Dacini
Year: 2024
Type: other
Abstract: Tribe Dacini To the four genera included by Drew and Hancock (1999) may be added Dacimita David & Hancock, described recently from India (David et al. 2022). Although not yet reared from bamboo, its association with adjacent tiger grass (Thysanolaena sp.) and broad, dorsoventrally flattened aculeus suggest a bamboo or grass host. Since Ichneumonopsis does breed in bamboo (Kovac et al. 2013; Freidberg et al. 2017) and both it and Dacimita have an enlarged proctiger, they are currently or frequently included within tribe Gastrozonini. However, they share several synapomorphies with other Dacini genera, suggesting further paraphyly of tribe Gastrozonini and homoplasious utilisation of non-bamboo host plants in both Ceratitidini and Dacini. Larvae of Ichneumonopsis also differ significantly from other Gastrozonini (Kovac et al. 2013), while those of Dacimita are currently unknown. An enlarged proctiger is possibly ancestral in both Gastrozonini and Dacini, as is the often coiled and convoluted spermathecae. The proctiger is greatly reduced in Dacus and Bactrocera (and in Ceratitidini) but much less so in Monacrostichus, resembling a moderately reduced version of that seen in Dacimita (cf. Hardy 1974 and David et al. 2022); it is also (homoplasiously) reduced in some Gastrozonini genera such as Dietheria Hardy and Taeniostola Bezzi (Hardy 1973) and its phylogenetic value is uncertain. Tables 1 and 2 list the character states in Gastrozonini and Dacini and their distribution, although scutellum shape (character 9) is a little variable in Dacus, with a shape similar to that of state 2 sometimes present. For comments on the secondary presence of Characters 3, 5, 7 & 8 see White (2006) and Hancock and Drew (2017, 2018a –c). In some Gastrozonini genera ocellar setae are vestigial or absent and male Chaetellipsis Bezzi lack frontal and orbital setae, but none shows the apomorphic states of the whole setal series 1–8. Apical scutellar setae are absent in Dietheria but always present in Dacini. Extreme setal reduction also occurs (slightly differently and homoplasiously) in Anastrepha Schiner species formerly included in its synonym Toxotrypana Gerstaecker, that also resemble wasps, but the uniformity of its expression in all five Dacini genera included here suggests a common ancestry. The presence of preapical spines on the ventral surface of the fore femora in Ichneumonopsis, Monacrostichus and the Dacus conopsoides group of Hancock and Drew (2006), also suggests a common ancestry. Ichneumonopsis was also grouped with Dacini in a morphological phylogeny by David and Ramani (2019). Generic relationships are clearly evident in Table 2 and computer analysis of the matrix is unnecessary. Tribe Dacini is believed to have originated on the Indian plate during its post-Gondwanan drifting phase (Drew and Hancock 1999; Krosch et al. 2012), with all genera except Monacrostichus originating there. Ichneumonopsis and Dacimita remain within India and Southeast Asia and, with their bamboo associations and enlarged proctiger, are regarded as ancestral sister-genera. Dacus spread to and diversified in Africa and, following unification of India with the rest of Asia, it and Bactrocera spread to and diversified in Southeast Asia and Australasia, with later minor spread of African Dacus to India and Indian Bactrocera to Africa (Drew and Hancock 1999). The indication that the Madagascan Dacus xanthaspis group utilises Cucurbitaceae rather than Asclepiadaceae (Rasolofoarivao et al. 2022) suggests that a relationship of its three included species (White 2006) with subgenus Neodacus Perkins (Hancock and Drew 2006) is incorrect—reinvestigation suggests that they are closely related to (or belong in) the Dacus (Mictodacus) sphaeristicus group of Hancock and Drew (2006); in both groups wing cells bc and c are fuscous and all or at least most of cell c (and often at least part of cell bc) is densely microtrichose. White (2006) also suggested a possible relationship between species in these two groups. Tythocalama Munro is therefore removed from synonymy with Neodacus and placed as a new synonym of subgenus Mictodacus Munro. Contrary to Krosch et al. (2012), there is therefore no evidence of dispersal from Madagascar to mainland Africa, or from mainland Africa to India via Madagascar; the Cucurbitaceae did not reach Madagascar prior to its first dispersal from the African mainland ca 50 Mya (Schaefer et al. 2008), long after its separation from India. The only direct India-Madagascar link in the Dacini appears to have resulted in the endemic Madagascan subgenus B. (Aglaodacus) Munro in the Zeugodacus group of subgenera (Hancock and Drew 2018c). The ca 40 million years since collision of India with Eurasia (Bouilhol et al. 2013) would have provided ample time for an ancestor of the relatively uniform African Dacus to reach there and proliferate. Subsequent dispersal to Madagascar likely occurred several times and consists of several lineages. The similar absence of Cucurbitaceae from India during the evolution of Dacini genera (Schaefer et al. 2008) rules that plant family out of consideration as an ancestral host plant in both Dacus and Bactrocera (Hancock and Drew 2018b). The same is true of Citrus (Rutaceae), a Southeast Asian genus that originated ca 8 Mya in Yunnan and radiated rapidly 6–8 Mya (Wu et al. 2018), and is used as a host plant by both Monacrostichus and some Bactrocera (Tetradacus) species. The absence of Monacrostichus from India and its utilisation of Citrus excludes it as a direct Dacus-Bactrocera ancestor, leaving only Ichneumonopsis and Dacimita as potential ancestors of the tribe. These two genera are linked to the other three by the synapomorphies of extreme setal reduction and, in Monacrostichus and (most) Dacus [cf. Hancock 2003; Drew and Romig 2013], a short, broad, subtriangular scutellum. The plesiomorphic absence of basal scutellar and prescutellar acrostichal setae (frequently but irregularly present (secondarily) in all groups of Bactrocera subgenera, including the Zeugodacus group) also unites these two genera with Dacus and Monacrostichus and it is likely that they represent the ancestral dacines as a sister-pair, with either Ichneumonopsis or Dacimita representing the ancestor of Dacus-Bactrocera, accompanied by a host plant shift from bamboo to Asclepiadaceae pods (Dacus) or forest fruit (Bactrocera).
Authors: Hancock, D. L., Drew, R. A. I.
Institution: Griffith University
Language: English
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W6949083193
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