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Identification & Distribution:

Wahlgreniella nervata apterae are spindle-shaped and yellowish or green, sometimes mottled with reddish anteriorly. 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.

Parthenogenetic populations on both Arbutus and Rosa have been introduced into Europe, and are treated as two separate subspecies (Wahlgreniella nervata arbuti & Wahlgreniella nervata nervata). They are shown below:

  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. The typical green form and the reddish form shown below were both found on Arbutus (strawberry tree) in UK.

  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. On rose (Rosa), but in culture able to live on Arbutus. An adult aptera and an alate are shown below.

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. In Europe the strawberry tree form Wahlgreniella nervata arbutiis also found on bearberry (Arctostaphylos) and occasionally crowberry (Empetrum nigrum). The form feeding on rose Wahlgreniella nervata 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

In UK we have found Wahlgreniella nervata several times on strawberry tree (albeit always the same strawberry tree), but only once on rose. They carry on reproducing parthenogenetically right through winter if the weather is not too extreme. The third and fourth instar nymphs shown below were found in late January.

By early February 2017 some of these had matured to adults, and were producing first instar nymphs (see picture below).

Colour

Most apterae seem to be a yellowish green, but a few are mottled with reddish anteriorly.

Certainly on strawberry tree the red colour may improve crypsis for the aphids.

 

Natural enemies

Later in the year predators such as syrphid larvae are often 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.

 

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 the tree, but there is little evidence it causes serious damage.

Acknowledgements

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 

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