Craspedochaeta

Introduction

Craspedochaeta Czerny ("Czernyola" in publications from 1907-1971) is relatively abundant in tropical regions, and is the only acalyptrate Diptera that has four to five fronto-orbitals with the third bristle from the back inclinate and proclinate (the remainder are reclinate). The group is most diverse in the Oriental and Neotropical Regions, but species also occur in the Australian, Afrotropical and (occasionally) Nearctic Regions (Lonsdale & Marshall, 2006b; McAlpine, 1960; Sasakawa, 1971).

Three species groups (described below) are currently recognized within the genus: the Craspedochaeta concinna (formerly C. atra), C. transversa and C. biseta groups (Lonsdale & Marshall, 2006b). The first two are found exclusively in the New World, but the latter is widespread in the Old World with one species in Bolivia and Ecuador.

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Heads of different Craspedochaeta species groups, left lateral (arista and bristles removed, excluding vibrissa and fronto-orbital bristles). © Owen Lonsdale

Most species have been collected in tropical forests, but several species have extended their range into North America, and Craspedochaeta australis (McAlpine) has been collected at 3000' in a cool region known to get winter snow (McAlpine, 1960). Some species frequent the undersides of leaves.

Very little is known about the biology and behaviour of Craspedochaeta, although males and females have been found to frequent downed branches or bare logs throughout the neotropics, particularly when dung baits are placed on the wood. 

As has been observed in species of other clusiodine genera such as Clusiodes, Hendelia (Marshall, 2000; Roháček, 1995) and Heteromeringia (Lonsdale & Marshall, 2007a), males of one Craspedochaeta species have been observed while engaging in agonistic behaviour at supposed lek sites.  Several specimens of the Bolivian C. pullipleura Lonsdale & Marshall were observed on a small fallen branch, where males on the most exposed and prominent parts of the branch returned quickly when scared off, and were repeatedly challenged by other males.  When one male invaded the territory of another, the resident responded to the challenge by facing the invader, and a head-pushing competition usually ensued. 

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Behavior of Craspedochaeta pullipleura males at supposed lek sites. © Steve Marshall

Characteristics

Craspedochaeta can be easily diagnosed by having four or five fronto-orbital bristles, all of which are reclinate excluding the third bristle from the back, which is inclinate and proclinate. Other defining characters of the genus are male genitalic: the surstylus is smooth or sparsely setose on the outer face (at least anteriorly), the ejaculatory apodeme is wide and flared at one end (appearing 'mushroom-shaped'), and the hypandrial arm is only weakly attached to the remainder of the hypandrium (Lonsdale & Marshall, 2006b).

Species of Craspedochaeta also have two pairs of dorsocentral bristles (a small third dorsocentral is rarely present ), the mid and hind tibiae have dorsal preapical tibial bristles, the arista is pubescent to short plumose, and the phallus is usually large and sac-like, although some species have elongate sclerotized sections or the phallus is reduced to absent (Lonsdale & Marshall, 2006b). As in other Clusiodinae, the spermathecae are longitudinally segmented, and the hypandrial complex exhibits extensive reduction and fusion of its components (Lonsdale & Marshall, 2006). Most Old World species exhibit a pronounced sexual dimorphism in size and colouration.

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Craspedochaeta concinna (Williston) male genitalia: external, left lateral (top); external, posterior (bottom); internal (left lateral, not drawn to scale). © Owen Lonsdale.

Discussion of Phylogenetic Relationships

Excluding the basal Allometopon Kertesz and Electroclusiodes Hennig, Craspedochaeta is the sister group to the remaining clusiodine genera, which have spermathecae that are pigmented and strongly telescoped (Lonsdale & Marshall 2,006). McAlpine (1960) divided Craspedochaeta into the C. transversa, C. concinna (formerly C. atra), and C. biseta species groups.

The Craspedochaeta concinna and C. transversa species groups form a single New World lineage characterized by wings that are entirely dusky (at least ancestrally; paralleled in several species of the C. biseta group) and an anterior dorsocentral bristle that is half the length of the posterior dorsocentral (Lonsdale & Marshall, 2006b).  The C. transversa species group is the most easily recognized, having an additional pair of reclinate fronto-orbital bristles at the anterior margin of the frons, characteristic spermathecae and pregonites, and a subterminal flagellum on the female ventral receptacle.  Most species also have lighter bristles, paler notal colouration, united cerci that are often large and plate-like, an elongate basiphallus, and an atrophied distiphallus and ejaculatory apodeme (Lonsdale & Marshall, 2006b). Conversely, the C. concinna group is poorly defined, characterized by an absence of the prescutellar acrostichal bristles (independently developed in several species elsewhere in the genus).

The Craspedochaeta biseta group is defined by a single plesiomorphic character (a long anterior dorsocentral bristle) and is almost certainly paraphyletic.  Most species in this group are also sexually dimorphic and have a reduced hind fronto-orbital bristle. The group is predominantly Indoaustralian in distribution, although specimens have been collected in India and Africa (unpublished data), and a single neotropical species (C. argoniae Lonsdale & Marshall) has been collected in Bolivia and Ecuador (Lonsdale & Marshall, 2006b).

McAlpine (1960) revised the Australian Craspedochaeta and Sasakawa (1971) revised those species in the Oriental and Pacific Regions. Lonsdale & Marshall (2006b) revised the New World species, providing a species-level phylogenetic analysis. 

References

Lonsdale, O. & Marshall, S.A. 2006. Redefinition of the Clusiinae and Clusiodinae, description of the new subfamily Sobarocephalinae, revision of the genus Chaetoclusia and a description of Procerosoma gen. n. (Diptera: Clusiidae). European Journal of Entomology, 103: 163-182.

Lonsdale, O. & Marshall, S.A. 2006b. Revision of the New World Craspedochaeta Czerny. Zootaxa 1291: 1-101.

Lonsdale, O. & Marshall, S.A. 2007a. Revision of the New World Heteromeringia (Diptera: Clusiidae: Clusiodinae). Beitr?ge zur Entomologie 57(1): 37-80.

McAlpine, D.K. 1960. A review of the Australian species of Clusiidae (Diptera: Acalyptrata). Rec. Aust. Mus. 25: 63-94.

Sasakawa, M. 1971. Studies on the Oriental and Pacific Clusiidae (diptera), pt. 2. Scientific Reports: Kyoto Prefactural University of Agriculture 23: 50-63.