Ichneumonopsis, Hardy, 1973

Hancock, D. L. & Drew, R. A. I., 2024, Phylogeny of tribe Dacini revisited (Diptera: Tephritidae: Dacinae), Zootaxa 5551 (2), pp. 380-386 : 383-384

Ichneumonopsis , Dacus and Bactrocera

The elongate, posteroventrally directed posterior surstylus lobe seen in Ichneumonopsis , some Dacus and the Bactrocera (Zeugodacus) group of subgenera ( Freidberg et al. 2017; David and Ramani 2019), absent in Dacimita and Monacrostichus , suggests that Ichneumonopsis is the ancestor of Dacus plus Bactrocera , the latter pair separated from Ichneumonopsis and the other genera by a vestigial tergite VI in females, the broad wing cell bm, the frequent presence of a dark anal stripe on the wing (always in the same place), the presence of shining spots (ceromata) on abdominal tergite V in both sexes (lost in subgenus Bulladacus ), a reduced proctiger in males and the widespread occurrence of a posterolateral pecten of fine setae on abdominal tergite III in males. Ichneumonopsis is characterised by the rounded, non-coiled spermathecae, a homoplasious condition also seen in some Gastrozonini (e.g. Acrotaeniostola Hendel , Galbifascia Hardy , Paragastrozona Shiraki ). Dacus is characterised by the fused abdominal tergites and Bactrocera by the additional setae noted above and the generally larger and subquadrate scutellum. The presence of preapical spines on the ventral surface of the fore femora in the Dacus (Mellesis) conopsoides group, also present in Ichneumonopsis and Monacrostichus , suggests that it is the most plesiomorphic in the genus; it breeds in the pods of Asclepiadaceae .

As with Monacrostichus , dispersal of ancestral Dacus to Southeast Asia from India would have enabled Dacus (Callantra) Walker to utilise Cucurbitaceae fruit and the Bactrocera (Zeugodacus) group of subgenera to proliferate in the fruit and flowers of Cucurbitaceae ( Hancock and Drew 2018c) . The indication that Southeast Asia itself was also a part of Gondwana ( Ridd 1971; Cooper 1980) and the presence of a sea barrier between it and India until 15–20 Mya ( Hall 2001), suggest that faunal interchange was not possible until well after the ‘Himalayan’ India- Eurasia collision ca 40 Mya. This would explain the relative uniformity of the Zeugodacus group cucurbit feeders in Southeast Asia and Australasia (see Hancock and Drew 2018c) and their lack of clear molecular distinctions at the subgeneric level (e.g. San Jose et al. 2018).

Within genus Bactrocera , presence of the elongate posterior surstylus lobe seen also in Ichneumonopsis , suggests that the Zeugodacus group of subgenera is the most plesiomorphic, followed by Tetradacus Miyake and the Melanodacus group, with a reversion to short, broad, posteriorly-directed surstylus lobes and retention of a slight to moderate indentation to the male abdominal sternite V. The male praeputium is patterned in Dacus , the Zeugodacus and Melanodacus groups and Tetradacus and not patterned in the Bactrocera group ( David and Ramani 2019), except for a weak pattern (homoplasy?) in B. prabhakari Maneesh, Gupta & Hancock ( Maneesh et al. 2023). The Bactrocera group of subgenera, with a deeply indented sternite V and short, broad surstylus lobes, appears to be the most apomorphic of the genus.

Hancock and Drew (2018b) suggested that Tetradacus originated in India and dispersed, as the Melanodacus group of subgenera, to Sundaland following the ‘glancing blow’ between India and Sumatra-Borneo ca 57 Mya (Ali and Aichison 2008) and subsequently, as the Bactrocera group, to the Papuan region ca 23–33 Mya (e.g. Starkie et al. 2022). However, it is more likely that Tetradacus represents the ancestral Sundaland subgenus, derived from the Indian ancestor of the Zeugodacus group ( Hancock and Drew 2018c). The Indian endemic B. (T.) brachycera (Bezzi) lacks a medial yellow vitta on the scutum and the patch of microtrichia below the apex of wing vein A 1 +CuA 2 and appears to belong to the apomorphic group A of Hancock and Drew (2018a), which includes the Citrus -feeding B. (T.) minax (Enderlein) and B. (T.) tsuneonis (Miyake) and is restricted to India and SE Asia, while the plesiomorphic Group B is widespread from Vietnam to the Solomon Islands ( Hancock and Drew 2019). The Melanodacus group of subgenera, represented ancestrally by Hemizeugodacus Hardy and also of probable Sundaland origin, was regarded as the ancestor of the Bactrocera group by Hancock and Drew (2018a), a view supported by Starkie et al. (2022). The Melanodacus group is widespread from India and SE Asia to Australia and Pacific Islands and is also represented in Africa ( Hancock and Drew (2018a). The suggestion of a Papuan origin for the Bactrocera group of subgenera is supported by the presence of all included subgenera within the Papuan- Australian-Pacific region, with Apodacus Perkins regarded as the most plesiomorphic subgenus by Hancock and Drew (2018a), a view also supported by Starkie et al. (2022).

The above scenario enables the ancestral Tetradacus - Melanodacus - Bactrocera group separation from the Zeugodacus group to be dated to the ‘glancing blow’ event ca 57 Mya. Separation of Dacini from Gastrozonini , and the Zeugodacus group from Dacus , must therefore have occurred during India’s drifting phase, ca 60–80 Mya. This dating is independent of the molecular dating highlighted in Krosch et al. (2012) and Starkie et al. (2022), but dates are closer to the former than the latter, which appear to be much too young. Family Tephritidae , for example, clearly arose well before the break-up of Gondwana.

Phylogenetic progression of the groups of subgenera suggested above, from the Zeugodacus group to Tetradacus to the Melanodacus and Bactrocera groups, is largely supported by molecular studies (e.g. San Jose et al. 2018; Dupuis et al. 2018; Starkie et al. 2022), but the placement of the Zeugodacus group as sister to Dacus in these molecular studies is not supported by the frequent but unstable presence of basal scutellar and/or prescutellar acrostichal setae and the larger, subquadrate scutellum (synapomorphies) shared by the Zeugodacus and all other groups of subgenera in Bactrocera . The fused abdominal tergites in Dacus and molecular studies in the Zeugodacus group (e.g. San Jose et al. 2018) indicate monophyly in both groups, with scutellum shape variation in Dacus evidently homoplasious. A Dacus-Zeugodacus sister relationship that excludes Bactrocera , based on assumed ancestral morphological and host plant similarities ( White 2006), was refuted by Hancock and Drew (2018a –c) on the grounds that the scutal medial yellow vitta also occurs in Tetradacus and both the Melanodacus and Bactrocera groups of subgenera and Cucurbitaceae were not available as host plants until well after their separation, while proposed molecular evidence (e.g. Virgilio et al. 2015) is regarded as an artefact of the analysis (see Drew and Hancock 2022). White (2006) suggested that the small notopleural lobe in Dacus and Zeugodacus also suggested a close relationship, but this character is plesiomorphic in the Dacinae , becoming larger in the other Bactrocera groups of subgenera.

Molecular phylogenetic studies within subgenus Bactrocera , however (e.g. San Jose et al. 2018; Dupuis et al. 2018; Starkie et al. 2022), contain numerous anomalous pairings and placements that are contrary to morphological and biogeographical evidence. Genetic variation in many species (often reflected in morphological variation: Leblanc et al. 2015), an overall genetic similarity, unreliable CO1 data and rapid speciation within subgenus Bactrocera also reduce the reliability of molecular phylogenies, further exemplified by the complete lack of agreement regarding the placement of B. endiandrae (Perkins & May). Included in the dorsalis complex by Drew and Hancock (2022) on morphology, it closely resembles B. parafroggatti Drew & Romig from the Solomon Islands, which was referred to the dorsalis complex by Doorenweerd et al. (2024). Three studies that focused on Australian species ( Krosch et al. 2012; Catullo et al. 2019; Starkie et al. 2022) showed very little agreement with either each other or the wider studies of San Jose et al. (2018) and Dupuis et al. (2018). Genetic homoplasy is likely to be rife and not just limited to those genes associated with morphology. Accordingly, these studies are regarded here as merely giving an indication of relationships, rather than being definitive in themselves. Due to the large number of species and their overall similarity, a detailed assessment of phylogeny within the subgenus is not possible at the present time, although the similar wing pattern (with a broad, transverse medial band enclosing both r-m and dm-m crossveins and no preapical band) seen in subgenus Apodacus and the distincta complex, known from Maluku to Australia, New Caledonia and Fiji, suggests that the latter is the basal complex in subgenus Bactrocera . Much of the speciation within the subgenus is associated with adaptation to the wide variety of available fruits as hosts and is too recent for fragmentary molecular analyses to be useful in determining their relationships.