﻿Demarchushsui (Coleoptera, Chrysomelidae, Galerucinae, Alticini), a new species from Taiwan, with notes on immatures and biology

﻿Abstract A new species of the little-known genus Demarchus Jacoby was discovered at Pilu, East Taiwan, and is here described as Demarchushsuisp. nov. The larvae and adults utilise showy mistletoes as food plants. Their remarkable biology is described in detail, including egg deposition and leaf mining behaviour. Their biology is compared with that of other members of the genus.


Introduction
Demarchus Jacoby, 1887 is a little-known flea beetle (Coleoptera, Chrysomelidae, Galerucinae, Alticini) with only three species described.The genus was proposed for D. pubipennis Jacoby, 1887 from Sri Lanka.A second species, D. javanus Bryant, 1941, was described from Indonesia.The third species, D. nigriceps Chen & Wang, 1988, was described from China.Odak et al. (1969) reported that D. pubipennis caused considerable damage to pigeon pea, Cajanus cajan (Linnaeus) (Fabaceae), in India.However, Mushtaque and Baloch (1979) observed that larval and adult D. pubipennis fed on leaves of Loranthus longiflorus Desr.(Loranthaceae) in Pakistan, but not pigeon pea, based on testing.Loranthus longiflorus is a species of showy mistletoes, a common name for members of the plant families Loranthaceae.Many members of both families are hemiparasites (Wikipedia 2023).Jolivet and Hawkeswood (1995) reported that Demarchus is the only chrysomelid genus whose members utilise Loranthaceae as a food source.Recently, Reid (2017) recorded that species of Cadmus (Cryptocephalinae) fed on a narrow range of families, Fabaceae, Myrtaceae, Loranthaceae, and Sapindaceae.Staines (2011) reported that members of Sceloenopla multistriata Uhmann (Cassidinae, Hispines) feed on Phoradendron sp.(Loranthaceae).Note that The Angiosperm Phylogeny Group (2016) placed Phoradendron within the Santalaceae.
Although the genus Demarchus had been redescribed by Maulik (1926), many diagnostic characters for genera proposed by Konstantinov andZooKeys 1177: 3-21 (2023), DOI: 10.3897/zookeys.1177.97854 Chi-Feng Lee & Jung-Chan Chen: Demarchus hsui Lee & Chen, a new species from Taiwan Vandenberg (1996) are still missing.Results of the current study include redescription of the genus, description of the new species, its immatures, and their remarkable biology.

Materials and methods
Dr. Yu-Feng Hsu, a butterfly taxonomist, discovered numerous chrysomelid leaf-miners on Taxillus rhododendricolus (Hayata) S.T. Chiu (Loranthaceae), at Pilushenmu (碧綠神木), east Taiwan, during late August 2020.However, rearing success in the laboratory was minimal, with only one adult reared from larvae.During the following year, many more larvae (~ 50) were brought into the laboratory for rearing.Eight adults were successfully reared from larvae but a further 18 adults were collected during late June 2022.This material was sufficient for a detailed taxonomic study.
For rearing studies, more than 50 larvae (see above) were placed in small glass containers (diameter 142 mm × height 50 mm) with cuttings from their host plants.When mature larvae began searching for pupation sites, they were transferred to smaller plastic containers (diameter 90 mm × height 57 mm) filled with moist soil (~ 80% of container volume).
For taxonomic study, five larvae collected from the type locality (see above), and the abdomens of four adults (two collected from the type locality, see above; two reared from larvae) were soaked in hot 10% KOH solution, followed by washing in distilled water to prepare genitalia for illustrations.Head and legs of larvae, and aedeagus, abdominal ventrites, spermatheca, and gonocoxae of adults were dissected from the abdomens, mounted on slides in glycerine, and studied and drawn using a Leica M165 stereomicroscope.For detailed examinations a Nikon ECLIPSE 50i microscope was used.Length of adults was measured from the anterior margin of the eye to the elytral apex, and width at the greatest width of the elytra.
The terminology for larval stages followed Ruan et al. (2020), and for the adult stage Konstantinov and Vandenberg (1996) and Furth (1988).
Exact label data are cited for all type specimens of described species; a double slash (//) separates different labels and a single slash (/) divides the different rows of data on a label. of abdominal ventrite V (Fig. 2I) with median, angular notch, internally covered by flattened sclerite.
Mature larvae.Length 9.5-9.6 mm, width 2.5-2.6 mm.Live specimens (Fig. 7E): body form elongate, flattened; pale yellow, head and legs blackish brown; prothoracic and abdominal tergite IX with large sclerotised patches; thoracic tergites with small, longitudinal, curved sclerotised patches at sides;  thoracic ventrites with small rounded sclerotised patches medially; lateral margins of meso-and metathoracic, and abdominal segments I-VIII expanding outwards, abdominal segments I-VIII each bearing one small process at lateral margins.body bearing tiny setae, the latter sometimes reduced to pores.Spiracles present on mesothorax and abdominal segments I-VIII (Fig. 3A).
Thorax.Prothorax: dorsum (Fig. 3B) with one pair of pores and two pairs of short setae at basal areas of sclerotised patches; two pairs of short setae near base halfway between sclerotised patches and bases of lateral process; three pairs of short setae at sides.Sternal region (Fig. 3D) with one small, sclerotised patch medially, two pairs of short setae at anterior and posterior parts of sclerotised patch respectively.Mesothorax: dorsal region (Fig. 3B) with pores and short setae arranged into two transverse rows, anterior row with two pairs of pores and one pair of setae, posterior row with four setae; lateral longitudinal, sclerotised patches bearing three short setae.Sternal region (Fig. 3D) with one very small, sclerotised patch, one pair of short setae and one pair of pores at anterior and posterior parts outside sclerotised patch.Metathorax: same pattern as mesothorax, except for absence of spiracle.Legs (Fig. 4F): five segments; trochantin (Tn) triangular, without setae or pores; coxa (Co) transverse, bearing several pores at basal half, and two short setae near apical margin; trochanter (Tr) triangular, lacking setae but with several pores; femur (Fe) small, with one long seta on mesal margin, and one small setae at inner face; tibia (Ti) enlarged at base decreasing toward apex, bearing seven short setae at apical 1/2; tarsungulus sclerotised, falciform, bearing one basal setae; pulvillus (Pu) bladder-like, as long as tarsungulus.
Abdomen.Segments I-VIII: dorsal region (Fig. 3C) lacking setae, pores arranged into two transverse rows, bearing three pairs of pores at anterior and posterior row respectively, and three pairs of pores on lateral process; sternal region (Fig. 3E) with pores arranged into three transverse rows, one pair of pores in anterior row, four pairs of pores in middle row, and two pairs of pores in posterior row, three pairs of pores on lateral process.Segment IX (Fig. 4G): pygidium moderately sclerotised; disc with pores arranged into two transverse rows, three pairs of pores in anterior and posterior rows respectively; three pairs of short setae along lateral margin.
Host plant.Loranthaceae: Taxillus rhododendricolus (Hayata) S.T. Chiu.Biology.Larvae are leaf miners of Taxillus rhododendricolus, which is a hemiparasite.More than 20 larvae (Fig. 5C-E) were collected from branches (Fig. 5A, B) cut from the host tree, Salix fulvopubescens Hayata var.fulvopubescens Hayata (褐毛柳) at a height of approximately six meters during late August 2020.Forest type is mixed coniferous, including Picea asperata Mast., Tsuga chinensis (Franch.)Pritzel ex Diels., and Cunninghamia konishii Hayata, with some evergreen broad-leaved and deciduous trees.During 2022, 18 adults were collected using sweep nets from the same plant on June 20 by Dr. Hsu (see types).Eight additional adults were collected from the host plant on trees of Carpinus rankanensis Hayata on July 13.Some other collecting trips were carried out during different months.These collecting events indicated that adults appear during June and July, egg masses during early August, and larvae only during late August and September, no life stages were found after October, and it is clear that D. hsui sp.nov. is an univoltine species.By contrast, populations of D. pubipennis in Pakistan are multivoltine, with up to four generations a year (Mushtaque and Baloch 1979).
Egg masses were deposited at some distance from each other on undersides of leaves (Fig. 6A).Females scratched the leaf surface several times (Fig. 6B) so that neonate larvae could burrow into the leaves easily.Then four or five eggs (Fig. 6C) were laid and covered by faeces.Usually only one larva hatched successfully from each egg mass (Fig. 6D) and began mining leaves.
Leaves of T. rhododendricolus decayed as soon as larvae constructed tunnels (Fig. 7A).Tunnels made by larvae were always transverse and turned towards the leaf apex (Fig. 7B, C).Larvae turned tunnels basally when conditions were not suitable to maintain the apical direction.Such a feeding pattern caused the entire leaf to decay from apex to base (Figs 5D, E, 6D, 7B).Larvae exited tunnels when conditions deteriorated and searched for more suitable leaves.They were able to tunnel into newly selected leaves and continue development (Fig. 7D).Mature larvae (Fig. 7E) emerged from tunnels and walked or fell to the ground, mainly falling when disturbed.They burrowed into soil and built underground chambers for pupation.
Adults on leaves of T. rhododendricolus were active during the day (Fig. 7F).They fed on the upper surface of leaves, leaving round feeding scars (Fig. 7B, E).
Remarks.Larvae of D. hsui sp.nov.exhibit unusual characters that are typical for leaf miners (Takizawa 2005), including flattened body and head, head with vertex incised in a U-or V-shape posteriorly, and body surface without setae or tubercles.Etymology.This new species is named for Dr. Yu-Feng Hsu (徐堉峰), who is a well-known butterfly expert and the first person to collect specimens.
Distribution.The new species is only recorded from the type locality --Pilu (碧 綠), in Hualien County, East Taiwan.It is located at 24°10'51.3"N,121°24'11.6"E,2150 m MSL, and protected by the Taroko National Park (太魯閣國家公園).This locality seems to be the biodiversity hotspot.The rarely collected chrysomeline Ambrostoma chinkinyui Kimoto & Osawa, 1995 is also only known from this locality (Kimoto and Osawa 1995), as well as multiple undescribed species (unpublished data).
Redescription.Body elongate rounded, head visible from above.Head (Fig. 8A) drawn into prothorax, hypognathous, broadly oval in frontal view; vertex large, covered with dense, coarse punctures and short setae; antennal calli rectangular, well separated from vertex by deep furrow, not separated from antennal sockets; antennal sockets large, distance between sockets smaller than diameter of socket, sockets separated by frontal ridge, not separated from eyes; frontal ridge triangular, anterior surface of frons convex, bearing short setae at the sides of frontal ridge; frontal area, including mouth region, not separated from genae; eyes small, convex, the longest diameter of eye smaller than the distance between eyes, not delineated by sulci from vertex and frons.Antenna (Fig. 2A, B) 11-segmented, filiform, long, extending beyond middle of body; antennomere I shorter than two following antennomeres combined.Labrum with two pairs of setae.
Abdomen.Ventrites short, wide, without projections or convexities, ventrite I shorter than metasternum; sexual dimorphism present in the shape of ventrite V (apical margin with median notch in males but absent in females); pygidium without medial longitudinal groove; tergite VIII well-developed.

Figure 1 .
Figure 1.Demarchus hsui sp.nov.female A dorsal view B lateral view C ventral view.

Figure 2 .
Figure 2. Demarchus hsui sp.nov.adult A antenna, male B antenna, female C apex of aedeagus, front view D base of aedeagus, dorsal view E aedeagus, lateral view F abdominal ventrite VIII, female G spermatheca H gonocoxae I abdominal ventrite V, male.

Figure 5 .
Figure 5. Field photographs taken from the type locality, Pilu (碧綠) A host plant, Taxillus rhododendricolus (indicated by arrows) B close-up and another angle of T. rhododendricolus C branch of T. rhododendricolus with egg masses (indicated by black arrows) and larvae (indicated by red arrows) D branch of T. rhododendricolus with young larvae (indicated by arrows) mining leaves E branch of T. rhododendricolus with older and younger larvae (indicated by red arrows) mining leaves F branch of T. rhododendricolus with egg masses (indicated by black arrows).

Figure 6 .
Figure 6.Egg masses of Demarchus hsui sp.nov.A typical distribution of egg masses of Demarchus hsui sp.nov. on underside of leaf B egg mass removed from point where it was deposited, scratch marks indicated by arrows C egg mass from a different angle with eggs exposed (indicated by arrow) D backlit image with tunnels constructed by the new hatched larvae indicated by arrows.

Figure 7 .
Figure 7. Larvae and adult of Demarchus hsui sp.nov.A young larva (indicated by arrow) mining leaf B larval tunnels and feeding marks made by adults on leaf (indicated by arrows) C diagrammatic illustration of larval tunnels for Fig. 9B D older larva starting to mine leaf E mature larva that emerged from larval tunnel F adult feeding on leaf.