaete Enchytraeus crypticus Westheide and Graefe (Haplotaxida: Megascolecidae), a nematode Turbatrix silusiae de Man (Rhabditida: Cephalobidae), and a 1:1:1 mix of F. candida:F. fimetaria:E. crypticus.
2.
Materials and methods
2.1.
Experimental design
H. aculeifer was originally obtained from Koppert Biological Systems (Rotterdam, The Netherlands), and a stock culture was reared at all the participating research facilities. A total of six 3-week diet experiments were performed consisting of one replicate of 10–11 levels of prey biomass supply (regressional approach), except for T. silusiae where each prey biomass supply was in triplicate. The test design followed the overall set-up outlined in the test protocol of the HASTE working group (Version 2004), which is based on Krogh and Axelsen (1998). The soil substrate was a 5% organic matter (OM) OECD artificial soil consisting of 5% finely grounded Sphagnum-peat, 21% caoline clay and 74% quartz sand (OECD, 1984). The initial water content was 15–20% corresponding to 40–50% of the water-holding capacity (WHC) with an initial pH of 6.0 0.5. Thirty grams soil wet weight (WW) were placed in each replicate microcosm (approximately diameter 5.0–7.0 cm and height 4.0–7.0 cm). Ten female and five male mites (18 1 days), synchronised according to Krogh (1995), were added within an hour after adding prey. H. aculeifer was fed on a weekly basis (days 0, 7 and 14) with one of the following prey
species: F. candida, F. fimetaria, E. crypticus, C. cf. michaeli, T. silusiae, or a 1:1:1 mix of F. candida:F. fimetaria:E. crypticus. The prey was added at 10–11 comparable biomass amounts ranging from 0.0 (nil prey) to 4.50 mg dry weight (DW) per week. Conversion factors, based on numbers (F. candida, F. fimetaria and E. crypticus) or WW (C. cf. michaeli and T. silusiae) were established for each prey (Table 1) to ensure a consistent feeding regime. With the exception of C. cf. michaeli and T. silusiae, where a complete range of prey life stages were supplied, only sexually mature prey were added to guarantee that juvenile H. aculeifer would be able to catch juvenile prey of a manageable size by the time they became protonymphs (equivalent to about day 10 of the test). Equally important, large adult prey of F. candida and E. crypticus especially were avoided, as they could be difficult to handle for the adult H. aculeifer. During the 3-week experiment, the vessels were kept in a climate room at 20 1 8C and with a 12-h light:12-h dark regime, except for T. silusiae which had a 16-h light:8-h dark regime. Soil moisture was checked weekly by weighing, and water content was adjusted if required. Experiments with F. candida, F. fimetaria, E. crypticus and the 1:1:1 mix were performed at the National Environmental Research Institute, Silkeborg, Denmark, whereas experiments with C. cf. michaeli and T. silusiae were performed at the University of Bremen, Bremen, Germany, and Springborn Smithers Laboratories, Horn, Switzerland, respectively. Permanent cultures of the prey species have been kept for years at the respective institutes. Following the experimental period, adult and juvenile mites (larvae, protonymphs and deutonymphs) were extracted by a modified MacFadyen-type high gradient extractor for 48 h (25 8C for 12 h, 30 8C for 12 h, 35 8C for 12 h and 40 8C for 12 h) similar to the equipment described by Petersen (1978). Mites from the T. silusiae experiment were extracted using a validated centrifugation–flotation technique in a colloidal silica suspension (Ludox extraction). Following extraction, mites were counted manually under a stereomicroscope, and female survival and the number of juvenile mites was recorded.
2.2.
Data analysis
The reproduction (number of juveniles per female), as a response to the added total prey biomass, was fitted to an asymptotic model: P ¼ Pmax ð1 erB Þ
(1)
Table 1 – Prey species parameters for the Hypoaspis aculeifer feeding trials Prey F. candida F. fimetaria E. crypticus C. cf. michaeli T. silusiae a b c
Preferred age/stage
FWW/DWa
16–19 daysc >60 days Young adults with visible clitellumc Adult (exact age trivial) Adult (exact age trivial)
– – – 4.70 2.73
Individual DWb 13.5 mg (n = 1000) 10.0 mg (n = 1000) 71.5 mg (n = 200) n.a. n.a.
FWW/DW refers to a conversion factor between wet weight (WW) and dry weight (DW) for a given prey at the preferred age/stage. Individual DW signifies the average individual DW for a given prey at the preferred age/stage. Older (i.e. larger) prey adults may be difficult to handle even for large H. aculeifer females. n.a. signifies ‘‘not applicable’’.
132
applied soil ecology 36 (2007) 130–135
Table 2 – Reproductive response of Hypoaspis aculeifer at different prey biomass Prey
Initial increase in juvenile production (no.) in response to an increase in prey biomass
Number of H. aculeifer juveniles at maximum prey biomass (13.5 mg DW)
86.7 a 54.1 bc 110.1 a 56.9 b 29.3 cd 7.7 d
F. fimetaria (fim) F. candida (can) E. crypticus (cryp) 1:1:1 mix of can:fim:cryp T. silusiae C. cf. michaeli
375a 290bc 254c 312b 218d 106e
Prey biomass needed to produce 200 H. aculeifer juveniles (mg DW) 3.2a (2.6–3.8) 5.7b (4.7–6.8) 3.6a (2.4–4.7) 5.2b (4.3–6.1) 10.9c (7.7–14.0) >13.5
(346–405) (260–320) (230–279) (280–343) (179–257) (72.7–138)
Different superscript letters (a–d) denote a significant difference (P < 0.05). Numbers in brackets signify the 95% confidence intervals.
Table 3 – Non-linear regression parameter estimates of reproduction response curves Prey
Pmax
95% C.L.
P-value (%)
r
F. fimetaria (fim) F. candida (can) E. crypticus (cryp) 1:1:1 mix of can: fim: cryp
395.6 323.9 255.1 350.9
346.6–444.6 257.5–390.4 229.4–280.8 277.2–424.6
0.01 0.01 0.01 0.01
0.22 0.17 0.43 0.16
0.15–0.29 0.09–0.24 0.24–0.63 0.09–0.24
T. silusiae
244.5 22.0a
105.9–383.1 20.5–64.5
0.09 30.4
0.12
0.03–0.27
7.7
3.8–11.7
C. cf. michaeli
–b
–
–
95% C.L.
P-value (%) 0.01 0.01 0.01 0.01 10.4
0.02
rB
Reproduction response model: P = Pmax(1 e ), where P is reproduction, r the rate of increase in reproduction in response to an increase in prey, Pmax the asymptotic reproductive maximum and B is prey biomass. P-values of t-statistics (see Section 2.2) and 95% confidence limits are shown for Pmax and r. a Y-intercept indicating the reproduction during starvation. b An asymptote could not be obtained.
where P is the reproduction (number of juveniles), r the rate of increase in reproduction in response to an increase in prey, Pmax the asymptotic maximum of reproduction and B is the prey biomass. The initial increase in juvenile production in response to an increase in prey biomass was estimated as the slope of the reproduction–food biomass model at zero addition of food. For the sigmoid model this value was Pmax r. For T. silusiae the reproduction was above zero with no food offered so an intercept was included in the model, and for C. cf. michaeli data did not allow for an estimate of an asymptote so a linear model was fitted to the data. PROC NLMIXED was used to fit the data to the consumption formulae, estimate model parameters, compute P-values of the t-statistics of the estimates being significantly different from 0, and to provide the tests of comparisons between parameters or point estimates of the models (SAS Institute Inc., 2004). The statistical tests were made by calculating contrasts between the estimates and PROC NLMIXED constructs approximate F tests (SAS Institute Inc., 2004).
3.
Results
3.1.
Reproduction
Production of at least 200 juveniles per 10 females during a 3week test is suggested in the HASTE soil mite test protocol as a validity criterion for control treatments. H. aculeifer produced well above the 200 juveniles threshold on all prey species at different prey biomass supplies with the exception of C. cf. michaeli, which was the only prey where this limit was not
achieved, even at the highest supplied prey biomass (Tables 2 and 3; Fig. 1.). A comparison of the prey biomass needed to meet the 200 juvenile threshold ranked the prey significantly (P < 0.05) into three groups: F. fimetaria = E. crypticus > 1:1:1 mix of F. candida:F. fimetaria:E. crypticus = F. candida > T. silusiae (Tables 2 and 3; Fig. 1). F. fimetaria and E. crypticus produced a significantly higher (P < 0.05) initial increase in H. aculeifer reproduction in response to an increase in prey biomass compared with the other prey (Tables 2 and 3; Fig. 1.). Overall, F. fimetaria was the best prey with an observed maximum H. aculeifer reproduction of almost 400 juveniles (Fig. 1.).
3.2.
Survival
The draft test protocol of the HASTE working group states that the average adult female mortality should not exceed 25% at the end of the test. Like the criterion on reproductive output, this ensures that control individuals are performing reasonably well. In our tests, the majority of diets resulted in H. aculeifer female survival rates of 80–100% even in control treatments where no prey was added. But, three of the treatments fed C. cf. michaeli had H. aculeifer female survival rates between 60 and 70%, independent of the amount of prey (data not shown).
4.
Discussion
We assessed how H. aculeifer performed during a 3-week test when fed one of six different diets. H. aculeifer is known to be a generalist predator (Sardar and Murphy, 1987) corresponding
applied soil ecology 36 (2007) 130–135
with our findings, which revealed that five of six of the tested diets (F. fimetaria, F. candida, E. crypticus, T. silusiae and a 1:1:1 mix of F. candida:F. fimetaria:E. crypticus) were suitable. Moreover, several prey, other than those tested in the present study, have been shown to be a suitable monotypic diet for H. aculeifer. Two storage mites Glycyphagus domesticus and Tyrophagus putrescentiae (also known as the cheese mite) have been shown to be of sufficient nutritional value for H. aculeifer (Barker, 1969), the latter being widely used as prey within the HASTE working group. Our results also showed that a single prey may be nutritionally sufficient for a 3-week period, as H. aculeifer performed equally well, or better, on a single species diet compared with a diet based on a 1:1:1 mix of F. candida:F. fimetaria:E. crypticus. Ten female H. aculeifer produced more than 200 juveniles during the 3-week test when reared on any but one diet. When fed C. cf. michaeli, H. aculeifer had a poor reproductive output and reduced survival. Several factors can affect the reproductive output of a predator, e.g. prey capture rates, preyhandling time and prey consumption time. There is no obvious reason why C. cf. michaeli should be more difficult for H. aculeifer to catch or handle, especially at high prey densities. But, there are two major possibilities for the low performance; a low nutritional value of C. cf. michaeli, or the
133
prey may be toxic to juveniles and/or adult H. aculeifer, as observed in different predator–prey interactions. For instance, Oelbermann and Scheu (2002) revealed that F. candida caused total mortality in offspring of the generalist predator wolf spider Pardosa lugubris. Low nutritional input may be a result of monotypic diets, which has been associated with lack of reproduction in some invertebrate predators, e.g. the cereal spider Erigone atra thrived on Isotoma anglicana and Drosophila melanogaster, but was unable to maintain reproduction when fed F. fimetaria (Marcussen et al., 1999). The mechanisms behind low nutritional value may be related to the chemical composition (carbohydrate, lipid, and protein content) of the prey species including elevated consumption/digestion time. Overall, there were two deviations in our study from the current HASTE ring-test version of the soil mite test protocol. Firstly, a 12-h light:12-h dark regime was applied in the majority of diet tests, except for T. silusiae which had a 16-h light:8-h dark regime. The latter corresponded with the light:dark regime of the ring-test protocol. Having a consistent light:dark regime is important during testing of different toxicants, especially when testing compounds with a low photo-stability. However, in our experimental context, we consider the differences in light:dark regimes to be of minor importance since no toxicants were applied. Furthermore, as
Fig. 1 – Total reproduction of Hypoaspis aculeifer when fed a comparable biomass of six different invertebrate prey: F. fimetaria; F. candida; E. crypticus; a 1:1:1 mix of F. candida:F. fimetaria:E. crypticus; T. silusiae; and C. cf. michaeli. The horizontal line crossing at 200 juveniles represents a reproductive validity criterion set by the HASTE (Hypoaspis aculeifer soil test) working group.
134
applied soil ecology 36 (2007) 130–135
H. aculeifer and most of the tested prey species are true soil dwelling (i.e. euedaphic) organisms, they would not be influenced by dissimilar light:dark regimes. The second deviation in our study was including five H. aculeifer males together with 10 females. In the ring-test protocol, only 10 females are added, as including males in the test has been found to be of minor importance since H. aculeifer females only use the first male spermatozoa deposit for fertilisation of all the eggs that they lay throughout their life (Ruf, 1995). Females originating from a synchronised culture are already mated when they are added to the test containers. Krogh (1995) has estimated the sex-specific consumption, revealing that male consumption would be approximately 20% of the total consumption throughout the test. Thus, if no males were present, one could expect a given reproductive output to be obtained at a prey biomass 20% lower than that outlined in Fig. 1. In a preliminary experiment, we found that 10 female H. aculeifer could produce more than 400 juveniles in a 3-week test when fed 1000 (13.5 mg DW) F. candida (16–19 days old) once at the onset of the test (unpublished results). Although a single feeding would have a great impact on the workload during the test, it would be a fragile set-up if the compounds to be tested were relatively more toxic to the prey than the test organism. For instance, under similar conditions, dimethoate is at least 4– 10-fold more toxic to F. fimetaria than H. aculeifer (Rundgren and van Gestel, 1998). Weekly or biweekly feedings ensure that live prey would be available throughout the test. Additionally, the possibility of choosing between different suitable prey species combined with specific data available for each of these species may not only improve the level of information obtained from a standard test, it may also strengthen the experimental set-up by choosing the more tolerant prey for a given toxicant. A literature search on the Web of Science (http://scientific.thomson.com/ accessed02-09-2006), on the occurrence of the studied prey species scientific names in peer reviewed publications, revealed that F. candida was by far the most studied prey: F. candida (119 publications) > F. fimetaria (20 publications) > E. crypticus (16 publications) > C. cf. michaeli (0 publications) = T. silusiae (0 publications). Although it would have no direct influence on the test outcome, we argue that if an experimenter has the choice between two suitable prey factors, such as published ecotoxicological/ecological data on the given prey should be considered. The overall conclusion is that during a 3-week test H. aculeifer thrives on an array of different single prey, such as collembolans, Oligochaeta, nematodes and mites as shown in the literature and the present study. Although regarded as a generalist predator, different strains of H. aculeifer may have diet-dependent preferences (e.g. Lesna and Sabelis, 1999) based on adaptation to the prey that they have been offered during generations of culturing. Our strain of H. aculeifer (Koppert Biological Systems, Rotterdam, The Netherlands) had the highest reproductive output on F. fimetaria, but we strongly disencourage using C. cf. michaeli as prey. Thus, in a future standardised soil toxicity test with H. aculeifer, experimenters may choose whichever prey they prefer, as long as it has been validated that weekly or biweekly feedings result in female survival above 75% and at least 200 juveniles per 10 females in the control treatments.
Acknowledgements We would like to acknowledge the HASTE working group for positive feedback and valuable discussions. Moreover, we would like to thank research technicians Karsten T. Andersen, Zdenek Gavor, Elin Jørgensen, Mette Thomsen and Annemarie Kissling for experimental assistance, and two anonymous reviewers for their valuable comments on the manuscript. This research was supported by the Department of Terrestrial Ecology, National Environmental Research Institute, Denmark, The Center for Environmental Research and Technology of the University of Bremen, Germany, and Springborn Smithers Laboratories, Switzerland.
references
Antunes, S.C., Castro, B.B., Goncalves, F., 2004. Effect of food level on the acute and chronic responses of daphnids to lindane. Environ. Pollut. 127, 367–375. Barker, P.S., 1969. Response of a predator Hypoaspis aculeifer (Canestrini) (Acarina–Laelapidae) to 2 species of prey. Can. J. Zool. 47, 343–345. European Commission, 2002. SANCO/10329/2002. Guidance Document on Terrestrial Ecotoxicology under Council Directive 91/414/EEC. http://europa.eu.int/comm/food/fs/ ph_ps/pro/wrkdoc/wrkdoc09_en.pdf. EPPO, 2003. Environmental risk assessment scheme for plant protection products. Chapter 8: Soil organisms and functions. EPPO Bull. 33, 195–209. Heckmann, L.-H., Maraldo, K., Krogh, P.H., 2005. Life stage specific impact of dimethoate on the predatory mite Hypoaspis aculeifer Canestrini (Gamasida: Laelapidae). Environ. Sci. Technol. 39, 7154–7157. Krogh, P.H., 1995. Effects of pesticides on the reproduction of Hypoaspis aculeifer (Gamasida: Laelapidae) in the laboratory. Acta Zool. Fenn. 196, 333–337. Krogh, P.H., Axelsen, J.A., 1998. Test on the predatory mite Hypoaspis aculeifer preying on the collombolan Folsomia fimetaria. In: Løkke, H., van Gestel, C.A.M. (Eds.), Handbook of Soil Invertebrate Toxicity Tests. John Wiley & Sons Ltd., Chichester, pp. 239–251. Larink, O., 1997. Sprintails and mites: important knots in the food web of soils. In: Benckiser, G. (Ed.), Fauna in soil ecosystems: Recycling Processes, Nutrient Fluxes, and Agricultural Production. Marcel Dekker Inc., New York, pp. 225–264. Lesna, I., Conijn, C.G.M., Sabelis, M.W., van Straalen, N.M., 2000. Biological control of the bulb mite, Rhizoglyphus robini, by the predatory mite, Hypoaspis aculeifer, on lilies: predator–prey dynamics in the soil, under greenhouse and field conditions. Biocontrol Sci. Technol. 10, 179–193. Lesna, I., Sabelis, M.W., 1999. Diet-dependent female choice for males with ‘good genes’ in a soil predatory mite. Nature 401, 581–584. Marcussen, B.M., Axelsen, J.A., Toft, S., 1999. The value of two Collembola species as food for a linyphiid spider. Entomol. Experiment. Appl. 92, 29–36. OECD, 1984. OECD Guidelines for Testing of Chemicals, No. 207. Earthworm, Acute Toxicity Tests, Organization for Economic Cooperation and Development, Paris, 9 pp. Oelbermann, K., Scheu, S., 2002. Effects of prey type and mixed diets on survival, growth and development of a generalist predator, Pardosa lugubris (Araneae: Lycosidae). Basic Appl. Ecol. 3, 285–291.
applied soil ecology 36 (2007) 130–135
Petersen, H., 1978. Some properties of two high gradient extractors for soil microarthropods. Natura Jutlandica 20, 95–121. Ruf, A., 1995. Sex ratio and clutch size control in the soil inhabiting predatory mite Hypoaspis aculeifer (Canestrini 1883) (Mesostigmata, Dermanyssidae). In: Proceedings of the 2nd EURAAC Symposium. pp. 241–249. Rundgren, S., van Gestel, C.A.M., 1998. Comparison of species sensitivity. In: Løkke, H., van Gestel, C.A.M. (Eds.), Handbook of Soil Invertebrate Toxicity Tests. John Wiley & Sons Ltd., Chichester, pp. 41–55.
135
Sardar, M.A., Murphy, P.W., 1987. Feeding tests of grassland soil-inhabiting gamasine predators. Acarology 28, 117–121. SAS Institute Inc., 2004. SAS/STAT1 9.1 User’s Guide. SAS Institute Inc., Cary, NC, USA. Schlosser, H.J., Riepert, F., 1992. Entwicklung eines pru¨fverfahrens fu¨r chemikalien an bodenraubmilben (Gamasina)-teil 1: biologie der bodenraubmilbe Hypoaspis aculeifer Canestrini, 1883 (Gamasina) unter laborbedingungen. Zoologische Beitra¨ge 34, 395–412. Usher, M.B., Davis, P.R., 1983. The biology of Hypoaspis aculeifer (Canestrini) (Mesostigmata)—is there a tendency towards social behavior? Acarology 24, 243–253.
available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/apsoil
Reproductive performance of the generalist predator Hypoaspis aculeifer (Acari: Gamasida) when foraging on different invertebrate prey Lars-Henrik Heckmann a,1, Andrea Ruf b, Karin M. Nienstedt c, Paul Henning Krogh a,* a
National Environmental Research Institute, Department of Terrestrial Ecology, Vejlsøvej 25, P.O. Box 314, DK-8600 Silkeborg, Denmark University of Bremen, UFT, Department 10-General and Theoretical Ecology, Leobener Strasse, 28359 Bremen, Germany c Springborn Smithers Laboratories (Europe), Seestrasse 21, Horn 9326, Switzerland b
article info
abstract
Article history:
In this study, we assessed the influence of prey quality and prey biomass during a
Received 5 October 2006
standardized 3-week test on adult survival and reproductive output of the predatory mite
Received in revised form
Hypoaspis aculeifer when fed one of six different diets: springtails (Folsomia candida and
18 January 2007
Folsomia fimetaria), a storage mite (Caloglyphus cf. michaeli), an oligochaete (Enchytraeus
Accepted 19 January 2007
crypticus), a nematode (Turbatrix silusiae), and a 1:1:1 mix of F. candida:F. fimetaria:E. crypticus. Our results revealed that a single prey species may be nutritionally sufficient for a 3-week period, as H. aculeifer performed equally well, or better, on a diet based on a 1:1:1 mix of F.
Keywords:
candida:F. fimetaria:E. crypticus. However, when fed C. cf. michaeli, H. aculeifer had a poor
Predator–prey interactions
reproductive output (<200 juveniles) and a reduced survival (60–70%). Thus, investigators
Prey quality
should validate their choice of prey prior to testing H. aculeifer performance during toxicant
Prey density
exposure. # 2007 Elsevier B.V. All rights reserved.
Survival Non-target arthropods Toxicity test
1.
Introduction
Among the soil mesofauna, predatory mites (Gamasida) play a key role in the soil ecosystem (Larink, 1997), especially in agriculture, where they may have a potential regulatory effect on pest populations, e.g. bulb mites (Lesna et al., 2000). Hypoaspis (Geolaelaps) aculeifer Canestrini (Mesostigmata: Laelapidae) is a good candidate representing the Gamasida as they do not overkill their prey nor exhibit cannibalism, unless during extreme starvation (Usher and Davis, 1983), and the species is easily cultured (Schlosser and Riepert, 1992). European guidelines on risk assessment of pesticides have
recently included H. aculeifer as a test species, but at the same time they have indicated the need for further development of existing protocols (European Commission, 2002; EPPO, 2003). This study is part of the research and development activities of the HASTE (H. aculeifer soil test) working group including European institutions and businesses engaged in developing a standard toxicity test with the predatory mite H. aculeifer (endpoints survival and reproduction). The aim of the HASTE working group is to satisfy the above-mentioned European need for soil toxicity tests. Different important test parameters have been tested, e.g. life stage specific sensitivity (Heckmann et al., 2005), by members of the group. However,
* Corresponding author. Tel.: +45 89201588; fax: +45 89201413. E-mail address: [email protected] (P.H. Krogh). 1 Present address: Environmental Biology, School of Biological Sciences, The University of Reading, Reading RG6 6AJ, UK. 0929-1393/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.apsoil.2007.01.002
131
applied soil ecology 36 (2007) 130–135
the consequences of test parameters, such as prey quality and prey biomass for the performance of H. aculeifer have not been considered. Furthermore, although H. aculeifer is a general predator thriving on a variety of different prey, e.g. collembolans, nematodes and oligochaetes (Sardar and Murphy, 1987), the feasibility of applying monotypic diets, as is the case in a standard toxicity test, needs to be validated. The added prey biomass and the nutritional value of a particular prey is an essential element in a standardised test protocol, as differences in food levels and quality may have a great impact on the susceptibility to toxicants (e.g. Antunes et al., 2004). Our aim was to assess the influence of prey quality and prey biomass during a 3-week test on adult survival and reproductive output of H. aculeifer when fed one of six different diets: springtails Folsomia candida Willem (Collembola: Isotomidae) and F. fimetaria Linnaeus (Collembola: Isotomidae), a storage mite Caloglyphus cf. michaeli Oudemans (Astigmata: Acaridae) (E. Wurst, personal communications), an oligochaete Enchytraeus crypticus Westheide and Graefe (Haplotaxida: Megascolecidae), a nematode Turbatrix silusiae de Man (Rhabditida: Cephalobidae), and a 1:1:1 mix of F. candida:F. fimetaria:E. crypticus.
2.
Materials and methods
2.1.
Experimental design
H. aculeifer was originally obtained from Koppert Biological Systems (Rotterdam, The Netherlands), and a stock culture was reared at all the participating research facilities. A total of six 3-week diet experiments were performed consisting of one replicate of 10–11 levels of prey biomass supply (regressional approach), except for T. silusiae where each prey biomass supply was in triplicate. The test design followed the overall set-up outlined in the test protocol of the HASTE working group (Version 2004), which is based on Krogh and Axelsen (1998). The soil substrate was a 5% organic matter (OM) OECD artificial soil consisting of 5% finely grounded Sphagnum-peat, 21% caoline clay and 74% quartz sand (OECD, 1984). The initial water content was 15–20% corresponding to 40–50% of the water-holding capacity (WHC) with an initial pH of 6.0 0.5. Thirty grams soil wet weight (WW) were placed in each replicate microcosm (approximately diameter 5.0–7.0 cm and height 4.0–7.0 cm). Ten female and five male mites (18 1 days), synchronised according to Krogh (1995), were added within an hour after adding prey. H. aculeifer was fed on a weekly basis (days 0, 7 and 14) with one of the following prey
species: F. candida, F. fimetaria, E. crypticus, C. cf. michaeli, T. silusiae, or a 1:1:1 mix of F. candida:F. fimetaria:E. crypticus. The prey was added at 10–11 comparable biomass amounts ranging from 0.0 (nil prey) to 4.50 mg dry weight (DW) per week. Conversion factors, based on numbers (F. candida, F. fimetaria and E. crypticus) or WW (C. cf. michaeli and T. silusiae) were established for each prey (Table 1) to ensure a consistent feeding regime. With the exception of C. cf. michaeli and T. silusiae, where a complete range of prey life stages were supplied, only sexually mature prey were added to guarantee that juvenile H. aculeifer would be able to catch juvenile prey of a manageable size by the time they became protonymphs (equivalent to about day 10 of the test). Equally important, large adult prey of F. candida and E. crypticus especially were avoided, as they could be difficult to handle for the adult H. aculeifer. During the 3-week experiment, the vessels were kept in a climate room at 20 1 8C and with a 12-h light:12-h dark regime, except for T. silusiae which had a 16-h light:8-h dark regime. Soil moisture was checked weekly by weighing, and water content was adjusted if required. Experiments with F. candida, F. fimetaria, E. crypticus and the 1:1:1 mix were performed at the National Environmental Research Institute, Silkeborg, Denmark, whereas experiments with C. cf. michaeli and T. silusiae were performed at the University of Bremen, Bremen, Germany, and Springborn Smithers Laboratories, Horn, Switzerland, respectively. Permanent cultures of the prey species have been kept for years at the respective institutes. Following the experimental period, adult and juvenile mites (larvae, protonymphs and deutonymphs) were extracted by a modified MacFadyen-type high gradient extractor for 48 h (25 8C for 12 h, 30 8C for 12 h, 35 8C for 12 h and 40 8C for 12 h) similar to the equipment described by Petersen (1978). Mites from the T. silusiae experiment were extracted using a validated centrifugation–flotation technique in a colloidal silica suspension (Ludox extraction). Following extraction, mites were counted manually under a stereomicroscope, and female survival and the number of juvenile mites was recorded.
2.2.
Data analysis
The reproduction (number of juveniles per female), as a response to the added total prey biomass, was fitted to an asymptotic model: P ¼ Pmax ð1 erB Þ
(1)
Table 1 – Prey species parameters for the Hypoaspis aculeifer feeding trials Prey F. candida F. fimetaria E. crypticus C. cf. michaeli T. silusiae a b c
Preferred age/stage
FWW/DWa
16–19 daysc >60 days Young adults with visible clitellumc Adult (exact age trivial) Adult (exact age trivial)
– – – 4.70 2.73
Individual DWb 13.5 mg (n = 1000) 10.0 mg (n = 1000) 71.5 mg (n = 200) n.a. n.a.
FWW/DW refers to a conversion factor between wet weight (WW) and dry weight (DW) for a given prey at the preferred age/stage. Individual DW signifies the average individual DW for a given prey at the preferred age/stage. Older (i.e. larger) prey adults may be difficult to handle even for large H. aculeifer females. n.a. signifies ‘‘not applicable’’.
132
applied soil ecology 36 (2007) 130–135
Table 2 – Reproductive response of Hypoaspis aculeifer at different prey biomass Prey
Initial increase in juvenile production (no.) in response to an increase in prey biomass
Number of H. aculeifer juveniles at maximum prey biomass (13.5 mg DW)
86.7 a 54.1 bc 110.1 a 56.9 b 29.3 cd 7.7 d
F. fimetaria (fim) F. candida (can) E. crypticus (cryp) 1:1:1 mix of can:fim:cryp T. silusiae C. cf. michaeli
375a 290bc 254c 312b 218d 106e
Prey biomass needed to produce 200 H. aculeifer juveniles (mg DW) 3.2a (2.6–3.8) 5.7b (4.7–6.8) 3.6a (2.4–4.7) 5.2b (4.3–6.1) 10.9c (7.7–14.0) >13.5
(346–405) (260–320) (230–279) (280–343) (179–257) (72.7–138)
Different superscript letters (a–d) denote a significant difference (P < 0.05). Numbers in brackets signify the 95% confidence intervals.
Table 3 – Non-linear regression parameter estimates of reproduction response curves Prey
Pmax
95% C.L.
P-value (%)
r
F. fimetaria (fim) F. candida (can) E. crypticus (cryp) 1:1:1 mix of can: fim: cryp
395.6 323.9 255.1 350.9
346.6–444.6 257.5–390.4 229.4–280.8 277.2–424.6
0.01 0.01 0.01 0.01
0.22 0.17 0.43 0.16
0.15–0.29 0.09–0.24 0.24–0.63 0.09–0.24
T. silusiae
244.5 22.0a
105.9–383.1 20.5–64.5
0.09 30.4
0.12
0.03–0.27
7.7
3.8–11.7
C. cf. michaeli
–b
–
–
95% C.L.
P-value (%) 0.01 0.01 0.01 0.01 10.4
0.02
rB
Reproduction response model: P = Pmax(1 e ), where P is reproduction, r the rate of increase in reproduction in response to an increase in prey, Pmax the asymptotic reproductive maximum and B is prey biomass. P-values of t-statistics (see Section 2.2) and 95% confidence limits are shown for Pmax and r. a Y-intercept indicating the reproduction during starvation. b An asymptote could not be obtained.
where P is the reproduction (number of juveniles), r the rate of increase in reproduction in response to an increase in prey, Pmax the asymptotic maximum of reproduction and B is the prey biomass. The initial increase in juvenile production in response to an increase in prey biomass was estimated as the slope of the reproduction–food biomass model at zero addition of food. For the sigmoid model this value was Pmax r. For T. silusiae the reproduction was above zero with no food offered so an intercept was included in the model, and for C. cf. michaeli data did not allow for an estimate of an asymptote so a linear model was fitted to the data. PROC NLMIXED was used to fit the data to the consumption formulae, estimate model parameters, compute P-values of the t-statistics of the estimates being significantly different from 0, and to provide the tests of comparisons between parameters or point estimates of the models (SAS Institute Inc., 2004). The statistical tests were made by calculating contrasts between the estimates and PROC NLMIXED constructs approximate F tests (SAS Institute Inc., 2004).
3.
Results
3.1.
Reproduction
Production of at least 200 juveniles per 10 females during a 3week test is suggested in the HASTE soil mite test protocol as a validity criterion for control treatments. H. aculeifer produced well above the 200 juveniles threshold on all prey species at different prey biomass supplies with the exception of C. cf. michaeli, which was the only prey where this limit was not
achieved, even at the highest supplied prey biomass (Tables 2 and 3; Fig. 1.). A comparison of the prey biomass needed to meet the 200 juvenile threshold ranked the prey significantly (P < 0.05) into three groups: F. fimetaria = E. crypticus > 1:1:1 mix of F. candida:F. fimetaria:E. crypticus = F. candida > T. silusiae (Tables 2 and 3; Fig. 1). F. fimetaria and E. crypticus produced a significantly higher (P < 0.05) initial increase in H. aculeifer reproduction in response to an increase in prey biomass compared with the other prey (Tables 2 and 3; Fig. 1.). Overall, F. fimetaria was the best prey with an observed maximum H. aculeifer reproduction of almost 400 juveniles (Fig. 1.).
3.2.
Survival
The draft test protocol of the HASTE working group states that the average adult female mortality should not exceed 25% at the end of the test. Like the criterion on reproductive output, this ensures that control individuals are performing reasonably well. In our tests, the majority of diets resulted in H. aculeifer female survival rates of 80–100% even in control treatments where no prey was added. But, three of the treatments fed C. cf. michaeli had H. aculeifer female survival rates between 60 and 70%, independent of the amount of prey (data not shown).
4.
Discussion
We assessed how H. aculeifer performed during a 3-week test when fed one of six different diets. H. aculeifer is known to be a generalist predator (Sardar and Murphy, 1987) corresponding
applied soil ecology 36 (2007) 130–135
with our findings, which revealed that five of six of the tested diets (F. fimetaria, F. candida, E. crypticus, T. silusiae and a 1:1:1 mix of F. candida:F. fimetaria:E. crypticus) were suitable. Moreover, several prey, other than those tested in the present study, have been shown to be a suitable monotypic diet for H. aculeifer. Two storage mites Glycyphagus domesticus and Tyrophagus putrescentiae (also known as the cheese mite) have been shown to be of sufficient nutritional value for H. aculeifer (Barker, 1969), the latter being widely used as prey within the HASTE working group. Our results also showed that a single prey may be nutritionally sufficient for a 3-week period, as H. aculeifer performed equally well, or better, on a single species diet compared with a diet based on a 1:1:1 mix of F. candida:F. fimetaria:E. crypticus. Ten female H. aculeifer produced more than 200 juveniles during the 3-week test when reared on any but one diet. When fed C. cf. michaeli, H. aculeifer had a poor reproductive output and reduced survival. Several factors can affect the reproductive output of a predator, e.g. prey capture rates, preyhandling time and prey consumption time. There is no obvious reason why C. cf. michaeli should be more difficult for H. aculeifer to catch or handle, especially at high prey densities. But, there are two major possibilities for the low performance; a low nutritional value of C. cf. michaeli, or the
133
prey may be toxic to juveniles and/or adult H. aculeifer, as observed in different predator–prey interactions. For instance, Oelbermann and Scheu (2002) revealed that F. candida caused total mortality in offspring of the generalist predator wolf spider Pardosa lugubris. Low nutritional input may be a result of monotypic diets, which has been associated with lack of reproduction in some invertebrate predators, e.g. the cereal spider Erigone atra thrived on Isotoma anglicana and Drosophila melanogaster, but was unable to maintain reproduction when fed F. fimetaria (Marcussen et al., 1999). The mechanisms behind low nutritional value may be related to the chemical composition (carbohydrate, lipid, and protein content) of the prey species including elevated consumption/digestion time. Overall, there were two deviations in our study from the current HASTE ring-test version of the soil mite test protocol. Firstly, a 12-h light:12-h dark regime was applied in the majority of diet tests, except for T. silusiae which had a 16-h light:8-h dark regime. The latter corresponded with the light:dark regime of the ring-test protocol. Having a consistent light:dark regime is important during testing of different toxicants, especially when testing compounds with a low photo-stability. However, in our experimental context, we consider the differences in light:dark regimes to be of minor importance since no toxicants were applied. Furthermore, as
Fig. 1 – Total reproduction of Hypoaspis aculeifer when fed a comparable biomass of six different invertebrate prey: F. fimetaria; F. candida; E. crypticus; a 1:1:1 mix of F. candida:F. fimetaria:E. crypticus; T. silusiae; and C. cf. michaeli. The horizontal line crossing at 200 juveniles represents a reproductive validity criterion set by the HASTE (Hypoaspis aculeifer soil test) working group.
134
applied soil ecology 36 (2007) 130–135
H. aculeifer and most of the tested prey species are true soil dwelling (i.e. euedaphic) organisms, they would not be influenced by dissimilar light:dark regimes. The second deviation in our study was including five H. aculeifer males together with 10 females. In the ring-test protocol, only 10 females are added, as including males in the test has been found to be of minor importance since H. aculeifer females only use the first male spermatozoa deposit for fertilisation of all the eggs that they lay throughout their life (Ruf, 1995). Females originating from a synchronised culture are already mated when they are added to the test containers. Krogh (1995) has estimated the sex-specific consumption, revealing that male consumption would be approximately 20% of the total consumption throughout the test. Thus, if no males were present, one could expect a given reproductive output to be obtained at a prey biomass 20% lower than that outlined in Fig. 1. In a preliminary experiment, we found that 10 female H. aculeifer could produce more than 400 juveniles in a 3-week test when fed 1000 (13.5 mg DW) F. candida (16–19 days old) once at the onset of the test (unpublished results). Although a single feeding would have a great impact on the workload during the test, it would be a fragile set-up if the compounds to be tested were relatively more toxic to the prey than the test organism. For instance, under similar conditions, dimethoate is at least 4– 10-fold more toxic to F. fimetaria than H. aculeifer (Rundgren and van Gestel, 1998). Weekly or biweekly feedings ensure that live prey would be available throughout the test. Additionally, the possibility of choosing between different suitable prey species combined with specific data available for each of these species may not only improve the level of information obtained from a standard test, it may also strengthen the experimental set-up by choosing the more tolerant prey for a given toxicant. A literature search on the Web of Science (http://scientific.thomson.com/ accessed02-09-2006), on the occurrence of the studied prey species scientific names in peer reviewed publications, revealed that F. candida was by far the most studied prey: F. candida (119 publications) > F. fimetaria (20 publications) > E. crypticus (16 publications) > C. cf. michaeli (0 publications) = T. silusiae (0 publications). Although it would have no direct influence on the test outcome, we argue that if an experimenter has the choice between two suitable prey factors, such as published ecotoxicological/ecological data on the given prey should be considered. The overall conclusion is that during a 3-week test H. aculeifer thrives on an array of different single prey, such as collembolans, Oligochaeta, nematodes and mites as shown in the literature and the present study. Although regarded as a generalist predator, different strains of H. aculeifer may have diet-dependent preferences (e.g. Lesna and Sabelis, 1999) based on adaptation to the prey that they have been offered during generations of culturing. Our strain of H. aculeifer (Koppert Biological Systems, Rotterdam, The Netherlands) had the highest reproductive output on F. fimetaria, but we strongly disencourage using C. cf. michaeli as prey. Thus, in a future standardised soil toxicity test with H. aculeifer, experimenters may choose whichever prey they prefer, as long as it has been validated that weekly or biweekly feedings result in female survival above 75% and at least 200 juveniles per 10 females in the control treatments.
Acknowledgements We would like to acknowledge the HASTE working group for positive feedback and valuable discussions. Moreover, we would like to thank research technicians Karsten T. Andersen, Zdenek Gavor, Elin Jørgensen, Mette Thomsen and Annemarie Kissling for experimental assistance, and two anonymous reviewers for their valuable comments on the manuscript. This research was supported by the Department of Terrestrial Ecology, National Environmental Research Institute, Denmark, The Center for Environmental Research and Technology of the University of Bremen, Germany, and Springborn Smithers Laboratories, Switzerland.
references
Antunes, S.C., Castro, B.B., Goncalves, F., 2004. Effect of food level on the acute and chronic responses of daphnids to lindane. Environ. Pollut. 127, 367–375. Barker, P.S., 1969. Response of a predator Hypoaspis aculeifer (Canestrini) (Acarina–Laelapidae) to 2 species of prey. Can. J. Zool. 47, 343–345. European Commission, 2002. SANCO/10329/2002. Guidance Document on Terrestrial Ecotoxicology under Council Directive 91/414/EEC. http://europa.eu.int/comm/food/fs/ ph_ps/pro/wrkdoc/wrkdoc09_en.pdf. EPPO, 2003. Environmental risk assessment scheme for plant protection products. Chapter 8: Soil organisms and functions. EPPO Bull. 33, 195–209. Heckmann, L.-H., Maraldo, K., Krogh, P.H., 2005. Life stage specific impact of dimethoate on the predatory mite Hypoaspis aculeifer Canestrini (Gamasida: Laelapidae). Environ. Sci. Technol. 39, 7154–7157. Krogh, P.H., 1995. Effects of pesticides on the reproduction of Hypoaspis aculeifer (Gamasida: Laelapidae) in the laboratory. Acta Zool. Fenn. 196, 333–337. Krogh, P.H., Axelsen, J.A., 1998. Test on the predatory mite Hypoaspis aculeifer preying on the collombolan Folsomia fimetaria. In: Løkke, H., van Gestel, C.A.M. (Eds.), Handbook of Soil Invertebrate Toxicity Tests. John Wiley & Sons Ltd., Chichester, pp. 239–251. Larink, O., 1997. Sprintails and mites: important knots in the food web of soils. In: Benckiser, G. (Ed.), Fauna in soil ecosystems: Recycling Processes, Nutrient Fluxes, and Agricultural Production. Marcel Dekker Inc., New York, pp. 225–264. Lesna, I., Conijn, C.G.M., Sabelis, M.W., van Straalen, N.M., 2000. Biological control of the bulb mite, Rhizoglyphus robini, by the predatory mite, Hypoaspis aculeifer, on lilies: predator–prey dynamics in the soil, under greenhouse and field conditions. Biocontrol Sci. Technol. 10, 179–193. Lesna, I., Sabelis, M.W., 1999. Diet-dependent female choice for males with ‘good genes’ in a soil predatory mite. Nature 401, 581–584. Marcussen, B.M., Axelsen, J.A., Toft, S., 1999. The value of two Collembola species as food for a linyphiid spider. Entomol. Experiment. Appl. 92, 29–36. OECD, 1984. OECD Guidelines for Testing of Chemicals, No. 207. Earthworm, Acute Toxicity Tests, Organization for Economic Cooperation and Development, Paris, 9 pp. Oelbermann, K., Scheu, S., 2002. Effects of prey type and mixed diets on survival, growth and development of a generalist predator, Pardosa lugubris (Araneae: Lycosidae). Basic Appl. Ecol. 3, 285–291.
applied soil ecology 36 (2007) 130–135
Petersen, H., 1978. Some properties of two high gradient extractors for soil microarthropods. Natura Jutlandica 20, 95–121. Ruf, A., 1995. Sex ratio and clutch size control in the soil inhabiting predatory mite Hypoaspis aculeifer (Canestrini 1883) (Mesostigmata, Dermanyssidae). In: Proceedings of the 2nd EURAAC Symposium. pp. 241–249. Rundgren, S., van Gestel, C.A.M., 1998. Comparison of species sensitivity. In: Løkke, H., van Gestel, C.A.M. (Eds.), Handbook of Soil Invertebrate Toxicity Tests. John Wiley & Sons Ltd., Chichester, pp. 41–55.
135
Sardar, M.A., Murphy, P.W., 1987. Feeding tests of grassland soil-inhabiting gamasine predators. Acarology 28, 117–121. SAS Institute Inc., 2004. SAS/STAT1 9.1 User’s Guide. SAS Institute Inc., Cary, NC, USA. Schlosser, H.J., Riepert, F., 1992. Entwicklung eines pru¨fverfahrens fu¨r chemikalien an bodenraubmilben (Gamasina)-teil 1: biologie der bodenraubmilbe Hypoaspis aculeifer Canestrini, 1883 (Gamasina) unter laborbedingungen. Zoologische Beitra¨ge 34, 395–412. Usher, M.B., Davis, P.R., 1983. The biology of Hypoaspis aculeifer (Canestrini) (Mesostigmata)—is there a tendency towards social behavior? Acarology 24, 243–253.