Hitchhikers at the dinner table: a revisionary study of a group of ant parasitoids (Hymenoptera: Eucharitidae) specializing in the use of extrafloral nectaries for host access

. Extrafloral nectaries (EFNs) are nectar-secreting glands found on plants independent of their flowers. EFNs are diverse in form, present on a wide variety of plants, and their secretions are known to recruit ants. However, much less information has been published on insects with known EFN associations other than ants. Two distinct species groups of OrasemaCameron (Hymenoptera: Eucharitidae) deposit their eggs close to the EFNs of their plant hosts. The simulatrix group comprises six species found in deserts and xeric shrublands of the southwestern United States and Mexico. This species group is revised, retaining O. aureoviridis, O. beameri and O. simulatrix as valid species, and describing O. cancellatasp.n., O. difrancoaesp.n. and O. zahnisp.n. The wayqecha group is from Peru and Colombia and includes the newly described O. wayqechasp.n. and O. quadrimaculatasp.n. Members of the simulatrix group oviposit near EFNs of Chilopsis linearisCav. (Bignoniaceae), Prosopis glandulosaTorr. (Fabaceae), Prosopis velutinaWooton (Fabaceae) and Populus angustifoliaJames (Salicaceae), whereas Orasema wayqecha oviposit on leaves of two species in the family Primulaceae. Monophyly of the two species groups is proposed based on a molecular analysis of ribosomal (28S and 18S) and mitochondrial (cytochrome c oxidase subunit I) DNA, morphological features of the adults and planidia larvae, and their shared behavioural association with EFNs. Adults of both species groups have an expanded postgena that encloses the mouthparts, but are otherwise morphologically divergent. The planidia of both groups also share several features, including long cerci that may facilitate their movements within EFNs. Oviposition near EFNs is proposed as a means of increasing encounter rates of the first-instar larvae with their myrmicine ant host; however, it remains unclear whether the planidia are transported directly by the foraging workers of their host Pheidole (Formicidae: Myrmicinae) or indirectly with the help of an intermediate host. This published work has been registered in ZooBank, .