Acanthococcus aceris Signoret

Gavrilov, Ilya A., 2010, Descriptions of two new species of Pseudococcidae (Homoptera: Coccinea) and additions to the scale insect fauna of Bulgaria, Zootaxa 2635, pp. 32-40 : 38-39

Acanthococcus aceris Signoret

Eriococcus melnikensis Hodhson & Trencheva, 2008 . syn. nov. К 569, Bulgaria, Osogovo Mts., about 10 km S of Kustendil, flank of the mountain road, on twigs of Quercus sp., 22. VI.2008. Additionally 29 adult females from different localities in Germany, Poland, Ukraine and Russia.

Notes. Recently, a new species Eriococcus melnikensis Hodgson & Trencheva (2008) , similar to A. aceris , was described from Bulgaria. Unfortunately, the diagnosis of the new species in the original description did not include a comparison of the adult females with those of A. aceris . Moreover, the description of A. aceris in Hodgson & Trencheva (2008) is very brief in comparison with huge description of the new species and was based on the short description by Williams (1985) and several females collected from one population in Padova ( Italy). The two characters used by Hodgson & Trencheva (2008) for the separation of these two species were included in the key only (p. 37, l.c.). These two characters were:

1) A. aceris , in contrast to A. (Eriococcus) melnikensis , has setae on antennal segment III. However, there is no enlargement of the antennae in the figure of A. aceris (Fig. 11, page 29, in Hodgson & Trencheva). Based on material preserved in Zoological Institute, St. Petersburg, and on descriptions by Borchsenius (1949) and Williams (1985), A. aceris can have 6 or 7 segmented antennae. When a female has 6 segments, segment III is rather long and bears 2 or 3 setae on its distal part. However, segment III is often more or less divided in two parts and then the new! segment III has no setae, because these remain on the new segment IV. It is well known, that the division or fusion of antennal segments often occurs in scale insects and sometimes a female can have different numbers of segments on two her antennae.

2) A. melnikensis has “ventral medium-sized macrotubular ducts only present submarginally, mainly on head and posterior abdominal segments” in contrast to A. aceris , which has “ventral medium-sized macrotubular ducts present medially on most abdominal segments”. However, in the figure (Fig. 7, p. 18, l.c.), only two sizes of ducts are enlarged. Moreover, the description of the new species does not include the size of these ducts; it is written (p. 14) that they are “slightly smaller” than the large ones. In the description of A. aceris (p. 28, l.c.), the sizes of the ducts are not mentioned at all.

In the description of A. aceris by Williams (1985), the medium-sized ducts are "... not numerous [and are present], in more or less single rows on abdominal segments and around submargins to head". So, there is no significant difference in this character even in the descriptions of A. aceris and A. melnikensis . Based on a study of material in St Petersburg of A. aceris from different localities, these two species appear to be identical. Unfortunately, this is not surprising because the distribution and number of ducts (or pores) varies very significantly in many scale insect species, especially in widely distributed common species, such as A. aceris Signoret.

Differences were also noted by Hodgson & Trencheva (2008) between first-instar larvae of these two species – in particular, the size and form of the spinose setae. These differences were based on a study of 3 larvae from one population of each species. As the variation of morphological characters in the larvae of scale insects has not been well studied, it is not known what the differences between larvae from different localities, different host plants, etc are likely to be significant. Until there is a clearer understanding of this variation, their taxonomic significance is unknown. Therefore, based on the above mentioned comments, I consider that A. melnikensis is a new junior synonym of A. aceris .