In 2012, during a survey he did for us of aphids on Dundreggan, Ed Baker discovered a species that had never been recorded in Britain before. This turned out to be the giant juniper aphid (Cinara smolandiae), which up until then had only been found in Sweden, Finland and north-west Russia. Restricted to juniper bushes (Juniperus communis), it is one of 10 species that have been found at Dundreggan that are not known from other sites in the UK, and which have led to our estate being described as a ‘lost world’ for biodiversity.
Ed found these aphids on two juniper bushes during his survey, and when two other aphid surveyors, Bob Dransfield and Bob Brightwell, carried out a follow up survey the next year, in 2013, they didn’t find any of them. I’ve also checked one of the bushes myself every year since 2012, and hadn’t see any of this rare aphid at all, although there were groups of the more common juniper aphid (Cinara juniperi) present on the bush each year, usually attended by wood ants (Formica lugubris).
Bob Dransfield and Bob Brightwell returned to Dundreggan in early July 2015, to do further survey work on aphids, and one of their main objectives was to see if they could find more of the giant juniper aphids. I joined them for the first two days of their survey, and the first thing we did was go to the juniper bush where Ed had found the species, and I had photographed it, in 2012. In 2013 and 2014 I’d found the common juniper aphids on this bush, but this year there were no aphids of any sort to be seen on it.
We began searching other nearby juniper bushes, looking on the woody stems where the giant juniper aphid usually feeds. This is in contrast to the common juniper aphid, which feeds on the new, soft growth near the tips of the branches. It’s almost as though the two species have divided up the available habitats on junipers between themselves, so that they don’t compete directly with each other for the same feeding locations.
After looking at quite a few junipers near the one where the giant juniper aphids had been in 2012, including one with a good population of the common juniper aphids being tended by wood ants, Bob Brightwell eventually found a small group of aphids on the stem of a juniper that he suspected were the rare ones. When Bob Dransfield took a closer look he confirmed they were indeed the giant juniper aphids, and, rather remarkably, they were on a bush only about 5 metres from the one where they’d been in 2012.
As with many aphid species, the giant juniper aphids are tended by wood ants, which feed on the ‘honeydew’ that the aphids secrete as a waste product. This is a major food source for the ants, and it is often easier to find aphids by looking for where ants are clustered on trees. Being significantly larger than the aphids, and more mobile, they are much more conspicuous and simpler to spot. (Aphids often remain relatively motionless on their host plant, each with its rostrum inserted into the tree, to suck the sap, which is their food source).
Because of their relative immobility, aphids are very susceptible to predation (eg by ladybirds or hoverfly larvae) or parasitism by tiny wasps, which lay an egg inside an aphid, with the resultant larva eating the aphid from the inside. The wood ants that tend the aphids provide protection from these predators and parasites, thereby making the ant-aphid relationship a mutually-beneficial or symbiotic one.
There were plenty of wood ants tending these aphids, and during the week they were doing their survey, the Bobs found more colonies of aphids on other juniper bushes, which had even more wood ants tending them.
They also noted a consistent pattern, in that the aphid colonies all appeared to be feeding on swollen sections of the stems of the junipers. This behaviour has previously been recorded in Sweden, where this species of aphid has been known for a much longer period than in Scotland. There, the swollen stems are linked to the fruiting of a fungus called the juniper rust fungus or tongues of fire (Gymnosporangium clavariiforme). This is an unusual fungus with a two host life cycle, fruiting in the spring on juniper as bright orange fingers (hence the name tongues of fire) and releasing spores which infect hawthorn (Crataegus monogyna), where the fungus induces galls on the leaves in late summer. Those galls have tufts on them that release spores which re-infect juniper, and so the cycle continues …
We have a lot of this fungus fruiting on the junipers at Dundreggan each year, and there are thickened stems on many of the bushes, so it seems likely that there is the same link between fungus and aphids in Scotland as well. It’s unclear what the exact relationship is between the fungus and the aphids at this stage. It’s possible that by causing the stems to swell, the fungus makes the wood easier for the aphids to penetrate with their rostra (as their feeding appendages are known). Another suggestion is that the distorted growth of the swelling entails more sap flowing there, and this in turn provides a greater food source for the aphids. Identifying the actual details of this relationship could make a good research project for a student, so we’ll see if we can find someone to work on this in the next year or two. Meanwhile, I’ve marked the bushes, where the aphids were feeding in the greatest concentrations, with red flagging tape so that they can be checked for the presence of the fungus next spring.
During our staff field trip to Norway in May this year, we saw a lot of this fungus on the junipers at Fidjadalen, about an hour east of Stavanger, and I wrote about this in a recent blog. There’s also more information about this fungus, and additional photos I’ve taken of it at Dundreggan, on the Scottish Fungi website. I suspect it’s unlikely there will be any of these aphids at Fidjadalen though, as there was no sign of wood ants in the valley.
I made a return visit to these aphid colonies a couple of weeks after the Bobs had left, and there were still plenty of them feeding there, but they seemed almost outnumbered by the large numbers of ants that were tending them.
Meanwhile, the Bobs have taken a few specimens away with them, to look at in more detail with a microscope, as there is very little information available about this species in the UK. Ed Baker’s report of his discovery of them at Dundreggan in 2012 is the only published material to date. I’m still waiting to receive the report from the Bobs about their survey this year, which will include details of the other species they found during it. However, it’s safe to say that the rediscovery of the giant juniper aphid, and in such good numbers, was the highlight of their visit, and it strengthens Dundreggan’s reputation as an important site for biodiversity.