Invertebrate Recording in Site Evaluation and Monitoring Countryside Changes: The Hymenoptera

By Geoff Trevis

"If nature conservation is not working for parasitic hymenoptera, then nature conservation is not working as it should". (Shaw and Hochberg, 2001)

A considerable literature exists describing and evaluating the use of invertebrates for monitoring countryside change and the achievement of conservation objectives. However, the paper from which the quotation at the head of this article was taken started me thinking about invertebrate recording in Worcestershire and, particularly, about my chosen group - the hymenoptera. As a starting point I used the British Journal of Entomology and Natural History, Vol. 7, supplement 1, 1994 that contains a series of papers under the general title of "Invertebrates in the landscape: invertebrate recording in site evaluation and countryside monitoring".

A quick survey of the BENHS papers revealed a wide range of organisms being used for monitoring. For environmental quality and change there is a significant literature from Foster and others on water beetles and from other workers on ground beetles, spiders and weevils. Water beetles and other stream invertebrates have been used to assess water quality whilst climate change has been monitored using dragonflies and mayflies. Long term monitoring schemes such as that run by Butterfly Conservation have also proved useful. In some cases the spread (or otherwise!) of individual species has been followed, including the Firethorn Leaf-miner Phyllonorycter leucographella, Roesel's Bush-cricket Metrioptera roeselii, the Long-winged cone-head Conocephalus discolor and the spider Argiope bruennichi. Individual species have also been employed in evaluating the effects of land-use change and management of individual sites. Species cited in the literature include Shining Ram's-horn Snail Segmentina nitida, Large Marsh Grasshopper Stethophyma grossum, the Black Darter Dragonfly Sympetrum danae, the Chequered Skipper Carterocephalus palaemon, the Glow-worm Lampyris noctiluca and, at Thorne and Hatfield Moors, the muscid fly Phaonia jaroschewskii, the ephydrid fly Pelina guttipenis and the byrrhid beetle Curimopsis nigrita. However, references to hymenoptera were absent or, if present, so deeply buried I failed to find them!

At a conference in 1996 Dr. M.E. Archer drew attention to the value of solitary wasps and bees in wildlife assessment. At this conference many groups of invertebrates were discussed and the reasons Archer gave for the use of hymenoptera were:

  1. Solitary species have a low reproductive rate of 8-12 per generation. Most species have only one generation per year though this is not universal. Any reproductive failure will, therefore, be reflected in a decline in the species.
  2. Each species has a complex mixture of resource requirements in terms of nest sites, microclimate and a nearby habitat with flowers for food and prey. These resource requirements are particularly associated with traditional countryside patterns.
  3. As traditional countryside disappears, species have become increasingly restricted to habitats which are not undergoing intensive agriculture.
  4. Most species have limited powers of dispersal so that, as suitable habitats become fragmented, re-colonisation of isolated patches becomes less likely.

It was following this conference that I became interested in the Aculeate Hymenoptera but I gave little thought to the "parasitica" which seemed a group of almost impossible complexity and often of morphological similarity which made identification to species level difficult. The second point remains a problem. However, the Shaw and Hochberg paper I acquired at the parasitic hymenoptera workshop organised by Rosemary Winnall for Wyre Forest Study Group this year caused a radical re-think.

The basic proposition of the paper is that the omission of hymenoptera from evaluation for conservation is a grave one since these insects have a disproportionately large role in maintaining the diversity of other plants and animals. This results from the profound and often highly specialised interactions between hymenoptera and other organisms and the fact that they are a large and ramified group. Current estimates are that about 25% of the entire British insect fauna is parasitic hymenoptera. Many groups of hymenoptera are also particularly sensitive to environmental disturbance which makes their populations especially prone to extinction. The threats to the parasitic hymenoptera come from two directions. They are intrinsically extinction prone because of their specialisation and high trophic level, and extrinsically vulnerable owing to our disregard for them.

Shaw and Hochberg summarise the situation in terms of these intrinsic and extrinsic threats. The intrinsic threats are:

Their genetic reproductive system can lead to male dominance at low densities which adds to the problem of finding a mate.
Many show high resource specificity and, therefore, have no fall back to alternative hosts when prey species density is low.
Adult parasitoid behaviour can depend strongly on climatic conditions, with the result that already vulnerable populations can rather easily be put over the brink of extinction simply by experiencing a string of bad weather conditions at crucial times. Thus, in response to climate change, in addition to having to adapt to the abiotic influences per se, parasitoids will inevitably be extremely sensitive to changes at the lower trophic level.

Extrinsic threats are easily summarised as:

Our lack of knowledge means they are easily ignored and their needs excluded from approaches to insect conservation that come to be dictated by the attributes of better understood groups.

The conclusions of this fascinating and important paper are best summarised by three direct quotes:

Because approaches to conservation are increasingly knowledge based, ignorance of a group places it in real danger as conservation effort becomes targeted to more well known groups with different requirements. Our ignorance of parasitic hymenoptera places them under real and specific threat. The bleeding away of our parasitic hymenoptera must be happening at a rate that would surely be considered alarming if only it could be noticed!
The brief statement in the Insect Red Data Book says that parasitic wasps must be considered among the most threatened of British insects, but that attempting a listing of endangered species would be quite hopeless in view of our poor knowledge.
If we have to accept a general land management strategy of conservation by proxy - hoping, that is, that getting it right of one set of organisms will also get it about right for most others within the habitat frame - it would seem only logical that the analysis and monitoring criteria should be pitched at the highest trophic level at which substantial organism-dependent specialisation exists, not (as at present) at a trophic level below that.

So, where does that leave us in Worcestershire? The problem of ignorance is present to an extreme extent. We have little knowledge of the common hymenoptera such as social wasps, bumble bees etc., next nothing of the solitary bees and wasps except for the historical records of J.E. Fletcher from the mid to late 19th century (which cover a very restricted number of sites) and the recent work of Dr. Archer on our north Worcestershire heathlands and as close to nil as you can get regarding the parasitic hymenoptera (except for records from John Mieklejohn and others on gall forming wasps).

We know that Hartlebury Common and Devil's Spittleful and Rifle Range are of national importance for aculeate hymenoptera but recent evidence that the Bredon area may also be of very high value has come as something of a surprise. John Clarke drew attention to colonies of a mining bee on the Kemerton Estate. John Meiklejohn, Harry Green and I have had the opportunity to visit the site and discovered the presence of staggering colonies of Andrena flavipes. An estimate by John Clarke suggests the colony contains about 40,000 nests! But is this a recent arrival or a long established colony? We have no way of knowing. Since A. flavipes has only relatively recently been recorded in Warwickshire in fairly low numbers (Steven Falk, personal communication) the probability is that its arrival in our county is also fairly recent and that the Bredon area is ideal for it. Also, the high density of nests suggests that the site must also be important for other species, including parasites. Steven Falk has suggested, for example, that we look for the Red Data Book bee fly, Bombylius discolor that should, almost certainly, be present along with the more common cleptoparasites such as the Nomada species. As for the rest of the county - who knows?

To help to address this situation I would like to encourage people to take up the study of this fascinating group, the hymenoptera. I would also be pleased to receive any specimens collected, with details of when, where and by whom plus anything else of interest such as the habitat type and plant from which the specimen came. I would also be pleased to swap specimens with anybody interested, to help each other to get to grips with identification. Many hymenoptera are difficult but as more recorders take up their study and more keys become available life is getting easier. And if you are interested, do join the Bees, Wasps and Ants Recording Society which is doing important work in addressing the current state of ignorance. I will let anyone who wants them have membership details.

The key message is - let's try not to ignore the hymenoptera any longer!


SHAW, MARK R. & HOCHBERG, MICHAEL E. 2001 The neglect of parasitic Hymenoptera in insect conservation strategies: The British fauna as a prime example., Journal of Insect Conservation 5: 253 - 263.
ARCHER, M E 1996 The use of solitary wasps and bees in site assessment for wildlife conservation. In
Environmental Monitoring, Surveillance and Conservation Using Invertebrates. M.D. Eyre (Ed.). EMS Publications.
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