Utamphorophora humboldti

Identification & Distribution

Adult apterae of Utamphorophora humboldti (see first picture below) are apple-green with a pale spinal longitudinal stripe bordered on each side by a broad darker green longitudinal stripe. The antennae are darker towards their apices, and tarsi are dark. The inner sides of the antennal tubercles are converging or nearly parallel, with low conical wrinkled processes. The median frontal tubercle is very low. The siphunculi are pale, or dusky especially on the apical two thirds, and have the apical two thirds swollen. The cauda is pale. The body length is 1.9-2.6 mm.

Micrographs of clarified mounts by permission of Roger Blackman, copyright AWP all rights reserved.

In North America the American grass-leaf aphid host alternates from ninebark (Physocarpus, Rosaceae) to the upper side of the leaf blades or flowerheads of various grasses (such as Poa, Dactylis, Festuca, Lolium). In Europe it mainly overwinters parthenogenetically on grasses. Utamphorophora humboldti is native to North America, but since 1975 has also been found in England, France and The Netherlands.

Biology & Ecology:

Colour

The literature would appear to be a little misleading on the colour of the adult Utamphorophora humboldti when alive. Stroyan (1979) and Heie (1980-1995) state that the adult apterous aphid is "apple green with a light brown head". No mention is made of the stripes in the adult but they do note that "as a nymph it has a pair of distinct dorsal darker green longitudinal stripes." Blackman (2010) does not mention the stripes on either the adult or nymphs.

We have found both adult apterae (see above) and immatures (see below) of Utamphorophora humboldti in life have a pair of distinct dorsal darker green longitudinal stripes, making it appear to have a paler spinal longitudinal stripe.

The same colour pattern is apparent in the image of the same species from the Netherlands, one of the other European countries where the species has got established in recent years (see below).

Guest image copyright Jochem Kuhnen, all rights reserved

The same is true for an image of Utamphorophora humboldti from its 'home' continent, North America (see picture below) and in images given by Piron (2010).

Image copyright Andy Jensen, Creative Commons (CC BY-NC-SA 2.0).

Many aphids have a darker spinal stripe, believed to function as countershading to help camouflage the insect. A paler spinal stripe would appear counter-productive in this respect, but may function to break up the outline of the aphid.

Phenology

Prior (1975) first reported the presence of Utamphorophora humboldti in Britain, both in suction traps and on Poa grass. Bell et al (2015) reviewed long-term phenological trends of 55 species of aphids in Britain over 50 years. He noted that Utamphorophora humboldti had the largest increase in numbers caught over the period - which was not surprising, given that species commenced its invasion of Europe in the early 1970's. The species also showed the most dramatic advancement in first flights, the most dramatic shift to later in the year of all last flights, and consequently the largest increase in the duration of flight season. This change in the flight season is most likely an artefact resulting from the increase in population size.

Other aphids on same host:

Blackman & Eastop list 43 species of aphid as feeding on annual meadow grass (Poa annua) worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists 29 as occurring in Britain (Show British list).

Acknowledgements We especially thank Jochem Kuhnen for the image shown above, and for his kind donation supporting this website. Our particular thanks to Roger Blackman for images of his clarified slide mounts. Whilst we make every effort to ensure that identifications are correct, we cannot absolutely warranty their accuracy. We have mostly made 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 Bell, J.R. et al. (2015). Long-term phenological trends, species accumulation rates, aphid traits and climate: five decades of change in migrating aphids. Journal of Animal Ecology 84 (1), 21-34. Full text Piron, P.G.M. (2010). The first observation of Utamphorophora humboldti (Essig, 1941) on its host, Poa annua, in The Netherlands (Homoptera, Aphididae). Mitt. internat. entomolo.Ver. 35 (1/2), 111-115. Full text Prior, R.N.B. (1975). Three North American aphid species recently found in Britain infesting cultivated rose, Cupressus macrocarpa and Poa trivialis. Plant Pathology 24(2), 123-124. Stroyan, H.L.G. (1979). Additions to the British aphid fauna (Homoptera: Aphidoidea). Zoological Journal of the Linnean Society 65, 1-54. Full text