PARASITC WASPS AND MOTHS.

With more than 5,500 species of parasitic wasps in Britain, many of which play a significant role in the life cycles of moths and butterflies, I thought it only right to devote an entire post to them. Many have life cycles more fascinating, complex and bizarre than their hosts, but despite this, they remain a very under studied group of insects with a very large majority of species having nothing known about their host associations.

Below is a sample of some of the encounters I’ve had with them during my few years of rearing moths.

ECTOPARASITOIDS ON A LIGHT BROWN APPLE MOTH LARVA

Aug 7th 08. Parasitoids differ from parasites in that they feed on the host, eventually killing it where as parasites rarely do so. Ectoparasitoids feed on the outside of the host where as endoparasitoids feed internally. Here the moth larva has become discoloured where the wasp grubs are feeding.

A day later and the grubs have greatly increased in size. Usually they keep the host alive as long as possible by feeding on none essential tissue such as body fat and reproductive organs.

Another 24 hours on and the moth larva is nothing more than a discarded shell. Having now become fully grown seven of the grubs have already pupated in whitish cocoons with two more about to do so.

13 days later and the twitching of antennae herald the emergence of the adult wasp.

This wasp has subsequently been ID-ed by Mark Shaw as an Oncophanes species, presumably minuta. 

ANOTHER ECTOPARASITOID - PNIGALIO SOEMIUS FEEDING ON AN ECTOEDEMIA SEPTEMBRELLA LARVA

Clockwise:
1. Day one - Aug. 5th 2012. The mine is on cultivated Hypericum found just a couple of gardens away.
2. The moth larva with two ectoparasitoids feeding on it.
3. Day four and one of the parasitoids has "disappeared" whilst the other has grown enormously. The host is little more than an empty skin.
4. Day eight and the fully fed grub is a translucent bag of waste products.

5. Day nine and the gut has been emptied with an unordinate amount waste matter strewn about.
6. Amazingly, two days later and a jet black pupa emerges from the white pre-pupal grub.
7. Eight days after pupating the wasp emerges leaving behind the empty pupal case.
8. It's the Chalcid wasp - Pnigalio soemius with a body length of 2mm. Thanks to Dick Askew for identifying it. It will be sent off to him to so he can place it in the appropriate reference collection.

HYPERPARASITOIDS FEEDING ON PHYLLONORYCTER LARVAE

Hyperparasitoids are a group of parasitic wasps that feed on other parasitic wasps. I rarely come across evidence for these so I've tried to document this encounter in detail.

Above is an oak leaf found at Sowerby Bridge on Nov. 16th 2023. It contains three mines of a Phyllonorycter moth species. 

So far so good.

The mine on the leaf edge was opened up to reveal what appears to be a straight forward "tombstone" parasitic wasp pupa. It belongs to the family Eulophidae. 

It probably attacked the moth in the larva stage as there was no sign of a pupal case.

The next opened mine revealed a distinctive "zeppelin" shaped cocoon made by a parasitic wasp larva prior to pupation. It's a Braconid wasp probably Colastes braconius. But instead of a fully fed larva or pupa inside there was a hungry grub feasting on the contents - a hyperparasitoid.

Nov. 18th: The opened "zeppelin" revealed a plump grub eating the remains of the original, larval occupant.

Nov. 28th: Ten days later and the fully fed hyperparasitoid grub has pupated. The small brown object is the larval skin of the primary parasitoid.

After overwintering the pupa outdoors the adult emerged on Mar. 16th 2024. It's a male and is thought most probably to be Sympiesis gordius. This species can attack either the moth larva or its parasitoid.

After opening up the third mine things got a little more complicated. There were two hyperparasitoid grubs, one having fed on a parasitoid pupa and the other feeding on a parasitoid grub.

When their food sources were exhausted the larger grub then latched on to other and appeared to start feeding on it.

A day later on Nov. 19th the smaller grub is all but dead, the larger is now fully fed and ready to pupate.

Nov. 28th and pupation has taken place. The black mass at the anal end of the pupa is the contents of the grub's gut which it emptied out prior to pupating.

After overwintering the pupa out doors the adult emerged on Mar. 19th 2024. It's a male and is thought most probably to be Sympiesis gordius - the same species as above.

PHYLLONORYCTER OXYACANTHAE AND WASP PUPAE

Feb. 23rd 2010. A Phyllonorycter oxyacanthae mine in Hawthorn found at New Lane the previous Autumn. The opened mine contains not one but three parasitic wasp pupae. I normally expect no more than one per mine so three was quite unusual.

Feb. 27th 2010. The three wasp pupae removed from their mine to be reared through along side four P. oxyacanthae pupae from other mines. Not surprisingly with three wasp grubs to one host they are considerably smaller.

Mar.17th 2010. One of the newly emerged adult wasps. It's the Chalcid wasp Achrysocharoides atys. At 1.4mm long this is the smallest insect I've attempted to photograph and so I make no apologies for the less than perfect photo.

A SELECTION OF REARED PARASITIC WASPS

 Clockwise from top left:

Sympiesis sericeicornis (male) from a Phyllonorycter mine in oak.

Pnigalio pectinicornis (male) from a Tischeria ekebladella mine in oak.

Pediobius saulius from a phyllonorycter mine on Sallow.

A chalcid wasp - family Eulophidae from a Stigmella aurella mine in bramble.

All beautiful and fascinating insects in their own right. Many thanks to Dr. Dick Askew for his invaluable help in identifying these wasps.

A PROBABLE DIADEGMA PUSIO

May 19th 2012: Caught in the act! This parasitic wasp grub was observed breaking out of a much prized Bucculatrix nigricomella larva.

The grub pictured above is now emitting an inky black liquid - emptying its gut contents prior to pupation as moth larvae do.

Pupation successful and the typically frail, exarate pupal case seems nothing more than a transparent second skin the day before emergence.

And finally the adult has emerged. It's probably Diadegma pusio, a male, which is one of two species of Diadegma that parasitises Buccalatrix species. Thanks to Mark Shaw for his comments on this wasp. He also says the blobs in the abdomen are probably uric acid (waste products) rather than eggs which is what I thought they might be.

A PARASITISED LADYBIRD

7-Spot Ladybird, Skicroat Green allotments, summer 07.

Not moths but along the same lines. This ladybird has been parasitised by the braconid wasp Perilitus coccinellae and to explain exactly what has happened I've taken this extract from Chris Raper's web page.

"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".