Pulvinaria rhododendri Kahrer & Hodgson, 2024

Kahrer, Andreas & Hodgson, Chris J., 2024, A new species of the soft scale insect genus Pulvinaria Targioni Tozzetti (Hemiptera: Coccomorpha: Coccidae) on Rhododendron spp. in Northern Europe, Zootaxa 5512 (2), pp. 233-239 : 234-238

Pulvinaria rhododendri Kahrer & Hodgson sp. nov.

( Figs 1–3 )

Material examined. Holotype: DENMARK: Fundort ; Hadsund Syd dk # Biotop : garden # Wirt : Rhododendron sp. # Funddatum : 25.05.2023 # leg: Overgaard # präpariert: Kahrer 2024 # gem. Malumphy —2008 # in Canada Balsam. # Präparat AK-4244/01 (1/ 1 adult female, in good condition, NHMW).

Paratypes: collection data as for holotype # AK-4244/02–AK-4244/06 (5/ 5 adult females; fair-good, NHMW; and 12/ 12 adult females, good, 3 deposited in each of NHML, MNHN, ELKU and ZIAS) .

Non-type slides: NORWAY: Arendal , on Vaccinium myrtillus , 14 th, 21 st and 30 th June, 2022, I.-L. Fonneland coll. (5/ 5 adult females, 3 L1, fair to good, NHMW); Grimstad, on Rhododendron spp. , 29 th and 30 th June 2023, I.-L. Fonneland coll. (2/ 2 adult females, fair to good, NMHW) .

Description of adult female

Live appearance. Adult female pale yellowish green ( Fig. 1 ), covered in a thin coating of white wax strands; body subcircular to oval. Ovisac white, fairly convex, with slight ridges (many transverse and 1 longitudinal), up to 10 mm long or more.

Slide-mounted adult female ( Fig. 2 ) [Data taken from 6 specimens] Body elongate oval, with shallow stigmatic clefts, and an obvious anal cleft about 1/7th of body length; probably not very convex in life, 2.23–3.30 mm long and 1.50–2.45 mm wide.

Dorsum. Derm membranous throughout but each pore or duct associated with thinner derm. Setae spinose and conical, of 2 sizes: (i) setae each about 8–12 μm long with a basal socket about 5 μm wide, frequent throughout apart from a broad medial band, where replaced by large conical spinose setae; and (ii) large conical spinose setae, mostly each about 10–16 μm long with basal socket about 8 μm wide, but those at anterior end becoming narrower; distributed more-or-less in a medial band from anal plates to head, distribution suggesting a possibly segmental arrangement; with small groups on meso- and metathorax; total number of setae highly variable, approximately 5–20. Preopercular pores closed, each slightly convex with a granulate surface and about 5 μm wide, forming a group of 20–37 anterior to anal plates. Tubular ducts, each with a rather narrow outer ductule about 13 μm long and with no inner ductule, frequent throughout. Microducts each with a narrow inner filament, abundant, scattered throughout. Simple pores each significantly larger than a microduct, with a strongly sclerotised rim about 3 μm wide and without an inner filament; present in sparse medial band between large conical spinose setae. Dorsal submarginal tubercles small, each about 8 μm wide; number present highly variable, with 1–4 on each side of abdomen, 0 or 1 on each side of thorax and 0 or 1 on head (no specimen had a total of 0). Anal plates together quadrate; anterolateral margin straight or slightly concave, posterolateral margin slightly longer and convex; combined width of plates 150–166 μm; each plate 133–152 μm long, with 4 long setose setae, approximately subequal in length, each 23–35 μm long. Ano‑genital fold with 2 pairs of long setae, inner pair 40–50 μm long, outer pair 55–60 μm long, and with 2, occasionally 3 shorter lateral margin setae on each side. Anal ring broad, bearing 6 setae, each about 175 μm long.

Margin. Marginal setae long, each 30–40 μm long, with a slightly broadened fimbriate apex: numbering 36– 57 between anterior stigmatic areas and, on each side, with 10–21 between stigmatic areas and 28–48 on abdomen. Stigmatic clefts shallow, each containing 3 (one with 4) stigmatic spines, medial spine much the longest; lateral spines conical, each 20–25 μm long; median spines with more parallel sides and generally with a curved apex, each 70–75 μm long. Eyespot small, situated on margin, with lens about 12 μm wide.

Venter. Derm membranous. Pregenital disc‑pores each 7–9 μm wide, mostly each with 7 loculi (occasionally 6, 8 or 9); present around genital opening and across all preceding abdominal segments, as follows (on each side): segment VII about 50, extending posteriorly almost half-way down each side of anal cleft; VI, 10–22; V, 10–15; IV, 12–17; III, 5–13, and II with 1–5 positioned just postero-laterally to each metacoxa. Spiracular disc-pores mostly each with 5 loculi, present in bands up to several pores wide near each spiracle; with a few pores extending medially, latter pores clearly larger, often each with 6 or 7 loculi; with 26–44 pores in each band. Ventral tubular ducts of 3 types: Type I: a large duct with inner and outer ductules both broad and about equally long (outer ductule 13–17 μm long), with a well‑developed terminal gland, present medially in head (extending anteriorly to between antennae), thorax and anteriormost 2 abdominal segments; Type II: a duct with a moderately long outer ductule (13–17 μm long) but inner ductule either narrow and quite long with a well‑developed terminal gland, or almost filamentous without a terminal gland, present medially in more posterior abdominal segments and extending laterally and posteriorly on abdomen, intermixed with marginal band of type (iii) ducts; and Type III: a small duct with a short outer ductule (6–7 μm long), a very short or no inner ductule and no terminal gland, present in a submarginal band from anal clefts to just posterior to anterior spiracular disc-pore band, submarginal band narrow anteriorly, becoming broader posteriorly. Ventral microducts sparsely present throughout. Preantennal pores present. Ventral setae: with a pair of long pregenital setae on each of segments VII, VI and V, each seta 115–175 μm long; with 5‒10 pairs of inter‑antennal setae, longest about 170 μm long; other setae sparse but submarginal setae relatively strong, almost spinose, each 16–30 μm long, numbering 6–8 between stigmatic clefts on each side. Spiracles normal; width of peritremes: anterior 46–62 μm, posterior 48–68 μm. Legs well developed, each with a distinct tibio‑tarsal articulation and articulatory sclerosis; claw without a denticle; claw digitules similar and broad; tarsal digitules slender, longer than claw digitules and capitate. Hind leg dimensions: coxa 200–230 μm; trochanter + femur 275–300 μm; tibia 200–280 μm and tarsus 95–130 μm. Antennae each 7 or 8 segmented; third segment longest, with a pseudoarticulation when 7 segmented, total antennal length 435–495 μm; setal distribution on 8‑segmented antenna: segment I with 3 hair‑like setae (hs); II with 2 hs; segment III with 1–3 hs; IV with 0–2 hs; V with 3 hs; VI with 1 fleshy seta (fs); VII with 1 fs + 1 hs; and VIII with 3 fs + 6 hs. Clypeolabral shield 180–193 μm long. Labium with 4 pairs setae.

Comments. Pulvinaria rhododendri Kahrer & Hodgson , sp. nov. is very similar to P. floccifera and P. camelicola but differs from both (and all other Pulvinaria species) in having the following combination of character-states: (i) a medial band of large conical spinose setae extending from the anal plates anteriorly onto the head; and (ii) simple pores with a strongly sclerotised rim present in a narrow medial band between the large conical spinose setae. It also differs from P. floccifera in having (character state of P. floccifera in parenthesis) type III tubular ducts present submarginally between the lateral stigmatic clefts (absent).

Etymology. This species is named after the plant genus on which it has been most frequently collected, namely Rhododendron L. The species epithet is a noun in apposition, borrowed from ancient Greek in the genitive case.

Discussion. Pulvinaria rhododendri Kahrer & Hodgson has been collected from Rhododendron spp. in Denmark and Norway; also, from Vaccinium myrtillus L. ( Ericaceae ) in Norway, but only when Rhododendron spp. was present nearby (Inger-Lise Fonneland, pers. comm.). In Denmark, it has been found in two gardens, namely on the mainland in Hadsund Syd, Jutland, and in Tyfelse on the island of Zealand, 25 km southwest of Copenhagen. These gardens are perhaps about 150 km apart. In Norway, P. rhododendri has been collected from Arendal and Grimstad on the south coast, some 250 km north of Jutland, Denmark. Thus, currently, the species is only known from a small area of northern Europe. The species was probably first noted on Rhododendron spp. in Norway in 2018, causing a heavy infestation of sooty mould (Inger-Lise Fonneland, Norway, pers. comm.). These plants were destroyed but the population seems to have persisted as specimens were collected in the same location in 2022. Thus, it seems extremely probable that I.L. Fonneland’s first discovery refers also to P. rhododendri and, as it is still present, it is clearly established and can overwinter under northern European conditions, having survived the intervening two winters (Bodil Damgaard, Denmark, 2024, pers. comm.). To date, no geographic surveys have been carried out to determine the wider distribution of the species; it could be more widespread because cultivated Rhododendron spp. are popular plants and are frequently moved about in the plant trade. The species could be potentially important as a pest of urban plants, particularly Rhododendron spp. , based on the distribution mentioned above. In the field ( Fig. 1 ), the new species is somewhat similar in appearance to P. camelicola , for which it may have been mistaken by non-entomologists in the past. At present, P. rhododendri has only been recorded on bilberry ( Vaccinium myrtillus L.) and Rhododendron spp. (both Ericaceae ).

Damage. Pulvinaria rhododendri , like other Pulvinaria species, produces copious honeydew, so sooty mould growths are a major problem, forming an unsightly, thick layer that covers the leaves ( Fig. 3 ). However, so far it does not appear to cause host die-back or other problems (Bodil Damgaard, pers. comm.).

Figures

FIGURE 1. Young adult females and late-stage nymphs of Pulvinaria rhododendri Kahrer & Hodgson, sp. nov. on Rhododendron repens ‘Scarlet Wonder’. Photograph by Inger-Lise Fonneland.

FIGURE 2. Pulvinaria rhododendri Kahrer & Hodgson, sp. nov., adult female.

FIGURE 3. Leaves of Rhododendron x yakushimanum ‘Percy Wiseman’ covered in sooty mould and with some Pulvinaria rhododendri Kahrer & Hodgson, sp. nov. on the twigs. Photograph by Inger-Lise Fonneland.