Descriptions of four new species of Bactrocera and new country records highlight the high biodiversity of fruit flies in Vietnam (Diptera, Tephritidae, Dacinae).

Recent snap-shot surveys for fruit flies in Vietnam in 2015 and 2017 using traps baited with the male Dacinae fruit fly lures methyl eugenol, cue-lure and zingerone, collected 56 species, including 11 new country records and another 11 undescribed species, four of which are described in this paper. This increases the number of described species known to occur in Vietnam from 78 to 93. Species accumulation curves, based on the Chao 2 mean estimate, suggest that we collected 60-85 % of the local fauna at the sites sampled, and that species diversity decreases with increasing latitude. The four new species are named: Bactrocera (Tetradacus) ernesti Leblanc & Doorenweerd sp. n. , B. (Asiadacus) connecta Leblanc & Doorenweerd sp. n. , B. (Parazeugodacus) clarifemur Leblanc & Doorenweerd sp. n. , and B. (Bactrocera) adamantea Leblanc & Doorenweerd sp. n. In addition to morphological data COI DNA sequence data of both the COI-5P and COI-3P mitochondrial DNA gene regions is provided. Three of the four newly described species are morphologically and genetically easily distinguished from all other members of Dacini. Bactroceraclarifemur sp. n. is superficially similar to B.pendleburyi (Perkins) based on morphology, but there are several apomorphic characters to distinguish the two. Both COI and a segment of the nuclear gene Elongation Factor 1 alpha separate the two species as well.