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Monterey pine aphid, wood ants massing, ivy-leaved toadflax aphid

in late winter 2014

Monterey pine aphid  Southern wood ants,  Ivy-leaved toadflax aphid 

  <February 2014>  

Winter 2013-14 never really 'happened' in the south-east of England. January's rain and mild weather continued for most of February with predictable effects on wildlife populations including the aphids. Many species are appearing well before usual which bodes well for aphid enthusiasts - but rather less well for farmers. We know for example that there are strong correlations between winter temperature and the timing and size of migrations of many pest aphid species. This enables forecasts to be made in March of the likely extent of problems from key pest species during the critical early part of the growing season. Whether such relationships hold for the many non-pest aphids remains to be seen.
 

Illegal aliens / British residents? - Aphids on Montezuma pine

The Monterey pine aphid, Essigella californica is an aphid new to Britain. This species is a North American native, but it has been introduced into Europe (France and Spain) in recent years. We now have two confirmed sightings in Britain. It was first found on samples of Scots pine and Bhutan pine (Pinus wallichiana) grown outdoors at the Royal Botanic Gardens at Kew in November 2010. Then, quite independently, we discovered it in 2012 and 2013 living on Montezuma pine (Pinus montezumae) along with a large population of Eulachnus rileyi  - at Bedgebury Pinetum in Kent (see picture below). One of our specimens from Kent was confirmed, by the Fera molecular diagnostics team, to be Essigella californica - a new species for Britain.

Sexual reproductive stages have been observed at high altitudes in North America, but where the species has spread out of the USA (Australia and parts of Europe), reproduction is entirely parthenogenetic. We wondered how the Kent population was getting through the winter in Kent, so on February 22nd we again visited Bedgebury Pinetum.

We usually find aphids by carefully hand-searching the vegetation,  but the Monterey Pine Aphid is difficult to find even when fairly common since at the slightest disturbance they hide at the bases of the needles. So we used a beating-tray to collect any aphids that fell off after delivering a few sharps taps to the branches. An hour of tapping branches, and peering at the results, produced one solitary aphid nymph along with a potential predator thereof, an adult pine ladybird (Exochomus quadripustulatus) both pictured below:

 

The came the problem (= 'challenge' in pseud-speak) of identifying such a young aphid.  Adults are easy to identify (Essigella have only 5 antennal segments versus 6 for Eulachnus, and Essigella also has have markedly shorter antennae), but there is no information available on the situation for nymphs. Hence we decided to try to rear it through to the adult stage. Unfortunately aphids that live on conifer needles are notoriously difficult to rear in captivity, and it died after a couple of days (maybe because beating is not the most aphid-friendly way to collect aphids).

It is certainly possible that the nymph above is Essigella californica. The lack of any wax rules out Eulachnus rileyi and the black spots are too weak for Eulachnus agilis, but we cannot rule out Eulachnus brevipilosus from the photograph - though we've yet to find brevipilosus on those particular trees. We will try again in a few weeks time to see if we can find some adults!

 

Middle-earth voyeur ogles massing wood-ants

Nearly all our photos are taken in the field using a custom-modified D3200 Nikon to facilitate ultra close-ups - which explains the plastic and parcel-tape accessory. On the eyepeice-end you may notice Bob D getting up-close and personal to a large wood ant nest, whose occupents were just starting to wake up. And yes they certainly do bite, albeit compared to African driver ants ('safari-ants', Dorylus spp.) their bites are scarcely noticeable. Also it has been suggested they are more docile early in the year. The first picture below shows the ants 'spring massing' in a dense aggregation in the sun on top of their nest.

We have often seen wood ants massing in March, but this was the first time we had seen it in February. It came as no great surprise since we had seen a few Formica rufa active close by a month earlier, in early January,  attending large pine aphids.

 

These ants were clearly warming up in the spring sunshine. As soon as the sun goes in the aggregations break up, and then reform when it comes out again. What is unclear is whether the purpose is primarily to warm the nest up upon their return, as suggested by Skinner, 1998,  or to warm up individuals so they can forage for food for their colony - as shown in the picture below.

 

Ivy-leaved toadflax - an unusual plant with a mystery aphid

Cymbalaria muralis, the ivy-leaved toadflax, grows on old walls (see below left). It is native to south and southwest Europe, but is invasive in many parts of the world - including Britain and the USA. It is unusual because the flower stalk is initially positively phototropic (it moves towards light) - but after fertilization it becomes negatively phototropic (so moves away from light). This results in the seeds being pushed into dark crevices of walls which is its preferred habitat.

 

We found small numbers of the aphid shown below on this plant in the East Sussex village of Firle. We have tentatively identified it as the ivy-leaved toadflax aphid (Dysaphis gallica). Stroyan (1957)  recorded it as one of the British Dysaphis (= Sappaphis) species and described it as 'leaden coloured'. Blackman & Eastop (2006)  described the same species as 'dark mottled blackish green, usually with a reddish tinge at bases of siphunculi'. We note that the aphid appears to be cryptically coloured, resembling the developing flower bud of Cymbalaria (see above right).

The aphid above was a fourth instar, and its developing wing buds are visible. We kept some alive, and over a few days two had moulted to a rather undistinguished looking winged (or alate) form, shown below left. A younger immature aphid is shown below right.

 

Not a lot is known about this species. There are records of occurrence in France, Switzerland, Italy and Sicily as well as UK. Sexual forms are produced, but will not reproduce on Cymbalaria. Various transfer experiments have been attempted, but the aphids failed to feed on a range of likely primary hosts. Despite being a southern European species, our observations suggest it does not host alternate in this country, but remains all year on its secondary host: Ivy-leaved toadflax.

If you are an entomologist, and are thinking the 'obvious answer is mark-release-recapture', you are clearly the very person to try it. We have marked a few hundred thousand tsetse flies in our time, and want no part of that particular study...

So why 'hunt' for aphids?? 

Acknowledgements

We have made provisional identifications from high resolution photos of living specimens, along with host plant identity. In the great majority of cases, identifications have been confirmed by microscopic examination of preserved specimens. We have used the keys and species accounts of Blackman & Eastop (1994)  and Blackman & Eastop (2006)  supplemented with Blackman (1974) , Stroyan (1977) , Stroyan (1984) , Blackman & Eastop (1984) , Heie (1980-1995) , Dixon & Thieme (2007)  and Blackman (2010) . We fully acknowledge these authors as the source for the (summarized) taxonomic information we have presented. Any errors in identification or information are ours alone, and we would be very grateful for any corrections. For assistance on the terms used for aphid morphology we suggest the figure  provided by Blackman & Eastop (2006).

Useful weblinks 

References

  •  Skinner, G.J. (1998). British wood ants. British Wildlife 10, 1-8.

  •  Stroyan, H.L.G. (1957). A revision of British species of Sappaphis Matsumura. H.M. Stationery Office.