Family: Scarabaeidae Subfamily: Melolonthinae Genus: Microserica Species: Microserica guamensis Gordon, 1971
Total body length 4.2 mm (0.17 in). Body shape short, stout, broadly oval; widest posteriorly. Color reddish-brown. Antennae 11-segmented; club 4-segmented; club more than twice the length of segments 1–7. Elytra weakly striated; lacking obvious setae. Females of this species are not known.
Undescribed. For Sericini (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.
Uncertain. Although this scarab was described from Guam, Cartwright and Gordon (1971) suggested that it was not native. Instead, they proposed a potential Bornean origin for the species.
Poorly known. Cartwright and Gordon (1971) noted that this species does not come to lights, thus suggesting a diurnal habit. It is likely that adults are folivores and that the larvae develop within soil where they feed on plant roots. Such habits are seen in related genera including Serica (Ratcliffe and Paulsen, 2008) and Maladera (Skelley, 2013).
Probably none. There are no records of this poorly known species acting as a plant pest.
Not established or recorded. There are no records of this scarab from Hawaii.
Recorded, not established. This scarab was described from Guam (Cartwright and Gordon, 1971) and is included on the Bourquin, 2002 checklist. However, it appears that the species is known only from the type specimen, and no further specimens have been taken on Guam. This suggests the species is not established.
If this species was introduced to Guam, it is likely that it arrived to the island by hitchhiking on marine or air cargo. Potentially, adults also could have arrived on incoming nursery plants, and larvae or eggs could have been transported in soil or sod.
This species is somewhat similar to the Maladera species recorded from Hawaii. Microserica guamensis can be separated from the Maladera species based on its much smaller size (3.7–4.7 mm [0.15–0.19 in] in M. guamensis versus 7.0–10.0 mm [0.28–0.39 in] in Maladera) and the form of its antennae (11-segmented antennae with 4-segmented club in M. guamensis versus 10-segmented antennae with 3-segment club in Maladera).
Report your observation of this rare and possibly native Guamanian species at our iNaturalist project.