Morphological. Key characters that separate the dryophthorids in question from other families of Coleoptera are:
1) Beak (=rostrum) extends anteriorly from head,
2) Antennae elbowed, and
3) Antennal club mostly glabrous with restricted area of dense pubescence.
Images of these characters can be found in the CAPS datasheet.
The genus Metamasius can be distinguished from other similar genera by looking at morphological characteristics which are listed in Anderson (2002a) and Brodel (2002).
Vaurie (1966) has a key to help distinguish species of Metamasius. Anderson (2002b) provides a key to the Metamasius spp. (including M. hemipterus,) found in Costa Rica and Panama.
Identification to the subspecies level will not be required to report negative or positive data for this species.
Metamasius species can be taxonomically difficult to distinguish because of the large number of species in the genus (O'Brien and Thomas, 1990). Metamasius hemipterus is similar to both M. benoisti (found in Ecuador) and M. ensirostris (found in South America) (Vaurie, 1966).
There is one native Metamasius species in the United States, M. mosieri. However, this species is easy to differentiate from most pest Metamasius spp. Metamasius mosieri is red and black with two round spots on the elytra and is only about 6 to 9 mm (approx. 1/4 to 3/8 in) long (Woodruff and Baranowski, 1985). Another Metamasius species found in Florida is M. callizona. Both M. mosieri and M. callizona attack bromeliads. Neither are likely to be captured in M. hemipterus traps. An image of all three Metamasius spp. can be found in Larson et al. (2001).
Another genus in the same tribe as Metamasius, Sphenophorus, may be confused with this species as well. Sphenophorus spp. have different hosts (grasses and corn). It is unknown if they would be attracted to the trap for M. hemipterus. Two keys illustrating the difference between Metamasius and Sphenophorus are Anderson (2002a) and Brodel (2002). Species of Rhynchophorus are much larger than species of Metamasius or Sphenophorus.