Tuesday, 26 July 2016

More parasitoid behaviour

I have written many times about parasitoid wasps and their lifestyle. In summary, the female wasp finds her target host - usually a caterpillar or larva of a sawfly - and deposits an egg inside it. The egg remains dormant until the host larva has grown sufficiently large and then it hatches and the wasp larva eats the host larva. Sometimes the wasp waits until the host larva has pupated, but the outcome is the same: the host dies and the wasp larva pupates and emerges as an adult wasp at a later date.

There are many variations on the theme: sometimes the host larva is kept alive and it can move away after the wasp larva has emerged. This is thought to be a distraction strategy where the host larva acts as a decoy, attracting secondary parasitoids that would normally target the primary parasitoids using the host as a vector.

I recently found specimens of the aphid Eucallipterus tiliae on lime and spotted this odd structure under one specimen.


This aphid has been parasitised by the Braconid wasp Praon flavinode which targets mid-instar aphids. The aphid is glued in place, although it can still feed (the specimen above is now an adult) and grow. The braconid feeds inside the aphid and then drops into the 'podium' where it pupates.

So in addition to using the aphid as a food source, it's also using it as shelter for pupation.

To give some sense of scale, the 'podium' is about 2 mm. diameter at the base.

Here's a shot of some of the earlier instar aphids on a leaf:

Eucallipterus tiliae aphids on Tilia

No matter how much I find out about these wasps, I am constantly surprised by their range of habits and techniques.

Both species are new to my Species list, and Praon flavinode is a first Irish record.

Tuesday, 24 May 2016

Cryptic Wood White survey in Craigavon

It has recently been discovered that Ireland has two species of Wood White butterfly: Leptidea sinapis, which is restricted to the Burren and nearby areas (and is the same species as that found in Great Britain) and the Cryptic Wood White - Leptidea juvernica - which is found in the rest of Ireland, including Northern Ireland, but is absent from GB.

Resolution of the conflicting and confusing identifications and distributions was temporarily further confused by the suggestion that one of the species was Leptidea reali, which is found in France. It seems that the situation has now been satisfactorily resolved, and it now remains to examine local populations to be sure we have the correct distributions. There is no sure way of separating the species by morphological characters, although differences have been proposed, so the only way to be sure is to sample populations and examine the genitalia.

The purpose of yesterday's visit to Craigavon was to train recorders in the identification of Cryptic Wood White (CWW) and to demonstrate a recording system for subsequent use in tracking this (and other) species.

But me being me, I didn't restrict myself to CWW, and I recorded more or less everything else we encountered.

First, though, a shot of the courtship behaviour of CWW:

Courtship behaviour in Cryptic Wood White, Leptidea juvernica
The male (left) usually sits higher and repeatedly swipes his antennae and proboscis over the face of the female. This courtship can take up to 30 minutes to complete. If the female accepts him, mating takes place. We saw one recently-emerged female being courted by two successive males before her wings had even fully inflated.

Gorse bushes were very fruitful, and were covered with Gorse Shieldbug:
Gorse Shieldbug
And their eggs: 

Eggs of Gorse Shieldbug

I also found many specimens of the minute (3 mm.) Gorse Weevil, Exapion ulicis:

Gorse Weevil, Exapion ulicis

New to my Species List.

There were a great many Common Blue damselflies: 
Common Blue damselfly (Enallagma cyathigerum)
And a few Blue-tailed damsels:

Blue-tailed Damsel

I found a few galls of the mite Eriophyes pyri quite early on in the walk:

The gall mite Eriophyes pyri on Rowan.

This appears to be the first record for NI, with one previous record from Ireland, and new to my Species List.

A record shot of the Mirid bug Harpocera thoracica. The male antennae have an interesting 'structure'.
Mirid bug Harpocera thoracica (male)
New to my Species List.

The day-flying Mother Shipton moth caught my eye, and it posed conveniently for a few shots:

Mother Shipton moth
I have seen the Lacehopper Tachycixius pilosus quite a few times, but this one seems to have a mite of some kind under the left wing. Mites usually position themselves in places where they can't be scratched off.
The Lacebug, Tachycixius pilosus

Finally, a Tetragnatha sp. 'Stretch Spider'. There are a couple of these that can't be separated without a microscope:

Tetragnatha sp. 'Stretch Spider'
Not bad for around 2 hours work, and we did count around 25 CWW. 

Monday, 16 May 2016

Benburb bioblitz

This bioblitz was based around Benburb castle, but also included the grounds of what is now known as Benburb Priory. The 17th century castle is being restored and the priory was formerly a manor house built in the 1880's.

The underlying geology is limestone and the site slopes downwards towards a river which is extensively engineered with cuts and sluices, and could almost be regarded as a canal. The riverside area has been allowed to run wild and is covered with Giant Hogweed, Bamboo, Japanese knotweed, Laurel and Himalayan Balsam. The grounds closer to the Priory are maintained as a decorative garden, but again, large areas are running wild, with a collapsed victorian greenhouse/orangery attached to outbuildings. This feature runs for some 50 metres and was clearly an important structure in its day. This is a shot of the old glasshouse:

Part of the glasshouse area with priory in the background
The south-facing glasshouse area contained a mixture of wild and cultivated plants, notably an overgrown herb garden, and attracted a huge number of hoverflies, butterflies, solitary bees and bumblebees.

Here's a shot of a Holly Blue on the approach path: 

Holly Blue butterfly
We made a quick survey to see where we should concentrate our efforts and it was clear that the riverside paths would be most productive. When I noticed that the area was limestone, we looked for Garlic Mustard, since this is a host plant for the Orange Tip butterfly and we immediately found an occupied flower:

Orange Tip egg on Garlic Mustard
We saw many Orange Tips, both male and female along the river bank. This female was nectaring on Herb Robert:
Female Orange Tip on Herb Robert
The same area yielded 14-spot Ladybird:

14 spot Ladybird

And a 10-spot ladybird with the rear spots missing. The 10-spot must be the ladybird with most variation in the spotting:

10-spot ladybird
Also from this area were the hoverfly Leucozona lucorum:

The hoverfly Leucozona lucorum landing on Bush Vetch

And I caught a glimpse of a huge pond skater down below in the cut next to the river. It's a poor shot, but there is only one pond skater this size. It's Aquarius najas, and is around 5 cm long from front foot to rear foot:

The River Skater Aquarius najas
New to my Species List.

We found a couple of leaf miners in the wooded area closer to the castle:

Phytomyza chaerophylli on Cow Parsley
And:

Phytomyza ranunculi on Celandine
Phytomyza ranunculi was also found on Creeping Buttercup.

Closer to the castle, I found a moth larva grazing on lichen on a fence post. It's Brussels Lace, Cleorodes lichenaria:

Larva of the Brussels Lace moth

That's a good example of the formal name clearly stating the nature of a species.

A final shot of Lords-and-Ladies or Cuckoo Pint, which I only ever find on lime:

Arum maculatum
Overall we submitted perhaps a hundred species on the day. This is far fewer than I would normally expect on a day's hunting, especially on a bright sunny day, but the habitat is essentially 'cultivated but abandoned', so the biodiversity could be expected to be low.

Thursday, 28 April 2016

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.

Monday, 18 April 2016

Leaf-miner recording scheme for Ireland

Last week the National Biodiversity Data Centre in Waterford launched a national recording scheme for leaf miners. I have been working on a national checklist for miners for several months and the scheme allows recorders to enter records of leafminers and upload images for verification.

Leaf-miners are a largely ignored group of insects from four groups: micromoths, flies, sawflies and beetles, and hopefully the scheme will raise awareness and produce many records for these groups and perhaps result in some new species for Ireland.

I also produced an introduction to leaf miners which will help people to identify their finds. The introduction and checklist can both be downloaded from here.

Leaf miners are the larvae of insects, and they can be detected by the track they make as they feed inside the leaf. Since they spend all of their larval life inside a leaf, they are very small: some of the adults are only 2-3 mm long.

Mines are identified primarily by knowing the host plant: many miners feed on a single plant or family of plants, so knowing the host plant immediately reduces the number of miners to be considered. Once we know the host plant, then further identification relies on shape of the mine, pattern of the frass (dung) in the mine and perhaps details of the larva or pupa.

Here's a shot I took of the fly miner Phytomyza ranunculi on Lesser Celandine:

Phytomyza ranunculi on Lesser Celandine


There are two main possibilities for this mine, the other being Phytomyza ranunculivora, which has the frass in more discrete lumps:

Phytomyza ranunculivora on Creeping Buttercup


Although Phytomyza ranunculivora hasn't been found in Celandine in UK or Ireland, it does use that plant in other parts of Europe, so it's always wise to check in case we can add a new foodplant for that species. The photograph above shows it on Creeping Buttercup, which is closely related to the Celandine, and was the first (and still only!) Irish record when I found it in 2010.


Friday, 15 January 2016

10 years for an id

Back in December 2005, I encountered a hair-like ice formation on grounded twigs in Steeple wood. I thought it might be related to some kind of fungus, since the twigs were clearly rotted to some extent, but I couldn't get an id. In July 2015, Swiss scientists discovered that the 'Hair Ice' is caused by the crusting fungus Exidiopsis effusa, but only when a precise set of conditions is met.

It seems that water is drawn into the twig, saturating it, and the crust fungus exudes the water through pores. When the temperature, humidity and air are exactly right, the extruded water freezes and forms the hair-like structures we see in these photographs.

'Hair Ice' caused by Exidiopsis effusa 

'Hair Ice' caused by Exidiopsis effusa 

There is one previous record of the fungus from Ireland, made in 1993, but I suppose that must have been the original crust, rather than the 'Hair Ice'. So I have to settle for a second Irish record, with a Donegal first.

10 years for an id isn't too bad I suppose.

Coincidentally, we are experiencing the first cold snap of the winter, with lying snow and sub-zero temperatures. This was the view from my front window this morning as the sun rose behind falling snow:


Wednesday, 14 October 2015

Sunflower (part two)

The Sunflower continues to attract butterflies. This Red Admiral is the third species I have seen nectaring after the Small Tortoiseshell and Peacock last week. A passing Speckled Wood didn't seem so interested. I have seen  this butterfly on the flower for three consecutive days, now.

Red Admiral on the Sunflower
Red Admirals have two generations each year. The first generation is migrant from France (or perhaps even further south) in springtime, and their offspring feed on nettles, emerging from late August to October and then heading south. In recent years, however, adults have been found overwintering in the south of Ireland (and England), So, as warming takes hold, we're seeing a transition from solely migrant to partially resident populations.

Phenology has also changed in some moths. Some species were described by their flying (or emerging) dates. So we have August Thorn, September Thorn, Winter Moth, November Moth, December Moth, etc. But in the couple of hundred years since they were named, weather patterns have changed, and their names are not so accurate nowadays. This August Thorn is a new species for my list, and can be separated from the September Thorn by the kink in the rear band of the forewing (arrowed).

August Thorn moth
This is a locally common moth, feeding on larger broad-leaved trees.

I suppose it's worth pointing out that the season for September Moth often starts earlier than the August Moth! Of course, it isn't just moths that are altering emergence and migration patterns. Birds like the Redstart and Fieldfare that used to arrive as winter visitors have become very scarce nowadays, since they stay in situ and overwinter further north. Flowering plants are also extending their flowering season. Have a look in plant books from a few decades ago, and their 'flowering seasons' will surprise you.