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Identification & Distribution:

Wahlgreniella nervata apterae are spindle-shaped and yellowish or green (see below first picture), sometimes mottled with reddish anteriorly (see below second picture). The femora do not have distinctly dark apices. Their siphunculi are slightly swollen rather symmetrically about their inner and outer faces, they have dark tips and a small flange. Winged viviparae of Wahlgreniella nervata have a green abdomen with variably developed dark dorsal cross-bands, sometimes coalescing into an irregular patch.

There are two subspecies (or divergent clones of the same species):

  1. Wahlgreniella nervata arbuti
    The apical segment of the rostrum is longer than 1.3 times the length of segment two of the hind tarsus (Blackman (2010) ). The live aphids are pale-yellowish to pale yellowish green. On Arbutus (strawberry tree) and Arctostaphylos (manzanitas and bearberries).

The image below shows an Wahlgreniella nervata arbuti aptera in alcohol.

  1. Wahlgreniella nervata nervata
    The apical segment of the rostrum is shorter than 1.3 times the length of segment two of the hind tarsus (Blackman (2010) ). This subspecies lives on rose (Rosa) but, in culture, able to live on Arbutus.

The clarified slide mounts below are of adult viviparous female Wahlgreniella nervata nervata : wingless, and winged.

Note however, in this aptera, the apical segment of the rostrum is about 1.4 times the length of segment two of the hind tarsus - which is more consistent with Wahlgreniella nervata arbuti.

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

In North America Wahlgreniella nervata apparently host alternates between rose (Rosa) and ericaceous plants (mainly strawberry tree, Arbutus), although the host alternation has not yet been experimentally verified. Parthenogenetic populations on both Rosa and Arbutus have been introduced into Europe, and are treated as separate subspecies. Wahlgreniella nervata is considered an invasive species, having been reported from Damask rose in Turkey (Barjadze, 2011 ), and as a new pest of rose in India (Joshi et al., 2014 ).

 

Biology & Ecology:

We have found both of the subspecies of Wahlgreniella nervata arbuti in Britain, but each of the subspecies was only found in one location. The nymphs shown below came from the same well established colony on strawberry tree as the two apterae from strawberry tree shown above.

Predators had found the colony and there were several syrphid larvae present (see picture below).

 

Parasitoids had also been active (see picture of mummy below), but we were unable to determine the identity of the primary parasitoid, as only hyperparasitoids emerged.

Sampling over three years has confirmed that that the population continues to reproduce parthenogenetically through the winter, at least during mild weather. The picture below shows some immatures found on January 31st 2017 in the midst of winter.

A few days later some of these had matured to adult apterae.

 

Other aphids on same host:

 

Damage and control

The strawberry tree is grown as an ornamental tree, and the fruits may be used to make preserves.

The strawberry tree aphid is one of the very few pests of this tree, but there is little evidence it causes serious damage.

Acknowledgements

We especially thank Middle Farm, East Sussex  for their kind assistance, and permission to sample.

Our particular thanks to Roger Blackman for images of his clarified slide mounts.

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

  • Barjadze, S. et al. (2014). Note on Wahlgreniella nervata (Gillette, 1908) (Hemiptera: Aphididae): a new pest of Damask rose in Turkey. Phytoparasitica 39 (3), 239-241. Abstract 

  • Blackman, R.L. (2010). Aphids - Aphidinae (Macrosiphini). Handbooks for the identification of British insects 2(7). Royal Entomological Society, London.

  •  Blackman, R.L. & Eastop, V.F. (1984). Aphids on the world's crops: an identification guide. J. Wiley & Sons, Chichester, UK.

  • Joshi, S. et al. (2014). Wahlgreniella nervata (Hemiptera: Aphididae), a new pest of rose in India. Florida Entomologist 97 (1), 162-167. Full text