Parasitic Wasps

Introduction

Contents

• What are parasitic wasps?
• Fascinating life strategies
• Koinobionts and Idiobionts
• Gall Wasps
• Some selected life histories
• Taxonomy
• Identification
• Collecting specimens
• Making a collection
• Appendix A: Study equipment
• Appendix B: Some suppliers of equipment & books
• Bibliography:
  • Selected & annotated bibliography
  • Which key do I use for UK Apocrita?
  • Additional References

What are parasitic wasps?

For taxonomic purposes, parasitc wasps (parasitica for short) a are grouped together with bees, ants and other wasps in the insect order Hymenoptera. The Hymenoptera are one of the most species-rich group of insects in the world - in Great Britain alone there are approximately 7100 species (6000+ parasitica), compared with ~6500 flies or ~4000 beetles.

In general, Hymenoptera have 2 pairs of wings (but some species are wingless), and they develop using complete metamorphosis (egg -> larva -> pupa -> adult). Nearly all are carnivorous or insectivorous - the main exceptions being the Sawflies and gall wasps. A less obvious feature, but one that sets all Hymenoptera apart from most other insect groups, is a haplo-diploid genetic makeup. This means that only the females in any species have a full compliment of chromosomes - the males have half a set. Sex determination is is done at the point of fertilisation - fertilised eggs develop into females and unfertilised eggs develop into males. A tremendously powerful consequence of this process is that females can actually control the sex ratio of their offspring by controlling how many fertile (female) or infertile (male) eggs they lay.

Technically speaking, 'Parasitic Wasps' are not actually parasites - they are parasitoids. This is because a true parasite is something that lives at the expense of its host but doesn't actually kill it, whereas parasitoids nearly always kill their host. In general though most people still use the term 'Parasitic Wasps'.

Parasitoid larvae usually develop by feeding on a single host - different species develop on anything from tiny aphids and insect eggs right up to large butterfly and moth larvae. They can live and feed inside the host's body cavity (endoparasitoids) or outside the host's body (ectoparasitoids). They can be solitary or gregarious - with anything from 1 to many 1000's of larvae consuming the same host.

Fascinating life strategies

Nearly all parasitica inject venom into their host along with or just prior to the egg. This venom is a highly complex mixture of chemicals and other agents used not just to paralyse the host, but to also modify the host's tissues. Tissue modification is a feature of nearly all venoms, making the host more nutritious for the developing wasp larva and helping to overcome the host's immune systems. The latter is an especially important consideration for internal parasitoids as a host's body will usually try to surround (encapsulate) a foreign body to prevent infection and to kill any parasitoid eggs or larvae. Parasitica have developed many ways of getting around this but I think the most devious must be the use of polydnaviruses (also known as Poly-DNA-viruses) (Edson et al., 1981). These viruses are injected by some endoparasitoids with the venom and have been shown to target and disable the host's immune system - thus protecting the developing parasitoid. Other, more basic, methods of bypassing the host's immune system include laying the egg directly into the host's brain (ganglion), where the immune system is unable to encapsulate it.

Whichever method the parasitoid uses to prevent encapsulation it must also protect itself against many other dangers. One of the most serious being the possibility that a host will succumb to a fungal or bacterial infection and die before the parasitoid has finished with it. To prevent this, many larvae secrete chemicals with antibiotic or antiseptic properties as they move around the host's body cavity. They also avoid damaging the host's gut (a massive source of bacteria) by eating non-essential areas first, like body fat and the reproductive organs. Many species also use teratocytes - bundles of cells that emerge from the egg with the embryo. These cells absorb food from the host's body cavity and the parasitoid larva feeds on them - removing the need for it to feed directly on the host's tissues until it is absolutely necessary.

Polyembryony is another complex strategy employed by parasitica (Ivanova-Kasas, 1970), but this time its aim is to ensure the maximum number of offspring from the fewest number of eggs. Some species lay a single egg that continues to divide, cloning itself into many independent larvae - in extreme examples one egg can produce thousands of larvae. Some species have even been shown to produce different types of larvae from the same egg - normal larvae that feed and develop fully into adult wasps and others, which never mature into adult wasps, that act as guards to protect the others from attack by other parasitoid larvae.

Koinobionts and Idiobionts

The Koinobiont / Idiobiont theory was developed over the years by many researchers but was most completely described by Dr Mark Shaw & Dr Richard Askew (Askew & Shaw, 1986). They showed how parasitic wasps could be divided by examining their lifestyles - and this analysis yielded two main types, Koinobionts and Idiobionts. The differences between Koinobionts and Idiobionts are listed and compared below. Each comparison is a gross generalisation in that there are quite a lot of species that differ from the norm in one or more respects, but most parasitica will fall into one or other grouping.

Gall Wasps

As I mentioned at the start of this article, not all 'parasitic wasps' are invertebrate parasitoids. Some, like the Gall Wasps (family Cynipidae), are true 'parasites' of plants. Although their host is totally different they still use similar strategies to the true parasitoids - they still inject venom with their eggs and this venom still modifies the host's tissues. In the case of the gall-wasps the tissue modification takes the form of strangely shaped growths, called galls. These galls both protect the developing larva and provide it with nourishing food.

Gall wasps frequently fall prey to a huge array of parasites/parasitoids and inquilines (cleptoparasites that don't attack the host directly but steal their food). These communities are often very complex, involving layers of inter-dependency that defy the imagination. In one gall you may have: a host that made the gall (usually a Cynipid wasp); different species of inquiline eating the host's food; and different species of parasitoid living on the host, the inquilines and themselves! The latter group (parasitoids on parasitoids) are called hyperparasitoids.

A good example of a large gall-wasp community is found in the Oak Marble Gall (caused by the Cynipid wasp Andricus kollari). This community has been studied extensively and has been found to contain 17 species of wasp - one causer (Andricus kollari); 5 inquilines (Ceroptres arator, Synergus gallaepomiformis, S. pallidipennis, S. reinhardi and S. umbraculus); and 13 parasitoids (Eurytoma brunniventris, Sycophila biguttata, S. variegata, Megastigmus dorsalis, M. stigmatizans, Torymus geranii, T.auratus, Caenacis lauta, Hobbya stenonota, Mesopolobus amaenus, M. fasciiventris, M. sericeus, Eupelmus urozonus).

To even further complicate the situation, many of these wasps have two generations in a year - with each generation having a slightly different body shape. Some Cynipids produce different galls in different plants according to whether they are a winter/spring or summer/autumn brood. Also, parasitoids of these species often change the shape of their bodies accordingly - for instance, one generation may require a different length ovipositor to reach the host. This has allowed the parasitoids to follow their hosts through each different generation.

As well as having differently shaped bodies the two broods of Gall wasp may also reproduce differently. For instance it is quite common for the winter/early spring brood to be entirely female (parthenogenic) and for those females to lay unfertilized eggs that develop into normal, sexual progeny that appear in summer/autumn. Of course, as I mentioned above, wasps have a haplo-diploid genetic structure and can all produce males from unfertilised eggs but the trick is making females from unfertilised eggs. The clever stuff goes on when the chromosomes inside the nucleus of the egg replicate and pair-up to form the full compliment. Once this has been done the cell can divide as normal.

Some selected life histories

Polysphincta tuberosa (Ichneumonidae:Pimplinae) is unusual in being a koinobiont ectoparasitoid - allowing the host to continue development but living outside the host's body. The adult lays a single egg on the front of a spider's abdomen - the host is often the common white & yellow/green spider Araniella cucurbitina. The position of the egg makes it impossible for the spider to remove it using its legs or mandibles and makes rubbing it off very difficult. When the egg hatches the larva stays in the same position and pierces the host's skin to drink its body fluids. In its first weeks the larva remains quite small (<=2mm) but this is because it is ticking over, waiting for the host to get big enough. Once it senses the host is the right size it will suck the spider dry over night and grow to 5-6mm in length! The larva then spins a silk cocoon and pupates - the adult hatching after a couple of weeks.

Perilitus coccinellae (Braconidae: Euphorinae) is another koinobiont, except this is an parthenogenic endoparasitoid of adult ladybird beetles. The wasp stalks a suitable ladybird before thrusting its ovipositor between the host's abdominal plates and laying a single egg inside. When the egg hatches the first job for the larva is to eliminate any competition. It is equipped with large, pointed mandibles and it uses these to stab other parasitoid eggs and larvae. Soon after this is will shed its skin revealing mouthparts suitable for eating the host. During development the larva takes very great care not to eat any of the ladybird's vital organs - in fact it seems to limit itself to the ladybird's fat store and gonads. When it is ready to pupate, it uses its mandibles to cut each of the six motor-neurones that control movement in the ladybird's legs before breaking out of the host's abdomen and spins a cocoon between the host's legs. This may seem strange behaviour but the wasp actually wants the ladybird to stand sentry over the cocoon. The ladybird can't move but it is still alive so the bright warning colours and reflex bleeding that once protected the ladybird from predators will now protect the wasp. Eventually the wasp hatches and flies off to find another ladybird leaving the host to starve.

Taxonomy

Hymenopteran taxonomy is a very complex subject and, although there is plenty of professional interest in the group (for biocontrol of crop pests etc), very few amateur have ventured into the field. This is due to many reasons - partly to the sheer numbers of species, the scarcity of good keys, and the confusing and ever changing classification of Hymenoptera. For this reason I have decided not to cover anything but the basics.

The following table shows the grouping of world Hymenoptera down to family level based on a table by M.G.Fitton - with my own comments.

Identification

Precise identification of specimens down to species level is usually very difficult - involving very close examination of microscopic features. A good microscope and a fine pair of tweezers are essential but you don't need much more specialist equipment.

If you are a keen entomologist and want a good introduction to the study of parasitica, I would recommend going on the Parasitic Hymenoptera course run by the Natural History Museum and Imperial College at Silwood Park. The course costs quite a lot but they might offer reductions if you are a self-funded amateur or you decide not to go residential. Details can be obtained from the organiser, Mike Fitton (M.Fitton@nhm.ac.uk).

In addition to the problems listed above, in the section on Taxonomy, many people also find the terminology used in the keys quite alien. For example, before going in to the key features we must tackle the subject of the propodeum. Normal insects have a body made up of three large segments - head, thorax and abdomen. In apocritan (waisted) Hymenoptera the abdomen is constricted between segments 1 and 2, near the thorax. The net effect of this is that the thorax appears to have an extra bit bolted on to the end - this is the propodeum. For this reason hymenopterists have had to make up some new words to describe the major segments. Thankfully we still use the word head to describe the first major segment. The middle segment is often called the thorax but you will sometimes hear it called the mesosoma - to allow for the fact that an apocitan wasp "thorax" is a normal thorax + the first abdominal segment. The most problems occur when trying to name the last major body segment (the abdomen in other insects). The most accurate name is metasoma as this refers to abdomenal segments 2 onwards (i.e. ignoring the propodeum) - gaster is used sometimes. In general the propodeum is not considered to be part of the last body segment.

"Hymenoptera of the world - an identification key to families" (see bibliography) has a very good glossary section with clear diagrams of the various body and wing parts.

Collecting specimens

By far the best way of collecting large quantities of specimens is to use a 'Malaise trap' - a tent-like construction that intercepts flying insects without bait or a lure. The insects meet a vertical barrier underneath a pitched canopy and instinctively fly up towards the sky where they are directed towards the collecting bottle. Once in the bottle they are unlikely to escape and soon fall into the collecting fluid - usually 70-95% alcohol. The knack to Malaise trapping is to site your trap in the best area - usually positioned across a natural flight-path, like a hedge or woodland ride, and with the collecting bottle pointed towards the sun.

Malaise traps catch a lot of insects so be prepared for plenty of specimens. I empty my collecting bottle every 3-4 days and decant all the specimens I want to mount into petri-dishes of alcohol. The other insects (wasp duplicates, flies, moths, butterflies etc) are all stored in jam-jars full of alcohol (labelled with date & location etc) in case another person wants the material in the future. If you must you can leave insects in the Malaise bottle for over a week but the softer-bodied insects tend to shrivel up when they have been removed and dried out.

Other 'in-field' methods include netting free-flying wasps; sweeping them from grassland or beating them from bushes (see 'The Hymenopterist's Handbook' in the bibliography). You won't get anything like the quantity of specimens that you would in a Malaise but it might allow you to note down any habitat or behavioural characteristics that could help you ID the wasp or learn more about its biology. Mercury-vapour light traps can also bring in many nocturnal species but, again, not as many as a Malaise trap.

One of the best methods of investigating gall-wasp communities is to pick galls and then wait for the inhabitants to emerge. Galls are best picked when they are fully mature and starting to dry out - but this can be difficult to judge accurately. As a guide, some Cynipids hatch in late summer/autumn but the Chalcids (and some late Cynipids) tend to hatch the next spring. Keep your galls in individual glass tubes or plastic boxes with a little paper to absorb moisture. Ideally you should keep them at outside temperature in a garage or outbuilding to make sure that they emerge at their normal times. If you are not worried about accurate emergence times you can keep them at normal room temperature.

See 'Redfern & Askew' in the bibliography for more detailed information on studying gall-wasp communities.

Making a collection

You must be prepared to take specimens and you must be able to maintain a voucher collection for reference and verification purposes. The following is just a guide - there are no hard & fast rules.

Direct pinning is preferable as long as it can be done without damaging or obscuring key features. Larger specimens should be pinned directly through the upper part of the thorax with a sharp, stainless steel, continental-sized, number 1 pin. Care should be taken not to obliterate any markings so try to pin asymmetrically, that is, push the pin through slightly to one side of the thorax so that it passes through at a slight angle - this way if you destroy a feature on one side of the body you are less likely to destroy it on the other side. This goes against normal 'lepidopterist' rules but we are after specimens that we can identify - not specimens that just look pretty!

Alternatively you can glue the specimen to the side of a #1 pin using Shellac. I don't use this method because it is messy and I don't have very much faith in my ability to do it right! With practice though it is supposed to be a very fast way of mounting medium-large wasps.

Anything too small for direct pinning with a #1 pin should be glued to a card mount. These mounts come in two types - card rectangles (used for very small parasitica - Chalcids & Cynipids etc.), and card points (used for medium-sized Ichneumonoids). The specimen is attached by gluing the right-hand side of the thorax (mesopleuron) to the card with a blob of water-soluble glue, like 'Seccotine'. As a general rule the blob should be around two-thirds the diameter of the pleura and should be diluted with water so that it is runny enough that it doesn't draw out into long strings or form a skin before you can get the specimen onto the glue.

The choice between whether to use points or rectangles really depends on how small and how fragile your specimen is. Rectangles give more protection but they hide more features and you can only see one side of the specimen. The classic position for a specimen on a rectangle is on its side and at a slight angle so that the top surface of the thorax (the mesoscutum & scutellum) is more visible than then the underside. If you have multiple specimens (and you are sure they are the same species!) try setting each at slightly different angles so that you can see all surfaces.

I have found side-pinning (through the pleura) can also work well with aculeates but be careful not to damage any suture lines or unusual areas of sculpturing. These specimens can be difficult to balance on a card point while waiting for the glue to dry but are too small for direct pinning with a #1 pin. I have found that if you use a very small pin (e.g. an A1) and chose your point of entry carefully under the microscope you can be sure you wont damage anything. Asymmetric, side pinning will also help here. Once dried the specimen must then be placed on a stage (a small (~2cm) strip of polyporous (or dense) foam) which in turn is pinned using a normal carding pin.

Whichever way you mount the specimen (pinned or carded) you must try and make sure that all relevant body parts are exposed and easily seen - before they dry and become brittle! So make sure the antennae and legs are extended from the body and that both the fore and hind wings are flat and easily seen. Personally, I like to see antennae & legs extended so that the sides of the thorax are visible - but not necessarily fully extended, otherwise they might stick out too much and get broken off. I like wings to be in a slight V shape so that they are easily visible but they don't obscure vital areas on the top of the thorax - like the mesoscutumm, scutellum or propodeum. Head, thorax and metasoma (the abdomen from segment 2 onwards) should be in line (not curled up) so that you can see all sides of the head and of metasomal segment 1.

Another important thing to remember is to retain as much of the specimen as possible - this means legs or other items that may have been broken off. It might also include cocoons or the remains of the host if the specimen was from reared stock. These miscellaneous pieces are usually stored in gelatine capsules, which is fixed to the same pin as the specimen.

Don't rely on memory or notes in a field notebook. A label giving full capture data must accompany each specimen - without this you might as well throw it away. Place of capture (including grid reference), date captured and collector's name are the minimum you should give - more information, like the habitat or the method of capture or what the specimen was doing, might help when it comes to identification. This label sits on the pin, just under the specimen. Additional information or field notes regarding habitat or other observations can be placed on another label.

Although the labels might look a little crowded, you must make sure the information is saved with the specimen. A simple rule would be "make the label fit the data, not the data fit the label". A typical data label might look like this:

Below this (hopefully!) comes the determination (or 'det') label giving the identification, who identified it and the date they identified it (usually the year is enough). A 'det' label might look something like this:

Appendix A: Study equipment

This is my equipment - there may be better but this works for me.

Microscope: Mine is a Meiji EMZ (with zoom from .7 to 4.5x magnification) with 10x eyepieces, giving from 1:7 to 1:45 magnification. Light is provided by a cool, fluorescent light on a bracket behind and above the subject. This level of magnification is just a little bit less than I need for the really small stuff but it provides just the right levels for the larger groups. A hand lens is sometimes useful for fieldwork but totally useless for identification and causes severe eyestrain. My advice is to save up and get a good microscope and lighting setup!

Tweezers: #4 stainless steel, pointed tweezers - the important thing is that the points must be hard and inflexible. I use a softer pair with a flatter tip to remove specimens from alcohol - the soft tip stops inadvertent damage when lifting out huge numbers of wasp! A pair of the traditional 'entomological' forceps can be useful for holding pins tightly but as a rule you shouldn't use them because they have a tendency to 'twang' pins, causing specimens to explode!

Pins: I use Henshaw HK3856 pins (stainless steel, 38mm x .56mm, £13/1000) for card mounting. These are cheap and sharp, though the steel sometimes isn't as tough as I would like and the points can bend easily against hard surfaces. For direct pinning I use #1 sized stainless steel, nylon-headed pins (available from W&D) £4-5/100. These are very expensive but they are well made and very sharp. Don't worry about the cost - you do so little direct pinning that you won't be buying many but it is worth having them for their points. Micro-pins for direct pinning (seldom used) can be bought from W&D - A1 pins are the finest and shortest but B2s are often the most useful.

Card points & rectangles: The key here is to have good, thick card to allow the pins to grip and stop the card mounts spinning round. I have found the Austrian ones from Lydie Rigout to be very good.

Pinning block: A nice little tool that really speeds up the process of putting pins through card and labels - and makes sure they are all at the right heights. I got mine from W&D. Be careful you don't blunt your points on the metal though!

Malaise Trap: A very efficient trap that catches flying insects, such as flies and wasps. Available from Marris House Nets for about £85-95.

IMS (Industrial Methylated Spirit): Used to kill & preserve specimens in a Malaise trap. Comes as 95% alcohol, which I dilute to 70% by adding 20% distilled water (the kind garages sell for topping up batteries). You can buy IMS quite cheaply 'over the counter' in any decent chemist but you must have a licence from Customs & Excise. The licences are very easy to obtain and last forever. All you do is to provide the chemist with a purchase order and a 'statement of authority to receive IMS' (a specifically worded letter quoting your licence number etc). Alternatives to IMS include car anti-freeze and salt water but I found that the former matted hairs and left a greasy film on the specimens, while the latter crystallised out on the specimen after drying.

Plastic Petri-dishes: Used to sort out specimens from Malaise trap catches. I tip the catch into a plant tray or other receptacle and then transfer the specimens I want to keep to more 70% IMS in a petri-dish.

Filter papers: Used to lift specimens out of alcohol without their wings crumpling - a very useful trick.

Polyporous stage mount strips can be bought from W&D.

Appendix B: Some suppliers of equipment & books

I give no particular endorsement of the following suppliers but I have used them at one time or another and have been satisfied with their service.

Watkins and Doncaster, Conghurst Lane, Four Throws, Hawkhurst, Kent, JN1 8 5ED.Tel: 01580 753133. Fax: 01580 754054. Sell a wide range of entomological equipment - plastic containers, nets, books etc. Access/Visa telephone orders.

Marris House Nets, 54 Richmond Park Avenue, Queen's Park, Bournemouth. BH8 9DR. Supplier of moth trapping equipment, Nets and Malaise Traps. Payment due on receipt of goods.

Lydie Rigout, 1 Hillside Avenue, Canterbury, Kent. CT2 8ET. Tel: 01227-769924, email: lr@insects.demon.co.uk Payment on Pro-forma, otherwise goods are sent recorded delivery with an invoice.

D.J. & D. Henshaw, 34, Rounton Road, Waltham Abbey, Essex. EN9 3AR. Tel: 01992-717663, email: djhagro@aol.com. Supplier of Pins and other miscellaneous entomological or microscopy equipment. Payment due on receipt of goods.

Hampshire Micro, 17 High Street, Nailsea, North Somerset. BS48 1AU. Tel: 01275-797750, email: enquiries@hampmicro.co.uk Sell Meiji microscopes.

Royal Entomological Society, 41 Queen's Gate, London, SW7 5HR. Tel: 0171-584-8361. Handbooks. VISA card orders accepted over the phone for RES publications - i.e. the Handbooks for the identification of British Insects series.

Pemberley Books, P.O. Box 334, Hayes, Middlesex, UB4 0XX. Tel: 0181-561-5494, email: ij@pembooks.demon.co.uk Sell a good range of new & secondhand entomological books.

Selected & annotated bibliography

I have chosen to split the bibliography into three sections to make it more useful. First is a list of books I have found useful (below). The next is a breakdown of parasitica groups and the keys you need to use to identify them. Lastly is a list of references that I have quoted in the main text of this article.

• Handbooks for the identification of British Insects: Volumes 6-8. Each volume is divided into many parts and each part has been written by a different author. These books must form the basis of any identification library but there are gaps and some large groups of wasps are not covered (see below). The earliest parts were written in the 1950s and many are now out of print but those still in print can be obtained from the Royal Entomological Society, while the others can usually be found in good entomological libraries like the British Entomological Society library at Dinton Pastures, Winnersh, Reading. In the following list parts that are out of print are listed in [italics].
  • Volume 6 (HYMENOPTERA SYMPHYTA & ACULEATA)
• [part 1: Introduction and keys to families. O.W. Richards, 1956]
• part 2(a): Symphyta (except Tenthredinidae). J. Quinlan & I.D. Gauld, 1981
• [part 2(b): Symphyta (Tenthredinidae). R.B. Benson, 1952]
• [part 2(b): Symphyta (Nematinae). R.B. Benson, 1952]
• part 3(a): Bethyloidea - Embolemidae, Bethylidae & Dryinidae. J.F. Perkins, 1976
• part 3(b): Scolioidea, Vespoidea & Sphecoidea. O.W. Richards, 1980
• part 3(c): Formicidae. B. Bolton & C. Collingwood, 1975
• part 4: Spider Wasps (Pompilidae). M.C. Day, 1988
• part 5: Cuckoo-wasps (Chrysididae). D. Morgan, 1984: The only problems I have had are with the chapter on the genus Chrysis, which according to other people I have talked to doesn't work very well anyway - too many wasps key to C.impressa. This genus obviously needs revision.
• Volume 7 (HYMENOPTERA ICHNEUMONOIDEA)
• part 1: Pimpline ichneumon flies (Ichneumonidae: Pimplinae). M.G. Fitton, M.R. Shaw & I.D. Gauld
• [part 2(ai): Ichneumonidae, key to subfamilies and Ichneumoninae (1). J.F. Perkins, 1959]
• part 2(aii): Ichneumonidae - Ichneumoninae (Ichneumonini), Alomyinae, Agriotypinae and Lycorininae. J.F. Perkins, 1960
• [part 2(b): Ichneumonidae - Orthopelmatinae & Anomaloninae. I.D. Gauld & P.A. Mitchell, 1977]
• part 11: Classification and Biology of Braconid Wasps. M.R. Shaw & T. Huddleston. 1991: Not strictly an identification guide (there is a good key to UK sub-families) but it is a very good introduction to the biology of this group.
• Volume 8 (HYMENOPTERA CYNIPOIDEA, CHALCIDOIDEA & PROCTOTRUPOIDEA)
• part 1(a): Cynipoidea - key to families & subfamilies and Cynipidae (Cynipinae). R.D. Eady & J. Quinlan, 1963: Reasonably easy to use but one or two diagrams could have been better arranged - most notably the first couplet in the sub-family Cynipinae in which the pictures are facing in opposite directions!
• [part 1(b): Cynipoidea - Eucoilidae. J. Quinlan, 1978: Quite a good key but you need a strong microscope and lots of light.]
• part 1(c): Cynipoidea - Charipidae, Ibialidae & Figitidae. N.D.M. Fergusson, 1986: Again, a good microscope and a lot of light are necessary. I have been struggling with Charipidae mainly because there is very little information to double-check the id. Recently I have been told that more recent authors have discovered many new species and split existing species. Therefore, until a new key has been written, I suggest non-experts should not attempt identifications.
• [part 2(a): Chalcidoidea - Agaontidae, Leucospidae, Chalcididae, Eucharitidae, Perilampidae, Cleonymidae & Thysanidae. Ch. Ferrière & G.J. Kerrich, 1958]
• part 2(b): Chalcidoidea - Elasmidae & Eulophidae (Elachertinae, Eulophinae & Euderiinae). R.R. Askew, 1968
• part 3(di): Proctotrupoidea - Diapriidae (Diapriinae). G.E.J. Nixon, 1980
• part 3(dii): Proctotrupoidea - Diapriidae (Belytinae). G.E.J. Nixon, 1957
• Zoologische Verhandelingen: Illustrated key to the subfamilies of the Braconidae (Hymenoptera: Ichneumonoidae). By C. van Achterberg, 1993. An essential and very well written key to Braconidae - one of the commonest groups. The key will only take you as far as sub-family level though - from there on you must get hold of papers & journal extracts.
• Identifying British Insects and Arachnids (an annotated bibliography of key works). Edited by Peter Barnard. An essential reference work for finding the most up to date papers on just about every group. Many papers on parasitica are in very obscure journals and this book can save you days of searching.
• The Hymenopterist's Handbook. Edited & revised Clive Betts, 1986. A very good introduction to the group with a very useful bibliography listing most of the key identification works for all the groups of Hymenoptera. If I need to identify a specimen I find the family description and this tells me the papers that cover the group. After a quick skim through the bibliography you have the exact name of the paper and can retrieve it from a good entomological library.
• The Taxonomy & Biology of Parasitic Hymenoptera. By Mike Fitton, Donald Quicke, Kees van Achterberg, Nigel Fergusson, Lohn LaSalle, John Noyes, Andy Polaszek & Mark Shaw. Course material to the course of the same name run annually but the Natural History Museum & Imperial College (Silwood Park).
• The Hymenoptera. Gauld & Fitton (eds). This is an excellent introduction to the Hymenoptera and provides more detailed information than I have given here. It also deals with non-parasitic groups.
• Parasitic Wasps. By Donald L. Quicke. A very good, in-depth look at the biology of parasitic wasps. Very well written, but probably not one for the beginner.
• Naturalist's Handbook - Plant Galls. By M.Redfern & R.Askew. A very good introduction to all forms of plant gall (not just wasp galls) and their associated communities.
• Rearing Parasitic Hymenoptera. By Mark Shaw. A very good guide to rearing parasitoids in captivity with a good, simple explanation of their biology.
• Zoologische Verhandelingen: Revision of the European species of Torymus Dalman (s.lat.) (Hymenoptera: Torymidae). By M.W.R. de Vere Graham & M.J. Gijswijt. A difficult key to get in to but the only/best species-level key to the genus Torymus.
• Hymenoptera of the world - an identification key to families. By Goulet & Huber et al. This is a very good starting point for working out which group your wasp belongs to. The key has its faults but it works for most things given a little patience.
• The Oak Marble-Gall in Britain. By Robin Williams. Available from the author in a paperback, ring-bound, A4 format. A good guide to the insects that come out of Oak Marble galls. Care must be taken if trying to use this book to identify the inhabitants of other galls, as there are so many other very similar species.

Which key do I use for UK Apocrita?