Mites that hitchhike

While I was leading a community wildlife walk across some cattle-grazed water-meadows yesterday, one of the younger members in the group used his youthful sharp vision to spot a small dung beetle (Aphodius fimetarius) which looked a little unusual with what appeared to be tiny bumps on the elytra. Although some sort of deformation is presumably possible, the 'bumps' were (as suspected) phoretic mites of the genus Macrocheles. 'Phoretic' means they practice 'phoresy' i.e. use other species as transport rather than feeding on them as a parasite might.

Aphodius fimetarius with phoretic mites on the pronotum and elytra. 1 square = 5mm.

Aphodius fimetarius with phoretic mites on the underside, especially of the abdomen. 1 square = 5mm.

On this occasion I haven't taken microscope photos of the mites as I don't intend to identify them beyond genus. Although these mites are possibly more familiar from larger dung beetles, research in France (Glida & Bertrand, 2002) suggests that, as they are active all year, Aphodius are important in distributing and establishing populations of Macrocheles mites because these beetles are active throughout the whole year, including cold periods. At least some Macrocheles species are predatory on fly larvae (and some are phoretic on adult flies), hence being moved between manure piles/cowpats presumably delivers them safely to new hunting grounds. Also, although the beetle presumably bears some burden in carrying sometimes large numbers of mites, there may be a trade-off if the mites reduce the populations of dung-feeding fly larvae and therefore increase the amount of dung available to their dung beetle hosts. I'm sure there's a potential experiment in there somewhere...

Reference

Glida, H. & Bertrand, M. (2002). The occurrence of Macrocheles mites (Acari: Macrochelidae) in relation to the activity of dung beetles: a field study in Southern France. In: Bernini, F., Nannelli, R., Nuzzaci, G. & de Lillo, E. (eds.). Acarid Phylogeny and Evolution: Adaptation in Mites and Ticks. Proceedings of the IV Symposium of the European Association of Acarologists, pp. 199-207.

Counting skins

As stated in Corbet & Brooks (2008), when looking at Odonata (dragonflies and damselflies), the 'value of the exuvia as a tool for quantitative ecological studies cannot be overstated'. This is because, in Britain at least, most species can be identified from their exuviae (moulted skins) which show where and, depending on the fequency of recorder visits, when an adult emerged, even if the adult is never seen. This is how, despite only seeing single adults, I know that 11 common darters (Sympetrum striolatum) have emerged from our garden pond even though it is only a year old and around 3m x 1.5m in size. The exuviae are easy to find and count - as the photo here shows, they can be clustered closely together and may be on even very short emergent vegetation.

6 of the 11 Sympetrum striolatum exuviae found in our garden pond (red rings) plus one more nymph just below the surface (blue ring)

Exuviae also provide an excellent way of investigating juvenile Odonata morphology as the key nymphal features can be readily seen without needing to capture a specimen. Several dragonfly identification guides include sections on exuviae, but if you want to look at this aspect in detail, I recommend Cham (2007 & 2009) which are not expensive (and are now available as a single volume).

References


Cham, S. (2007). Field Guide to the Larvae and Exuviae of British Dragonflies. Volume 1: Dragonflies (Anisoptera). BDS, Peterborough.
Cham, S. (2009). Field Guide to the Larvae and Exuviae of British Dragonflies. Volume 2: Damselflies (Zygoptera). BDS, Peterborough.
Corbet, P. & Brooks, S. (2008). Dragonflies. Collins, London.

It's OK to be takeyai

It's time to look at a family of insects I've not written about before - the Tingidae or 'lacebugs'. These are true bugs (Hemiptera) and, though small, are distinctive due to having a lace-like network of reticulation covering the pronotum and forewings. The function of this isn't immediately obvious, but as they often look like dried seeds or similar, it may be a form of camouflage. They are also flattened dorso-ventrally, with the head, in many species, hidden beneath a hood-like or bulging extension of the pronotum. Although generally unfamiliar to non-entomologists, they can be quite common and there are over 2,000 known species worldwide (25 in the UK, 8 of which are listed as scarce or rare).

All Tingidae are plant-feeders, and being mostly host-specific, some are considered pests. One of these, a Japanese species first recorded in Britain in 1998 (Halstead & Malumphy, 2003) was found in our garden yesterday - the andromeda lacebug Stephanitis takeyai. It feeds on the 'Japanese andromeda' Pieris japonica and has been introduced into the USA and Europe via the ornamental/garden plant trade. It also uses other Pieris species, as well as rhododendrons and azaleas - as such it is sometimes considered a pest in ornamental gardens, though in ours it is welcome to eat what it can find as we don't grow these!

Stephanitis takeyai, approx 4mm long (excluding appendages)

The dark reticulation is clearly visible here and, along with the dark wing markings (which break up the outline) and leaf-coloured legs/antennae I suspect provides effective camouflage. The bulbous hood of the pronotum is visible, almost entirely obscuring the head/eyes, but can been seen more clearly from different angles.

Stephanitis takeyai, side view showing the pronotal hood and, just behind it a thin longitudinal pronotal keel. The flattening of the body is also clear.

Stephanitis takeyai, front view, again showing the pronotal hood.

Although some North American tree-pest species have been well studied, there is a lack of information about the Tingidae in more general sources. There is a short section including keys in Southwood & Leston (1959) and although Ryan (2012) updated the list in this publication, adding S. takeyai and Corythucha ciliata, identification details were not included. However, S. takeyai is a distinctive species, only likely to be confused with another rhododendron-feeding introduction, S. rhododendri which is broadly similar, but has mainly pale wings with a brown band near the base.

S. rhododendri is covered briefly in Becker (1974), Buczacki & Harris (1981) and similar publications, as well as in Southwood & Leston (1959), while Alford (2011) covers the platanus lacebug C. ciliata, a North American pest of various plane trees first found in Britain in 2006, again via the plant trade. However, there is much to learn about these insects, and it seems likely that more will be accidentally imported, so definitely a group worth keeping an eye out for, including on garden/ornamental plants.

References
 
Alford, D.V. (2011). Plant Pests. Collins, London.
Becker, P. (1974). Pests of Ornamental Plants. HMSO, London.
Buczacki, S. & Harris, K. (1981). Guide to the Pests, Diseases and Disorders of Garden Plants. Collins, London.
Halstead, A.J. & Malumphy, C.P. (2003). Outbreak in Britain of Stephanitis takeyai Drake & Mao (Hemiptera: Tingidae), a pest of Pieris japonica. British Journal of Entomology & Natural History 16: 3-6.
Ryan, R. (2012). An addendum to Southwood & Leston's Land and Water Bugs of the British Isles. British Journal of Entomology & Natural History 25: 205-215.
Southwood, T.R.E. & Leston, D. (1959). Land & Water Bugs of the British Isles. Warne, London. [there is a 2005 reprint which is much cheaper, and a CD-ROM version from Pisces Conservation Ltd.]

Bindweed beauty

I like gardening. I like invertebrates. Most invertebrates are either neutral (from a simplistic human perspective) or beneficial. Some of the latter are also beautiful, and this is a fairly common example, the White Plume moth Pterophorus pentadactylus.

White Plume moth Pterophorus pentadactylus

The plume moths (family Pterophoridae, plus in Britain, one species in the Alucitidae) are easily recognisable as adults by their deeply lobed wings. Most are camouflaged as mottled greys and browns, but this species is very different, being unmistakably bright white, possibly mimicing a discarded (and of course inedible) downy feather. Certainly they rest on the tops of leaves where a feather might land, but scuttle out of sight if disturbed.

So, why is it beneficial in gardens? The answer lies in the larva which feeds on the leaves and flowers of bindweeds (Convolvulus spp. & Calystegia spp.) which gardeners otherwise spend a lot of time untangling and uprooting. Personally, I leave it most of the time (it covers some bare areas with greenery) which may be one reason the moth has colonised our garden - plenty of undisturbed food.

If you want to know more about this and other British plume moths, Hart (2011) is excellent, including dissections of genitalia used to separate difficult specimens, and photos of juvenile stages. Well worth getting hold of.

Reference

Hart, C. (2011). British Plume Moths. BENHS, Hurst, Reading.

Robins good

About a year ago, I wrote about a thrush nest hidden away on our community farm. As it is a wildlife-friendly enterprise, it wasn't too surprising when we found another nest recently - this time a robin (Erithacus rubecula) tucked away in our plant-pot storage area. Obviously, disturbance is a sensitive issue (I covered this in my previous post) and although the birds had chosen to nest in a location with a lot of human activity, we wanted them to experience as little stress as possible. So, a few photos were taken quickly, then a sign erected to ensure no-one tried to take pots from that part of the store. This was the outcome.

Robin nestlings, one gaping to elicit feeding.

An adult robin incubating the hatched brood.

After fledging, one infertile/addled egg remains unhatched.

Although there was concern that the nest had been abandoned, this seems unlikely. There was no evidence of dead young, nor of the nest having been disturbed by a predator. Also, a couple of young robins have been noted nearby, so the evidence is strong that this was a successful nest, hopefully helped by a little care from the surrounding humans!