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Pseudoregma is a genus of medium-sized wax-tufted / wax-dusted Cerataphidini (horned aphids). Their only known primary hosts are snowbells (Styrax spp.). Their secondary hosts are bamboos / grasses, or ginger (Zingiberaceae). DNA analysis shows Pseudoregma are most closely related to Ceratovacuna (which are paraphyletic), followed by Astegopteryx. Together with Ceratoglyphina and Chaitoregma, these 5 genera form a monophyletic clade which induce peculiar, multiple-cavity galls (albeit those of many species, and all Chaitoregma, are unknown). Prior to the early 1950s many cerataphidine species on the primary host were grouped as genus Astegopteryx while those on the secondary host were assigned to genera Cerataphis, Ceratovacuna & Oregma. A number of these species were subsequently synonomized &/or moved to sister genera, and Oregma was replaced by Pseudoregma. Published diagnoses of this genus (Doncaster, 1966, Noordam, 1991) are incomplete, referring only to apterae, alatae (sexuparae / viviparae) and nymphs of secondary host generations. Emigrant alatae and immature forms of a few species on the primary host have been described, but their apterae are remain undescribed. Gall emergent alatae have 5 antennal segments. ANT III is 0.96-1.15 times as long as ANT IV+V. The PT is short. ANT III, IV, V have 16-27, 7-15, 6-11 narrow secondary rhinaria, which almost encircle the antenna. Forward-pointing horns are absent or reduced to setae. Their siphunculi bear 3-7 setae. Abdominal tergites 7-8 are dusky and at least weakly sclerotized. Blackman gives a tentative key to alatae of 2 Pseudoregma spp. from Styrax - but suggests confirming any identifications using their host plant species and gall form.
Pseudoregma apterae on the secondary host have an oval-shaped body. The vertex of the head, and much of the thorax and abdomen, are covered with denticles. The head has two blunt, or sharp, conical frontal horns. The antennae are 4- or 5-segmented; when 4- segmented, segment III may have an incomplete division. The rostrum is short, not reaching the second coxae. Wax glands are present on the pro-, meso- and metathorax. The abdominal dorsum has numerous small dark scleroites bearing fine hairs, and large marginal sclerites, the latter sometimes fused with dorsal sclerites. The siphunculi are circular, slightly elevated on narrow sclerotic cones. Tergite VIII has a transverse sclerotic patch and several long fine hairs, and the cauda is transversely elongate with a knob. The anal plate is bilobed. There are few differences between Pseudoregma and Ceratovacuna apterae: Pseudoregma are said to have two pleural grooves on their pronotum, separated by a median ridge, while Ceratovacuna species have no obvious pleural grooves. Unfortunately this morphological characteristic varies within and among species. Wax glands have also been used, but their development in Pseudoregma varies with colony age and degree of alatiformity. Blackman gives a key to aphid apterae on bamboos.
Pseudoregma alatae on the secondary host may or may not have short horns on the head. Their antennae are 5-segmented, 0.32-0.50 times as long as the body. Antennal segments III-V bear ring-shaped secondary rhinaria. The apical rostral segment 0.58-0.89 times as long as the second hind tarsal segment. The fore wing has the medial vein once branched, and the hind wing has 2 oblique veins. The siphunculi have postsiphuncular sclerites. Tergites VII and VIII have transverse dorsal sclerites. The cauda is knobbed, and the anal plate is bilobed.
Pseudoregma, like many other gall-forming Cerataphidini on their primary host (Styrax spp.), produce sterile second-instar soldiers which clean the galls and defend using their stylets. Pseudoregma (other than one unnamed species) are exceptional in having large sterile first-instar pseudoscorpion-like soldiers in exposed colonies on their secondary hosts. All apterous secondary host forms of Cerataphidini use their horns to butt colony mates, but these horns are piercing weapons in Pseudoregma and Ceratovacuna (alatae and primary host forms have reduced horns, or setae). Two Ceratovacuna species also produce first-instar soldiers, but their primary hosts are unknown and they may be misclassified Pseudoregma species. Other aphids produce defensive nymphs but they are not, or are only partly, sterile. Primary host nymphs have setae instead of horns (first-instar nymphs on both hosts also lack siphunculi). Second instar soldiers have sclerotized tergites, longer setae & claws, protruded siphunculi, and one or more pairs of spine-like setae on the frons. Their forelegs are thickened, as are those of first-instar soldiers produced on the secondary host.
Genus Pseudoregma has perhaps 12 species. Of these Pseudoregma koshunensis, Pseudoregma nicolaiae, Pseudoregma sundanica and the Pseudoregma bambucicola/carolinensis species group appear very closely related. The primary hosts of Pseudoregma species are currently only known for 4 species: Pseudoregma carolinensis galls Styrax benzoides, Pseudoregma sundanica galls Styrax paralleloneurus, Pseudoregma bambucicola and Pseudoregma koshunensis gall Styrax suberifolius. As is the case with aphids of genera Astegopteryx and Ceratoglyphina, these Styrax spp. are all from series Benzoin of section Valvatae, and are evergreen trees occurring in Southeast Asia (Aoki & Kurosu, 2010). Secondary hosts include several bamboos (e.g. Bambusa, Dendrocalamus), grasses (e.g. Andropogon, Eragrostis and ginger (e.g. Elettaria, Etlingera). Sexuales are tiny, apterous, with a short rostrum. Oviparae lay one egg. Most species are restricted to south-east Asia, but as is common among host alternating species, their secondary host generations are more widespread and may be anholocyclic. Pseudoregma panicola (on grass) has a near pan-tropical distribution - having been found in Africa, India, east and south-east Asia, Australia and New Zealand. Pseudoregma sundanica was recently introduced to Australia.
Pseudoregma bambucicola (Bamboo woolly aphid)
Pseudoregma bambucicola induce galls from developing flower buds on their primary host, Styrax suberifolius. Each gall consists of a small central gall from which extend clusters of brown, elongate pod-shaped subgalls (see first picture below) (cf. subgalls of Pseudoregma sundanica on Styrax paralleloneura, which are velvety-white with green internal projections). The subgalls have petiolate bases and osteoles (apical openings) (cf. subgalls of Pseudoregma koshunensis on Styrax suberifolius, which lack a distinct petiole). Also their walls are thinner and softer than those of Pseudoregma koshunensis. The subgalls do not have a clearly marked longitudinal suture (cf. Pseudoregma carolinensis subgalls on Styrax benzoides, which have a conspicuous longitudinal suture). Field-collected Pseudoregma bambucicola galls have 1-15 subgalls, depending upon how many are lost. Each subgall is 24-43 mm long and 5.5-8.9 mm wide.
First image above by permission, copyright Aoki & Kurosu, all rights reserved.
Pseudoregma bambucicola may host alternate between Styrax suberifolius and bamboo, or it may persist anholocyclically on bamboos whether or not the primary host is present. Colonies are usually formed on the culms or twigs. Pseudoregma bambucicola sexuales are produced on the primary host where it is available, but over much of their range it is not. Sexuales are tiny, wingless, with a short rostrum and are produced by sexuparae originating either from either primary or the secondary host. After mating, oviparae lay a single egg. Studies have indicated that Pseudoregma bambucicola is found in Japan (anholocyclic populations only), China (Guizhou Province, Zhou et al., 2020), Taiwan, Hong Kong and northern Vietnam. This contrasts with the more southerly distribution of Pseudoregma carolinensis, which is found in Thailand, Malay Peninsula, Java, Irian Jaya and Micronesia. The identity of those in India, Sri Lanka and Fiji is unconfirmed.
Pseudoregma carolinensis (Southern bamboo woolly aphid)
Fundatrices of Pseudoregma carolinensis induce "fresh green"-coloured galls on their primary host, Styrax benzoides. The mature gall comprises a cluster of petiolate rolled sub-galls formed from a flower bud (see picture below) (cf. Pseudoregma bambucicola, which forms galls on Styrax suberifolius that are smaller and flatter, with beak-like apical extensions; and cf. subgalls of Pseudoregma sundanica on Styrax paralleloneura, which are velvety white with green internal projections). The Pseudoregma carolinensis gall is one of the smallest multiple-cavity galls of ceraphidines, with 2-10 subgalls, each subgall being 4-6.9 mm wide and 12-24 mm long (excluding the apical hairlike projection). The subgall outer surface is almost smooth, with a short hairlike projection at the end. Towards the apex there is long slit or suture with several small osteoles (cf. Pseudoregma bambucicola, which has no longitudinal suture). At the base of each subgall cluster there is a fringe of several, shorter, needle like projections. Each gall contains 50-1500 aphids, of which 21-66% are soldiers (described below). Gall production probably varies according to the local rainy season, but their inhabited duration is unlikely to exceed a year.
Images above copyright Aoki & Kurosu (2010) under a creative commons licence.
Images above copyright Aoki & Kurosu (2010) under a creative commons licence.
In August Pseudoregma carolinensis host alternate from their galls on Styrax benzoides to their secondary hosts bamboo, especially Bambusa and Dendrocalamus species. Where the primary host is available, alate sexuparae (containing hornless dimorphic embryos) return to it in November-December where they produce sexuales - tiny, apterous males and females with a short rostrum. After mating, oviparae lay a single egg. Some populations are anholocyclic and continue with parthenogenetic reproduction on bamboos all year. Secondary migrants also occur on bamboos - these viviparous alatae disperse between bamboo plants (such secondary migrants are not known from Pseudoregma bambucicola). Pseudoregma carolinensis has a more southerly distribution than Pseudoregma bambucicola, being found in Thailand, Malay Peninsula, Java, Papua (Irian Jaya) and Micronesia.
Pseudoregma panicola (Grass soldier aphid)
Pseudoregma panicola are only known from what are presumed to be their secondary hosts, where they reproduce entirely parthenogenetically. They live in dense wax-covered colonies on many species of grasses in the southern hemisphere (see first picture below). Adult apterae (see second picture below) are oval-shaped brownish black or brownish red-violet, with dark antennae and pale legs. The front of the head has a pair of short forward-pointing conical 'horns' with rounded tips sited between the antennal bases. The antennae have 4 or 5 segments. The apical rostral segment is 0.58-0.63 times as long as the second hind tarsal segment. The head and prothorax are fused. The sclerotised areas of cuticle are warty, particularly at the posterior margin of the prothorax (cf. Ceratovacuna spp., where those areas are smooth or wrinkled, not warty). Spinal and marginal wax glands are often present on all or most tergites. The siphuncular pores are slightly raised on dusky or dark-pigmented cones, with a few surrounding hairs (cf. Ceratovacuna, where these pores lack raised cones or surrounding hairs). The body length of adult Pseudoregma panicola apterae is 1.1-1.9 mm.
Images above by permission, copyright Nicholas A. Martin, Plant & Food Research.
Pseudoregma panicola alatae (see third picture above) are black with or without some dusting of wax. The pterostigma of the fore wings is greyish black. The frons has two short 'horns' with rounded tips. The antennae are 5-segmented. Antennal segment III bears 16-24 secondary rhinaria, segment IV has 6-9 and segment V has 4-11. Like other Pseudoregma, these are eusocial aphids. Larvae of the apterae exist as two types - one of which develops into adults, and the other into a defensive 'soldier' form. These soldier forms are 'pseudoscorpion-like' nymphs with elongated legs and prominent pointed horn-like projections on the frons, and their fore legs are more sclerotic and sturdy. These soldiers attack by butting and gripping with their forelegs. Specialized 'horned soldiers' on the secondary host are unique to Pseudoregma, and perhaps half of the Ceratovacuna species.
Pseudoregma panicola is found on many genera and species of tropical grasses including beard grass (Andropogon spp.), lovegrass (Eragrostis spp.), large-leaf bamboos (Indocalamus spp.), basket grass (Oplismenus spp.), panicgrass (Panicum spp.) and foxtail grass (Setaria spp.). They feed on the undersides of the leaves, stems and inflorescences. Sexual forms are not known, and populations are assumed to be anholocyclic. Pseudoregma panicola has a wide distribution in the southern hemisphere from Africa, southern India, east and south-east Asia to New Zealand and Australia. Their primary host, assuming it exists, is presumably an Asian Styrax species, upon which they make galls.