http://www.collembola.org/publicat/barbro.htm - Last updated on 2001.09.05 by Frans Janssens

Janssens, Frans, Department of Biology, University of Antwerp (RUCA), Antwerp, B-2020, Belgium
Nedstam, Barbro, Swedish Board of Agriculture, Plant Protection Centre, P.O.Box 12, S-23053 Alnarp, Sweden.
Hesseldahl, Kersti, von Essens v. 16, S-18494 Akersberga, Sweden.

Currently being updated!

Note: open any image to observe details in a larger magnification

Preamble

On 1998.02.04, Kersti Hesseldahl, selling biocontrol products to pot plant producers around Stockholm, Sweden, contacted Barbro Nedstam of the Swedish Board of Agriculture, Plant Protection Centre, Alnarp, Sweden, requesting for help. Being very successful with biocontrol methods, some pot plant producers have now quitted spraying completely, and then the field is free for surprises to show up: such as springtails (Collembola).

Fig.1. Impatiens hawkeri x hybrida ("New Guinea")

When the Collembola population gets larger it seems to damage the flowers. Apparently, the damage is more direct on the petals: some specks of cell death, turning brown. Similar to what has been seen on cotyledons of field gherkin, caused by Bourletiella hortensis. The damage was, in this particular case on "Impatiens New Guinea" hybrids (Impatiens hawkeri x hybrida) (Fig.1) (Balsaminaceae). The damage can be an economical problem for the grower of course, when high numbers of Collembola in the flowers make some plants unsaleable.

All around the world it is very rare to find a grower not spraying his Impatiens regularly, so possibly noone else has so far noticed this still relatively small problem.

What to do? The first question : what is causing the damage?
A preliminary description, as observed by the grower with the naked eye: "elongate, cream-coloured with black stripes across the body." This description matches some species of the genus Entomobrya. A preliminary determination: Entomobrya multifasciata.

Fig.2. Degeeria annulata LUBBOCK, 1873. Lithograph Hollick, A.T., [1860].

The closely related Podura nivalis was already described from Sweden by Linnaeus himself in the year 1758. Since the specimens were found in a greenhouse, chances are higher to find Entomobrya multifasciata than Entomobrya nivalis due to its higher temperature tolerance/preference.

Fig.3. Degeeria nivalis LUBBOCK, 1873. Lithograph Hollick, A.T., [1860].

Lubbock's (1873) Degeeria annulata (Fig.2) has been synonymised to Entomobrya nivalis and his Degeeria nivalis (Fig.3) has been synonymised to Entomobrya multifasciata. Taxonomists are still discussing whether or not this synonymy is correct. Several conflicting opinions exist...

Methods

The easiest way to catch those jumping springtails and collect them in a proper condition for identification, is to use a simple exhaustor (Fig.4). You can make one yourself with recycled plastic waste material :

       ----------+  +--------------
  in   --------+ |  | +------------   out
               | |  | |
               | |  | |
           |XXX| |XX| |XXX|
           |   | |  | |   |
           |        ...   |
           |              |
           |              |
           |              |
           +--------------+

       Fig.4. Exhaustor.

To use the exhaustor : just put the inlet in the neighbourhood of the springtail and suck the air from the outlet. The springtail will be sucked up by the airstream. The small filter in front of the outlet will prevent that you end up eating the springtails :-)

It becomes more easy to collect them with the exhaustor when you put an infested flower in a small white plastic box (about 5 cm high). Then disturb the springtails by ticking on the box/flower, so the irritated springtails jump from the flower onto the box floor. Then with the exhaustor it becomes very easy to collect them.

To preserve the springtails for taxonomic purposes it is best to put the live springtails into Gisin's fixative ¹. If the specimens keep floating on the surface of this mixture, put a few extra drops of ethyl ether on top of the floating specimens, so they sink.

According to von Törne, the 750 ml ethanol + 250 ml ethyl ether can be replaced by 1000 ml isopropanol. von Törne adviced this to make the mixture more stable in time. The ethyl ether evaporates gradualy. So, Gisin's fixative tends to degrade in time... The isopropanol makes the fixative stable.
After 2-3 days in this mixture, put the specimens in 96% ethanol. This will make sure that body shape and colours are preserved at best.

For transport : put the preserved specimens in a glass vial with screw cap. (use a cap with rubber seal inside). Tape the cap firmly to the vial, to make sure it will not get loose by vibrations, and to prevent loss of ethanol due to heat expose during transport. Pack the vial into some loose paper tissue, and put it together into a properly sized plastic bag (blow some air into the bag, so it functions as a real air bag to protect the vial against shocks). Put the bag into a cardboard tube with metal screw caps (so the customs can check the contents...) Make sure that you put the customs sticker 'of no commercial value' onto the tube and put some description of contents (eg. scientific material : sample of Collembola, place, date, etc...) inside it.

Material

The sample contains 6 specimens : 1 adult and 5 juveniles. The specimens are rather small, possibly the result of starvation or a highly specialised diet of Impatiens pollen... Entomobrya multifasciata TULLBERG, 1871 (Sweden), is a widely ditributed species, closely related to Entomobrya nivalis. That close related that some taxonomists make multifasciata a colour variant of nivalis. Anyway, Entomobrya nivalis is easely distinguished from multifasciata by the dark U shaped colour pattern on the tergite of the fourth abdominal segment. See the nice reproduction of the lithograph made in 1860 of Degeeria annulata (= Entomobrya nivalis) (Fig.2). The dorsal colour pattern of the specimens from Färentuna matches nicely with the drawing of Entomobrya decemfasciata PACKARD, 1873 (US) (cf. Handschin 1929:81(fig.150)). Schött (Sweden) has synonymised this species with Entomobrya multifasciata in 1891:17. Stach (Poland) in 1963 has made a very detailed drawing of a specimen from Samsun (Turkey) : Pl.VI fig.8, that has exactly thesame colour pattern as these specimens from Sweden. Typical for this population are the dark transverse regular stripes on thorax II to abdomen III, with triangular patches on abdomen II and III. Stach has also described a new colour variant in 1963 : regularis, that lacks the triangular patches. The pale juvenile specimens resemble that variant even more.

Discussion

Fig.5. Gut pellet with pollen fragments. 400x. Photograph Frans Janssens © 1998.

Fig.6. Pollen of Impatiens. 1000x Photograph Dr Keith D. Bennet © 1995.

Compare the pollen fragments with the images of the 35 x 20 microns small isopolar prolate pollen grains of Impatiens glandulifera (Fig.6) from the catalogue of pollen types of Dr Keith D. Bennett of the University of Cambridge, Department of Plant Sciences. The typical homobrochate pattern of the reticulum of the Impatiens pollen grains is easely recognised in the fragments. For a detailed clarification of the pollen terminology see the "Glossary of Pollen and Spore Terminology" of Wim Punt et al. of the Laboratory of Palaeobotany and Palynology of the University of Utrecht.

Fig.7. Mandibula of E. multifasciata Photograph Frans Janssens © 1998.

Note that the mandibula of Entomobrya multifasciata (Fig.7) is equipped with a strong molar plate that will easely crush the indigestible pollen grain shells to free their digestible contents.

As Kersti Hesseldahl never found the eggs in the flowers they should be in the potting substrate (mainly peat). According to Dr Tryggve Persson (in litt.) eggs of Entomobrya sp. are put in the soil and the juveniles also stay in the soil (they are more sensitive to drought than the adults) before entering up on the plants. Gamasid mites will probably eat the juveniles, so the question is to find suitable predators in the soil.

Fig.8. Hypoaspis miles. Photograph Koppert Co. © 1998.

The simplest way of inoculating gamasid mites to the pot soil is to add 10-20 g of forest litter and humus layer (deciduous or coniferous) to the pot soil. This will increase the diversity in the plant pot with new predators, but the risk to add some unwanted pest (fungus, root-feeding insect or whatever) should be taken into account. Consequently, this addition must be considered as an experiment but definitely worth trying. To avoid pest fungi, coniferous litter should be used as an inoculum, because the coniferous microflora will have less chance to survive in a plant pot, whereas the gamasid predators are actually the same as in deciduous litter (with few exceptions).

According to Kersti Hesseldahl's observations the infestation was reduced some time after high numbers of soil-dwelling predatory mites, such as Hypoaspis miles (Fig.8), had been introduced.

Conclusion

As a preliminary conclusion, Entomobrya multifasciata will not cause a lot of damage to the flowers but the commercial value of the with Collembola excrements contaminated flowers is reduced anyway... It could be that these springtails mainly feed on pollen and that the flowers get a dirty look because of over-crowding, bad table manners, excrementa... They are rather unwanted guests than pests, but for the grower this still means part of his production might not even reach the market. Biological control using polyphagous predatory mites could be a practical solution to the problem.

Acknowledgements

• Dr Keith D. Bennet of the University of Cambridge for giving permission to reproduce the image of the pollen of Impatiens glandulifera;
• Dr Gordon J.L. Ramel of the University of Exceter for giving permission to reproduce the images of the lithographs of Degeeria annulata and Degeeria nivalis made by Hollick, A.T. in 1860;
• Dr Luc De Bruyn of the University of Antwerp for providing the facilities to make the photographs of the gut pellet and mandibula of the specimen of Entomobrya multifasciata;
• Prof. Dr Tryggve Persson of the Swedish University of Agricultural Sciences for his advice on using predatory mites to control the springtail population;

References

Endnotes

² Gisin's clearing medium (1960) :

lactic acid	100 ml
glycerol	20 ml
40% formaldehyde	4 ml