Didesmococcus unifasciatus

Didesmococcus unifasciatus (Archangelskaya) (Fig. 20, Plate 2D, distribution map Fig. 89L) Physokermes unifasciatus Archangelskaya, 1923: 265. Didesmococcus unifasciatus (Archangelskaya); Borchsenius 1953: 282. Didesmococcus megriensis Borchsenius, 1953: 282. Field characteristics: Live adult female circular, up to 4 mm long; dorsum highly convex, with a small marginal lip. Specimen preserved in alcohol brown with a pale brown pattern, sclerotized area around anal plates darker. Microscopic diagnosis: Slide-mounted adult female body oval to almost circular, with stigmatic clefts indistinct; anal cleft fairly short. Eyespots situated just dorsad to margin. Anal cleft of moderate depth. Dorsum. Derm with sclerotization mainly around anal plates and along posterior margin on either side of anal cleft. Setae of 2 types: (i) extremely long, fine setae present in 2 large groups, one just anterior to anal plates, other group situated near anterior margin on head; and (ii) much shorter setae, sparsely present throughout. Pores numerous, all bilocular. Preopercular-type pores circular, slightly convex, confined to both groups of long dorsal setae. Duct tubercles and tubular ducts absent. Anal plates together quadrate, each with 4 long setae towards apex. Anal ring bearing 6–8 setae. Margin. Marginal setae similar to type (ii) dorsal setae but shorter, numbering about 10−15 setae between anterior and posterior stigmatic clefts on each side. Stigmatic clefts shallow; stigmatic setae each quite stout, bluntly spinose, with a broad basal socket, longest exceeding a marginal seta in length; numbering about 10 setae in each cleft, but also present along margin between clefts and as far as eyespots anteriorly. Venter. Derm membranous. Pregenital disc-pores usually each with 9−11 loculi, abundant across all abdominal segments and frequent across meso- and metathorax, a few also present on prothorax and lateral to each metacoxa. Spiracular disc-pores variable in size, each with 4−13 loculi, present in very broad bands between each spiracle and margin, widest near margin and extending mesad beyond spiracle orifice. Ventral pores present. Tubular ducts absent. Three pregenital segments each with a pair of long setae; also a pair of long setae and a pair of small setae between antennal bases. Legs well developed, each without a tibio-tarsal articulatory sclerosis; claw with a distinct denticle; claw digitules both fine, but slightly stouter than tarsal digitules. Antennae each with 9 segments. Distribution: Didesmococcus unifasciatus is known from 11 countries in the Palaearctic region (García Morales et al. 2016); in Iran, it is found in Azarbaijan -e Sharghi, Hamadan, Kermanshah and Markazi provinces (Moghaddam 2013). Host-plants: The species has been recorded on host-plants mostly belonging to the family Rosaceae but there are also records on species in Moraceae, and Ulmaceae (García Morales et al. 2016). In Iran, it has been recorded on Amygdalus communis, A. lycioides and Persica vulgaris (Rosaceae) (Moghaddam 2013). Economic importance: Didesmococcus unifasciatus is one of the most important pests on trees in Iran, particularly on stone fruits. The species produces copious sugary honeydew, which promotes sooty mould growth. The sooty mould associated with heavy infestations of D. unfaciatus can kill plant shoots. Natural enemies: In Iran, D. unifasciatus is attacked by the parasitoid wasps (Hymenoptera) Coccobius annulicornis Ratzeburg and Coccophagus lycimniia (Walker) (Aphelinidae); Metaphycus pulvinariae (Howard) and Microterys cuprinus Nikol’skaya (Encyrtidae), and Pachyneuron muscarum (L.) (Pteromalidae) (Davoodi et al. 2004; Abolmasoumi et al. 2009; Golpayegani et al. 2010; Lotfalizadeh et al. 2014).