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The Behavior and Systematics of Extrafloral Nectary Associated Orasema (Hymenoptera: Eucharitidae)


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 Orasema Cameron (Hymenoptera: Eucharitidae) are associated with EFNs of their plant hosts. The Orasema simulatrix- and wayqecha- species groups are proposed as sister groups based on morphological and molecular evidence. The simulatrix-group is comprised of 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. cancellata n.sp., O. difrancoae n.sp., and O. zahni n.sp.. The wayqecha-group is from Peru and Colombia and includes the newly described O. wayqecha n.sp. and O. quadrimaculata n.sp.. Members of the simulatrix-group oviposit near EFNs of Chilopsis linearis Cav. (Bigoniaceae), Prosopis glandulosa Torr. (Fabaceae), Prosopis velutina Wooton (Fabaceae) and Populus angustifolia James (Salicaceae), whereas Orasema wayqecha oviposits on leaves of two species of Myrsine (Myrsinaceae). Relationships are proposed based on a molecular analysis of ribosomal (28S and 18S) and mitochondrial (COI) DNA, and their shared behavioral association with EFNs is discussed. Adults from both species groups have an expanded postgenal margin that encloses the mouthparts, but are otherwise morphologically distinct. 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. It is thought that the EFN associated planidia are carried to the ant brood via the infrabuccal pocket of Pheidole foragers. These host-planidia interactions are examined in a variety of field and laboratory setting trials.

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