Family: Scarabaeidae Subfamily: Melolonthinae Genus: Maladera Species: Maladera japonica (Motschulsky, 1860)
Total body length 7.0–10.0 mm (0.28–0.39 in). Body shape oblong-oval, widest posteriorly; convex when viewed laterally. Color dark-brown without iridescent sheen. Clypeus with anterior margin strongly reflexed. Antennae 10-segmented; club 3-segmented. Pronotum with distinct, moderately deep punctation. Elytra lacking obvious setae. Male and female lacking obvious characters for separation.
Undescribed in English. For Maladera spp. (Ritcher, 1966): Grub C-shaped, not hump-backed, cylindrical, whitish. Cardo, maxillary articulating membrane, and many other body parts with numerous black dots. Galea and lacinia fused proximally, but separated distally or tightly fitted together. Last antennal segment always with a single, large, oblong, dorsal, sensory spot. Haptomerum with 3 or 4 heli. Dorsal anal lobe much smaller than the ventral anal lobes. Anal lobes densely setose. Raster with a curved, transverse row of prominent setae anterior to the ventral anal lobes. Anal opening Y-shaped with base of the Y much more elongate than the arms.
Host plants for this scarab are poorly recorded. There are records of larvae damaging rice (Oryza sativa) (Litsinger et al., 1987) and sweet potato (Ipomoea batatas) (Yokoyama et al., 1998). Adults are recorded causing damage to the tung tree (Vernicia fordii) (Sikharulidze, 1975).
Poorly known. The life history of this species is probably similar to that of the closely related Asiatic garden beetle (Maladera castanea). The Asiatic garden beetle (Maladera castanea) is a generalist herbivore both as adult and larva. Larvae develop deep in the soil where they feed on plant roots in moist, shaded, weedy areas (Woodruff and Beck, 1989). Adults are nocturnal, hiding on or near host plants by day (Eckman, 2015).
Probably minor. There are relatively few records of this scarab causing damage to crop or ornamental plants. However, both adults and larvae are likely generalist herbivores and could potentially cause some degree of damage to a wide range of plant species. Both rice (Litsinger et al., 1987) and sweet potato (Yokoyama et al., 1998) are recorded hosts.
Recorded, not established. Nishida (2002) recorded this species being intercepted in quarantine. Details of the interception, however, could not be located.
Not established or recorded. There are no records of this species from Guam.
This species probably comes to lights at night, and it is likely that it would be attracted to well-lit ports and airports. This would allow for hitchhiking on marine or air cargo. Further, it is possible that larvae or eggs could be transported in shipments of commercial turf or potted plants.
This species is very similar to the closely related Maladera castanea. These species can be separated by comparison of the male genitalia, examination of pronotal punctation (M. japonica with punctation moderately deep and distinct versus M. castanea with punctures shallow and indistinct), and more superficially by color (M. japonica dark brown without an iridescent sheen versus M. castanea a rusty-brown to orange-brown with an iridescent sheen).
Aserica japonica Motschulsky
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