Ambrosia Beetles are one of the most diverse groups of Bark Beetles, with over 1300 described species in 43 genera, found throughout the world's tropical and temperate regions. The biology of these Beetles enables them to colonise new areas rapidly, with many species considered to be highly invasive pests, causing significant economic and ecological damage in forests, orchards, nurseries as well as urban and suburban gardens. This is because the Beetles bore into the wood of trees and cultivate gardens of Fungus, feeding on an ambrosia produced by the Fungus rather than the wood of the tree. This means that, unlike most wood-boring Insects, they are not tied to a single species of tree, although some species and genera are restricted to a single family of hosts. The reproductive cycle of the Beetles also favours dispersal, with diploid females mating with haploid males within their birth tree before dispersing to new trees to lay eggs.
The taxonomy of Ambrosia Beetles can be challenging, due to the small size of these Insects, and their wood boring lifestyle, which means both that they are out of sight and that they are not under any evolutionary pressure to become visually distinct. Members of the genus Amasa can be distinguished from other genera by their truncated abdomens and elytra (wing cases) which have a distinct declivity (downward fold) at the rear. However, telling species apart can be difficult, particularly as most species are known only from a single, or very small number of, specimen(s) held in widely distributed collections. There are currently 47 species of Amasa, from across tropical Asia and Oceania; two species from Madagascar have been assigned to the species, but this is probably erroneous.
In 2011 a species of Amasa found infesting a Eucalyptus grandis plantation in São Paulo State, Brazil, was provisionally identified as Amasa truncata, a widespread invasive species, although further investigation led to the conclusion that this was a morphologically similar, but unknown, species. This new Beetle was reported from Minas Gerais State in Brazil as well as in neighbouring Uruguay in 2015. In 2016 it was reported from Valparaíso in Chile, and by 2018 it had reached Argentina.
Similar specimens found in Cádiz, Spain, in 2009, were initially identified as Amasa resecta, but again were later shown not to belong to this species. In 2018 the same species was found in Antibes, France, and in 2019 in Lisbon, Portugal. A genetic analysis of specimens collected in France found them to be 100% identical to members of an unknown species from New South Wales.
In a paper published in the journal Zootaxa on 12 January 2024, Miloš Knížek of the Forest Protection Service at the Forestry and Game Management Research Institute, and Sarah Smith of the Department of Entomology at Michigan State University, formally describe the unknown Amasa species based upon specimens from Australia, South America, and Europe.
The new species is named Amasa parviseta, where 'parviseta' means 'small hairs' as the hairs on the elytral declivity is almost hairless, with only a few microscopic hairs. The new species is described on the basis of specimens from New South Wales, the Australian Capital Territory, and Queensland in Australia, Alpes-Maritimes Department in France, Galicia in Spain, São Paulo State in Brazil, and Tacuarembó Department in Uraguay. It is also thought to be present in Corsica, Portugal, Minas Gerais, Argentina, and Chile.
Females of Amasa parviseta are 2.38–3.00 mm long and light brown in colour, with slightly darker elytra. Males are unknown. The species was found on Eucalyptus trees and in Eucalyptus leaf litter; some were captured in traps in mixed Eucalyptus and Pine woodland.
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