Abstract
Flies of the family Tachinidae are known for being arthropod parasitoids. Phasiinae, the bug-killing flies, is one of its subfamilies, which is specialized in heteropteran hosts (Hemiptera: Heteroptera). Flies of this group are known to oviposit directly on their heteropteran hosts, and many parasitize important agricultural pests, making them relevant for biological control. Among phasiines, the tribe Leucostomatini is easily distinguished by their characteristic female terminalia, which has structures that resemble a pincer. Leucostoma Meigen is the largest genera with 28 species, and only 10 being recorded in the Neotropical Region. Herein, we present the first direct evidence of an indirect oviposition strategy in bug-killing flies. We observed females of Leucostoma acirostre Reinhard ovipositing directly on the host plant of their hosts. This possibility has already been considered in the literature, and a discussion of this new strategy is presented, as it is relevant for understanding Tachinidae evolution, as well as developing biological control strategies. This is the first record of L. acirostre for the Neotropical Region, as well as a new host record for the rhopalid Harmostes parafraterculus Göllner-Scheiding. Alongside, Leucostoma aterrimum (Villers) specimens were collected from Liorhyssus hyalinus (Fabr.) of Peru, an important quinoa pest from the region, and the first record of the species and host association for the country. We update the distribution of both species, with new records for South America. Both species are redescribed, including photographs, new data for the puparium, and male and female terminalia (both illustrated). Lastly, we discuss the validity of the few Leucostoma non-heteropteran host records, as they are all probably mistakes, and comment on the widespread distribution of some of the genus' species and host use.