Diptera

Mcevey, Shane F. & Polak, Michal, 2021, Drosophilidae (Diptera) of the Cook Islands, Records of the Australian Museum (Rec. Aust. Mus.) 73 (5), pp. 153-170 : 155-158

Diptera surveys

Bezzi (1928) offers a comprehensive summary of the known Diptera of the islands of the South Pacific up to 1925, he refers to the specimens taken by H. W. Simmonds who, in 1921, collected a range of dipteran families on Rarotonga—but apparently not drosophilids. Curran (1936) lists Drosophila ananassae from Pukapuka ( Fig. 1 , Cook Islands Northern Group), giving collection date 9 April 1933. Among insects reported by Krauss (1961) from Aitutaki ( Cook Islands Southern Group, Fig. 1 ), Drosophilidae are not mentioned. Futch (1966) refers to a dark form of Drosophila ananassae from Rarotonga and, presumably another culture, from Aitutaki, held as live cultures at the University of Texas, Austin. The Texas stock number 3036 is used. In other publications additional precision is given, Texas stock 3036.1 is Rarotonga D. simulans Sturtevant, 1919 , and Texas stock 3036.2 is dark form Rarotonga D. ananassae (Narise, 1966; Spieth, 1966; Johnson et al., 1966). Drosophila surveys were extensive throughout the TSP in the 1960s related to US thermonuclear testing; McEvey & Schiffer (2015, 2018) provide an overview of the rather convoluted history of discovery of the several D. ananassae complex species that resulted. There is, unfortunately, no known traceable connection between behavioural or cytological observations of the then available cultures (e.g., Spieth, 1966) and species subsequently described (Bock & Wheeler, 1972). From these and other sources it is deduced that Stone and Wheeler were sampling Drosophila in the South Pacific (quite likely also in Rarotonga) in April 1962. In summary: the first and only records of Drosophilidae from Rarotonga are of D. ananassae and D. simulans , they were probably collected—and live stocks were established—in 1962 by Stone and Wheeler. Their work in the Cook Islands is probably also the source of Futch’s (1966) mention of D. ananassae in Aitutaki.

Prior to the present study only two drosophilid species have been reported: Drosophila ananassae from the Northern (Pukapuka) and Southern Groups (Rarotonga and Aitutaki); and D. simulans only from Rarotonga in the Southern Group.

Other islands of the TSP (including Vanuatu, Fiji, Samoa, French Polynesia) have previously been surveyed by the authors, Samoa has 54 species (well-collected with a few undescribed species), Fiji has 27 described species (with many undescribed species) and French Polynesia including the Marquesas Islands has 29 described species and at least 38 undescribed species (from work unpubl. and in prep.).

There are few endemic Diptera from the Cook Islands, exceptions include the tephritid Bactrocera melanota (Coquillett, 1909) and the simulid (Black Fly) Simulium teruamanga Craig & Craig, 1986 .A few other insects are also endemic: examples include the spittle-bug Lallemandana rarotongae Dumbleton, 1950 and the fulgoroid bug Atylana rarotongae Eyles & Linnavuori, 1974 . Endemic molluscs, e.g., Mautodontha rarotongensis (Pease, 1870) , and endemic birds, e.g., Lilac-crowned Fruit Dove Ptilinopus rarotongensis Hartlaub & Finsch, 1871 , are also known (Butler, 2017; McCormack, 2015).

In January and February 2017, one of us (MP), conducted a survey of the Drosophilidae on Rarotonga, Aitutaki and Mangaia during the course of ongoing research into the evolutionary dynamics and biogeography of the Drosophila bipectinata sex comb across the TSP (Polak & Taylor, 2007; Polak et al., 2015). A range of collecting methods (including fruit-baiting, sweeping, direct aspiration from fungi, flowers and sap flux on cut stems), at different elevations (from coastal and lowland vegetation to forests at 225 m) and in different habitats (domestic, rural, and montane forest) ( Tables 2 and 3) were used during the survey; 8036 specimens of Drosophilidae were collected. Data for all specimens collected is summarized in Table 3 and published in full separately as supplementary data— Tables S1–S 3 ( McEvey & Polak, 2021). As noted above, only two (collected by Michal Polak): Aitutaki, Mangaia and Rarotonga. Em-dash is zero specimens collected; 55 specimens of

Drosophila rarotongae sp. nov. (circled) all collected at or above 135 m on Rarotonga.

species of Drosophilidae have previously been reported from the Cook Islands: Drosophila ananassae and D. simulans . Therefore, in the following list ( Table 3), all except these two species, represent new records for the Cook Islands (Okada & Evenhuis, 1989).

Among the species reported is a new one belonging to a group that was the subject of a recent comprehensive investigation ( McEvey & Schiffer, 2015); our familiarity with that group allowed us to immediately recognize that the Cook Island specimens belonged to yet another nameless taxon from the TSP (see below).

These Cook Island records provide baseline data that will allow dating of the arrival of invasive species of human health or agricultural concern. Culicoides belkini Wirth & Arnaud, 1969 (one of the biting midges, Culicidae ) was found for the first time during a survey of Aitutaki and Mitiaro in 2005 ( McCormack, 2015). Drosophila suzukii is currently spreading throughout the world not having yet reached the Cook Islands, New Zealand or Australia, but recently reaching Moorea and Tahiti. The species was absent in the Marquesas and Society Islands during the extensive French Polynesian Terrestrial Arthropod Surveys of 2006–2008 (McEvey, Gillespie unpublished). An IPPC (2017) report notes: Des specimens de Drosophila suzukii ont été collectés par un scientifique en vacances et de passage à Moorea en janvier 2017. Leur identification a été confirmée par l’Australia Museum Research Institute en février 2017. Une prospection a montré que cette mouche était également présente sur Tahiti, mais en faible nombre. Sa présence ne semble pas avoir d’impact économique sur les vergers de fruits. The presence of this species in small numbers in Moorea and Tahiti, was an observation made and confirmed in 2017 with our colleagues Grandgirard and Putoa at the Service du développement rural, Laboratoire d’entomologie agricole, Département de la recherche agronomique, Papeete. High resolution images of Drosophila suzukii (specimens from Italy) have been published by McEvey (2017).

All specimens discussed below are preserved, either pinned or in alcohol, in the Australian Museum, Sydney (abbreviated AM and with register numbers prefixed “K.”).

Figures

Figure 1. Main islands or archipelagos of the Tropical South Pacific (TSP, above).The Cook Islands, as a country, includes Pukapuka coral atoll in the northern group; the present survey is restricted to the three large islands—Rarotonga, Aitutaki and Mangaia—of the Cook Islands southern group, boxed in blue above and enlarged below. Atolls and smaller islands in the Cook Islands southern group are named in grey below (see also Fig. 2 and Tables 1–3).