New Rhododendron Aphids on the Move.
A Rhododendron aphid (Ericolophium holsti (Takahashi)) first recorded in 2011 as new to Europe and which has only been found in the UK in the Rothamsted Insect Survey’s suction-traps seems to have significantly spread geographically in 2014. A single winged specimen was trapped in 2011 at Ascot, Berkshire, subsequently in 2012, three were caught at Rothamsted, Harpenden 60km away (Eastop et al. 2012) but none at all in the poor aphid year 2013. So far this year we have caught four specimens, one each at Warwick, Harpenden, Boston, Lincs., Starcross, (near Exeter). This species has not yet been found in the field in Britain, but with widespread cultivation of Rhododendrons across the UK it is should now be detectable. Both the aphid species and its host plants originate in India and the Far East.
The alatae (winged forms) of E. holsti have several distinctive features that enable them to be easily recognised (see image below). The antennae are long and dark, the third antennal segment being particularly long and bearing a very large number (often 100 or more) of small rhinaria (sensory pores) distributed over most of its length. The terminal process of the antenna is however quite short, usually less than twice as long as the base of the sixth segment. These antennal characters, when combined with the elongate oval body shape and long cylindrical siphunculi and long tail (cauda), distinguish the alatae of the new arrival from those of all other British aphids.
The only hosts of E. holsti identified to species in its countries of origin are Rhododendron arboreum Smith and R. morii Hayata (Blackman & Eastop, 2006), but it seems likely that it can colonise other species, cultivars and hybrids, including azaleas. If colonies of E. holsti are found on Rhododendron then the apterae (wingless forms) with their pale, dark-tipped cylindrical siphunculi will be easy to distinguish from those of the more common species of Rhododendron aphids Illinoia spp., which both have siphunculi darkened and swollen on the distal half, with Macrosiphum-like polygonal reticulation on a constricted region distal to the swollen part (see Blackman, 2010). The short antennal terminal process of E. holsti, only about twice as long as the base of the last antennal segment, also distinguishes it from both Illinoia species, which have the terminal process more than four times longer than the base. Another distinctive feature of the aptera of Ericolophium is that, in contrast to the alata, the third antennal segment completely lacks rhinaria, but is thickened on the basal half and has a pronounced outward curve. Apterae of both species of Illinoia have 1–6 rhinaria on the basal part of the third antennal segment. Blackman & Eastop (2006) provided a key to apterae of all the Rhododendron-feeding aphids.
We at Rothamsted Insect Survey would welcome any reports of this aphid found in the field in the UK or the rest of Europe.
Blackman, R. L. 2010. Aphids – Aphidinae (Macrosiphini). Handbooks for the Identification of British Insects 2 (7): 413pp. + CD.
Blackman, R. L. & Eastop, V. F. 2006. Aphids on the World’s Herbaceous Plants and Shrubs. (2 vols) Wiley, Chichester, 1439pp
Eastop, V.F., Blackman, R.L. and Taylor, M. S. 2012 Ericolophium holsti (Hemiptera: Aphididae), a new rhododendron-feeding aphid for Britain and Europe. Br. J. Ent. Nat. Hist., 25 65-66