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Identification & Distribution

Adult apterae of Plocamaphis flocculosa (see first picture below) are grey or yellowish grey and are more or less densely covered with white wax. The head, antennae, legs and part of the thorax are dark. The mesonotum and metanotum and abdominal tergites I-IV have rather large, dark, paired dorsal sclerites. There are well developed marginal tubercles present on the prothorax and abdominal tergites I-IV, and often also on V. The siphunculi are bright orange, and have a swollen distal part, with an extremely small aperture in the end of the rounded apex. They are quite long at 0.8-1.1 times the length of the second hind tarsal segment (cf. Plocamaphis amerinae in which the siphunculi are only 0.4-0.5 times the length of the second hind tarsal segment). The body length of the adult Plocamaphis flocculosa aptera is 3.1-5.0 mm.

Images copyright Andy Brown,  all rights reserved.

The alate viviparous female lacks dark dorsal sclerites on the abdomen, the wing veins are bordered brownish and the siphunculi are more slender than in the apterae.

Four subspecies, distinguishable by the length of the siphunculi, have been recognised: the nearctic Plocamaphis flocculosa flocculosa and three palearctic subspecies Plocamaphis flocculosa brachysiphon, Plocamaphis flocculosa goernitzi and Plocamaphis flocculosa macrosiphon. These subspecies are of somewhat questionable validity given the wide range of variation within them. The pictures above show Plocamaphis flocculosa brachysiphon from Britain.

Plocamaphis flocculosa feeds on the trunk and branches of sallow (Salix caprea, Salix cinerea), black willow (Salix nigricans) and creeping willow (Salix repens) in Europe - and American pussy willow (Salix discolor) and arroyo willow (Salix lasiolepis) in North America. Oviparae and alate males of Plocamaphis flocculosa brachysiphon have been found in October. The large waxy willow aphid is found in Europe and North America, and has also been reported from China.

 

Biology & Ecology

Wax

Wax performs a number of functions for aphids. Kanturski et al. (2016)  noted that the whitish or greyish wax on Plocamaphis aphids makes colonies difficult to see, a point supported by Moss et al. 2006   who looked at predation by the salticid (jumping spider) Marpissa marina on the waxy apple aphid Eriosoma lanigerum.

Image copyright Andy Brown,  all rights reserved.

Experiments indicated that the aphid's wax covering functioned in part to hide prey-identification cues from vision-guided predators.

Population dynamics

Molnar (2003)  sampled willow-feeding aphid colonies on scattered trees (Salix alba) from April until November, in 1999. The collected individuals belonged to 9 aphid species of 3 families (sensu Heie: Lachnidae, Chaitophoridae, Aphididae). The aphid populations showed two peaks in May and in October. The indirect negative effect of the rainfall seems to be responsible for this temporal pattern. The Shannon diversity index also exhibited spring and autumn peaks during the year. The willow-feeding aphid guild varied seasonally, with different species dominant in each period. Four types of population dynamics were established for the nine species, based on the abundance changes. Tuberolachnus salignus  and Plocamaphis flocculosa brachysiphon were classified as being in the third type: those species present only in the autumn in the canopy of willows.

Image copyright Andy Brown,  all rights reserved.

Tuberolachnus salignus and Plocamaphis flocculosa are often present together in mixed colonies. The picture above shows a single adult Plocamaphis flocculosa (with orange siphunculi and wax) in amongst a large colony of adult and immature Tuberolachnus salignus.

 

Other aphids on the same host

Acknowledgements

We especially thank Andy Brown  for the photographs above.

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

  •  Kanturski, M. et al. (2016). Fundatrix of Plocamaphis flocculosa (Weed, 1891) (Hemiptera: Aphididae): a description. Acta entomologica silesiana 24, 1-5. Full text 

  •  Molnár, N. (2003). Population dynamics features of willow-feeding aphids. Acta Phytopathologica et Entomologica Hungarica 38 (1-2), 125-135. Full text 

  •  Moss, R. et al.. (2003). Mask of wax: secretions of wax conceal aphids from detection by spider's eyes. New Zealand Journal of Zoology 33, 215-220. Full text 

  •  Pérez Hildago, N. (2016). Primera cita de Plocamaphis flocculosa (Weed, 1891) (Hemiptera: Aphididae: Aphidinae: Macrosiphini) en la Peninsula Iberica. Arcquivos entomoloxicos 15, 25-28. Full text