Sawflies

Sawflies (Symphyta) are a very understudied group of insects. They belong to the Hymenoptera, which includes Wasps, Bees and Ants, but the female has a saw instead of a sting, hence the common name. The saw is used to cut slots in leaves, and she then lays her eggs into the slots as an anchor to hold them in place, often laying many eggs on a single leaf. The larvae look very much like the caterpillars of moths and butterflies, but they have more prolegs and are generally more tapered, with wider 'shoulders' and narrower rear ends. They also have very simple ocelli on the larger eyes, only a single dot rather than multiple dots as found on moth larvae.

Larva of Arge gracilicornis

The eggs are laid on particular plants, sometimes a single species of plant, but often within a closely-related family of plants. Some species are leaf miners and some others make galls, although the majority of larvae are free-ranging.

I'm not quite sure why Sawflies are so studiously ignored by many entomologists. True, there are many species and many are very similar to each other, often requiring a specimen and a microscope to identify accurately, but other groups are like this, so I'm not quite sure why they are seen as 'difficult'. I suppose it must be a lack of literature: there is very little out there: the main key (Benson in 3 volumes) is now over 60 years old, but I have found the key to be no more difficult than other groups such as beetles or flies. One difficulty is the larvae: they go through a series of moults (instars) as they grow, and can vary their colour pattern quite substantially when they do so. So in order to identify the larvae we need to know all the variations for each species. Cameron's four-volume monograph, written in the late 19th century, includes coloured drawings of some larvae. A further difficulty is that we don't yet have a full knowledge of which larvae turn into which adults. With moths and butterflies, the match is more or less complete, since a great deal of work has been done with them and they are relatively easy to breed through in captivity, but with sawflies the life cycle can sometimes be a bit more complex, and many attempts to raise them in controlled conditions have failed. So we have a situation where some larvae are as yet unidentified, and the larvae of some of the adults are unknown. Clearly, much work needs to be done here.

Adult sawflies can be difficult to distinguish from other groups, but they always have a thick waist like bees, rather than a narrow one like wasps. The thorax is often strongly sculptured.

Tenthredopsis nassata

 

Tenthredo livida, male

Larvae often adopt a tail-up stance when disturbed. The movement is quite sudden, and I have seen parasitoids being propelled through the air if they approach too closely. This is the larva of Nematus pavidus, which is a common Willow feeder:

Larva of Nematus pavidus

The differences between species are often microscopic, and we need to examine a specimen under magnification. With some species we need to see further details, such as the shape of the teeth on the saw. This is the (2 mm,) saw of a Tenthredo:

Saw of a female Tenthredo sp. Sawfly

A few years ago I studied a series of colonies of Nematus pavidus on my local Willow and it is documented here.

Sawflies certainly need attention, and I intend to focus on them this year.

Full circle

I often struggle to find a suitable title for the posts that I make, but I think you'll agree that today's title certainly applies to the first two images, but in completely different ways.

The Nematus pavidus larvae are now in their final instar (final colouration pattern) and are getting larger:

There's still no sign of the secondary parasites, which makes them a bit late in terms of the early appearance of the larvae this year. I had a think about that, however, and they don't actually have the same imperative to synchronise that the primaries do: the egg of the primary is their target and since the egg stays inert inside the larva until it is fully grown, the secondaries can wander along any time they like.

I rather liked this shot of the Tetanocera being killed by the spider:
Tetanocera are snail-killers. Full circle, indeed.

I flipped over a specimen of Cloud Agaric to confirm my identification and found this tiny Springtail:
It's Tomocerus minor and as I was keying it out I had to laugh when the key said: "This may be called 'minor', but it can reach fully 4.5 mm long"! That gives you some idea of how small Springtails usually are.

While I was looking at the Nematus larvae, I spotted this Pug Moth larva stretched out on the skeletal leaf they had left behind:
It occurs to me that it might have chosen that spot to pupate in. A quick check later will confirm.

This Angle Shades moth larva caught my eye. Camouflage seems not to work on me:

Another new moth came to light, and it's the excellent 20-plume micromoth - Alucita hexadactyla. The wings are each made up of six 'plumes':

And, just for the record, a (very!) worn Common Rustic. It's amazing that the diagnostic kidney mark is just about the only part of the wing pattern still in place:

More clockwork

Last Thursday I predicted that parasitisation of the Nematus pavidus sawfly larvae would take place either on Monday or Tuesday. Monday was a complete washout, but sure enough yesterday saw the initial egg-laying taking place.

I need to set this next image in context. The leaf is now a bare skeleton and most larvae have moved to another leaf. A few are still left on the original leaf and the female Campodorus is busy making sure each one is parasitised.

She moves to the underside of the leaf and curls her abdomen round close to where the larvae are:

Then she moves her abdomen around in the direction of the larvae (you can just make out the stubby little ovipositor in this shot):

Her abdomen approaches the larva (I have no idea how she senses their position so accurately), and the larva attempts to make an avoiding manoeuvre:

But the stabbing move is made unerringly, and the parasitisation takes place:
The egg will now remain unhatched inside the sawfly larva until it pupates, at which time the Campodorus egg will hatch and the Campodorus larva will consume the contents of the pupa.

Unfortunately for the Campodorus, a certain Mesochorus hyperparasite has different ideas. Perhaps Thursday or Friday will enable me to show another twist in this saga.

Post-script: Whilst I was musing about the amazing similarity between the abdomen and an elephant's trunk, I thought I would look a bit more closely, and I wonder if the abdomen is fitted with sensors of some kind. A trawl through yesterday's images delivered this shot showing the ovipositor and what seems to be two holes. 'Nostrils', anyone?

Where to start?

At the beginning, I suppose.

(Keep your eyes peeled for hidden insects....I'll be asking questions at the end.)

Earlier on, I was over on Weaver's blog identifying a pincushion gall, and this is the first shot I took this morning:

It's a gall caused by the plant louse Livia juncorum on Juncus rushes. Galls are abnormal growths caused by insects or fungi for their own benefit: usually food and/or shelter. Other insects know about these benefits and some galls attract lodgers (inquilines) and, of course, predators and parasites. The record number of species found inside a single Oak Apple gall was over 50!

The Marigolds at our front window attract plenty of hoverflies and this sunny morning saw the wonderful Eupeodes luniger:

I also saw Leucozona glaucia on the last of the Angelica:

This all-black hoverfly made my heart flutter a bit, but after a lot of analysis (finally concluded by detailed examination of the wing veins) I determined it was just a very dark Eristalis tenax:

This more usual version was conveniently to hand so that I could show the comparison:

As some of you will know, I've been carrying out a study of sawfly larvae on willows for the past few years, and I thought I would check to see if any Nematus pavidus sawfly larvae were in evidence. Just as well I did, because this lot hatched yesterday:
So this is officially DAY 2. I'll be tracking these larvae and their parasites for the next month or so. They're a bit earlier than usual, so it will be very interesting to see if the parasites are correspondingly early.

This is the next batch ready to go:

It's amazing what catches your eye, even from a distance. This is the larva of one of the Pug moths:
These are very difficult to identify as larvae and the best way of finding out what they are is to breed them through and then identify the adults (which, unfortunately, is also difficult with Pugs!)

On the same Willow as the Nematus pavidus larvae, I found this Baetid Mayfly. I have no idea why it has emerged so late in the year:

Ok.......hands up who spotted the Frog Hopper in the centre of the Livia juncorum. (easy)

And who spotted the bright orange Tephritid fly larva at the bottom right corner (very carefully cropped) of the image of the Pug moth caterpillar? (difficult)

Late Campodorus shots

Since the sawfly larvae are now nearly full size, and the leaves are turning brown, I don't think I'll get too many more shots of the Campodorus.

The first shot shows the Campodorus ovipositing into a pavidus larva that is just on the other side of the leaf, through the hole. I have no idea how she knows where it is. Note the wings held high, presumably to protect them from damage should the sawfly flail around, which they often do.


In this next instance I watched the whole approach. The Campodorus walked from a higher leaf and arrived on the leaf shown. Within a second she had spun round and tried to lay in the tail of the larva, but its reflex triggered and she was thrown about a centimetre away. Undaunted, she tried a very slow, sneaky, second approach, this time aiming for the front of the larva, which doesn't move during the reflex. The reflex was triggered a second time, but she was untouched and continued to lay.

Sawflies again

The first batches of Nematus pavidus larvae are almost full size now, so I suppose they'll soon be moving down the branches to overwinter.


The Campodorus females are still lurking, laying eggs when they get a chance, although I haven't seen any of the Mesochorus females for about a week, now. This shot shows full-size larvae with a Campodorus female in the centre of the leaf:



Notice a family resemblance? This is another sawfly larva that I find from time to time on either Bramble or Raspberry. No id, yet.

Full Sun

At last, a shot of the primary parasite at work:

Every batch of larvae had an attendant female wasp.


The summer weather has been so bad that this is the first dragonfly I have seen this year. Red Darter, female:


And last night to light, along with several Dark Marbled Carpets and Frosted Orange moths, this Nicrophorus investigator beetle with its obligatory mites (notice the two behind the eyes).

New to me.

Campodorus/Mesochorus timings confirmed

The secondary parasite - Mesochorus sp. was seen ovipositing late on September 9th. First as an atmospheric sillhouette:

And then in full glorious colour:

Notice that the larvae are not exhibiting their normal defensive reflex. I think this is how the Mesochorus females detect the presence of the egg of the Campodorus.

So we have a timing of 2 days from primary parasitisation to secondary parasitisation. It is clear that the secondary parasite is targetting the egg of the primary parasite. This actually makes more sense. (See the full discussion on http://homepage.eircom.net/~hedgerow26/nematus-pavidus-parasitoids.htm)

As an aside, the primary parasite was still lurking: there are other batches waiting for her attention:

Hateful weather

The Nematus pavidus larvae continue to grow and are currently on their third leaf. The oldest specimens have shed twice and are now in their third instar. The colour pattern is more or less set now and larvae are about 10mm long:

Primary parasitisation by the Campodorus was observed yesterday, but I didn't manage to get a photograph.

The second batch, based on the eggs I showed on 27th August is still on the first leaf, and has been reduced to 21 from the original (very small) batch of 29 eggs and hatchlings.

I suspect this was a final, almost throw-away, batch (most 'normal' batches contain 50-100 eggs), and the benefit of safety in very large numbers will not apply to this batch.


I spotted a pair of Picromerus bidens in cop on Bramble:


A local chap proudly brought me a pair of Giant Puffballs that he'd spotted on a nearby verge. Sadly, he didn't want to leave one with me for dinner:

Specimens about 30 cm. across.

Just for the record, we have had rain every day since 15th June.

Nematus update

The first willow leaf has now almost been consumed, so the trek to the next leaf will commence very soon. Notice how all of the larvae have migrated to the stalk end of the leaf in preparation for the journey. Larvae are currently about 4-6 mm long.


And here's the bad news as far as the larvae are concerned. This is the primary parasite, a Campodorus sp. Ichneumonid. This is the one that oviposits from under the leaf, curling its long abdomen round the leaf edge. The larvae are currently too small to target, but I suspect egg-laying will commence in a day or two.

Interestingly enough, this specimen was checking out individual leaves and then walking along the willow twig to the next leaf. I suppose it's making sure the trekkers don't escape its attention.

A very common leaf-miner found on Alder is the Sawfly Fenusa dohrnii. This makes a brown blotch mine that wanders between two veins, heading towards the leaf edge.


This close-up of the larva shows the distinctive shape, with wide 'shoulders', which confirms that we are looking at a sawfly rather than a fly, which has simple bullet-shaped larvae.

Who would be a sawfly?

Each time I look at the Nematus pavidus larvae I seem to see a different predator. This Flower Bug - Anthocoris nemorum - wandered into the area of leaf where the sawfly larvae were feeding, picked up this specimen and carried it to the edge of the leaf where it began to consume it.


The area of leaf shown is about 8 mm x 6 mm.

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I update my species list in batches: it's more convenient that way. During yesterday's update, the list passed a new milestone: I now have 1302 species on the list, 7 of which are new to Ireland and dozens are new to Co. Donegal.

More Nematus pavidus hatching

The batch of eggs that I showed yesterday is in the process of hatching:


A couple of things are worth mentioning, here: Firstly, sawfly larvae (in common with moth and butterfly larvae) go through a series of skin moults, after which they may change colour. These different colour forms are called 'instars'. The instars may vary in colour and/or in pattern, leading to some difficulty in identification, since all instars need to be known for a positive identification in each case. Some of the sawfly larvae in the above image have just started to eat and have turned green, the expected 1st instar colour for this species. The larvae which have eaten only the eggshells are still pale and are really instar 0 larvae.

Also note the marks (top left) where the eggs were attached. These indentations are used to anchor the eggs, and are made by the modified ovipositor, or saw, of the female, which gives rise to the name 'Sawfly'.


Despite the more-or-less continuous rain, a few moth species are still coming to light.


This is Lesser Yellow Underwing - Noctua comes - and is new to me.


And this is Dark Marbled Carpet, which I see every year.

Nematus pavidus

Those of you who have been following my exploits will know that I have been following the larval stages of the Sawfly Nematus pavidus for a few years.

To summarise very briefly, the larvae appear around this time of year in large batches, and consume vast swathes of Willow leaves, defoliating entire branches. During that time they are visited by parasites and predators of all kinds, with secondary parasitisation taking place. I tend to follow the life-cycle very closely, and keep a photographic record of what I see, so today is day 1 of that process for 2009.

The eggs are laid in batches on the underside of the leaf:

You can clearly see the single ocellus (eye cell) of the larva inside the egg, which is about 1mm long.

The larvae hatch out and spread over the surface of a single leaf:

Notice the characteristic s-shape of the larvae, which are about 2mm. long at the end of day 1.

When I took the shots, I had no idea that surprise number one was already waiting for me. When I got the pictures onto the computer, I spotted this truly minute (1 mm!) parasitoid exploring the larvae:

Based on size and shape, I'd venture that this is one of the Chalcids (parasitic wasps, related to Ichneumonids). So already we have something new for this increasingly interesting project.

The orange spots are a fungal rust.

While I was taking the shots of the larvae, I spotted this Chironomid (non-biting midge) wandering over the leaves: