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Hormaphidinae : Cerataphidini : Pseudoregma bambucicola
 

 

Identification

Taxonomy

Pseudoregma bambucicola is a member of the bambucicola / carolinensis group of aphids which typically host alternate from galls on Styrax to bamboo. The two species within the group, Pseudoregma bambucicola and Pseudoregma carolinensis were differentiated using molecular techniques by Fukatsu et al. (2001). Since then several extremely similar species feeding on bamboo have been synonomized with Pseudoregma bambucicola. These include Pseudoregma albostriata, in Taiwan, described as having four longitudinal wax stripes in life, not three as in Pseudoregma bambucicola; and Pseudoregma carolinensis, which has greater sclerotisation of the dorsum. Aphids which have in the past identified as bambucicola also occur in India, Sri Lanka and Fiji. Fukatsu et al. (2001) suggest they are Pseudoregma carolinensis, but Blackman thinks they may represent a third (unidentified) species.

Other closely related Pseudoregma species are Pseudoregma koshunensis, which also host alternates to bamboo, and Pseudoregma sundanica, which has ginger (Zingiberaceae) as its secondary host. Species in other closely related genera which gall Styrax and host alternate to bamboo include Astegopteryx bambusae and Cerataphis bambusifoliae. The Styrax gall-dwelling Pseudoregma bambucicola was originally named Astegopteryx swinhoei, whilst the secondary host dwellers were named Oregma bambucicola. When they were recognised as different life stages of the same species, these were renamed Pseudoregma bambucicola.

Primary host

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, and are smaller). 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.

Image above by permission, copyright Aoki & Kurosu, all rights reserved.

At maturity each gall contains 280-1500 aphids, 23-41% of which are soldiers (described below). First-instar fundatrices, which feed on a developing flower bud, have well-sclerotized tergites with long hairs, well-developed hairs on the tarsi and a long slender ultimate rostral segment. The second instar, by then enclosed by plant tissues, has membranous tergites and a shortened rostrum. The adult fundatrix enclosed in a gall is apterous, with membranous tergites and no siphunculi. The gall surrounding the fundatrix develops subgalls which her first-generation nymphs (but not her) move into, mature and reproduce for a number of generations. The subgalls are then sealed off, and the main gall may open revealing the fundatrix. Any further first-generation nymphs cannot enter the sealed subgalls, and presumably do not survive to maturity, but may defend the gall. Adults maturing after the second generation are generally larger and have siphuncular pores. As subgalls develop further, they open at their distal end to permit egress of soldiers which eject honeydew balls and exuviae and repel some but not all uninvited guests. Some first instars leave their parent gall and move to others.

Whilst the galls (see above) and emigrant alatae (see below) are readily distinguishable from those of other Pseudoregma species which also form galls on trees of the Styrax genus (series Benzoin), the gall-dwelling adults of these species being 'very similar' are usually ignored. Thus, whilst Tao (1969) showed an antenna, the aptera was not otherwise described. This is frustrating since alatae are only produced when the gall matures - which is by no means assured for galls once collected from the field!

Image above copyright Tao (1969).

The colour of live gall-dwelling Pseudoregma bambucicola apterae is unknown, albeit presumably waxy. The adult aptera (hitherto undescribed) has 4-segmented antennae which are 0.18 times the body length and have a terminal process that is 0.44 times the base of the last antennal segment (cf. Pseudoregma carolinensis, which has 5-segmented antennae and a terminal process 0.35 times the base of the last antennal segment). The eyes of apterae and young nymphs have only 3 ommatidia. There is a pair of forward-pointing horn-like processes on the front of the head, much smaller than on the secondary host apterae. The apical rostral segment (RIV+V) is 0.067 mm, and 0.75 times the second hind tarsal segment (HTII) (cf. Pseudoregma carolinensis, where RIV+V is 0.09 mm and 0.89 times HTII). The abdominal segments appear unsclerotized (cf. Pseudoregma carolinensis, where areas around the siphuncular pores are distinctly sclerotized). The cauda is knobbed, and the anal plate bilobed (both are upturned in the image below). The body length of the adult aptera is 1.37 mm (cf. Pseudoregma carolinensis, where it is 1.20 mm). Please note that for each species these measurements are currently from the clarified mount of one specimen (see below).

Image above by permission, copyright Aoki & Kurosu, all rights reserved.

First instar nymphs have the front femora stouter than other femora, and setae on the basal tarsal segments which are similar to those of the adults. They have 2 pairs of spines on the frons, which are shorter in later instars. Normal first-instars which develop to adult apterae have 4-segmented antennae, those destined to become soldiers in their second instar have 5-segmented antennae. Soldier morphs do not progress beyond their second instar, and are hence sterile. Unlike normal second-instars, these soldier forms have thickened forelegs, sclerotized tergites with longer setae, longer claws, protruded siphunculi, and pairs of spine-like setae on the frons. Second instar soldiers attack via their stylets (cf. first instar sterile soldiers on the secondary host, which use their horns).

The emigrant alatae (and nymphs) of Pseudoregma bambucicola were described by Takahashi (1936) as Astegopteryx swinhoei and shown by Aoki & Kurosu (1992) to be the gall-dwelling stage of Pseudoregma bambucicola. Winged viviparae from the primary host (emigrant alatae) have the head broadly rounded on the hind margin, with about 40 rather short dorsal hairs. The antennae are long, with 23-27 annular secondary rhinaria on segment III, 13-15 on segment IV and 8-11 on segment V. The rostrum reaches beyond the first coxae. The wing veins are stout, the first and second obliques on the front wing a little curved, united basally, the third oblique nearly as stout as the second. The legs are slender with many hairs; the hind tarsi have two very long hairs on the basal segment. The abdomen is thickened and dusky on tergites VII & VIII, and around the bases of hairs on tergite VI. The siphunculi are small, and surrounded by 3-5 hairs. The cauda is broadly rounded , not constricted basally, much wider than long, and with about 18 long bristles. The anal plate is divided (bilobed), the lobes as wide as the cauda. Body length of the alate is about 2.0 mm.

Secondary host

Viviparous emigrant alatae migrate to the secondary host, bamboo, where they deposit nymphs. These first generation nymphs are all of the 'normal' type (not soldier forms). The head is completely fused with the prothorax. They have well-developed sharp frontal horns, bearing a number of minute hairs. Their antennae are 4-segmented, and the rostrum reaches the hind coxae. There are large granular sclerites on the thoracic and anterior abdominal tergites, and smaller sclerites on the posterior abdominal segments. Siphunculi are absent. The cauda and anal plate have one and two pairs of hairs respectively.

Subsequent secondary-host generations have 2 types of nymph, normal and soldiers.

  • Normal first instar nymphs have a soft cuticle and thin forelegs.
  • Soldier first-instars (see picture below of soldier of bambucicola / carolinensis group from India) are larger, have a sclerotized cuticle and a pair of sharp frontal horns and greatly enlarged forelegs. They clasp, for example a syrphid larva, with these thickened forelegs and pierce it with their sharp frontal horns. They differ from primary host soldiers, which are second-instar, smaller (0.8 mm vs. 1.2 mm), attack with their stylets and lack stout frontal horns.
In order to gain access to feeding sites all secondary host forms other than alatae (which have reduced horns) use their horns to butt opponents, including their kin.

Image above by permission, copyright Sunil Joshi & Poorani, J. Aphids of Karnataka (accessed 12/2/20).

The adult viviparous aptera of (putative) Pseudoregma bambucicola from Sri Lanka on bamboo is described by Doncaster (1966) (as Oregma bambusicola, see taxonomy above). In life they are grey-brown or dark purplish to greenish-brown or black, dusted with granular wax (see picture below of apterae of bambucicola / carolinensis group from India). Individuals in young colonies have three longitudinal rows (two marginal, one spinal) of white wax tufts, but in older colonies these are less developed and adults have a thick cushion of wax posterior to the siphunculi. The second picture below is a clarified mount of a confirmed Pseudoregma bambucicola adult aptera from bamboo.

First image above by permission, copyright Sunil Joshi & Poorani, J. Aphids of Karnataka (accessed 12/2/20).
Second image above by permission, copyright Aoki & Kurosu, all rights reserved.

The vertex of the aptera is covered with small denticles and the frontal horns are quite small, conical and sharp. Their antennae are 4-segmented, but with segment III showing an incomplete division about 0.67 of the length from the base. The rostrum is short, not reaching the second coxae. The pronotum is fused with the head and has two low swellings on each side of the median line also bearing denticles. The mesonotum has a pair of larger, more heavily sclerotized but less prominent denticulate (=small toothlike) swellings. The metanotum is almost covered by irregularly broken sclerotic areas covered with denticles. The abdominal tergites are more or less evenly covered with denticles, and bearing numerous small dark scleroites each bearing 1 or 2 hairs. The siphunculi are circular, slightly elevated on narrow sclerotic cones. Tergite VIII has a median transverse sclerotic patch. The cauda has 20 hairs and the anal plate is bilobed. The body length of the adult aptera is 1.5-2.6 mm.

The alate Pseudoregma bambucicola / carolinensis (see picture below of alate of bambucicola / carolinensis group from India) is greenish black, and the pterostigma of the forewing on the side of the subcosta is bordered with black. All alatae of Pseudoregma bambucicola from the secondary host described to date appear to be sexuparae, with no secondary migrants (alate viviparae) having been recorded. Instead first instar nymphs of this species often wander about, and can be dispersed via the wind to found new colonies or join existing ones.

Image above by permission, copyright Sunil Joshi & Poorani, J. Aphids of Karnataka (accessed 12/2/20).

Ant attendance

It is not known to what extent Pseudoregma bambucicola galls on the primary host are ant attended. (Pseudoregma carolinensis may be ant-attended on their primary host, but the relationship is more one of gleaning - cleaning ejected honeydew from around the gall - than of actively 'attending'; the ants are not attacked by the soldier aphids). Pseudoregma bambucicola colonies on the secondary host are variably ant attended. Continuously ant-attended colonies tend to remain small and have few soldiers, because the ants eat some soldiers and fewer are needed. Colonies that grow too large produce excessive honeydew; these may be abandoned by the ants and become larger still, with a large proportion of soldiers.

Summary & distribution

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 from 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.

 

Other aphids on the same host

Primary host

The only recorded primary host of Pseudoregma bambucicola is Styrax suberifolius.

Secondary hosts

Acknowledgements

We especially thank Shigeyuki Aoki (Professor Emeritus, Rissho University) and Utako Kurosu for sending us many of the images used on this page - and Aoki for his most helpful comments. We are also grateful to Sunil Joshi & J. Poorani for permitting us to use their images from Aphids of Karnataka.

We have used the keys and species accounts of Doncaster (1966), Noordam (1991), Aoki & Kurosu (1992), Fukatsu et al. (2001) and Aoki & Kurosu (2010) together with those of Roger Blackman & Victor Eastop in Aphids on Worlds Plants. We fully acknowledge these authors and those listed in the reference sections 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

  • Aoki, S. & Kurosu, U. (1992).. Gall Generations of the Soldier-producing Aphid Pseudoregma bambucicola (Homoptera). Jpn. J. Ent. 60(2), 359-368 Full text

  • Aoki, S. & Kurosu, U. (2010). A review of the biology of Cerataphidini (Hemiptera, Aphididae, Hormaphidinae), focusing mainly on their life cycles, gall formation, and soldiers. Psyche 2010, Article ID 380381, 34 pp. Full text

  • Doncaster, J.P. (1966). Notes on some Indian aphids described by G.B. Buckton. The Entomologist 99, 157-160.

  • Fukatsu, T. et al. (2001). Genetically distinct populations in an Asian soldier-producing aphid, Pseudoregma bambucicola (Homoptera: Aphididae) identified by DNA fingerprinting and molecular phylogenetic analysis. Mol. Phyl. Evol. 18, 423-433. Behavioural Processes 40(1), 75-83. Abstract

  • Noordam, D. (1991). Hormaphidinae from Java (Homoptera: Aphididae). Zool. Verh. Leiden 270, 1-525. Full text

  • Takahashi, R. (1936). Aphids of the genus Astegopteryx Karsch, with descriptions of new species from Sumatra and Formosa (Aphididae, Hemiptera). Proc. R. Ent. Soc. Lond. (B) 5(5), 96-102.

  • Tao, Charles Chia-Chu (1969). Aphid fauna of China. Science Yearbook of the Taiwan Museum. 12, 40-99.

  • Zhou, X. et al. (2020). Sequencing and characterization of the complete mitochondrial genome of Pseudoregma bambucicola (Hemiptera: Hormaphidinae) from Guizhou, China. Mitochondrial DNA Part B. (B) 5 (3), 3738-3740. Full text