An annotated checklist of the Cook Islands psyllids with keys to the species and two new records (Hemiptera, Psylloidea)

Abstract An annotated checklist of the psyllids of the Cook Islands is presented. The presence of Syntomozatahuata (Klyver, 1932) and Triozaalifumosa Klyver, 1932 in the archipelago, based on new material collected, is reported for the first time. This is the first record from these islands of the genus Syntomoza and the family Liviidae. An identification key to the psyllid species known from the Cook Islands is provided, and their origin and provenance are discussed in relation to their biogeographic implications.


Introduction
The superfamily Psylloidea (Hemiptera: Sternorrhyncha) is composed of almost 4000 described species worldwide (Ouvrard 2018). These include taxa used for biological control, such as Arytainilla spartiophila (Förster, 1848) released in New Zealand to control Scotch broom, Cytisus scoparius (L.) Link (Fabaceae) (Syrett et al. 2007), and also a number of species listed as pests (EPPO/CABI 1997). Among these, a few taxa are known to vector plant pathogenic bacteria (e.g. Munyaneza 2007Munyaneza , 2014. Such a broad range of ecological functions ensures that psyllids' movement between countries is of interest. For example, a recent study implemented modelling analyses to assess the risk and predict the spread of the pest species Russelliana solanicola Tuthill, 1959, the South American potato psyllid, to several countries where it is not yet present (Syfert et al. 2017). Similarly, the recent establishment of the tomato/potato psyllid Bactericera cockerelli (Šulc), vector of Candidatus Liberibacter solanacearum and agent of the zebra chips disease, has caused great economic losses in New Zealand (Vereijssen et al. 2018). Therefore, understanding psyllid distributions is fundamental to assess the risk associated with new invasions. In recent years, research on psyllid biodiversity has been conducted in a number of regions and islands of the Austro-Pacific. These include the description of taxa in Australia (Taylor et al. 2016, Taylor 2018, the reclassification of Pariaconus Enderlein, 1926 andSwezeyana Caldwell, 1940 in the Hawaiian Islands (Percy 2017(Percy , 2018 and reports of the arrival of alien species in Australia (Taylor and Kent 2013), New Zealand (Thorpe 2013, Martoni et al. 2016, Martoni et al. 2018 and French Polynesia (Claridge et al. 2014). However, the psyllid fauna of most other Pacific Islands has not been updated for many years (Ouvrard 2018).
The first report on the psyllid fauna of the Cook Islands appears in Hodkinson's checklist of the Austro-Oriental and Pacific area that listed three species: Mesohomotoma hibisci (Froggatt, 1901); Leptynoptera sulfurea Crawford, 1919; and Trioza vitiensis Kirkaldy, 1907(Hodkinson 1983). An additional species, Heteropsylla cubana Crawford, 1914, was reported a few years later (Muddiman et al. 1992). The most recent addition was a Trioza species similar to T. zimmermani Tuthill, 1942, identified by P. Dale and recorded in the online Cook Island Biodiversity and Natural Heritage database (McCormack 2007).
The geographical location of the Cook Islands puts them in a central position between French Polynesia and other countries such as Samoa, Tonga, Fiji, and New Zealand. This makes this small archipelago important for evaluating biogeographic hypotheses and testing theories of biological dispersal within the Pacific. Additionally, due to the high movement of people and produce between the Cook Islands, New Zealand and Australia, understanding the biodiversity of the Cook Islands allows evaluation of potential biosecurity risks for New Zealand or Australian agriculture.
For these reasons, recent field collections from the Cook Islands presented in this work have contributed to updating our knowledge of the psyllid biodiversity of the Islands, with the discovery of two additional taxa: Syntomoza tahuata (Klyver, 1932), and Trioza alifumosa Klyver, 1932, both originally described from French Polynesia (Marquesas) (Klyver 1932).

Materials and methods
Specimens were collected by SDJB on the island of Rarotonga, Cook Islands, in March and April 2017. Collections were made by beating host foliage over a beating tray. Insects were stored in propylene glycol until morphological identification was per-formed. Photographs were taken using a Nikon DS-Ri2 camera connected to a Nikon SMZ25 microscope. Pictures presented in the plates are the result of stacking photographs using the software Nikon NIS-Elements D v4.5 resulting in a single image with an extended depth of field. Plates were prepared using GIMP version 2.8.14. For closer examination, two specimens of each species (male and female) were mounted on microscope slides following the protocol of Taylor et al. (2016). Morphological terms follow Taylor et al. (2011) and wing venation follows Hodkinson and White (1979) and Hollis (1984). Psyllid specimens from the recent field collection have been deposited in the New Zealand Arthropod Collection (NZAC, Manaaki Whenua Landcare Research, Tamaki, Auckland), and the Lincoln University Entomology Collection (LUNZ, Canterbury). Plants were identified by SDJB using Sykes (2016). Specimens of the host plants collected at the same time as insect specimens were deposited in the Allan Herbarium (Landcare Research, Lincoln, New Zealand), with catalogue numbers CHR644589 (Homalium acuminatum), CHR644590 (Weinmannia samoensis), and CHR644584 and CHR644585 (Metrosideros collina). Paratype specimens of T. alifumosa and T. alipellucida Klyver, 1932 were examined in the Bernice Pauahi Bishop Museum (BPBM, Honolulu, Hawaii).

Trioza alifumosa Klyver, 1932
Description. This psyllid can be identified by the following combination of characters: habitus as in Figures 11-14, with a dark brown colour, fore wings with an infuscate spot in the apical costal cell as in Figures 13, 17, female proctiger short and bearing setae on the subgenital plate ( Figure 19); male parameres elongate, slightly back-turned apically and bearing setae ( Figure 20). Both this species and T. alipellucida Klyver, 1932, were described from material collected on Metrosideros collina. The evenly dark colouration of the dorsal surface and head, the presence of an infuscate spot in the apical costal cell (c+sc), the rounded but elongated shape of the aedeagus, the elongated shape of the male proctiger and the slightly back-turned parameres lead us to place it in T. alifumosa. Trioza alipellucida differs from T. alifumosa by most specimens having a wide lighter brown stripe on the pronotum, not having an infuscate spot at the base of the forewing, and for a shorter male proctiger associated with parameres that are not as back-turned. The morphological distinction between T. alifumosa and T. zimmermani appears more immediate, with the latter presenting light stripes dorsally on a dark brown abdomen and having hyaline wings without any dark spot in the cell c+sc (Tuthill 1942).

Checklist of the Cook Islands psyllids
The following checklist includes all species known to be present in the Cook Islands. Information on their taxonomy is reported together with their worldwide distribution and host plant associations. For species of socio-economic interest, such as pests, basic information on their biology is summarised.

Family Carsidaridae
Mesohomotoma hibisci (Froggatt, 1901  Remarks. the genus Mesohomotoma Kuwayama was reviewed by Hollis (1987). The species included in the genus have a lot of variation between populations, and subtle differences between species. Although Hollis (1987) suspected all nominal taxa may represent a single species, he did not formally synonymise them, recommending that further research into their biology and hostplants be undertaken to further investigate species boundaries in the genus. This species breeds in the tips of Hibiscus tiliaceus branches. The nymphs produce filamentous exudates, which forms a woolly coating on the leaves and stem of the plant (Figure 21). Mesohomotoma hibisci is considered a pest (David Hockings 2013). Figures 1-10 (Burckhardt and Mifsud 2003;Ouvrard 2018). In June 2002, however, Percy (pers. comm.) collected a high number of adult specimens (> 30) from Weinmannia parviflora in French Polynesia (Marquesas) with no specimens found on surrounding plants. Figure 25 Heteropsylla cubana Crawford, 1914. Distribution. Reported on the Cook Islands by Hodkinson (1983 (Muddiman et al. 1992, Martin and Lau 2011, Inoue and Miyatake 2001, Geiger and Gutierrez 2000], Pacific Islands [Fiji, French Polynesia (Australs), Guam, Haiti, Hawaiian Islands, New Caledonia, Niue, Papua New Guinea, Samoa, Solomon Islands, Tonga (Beardsley and Uchida 1990, Claridge et al. 2014, Muddiman et al. 1992, FAO 1994], Europe [Ireland (Muddiman et al. 1992)].
Biology. The biology and life cycle of H. cubana is reported here with the intent of summarising information (mostly from Showler andMelcher 1995 andCABI 1990) that may be relevant for a better understanding of this pest species. The incubation period for eggs is generally 2-5 days. Immature stages grow from the egg through five instars to adulthood in 10-20 days. Nymphs feed at first gregariously near the oviposition site and then, more and more solitarily, they colonise and feed on other parts of stems, branches, and petioles of young leaves. Generations are overlapping, and longevity of adults is on average 14.5 days for females and 9.7 days for males. Mating can occur more than once for both males and females (Rauf et al. 1990) and eggs are laid in groups on very young shoots, often covering the whole leaflet. Each female can produce 300-500 eggs throughout a lifetime and can lay as many as 60 eggs in one day. Heteropsylla cubana is diurnal, and flight of adults can occur in the morning and afternoon. Figure 22 Leptynoptera sulfurea Crawford, 1919: 147. Distribution. Reported on the Cook Islands by Hodkinson (1983). Known only from Rarotonga. Other locations include: Australia (Hollis 2004), Asia [China, Chagos Islands, Cocos Islands, India, Indonesia, Japan, Malaysia, Philippines, Ryukyu Islands, Singapore, Sulawesi, Taiwan, Thailand (Martin and Hollis 1992, Hodkinson 1983, 1986, Neville et al. 2015], Pacific Islands [Caroline Islands, Fiji, French Polynesia (Australs), Guam, Hawaiian Islands, Mariana Islands, New Caledonia, Palau, Papua New Guinea, Tonga (Hodkinson 1983, Martin and Hollis 1992, Percy 2017.

Trioza vitiensis Kirkaldy, 1907
Distribution. Reported on the Cook Islands by Hodkinson (1983). Known only from Rarotonga. Other locations include: Asia [China, India, Indonesia, Malaya, Malaysia, Philippines, Singapore, Sri Lanka (Hodkinson 1983(Hodkinson , 1986], Pacific Islands [Caroline Islands, Fiji, French Polynesia (Societies, Marquesas), Samoa (Kirkaldy 1907, Hodkinson 1983]. Remarks. no specimens of this psyllid were collected by the authors. Photographs provided by G McCormack were consistent with the morphology of T. zimmermani, with the greatest difference shown in the wings (Figures 24, 27), with the Rarotongan specimens being shorter and with a less acute apex (Figure 24), than those from Raivaevae drawn by Tuthill (1942, Figure 27). However, since no specimens could be examined in person, this taxon is reported here based on the identification made by Dale. The distribution of T. zimmermani includes French Polynesia (Australs) (Tuthill 1942, Percy 2017.

Discussion
Based on the similarity of the samples analysed with the description and the drawings provided by the literature, the presence of the psyllids Syntomoza tahuata and Trioza alifumosa is reported on the Cook Islands for the first time. Host plants for these two species in the Cook Islands are hypothesised to be Weinmannia samoensis or Homalium acuminatum and Metrosideros collina respectively, based on collection data. Percy's collection of a large number of individuals of S. tahuata from Weinmannia parviflora suggests this genus could be a true host plant (Percy, personal communication). However, we consider that H. acuminatum should remain under consideration as a possible host. No specimens of W. samoensis were seen near the Avana Valley site where S. tahuata was collected from H. acuminatum, and the elevation of the site is well below the lower elevational limit of W. samoensis (Sykes 2016). The number of S. tahuata observed during this collecting event was much greater than were captured, and were much more abundant than on the occasions when S. tahuata was beaten from W. samoensis. A search for immature stages of S. tahuata on both H. acuminatum and W. samoensis should be undertaken to differentiate between these host plant hypotheses or confirm whether S. tahuata is a generalist (Burckhardt et al. 2014).
We consider these two species to be indigenous to the Cook Islands, despite their not having been recorded here previously. The Cook Islands are underexplored entomologically, with relatively little collecting having been done in indigenous vegetation in particular. Moreover, these species were found in areas of relatively intact vegetation, with little human modification, which tend to be more resistant to invasive species (Brockerhoff et al. 2010). We hypothesise that further investigation of the psyllid fauna in other islands of Eastern Polynesia will locate these species there also, in areas where Metrosideros collina and Homalium species may be found. However, this in itself would not provide sufficient evidence to distinguish between hypotheses of recent or distant arrival in the Cook Islands. In the absence of past collections, analysis of rapidly evolving DNA regions would be necessary to provide further data to infer the arrival of these species in the Cook Islands.
The psyllid fauna of the Cook Islands now includes seven psyllid taxa from five genera and four families. The addition of S. tahuata is not only the first report for the genus in the Cook Islands, but also for the family Liviidae.
Compared with the psyllid fauna of other nearby archipelagos, the Cook Islands appear to have a very similar psyllid biodiversity. In fact, the single taxon present in Niue (H. cubana) and three of the four taxa present in Tonga (H. cubana, M. hibisci, and L. sulfurea) are also present in the Cook Islands (Ouvrard 2018). Similarly, the psyllid fauna of French Polynesia lists eight species, four of which are in common with the Cook Islands: M. hibisci, T. zimmermani, T. alifumosa, and S. tahuata (Ouvrard 2018). On the other hand, the Cook Islands do not share any of the three taxa present in American Samoa (Ouvrard 2018). A recent review indicates that the biota of the Society islands in many cases show close sister-taxon relationships with the Cook, Austral, and Marquesas Islands (Hembry and Balukjian 2016). They also found that many taxa showed patterns of multiple colonisation of the islands, indicating high species turnover in the Eastern Polynesian region (Hembry and Balukjian 2016). We believe that the records of the two psyllid species reported here for the first time from the Cook Islands provides further evidence of the recognition of a distinctive Eastern Polynesian fauna.
was supported by a Winston Churchill Memorial Fellowship awarded to SDJB, and Plant and Food Research Strategic Science Investment Funding (SSIF).