Insectivorous Plants and Entomology

Hartmeyer, S. (1996) Bulletin of the Australian Carnivorous Plant Society, Volume 15

Translation by Mrs. Lois Glass, England

Thanks to the notes on the literature, photocopies and opinions sent to me as a result of my report in "TAUBLATT" under the heading "EINE KLEINE PFLANZEN- UND WANZEN-KUNDE" as well as its translation: "FRESH LIGHT ON PLANTS AND THEIR BUGS" which appeared in the journal of the Australian "ACPS", I have benefitted from much additional information. My warmest thanks go to all those people who spared neither time, effort or postage in order to extend my entomological knowledge to such an extend. And for all those interested in the subject I would now like to contribute a brief summary.

My belief that the insects recorded in my video "BEAUTIFUL & HUNGRY PART 2 - CP" on Byblis liniflora and Drosera ordensis near Kununurra and on different D. indica near Darwin appear to be related to the South African Pameridea bugs on Roridula - with which my wife and I have shared our living-room now for several years - has been confirmed by the following entomological data: These are clearly true bugs (Hemi - ptera = half - wings) since the wing covers, in contrast to those of the beetles, only half or more accurately partially cover the membranous wings used for flight. There are of course sundry lower taxa within the Order Hemiptera (e.g. Heteroptera, Homoptera, Corrodentia, Thysanoptera, ... - see table 1), each in turn subdivided into Families, Subfamilies, Tribes, Genera and Species; so that I, as a layman, would have been hopelessly bogged down, and have been saved only by the publication of W.E. China in "THE WESTERN AUSTRALIAN NATURALIST" of 30.6.1953. Here he reports the Genus Cyrtopeltis, new at that date, found occuring near Perth on Drosera pallida, D. stolonifera and D. erythrorrhiza. Both these Genera of bugs belong to the Suborder Heteroptera, Family Miridae (also known as Capsid bugs) in the Tribe Dicyphini (see table 2), possessing the extraordinary ability to move arround unrestrictedly on the extremely sticky trapping leaves of Biblis gigantea and the above-named Drosera species.

The same characteristics were discovered by the German botanist R. Marloth in South Africa, in bugs of the Genus Pameridea living on Roridula. These too obviously belong to the Dicyphini, all of which are predatory species which have specialised on plants with mucilaginous secretions.

Throughout the world there are many plants which utilise adhesive substances as a defence against enemies which chew or bite. Obviously where strategies of this kind are called for, there is ready booty available for predators able to operate unhindered. To me the amazing thing was that everywhere in the world there are quite different, well-known plants- such as Tobacco, Digitalis (Foxglove), Epilobium (Willow herb) and others to which Capsid bugs of the Tribe Dicyphini are attached. In the course of evolution the creatures have adapted ever more perfectly to "their" host plant, whose defensive zones arround buds, flowers and leaf -undersides or new shoots always provide a certain and ready source of victims.

Provided with this resistance to adhesive substances (which presumably depends in a sophisticated arrangement of short bristle-hairs capable of protecting the body against adhesives), some species undertook the further step of adopting those plants which - in their overall morphology - had specialized in the capture of insects. Perhaps they simply remained in "their" plant species which had made the advance from defensive mucilage-barriers to "attack" on insects, as a result of developement of effective mucilage-traps, thus becoming insectivorous. The advantage is crystal-clear: a plant which captures insects many times the size of the bugs provides not only food but also protection against other predatory Arthropods.

Anyone who has studied the phenomenon of co-evolution, the intricate developement of biological systems such as rain-forest or coral-reef knows that interactions always occur in such cases, climaxing in symbioses between very widely different life-forms. Trees optimise their supplies of nutrients by symbiosis with fungi, ants defend plants in which the leaves provide them with the best possible living cavities in return for which they offer their waste products, to name but two of the innumerable examples. But what benefit is derived by the plants on which predatory bugs have settled? I cannot claim, here and now, that I know the correct answer, but I put before my readers for discussion a few considerations on the subject.

1. Non-carnivorous Plants

Anyone familiar with Carnivorous Plants will have noted that large prey animals on mucilaginous traps are very quickly attacked by various moulds. These, if present in sufficient force, most certainly also destroy the trapping leaf; and any collector who fails to watch over his plants and remove these mildew-affected areas, will most probably soon lose some plants to Botrytis (Grey mould). If the plants are healthy, Botrytis is less damaging; but if the plants are already suffering damage (e.g. from the moulds or bacteria brought to them by their captives) then the attack is fare more serious. Here the bugs, by sucking dry the unfortunate victims, take on the same role as the cleaner-fish and shrimps at the so-called "cleaning stations" on the coral-reef. Moreover, any plant with its own colony of bugs should have no difficulty with aphids, scale-insects or other parasites of the kind, because they will certainly come under the attack of the predatory vigilantes. In some cases the latter may also even ensure pollination of flowers which are protected by mucilage.

2. Carnivorous Plants

a) No and low enzym-production

In Carnivorous Plants which have a low or non-existent enzyme production, symbioses are known to occur in every case. The traps of Darlingtonia californica are inhabited among others by the larvae of the mosquito Metriocnemus edwardsii which decomposes insect-captives with its enzymes, "... and apparently do not damage the plant", as Donald Schnell reports in his book (CARNIVOROUS PLANTS OF THE UNITED STATES & CANADA). Quite so - indeed, they do actively benefit the plant. A similar service is provided by the larvae of Wyeomyia smithii ( and its kin) for Sarracenia purpurea and other midge-larvae for Heliamphora. The Pameridea bugs on South African Roridula have already been mentioned, but I would like to add that the plants in my sitting-room, which have now attained a height of more than a meter (40 inches) , carry healthy bug-populations, and in the course of years the plants have suffered no attack from any pests. During this time, other Insectivores nearby have on a number of occations been invaded by aphids and mealy-bugs. I see this as clear proof of the bodyguard-function of the bugs. But of course this is not the case with the midge-larvae in the digestive juices of pitcher plants.

b) Adequate enzym-production

Where plants with mucilage traps have an adequate enzyme production, they can normally cope well digesting their prey, without risk of any dangerous mildew developing, since oversized prey-creatures are usually able to escape. Nevertheless there remains the possibility that Byblis and the a.m. Sundew profit additionally from the more effective digestion of the bugs, as their faeces matter must certainly be an ideal supplemantary nutrient. But however that may be, the prevention of parasite-attack for the one party, and the provision of protec-tion and food for the other, make this mutual relationship a true symbiosis.

For the sake of completeness I would like to draw attention to the fact that in various tropical Pitcher plants (e.g. Nepenthes mirabilis in Australia) , symbioses with midge-larvae are known. And in the pitcher of Sarracenia flava there occur the larvae of the Sarcophaga fly which - by producing anti-enzymes (D. Schnell) - is well able to live (survive) among the prey-creatures. Presumably the predatory bugs in Drosera and Byblis also possess protective mechanisms of this type, since digestive enzymes normally act like chemical scissors on the organism’s protein molecules. Were some protection lacking, this would obviously have fatal consequences if the bugs were to bathe in the trap fluid in the manner clearly visible in my video. A wide field awaits further research!

Hemiptera on North Australian CP

I am as yet unable to trace any literature regarding the bugs I observed in tropical North Australia, except a message from Mr. Trevor Hannam (Cairns, QLD.), that they also appear in North-Queensland on Drosera indica. The creatures living on Drosera ordensis, on the basis of the red markings on the back, admittedly resemble the two Cyrtopeltis species in South-West Australia, but these are distinguished mainly by the form of their genitalia. It was impossible for me, as an entomological layman, to determine whether they were C. droserae, C. russellii or some other as yet undescribed species. Nevertheless I hope that some qualified entomologists will soon be able to clarify the problem and also determine whether the bugs on Byblis liniflora near Kununurra and Drosera indica near Darwin and Cairns are Setocornis bybliphilus or some new species. The comprehensive term …"Assassin bugs"- up to now current - should however not be used since this name is already given to the bug Coranus subapterus.

In conclusion I would ask everyone in future visiting the Insectivorous Plant habitats to pay careful attention to any insects moving with unexpected nonchalance on the leaf traps. The various societies for Carnivorous Plants and Entomology will both certainly be pleased to accept reports on the subject, so that they can appear in their publications. I myself would also be delighted to receive further communications on that subject.

Bibliography

Carow, Th. (1996) Todesfallen oder Lebenspender ? Die neue Sicht der Fleischfressenden Pflanzen (Dokumentarfilm). ‚Naturzeit‘ ZDF, as video (45 minutes) available.
Carow, Th. und Fürst, R. (1990) Fleischfressende Pflanzen, Verlag Thomas Carow
China, W.E. (1953) Two new species of the genus Cyrtopeltis (Hemiptera) associated with Sundews in Western Australia, The Western Australian Naturalist, 4/1: 1 – 8
China, W.E. and Carvalho (1951) A new ant-like Dicyphinid, Setocornis bybliphilus, Annual Magazine of Natural History, 12/4: 221
Ellis, A.G. and Midgley J.J. (1996) A new plant animal mutualism involving a plant with sticky leaves and a resident hemipteran insect, Öcologia, 106: 478 – 481
Evans, J.W., Woodward T.E. and Eastop E.F. (1970) Hemiptera In-Insects of Australia,
Hartmeyer, S. (1995) Eine kleine Pflanzen und Wanzenkunde. Das Taublatt Heft 25, 1995/1:13-18.
Hartmeyer, S. und Hartmeyer, I. (1995) Reiseziel Insektivoren (Fleischfressende Pflanzen), private video-production (80 minutes).
In the English language: BEAUTIFUL & HUNGRY CP Part 1 & 2
Hartmeyer, S. (1997) Carnivory in Byblis revisited (I): A simple method for enzyme testing on carnivorous plants, Carnivorous Plant Newsletter (ICPS), 26: 39 - 45
Juniper, B.E., Robins, R.J. and Joel, D.M. (1989) The Carnivorous Plants, Academic Press Limited (London)
Lloyd, F.E. (1942) The Carnivorous Plants, Dover Publications, Inc. (New York)
Schnell, D.E. (1976) Carnivorous Plants of the United States & Canada, John F. Blair (Publisher)
Schulz, B. (1965) Fleischfressende Pflanzen: Die neue Brehm Bücherei, (Lutherstadt, Germany)
Spektrum Videothek (1988) Todesfallen Teil 1 & 2 (video 2 x 27 minutes), Verlag Spektrum der Wissenschaft (Also available in the English language, title: "Death Trap")