Midway emerald beetle
Family: Scarabaeidae Subfamily: Cetoniinae Genus: Protaetia Species: Protaetia pryeri (Janson, 1888)
Total body length 19.0–28.0 mm (0.75–1.1 in). Body broad oval; dorsoventrally flattened. Color shiny bright green, rarely shiny olive-green, lacking pale markings. Clypeus broad, anterior margin entire to sinuate. Front tibia of male with 2 or 3 external teeth (third tooth weak); female with 3 external teeth. Hind tibia with single lateral ridge. Elytra lacking apical spine in both sexes.
Undescribed. For Cetoniinae (Ritcher, 1966): Like other Protaetia species, when alive, larvae crawl on their backs with their legs up, and they feel distinctly "squishy" rather than firm (a characteristic of coconut rhinoceros beetle (Oryctes rhinoceros) larvae). Grub C-shaped, not hump-backed, cylindrical, whitish. Maxilla with galea and lacinia fused, or nearly so. Labrum symmetrical. Claws of hind legs large, cylindrical and hairy. 9th and 10th abdominal segments fused. Anal opening transverse, straight to slightly curved.
Japan. In Japan this species is found on Okinawa and the Ryuku Islands (Arakaki, et al. 2009).
Adults of this species are associated with the overripe or damaged fruit of a number of plant species. These plants include papaya (Carica papaya), guava (Psidium guajava), and wax apple (Syzygium samarangense) (Arakaki, et al. 2009). While only a handful of plants have been formally described as hosts, it is likely that this beetle, like the related Protaetia orientalis, is a generalist frugivore capable of damaging a wide range of fruit species (Ijima and Takeuchi, 2007). Protaetia pryeri is also known to visit flowers for nectar and pollen (Nishida and Beardsley, 2002) and may visit sap flows like Protaetia orientalis (Ijima and Takeuchi, 2007). While it has been suggested that larvae of this beetle may attack plant roots (Nishida and Beardsley, 2002), this is not typical of cetoniine scarabs (Ritcher, 1966), and related species are known to subsist entirely on organic soil debris and compost (Gujarathi and Pejaver, 2014).
On Midway Island, larvae were found in organic-rich soils, particularly near ironwood (Casuarina species) or occasionally naupa-ka (Scaevola species) (Nishida and Beardsley, 2002). Adults emerged beginning in April, with numbers declining until December.
Moderate. Like the Asian flower beetle (Protaetia orientalis), this species is often noticed in large feeding aggregations on fruit. While the sight of these aggregations may be alarming for plant owners, beetles rarely cause significant damage to healthy fruit (LeBlanc et al., 2013). Instead, beetles prefer overripe or already damaged fruit, perhaps attracted to the odors of fermentation (LeBlanc et al., 2013). Beetles are, however, capable of causing minor damage to surrounding healthy fruits or flowers with their sharp tarsal claws when they clamber towards target fruit (LeBlanc et al., 2013).
Recorded, not established. Although not yet known from the main Hawaiian Islands, this species is established on Midway (Nishida and Beardsley, 2002), where it is sometimes abundant.
Established. This beetle was first recorded on Guam in 1990 and has since become one of the island's most conspicuous scarab species (Moore, 2010).
In Japan, this species has been found aboard marine vessels (National Institute for Environmental Studies, 2014). Further, because adults are attracted to fermenting fruits and nectar-bearing flowers, it is possible that Protaetia pryeri could hitchhike on nursery plants. Adults could also be accidentally spread in shipments of commercially grown fruits.
This beetle is one of the three species in the genus Protaetia known from Hawaii and Guam. The remaining two species are the Protaetia pryeri and Protaetia fusca. These three species are separated by size (P. orientalis at 19.9–26.8 mm [0.78–1.1 in] versus P. fusca at 12.0–17.0 mm [0.47–0.67 in]), examination of the elytral apices (P. orientalis and P. pryeri always without apical spines versus P. fusca with apical spines in the male), and hind tibia (P. orientalis with 2 lateral ridges versus P. fusca and P. pryeri with a single lateral ridge).
Cetonia pryeri Janson, Protaetia nitidicosta Yawata, Protaetia okinavana Miksic, Pyropotosia pryeri Reitter
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