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

Abstract

Abstract. 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) 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. cancellata sp.n., O. difrancoae sp.n. and O. zahni sp.n. The wayqecha group is from Peru and Colombia and includes the newly described O. wayqecha sp.n. and O. quadrimaculata sp.n. Members of the simulatrix group oviposit near EFNs of Chilopsis linearis Cav. (Bignoniaceae), Prosopis glandulosa Torr. (Fabaceae), Prosopis velutina Wooton (Fabaceae) and Populus angustifolia James (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, http://zoobank.org/urn:lsid:zoobank.org:pub:EA112E3D-52BE-45D1-B03B-8764E8C94BE0.

Interspecific Eavesdropping on Ant Chemical Communication

“…The cues that guide female Orasema wasps to certain plants within their host ant territories currently are unknown (Torréns, 2013), but plant-derived volatiles likely attract the gravid female wasps, as is the case in other parasitoid systems (e.g., Wei et al, 2007). Once the wasps locate their host habitat (Figure 1A, top panel) they lay their eggs on specific plant structures (e.g., extrafloral nectaries or leaves) (Box 3A) (Heraty, 1994;Carey et al, 2012;Herreid and Heraty, 2017). The active wasp larva is then picked up by, or attaches itself to a host ant forager, suggesting that the wasp larva eavesdrops on CHCs or other host recognition pheromones ( Figures 1B,C, top panel).…”

New species of Orasema (Hymenoptera: Eucharitidae) from Central and South America

“…The following changes to the diagnosis provided by Herreid and Heraty (2017) are made: postgena expanded to cover the maxillary complex or open exposing the maxillary complex, labrum with 6-10 digits, face mostly smooth and shining or reticulate, clypeus longer than broad or broader than long. With these changes, the wayqecha group is still easily diagnosed from all other species groups by containing the only Orasema species with maculations on the fore wings.…”

“…Changes to the key provided in Herreid and Heraty (2017) to accommodate the new species are provided below. In the Burks et al (2018) species group key, O. masneri keys to 'undescribed Neotropical species' in couplet 8.…”

“…Confirmed host associations are all with Myrmicinae (Formicidae), with the ancestral host postulated as the genus Pheidole Westwood (Baker et al 2020). Orasema is diverse and has been divided into several species groups starting with Heraty (1994Heraty ( , 2000, with revisions completed for species in the festiva group (Burks et al 2015), xanthopus group (Heraty et al 1993), stramineipes group (Burks et al 2018) and the simulatrix and wayqecha groups (Herreid and Heraty 2017). The lasallei species group described herein is new, one species is added to the wayqecha group, and one new species cannot be placed in existing species groups.…”

Neotropical ant parasitoids (Hymenoptera: Eucharitidae): interpreting taxonomy, phylogeny and divergent morphologies

“…Female eucharitids do not enter the ant nest; eggs are laid on appropriate host plants where they hatch into active, heavily sclerotized first-instar larvae called planidia. The planidia must gain access to the host nest, either by phoresy on ants or on their prey items (Clausen, 1923;Clausen, 1940aClausen, , 1940bDas, 1963;Wilson & Cooley, 1972;Carey et al, 2012;Herreid & Heraty, 2017). Development is completed on the ant pupa within the nest (Lachaud & Pérez-Lachaud, 2012).…”