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Wahlgreniella nervata

Strawberry tree aphid

On this page: Identification & Distribution Biology & Ecology Other aphids on the same host Damage & Control

Identification & Distribution

Wahlgreniella nervata apterae are spindle-shaped and yellowish or green sometimes mottled with reddish anteriorly . Their antennal tubercles have smooth divergent inner faces. The femora do not have distinctly dark apices. Their siphunculi are slightly swollen rather symmetrically about their inner and outer faces, and have dark tips and a small flange (cf. Macrosiphum euphorbiae and Macrosiphum rosae on rose, and cf. Aulacorthum solani on Arbutus, all of which have tapering, non-swollen siphunculi). The first two images below show Wahlgreniella nervata ssp. arbuti from strawberry tree (Arbutus). The second three images show Wahlgreniella nervata ssp. nervata from rose (Rosa).

Winged viviparae of Wahlgreniella nervata (see third picture above) have a green abdomen with variably developed dark dorsal cross-bands, sometimes coalescing into an irregular patch.

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

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

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

  1. Wahlgreniella nervata arbuti
    The apical segment of the rostrum (RIV+V) is longer than 1.3 times the length of segment two of the hind tarsus (HTII). The apterae in spring and summer are shining yellowish green. The aptera body length is 2.1-2.9 mm. This subspecies lives naturally on strawberry tree (Arbutus) and manzanitas and bearberries (Arctostaphylos), but in culture is able to live on rose.
  2. Wahlgreniella nervata nervata (=Wahlgreniella nervata sensu stricto)
    RIV+V is shorter than 1.3 times the length of HTII. The aptera body length is 1.4-2.5 mm. This subspecies lives naturally on rose (Rosa) and now also on Pyracantha, but in culture is able to live on strawberry tree.

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:

Life cycle

We have found both of the subspecies of Wahlgreniella nervata in Britain apparently living parthenogenetically on their respective hosts.

The immatures below are of Wahlgreniella nervata arbuti and were living on their presumed secondary host, strawberry tree.

Sampling over several years has confirmed that that strawberry tree populations in Britain continue 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.

Immature viviparae of Wahlgreniella nervata nervata were found on rose (their presumed primary host) in October 2017.

Then in in January 2019 we found flourishing populations of Wahlgreniella nervata nervata on roses in an East Sussex village.

In a Hampshire village, we also found Wahlgreniella on another host in the Rosaceae, namely Pyracantha (see picture below). As far as we can tell, Wahlgreniella nervata has not previously been recorded from Pyracantha.

Natural enemies

Natural enemies take a heavy toll of Wahlgreniella nervata. Several syrphid larvae (see first picture below) were found preying on populations on strawberry tree.

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

Another group of natural enemies is pathogenic fungi (e.g. Neozygites fresenii, Beauveria bassiana, Lecanicillium lecanii) which commonly attack and kill aphids. The fungus grows in the aphids haemolymph, soon killing the aphid.

Infected aphids become covered with a woolly mass of hyphae (see picture above). The fungus then sporulates and releases spores into the air to infect other aphids.

 

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.

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

  • 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