The Ctenopelmatinae is a species-rich subfamily that includes mostly koinobiont endoparasitoids of sawfly larvae (Hymenoptera: Symphyta). The subfamily is expected to be more diverse in temperate than tropical zones as the primary host groups are relatively scarce in tropical rainforest habitats (Gauld et al. 1997, Veijalainen et al. 2012). In the Neotropics, the subfamily’s distribution extends across the entire region, but ctenopelmatines are still rarely encountered in Neotropical arthropod samples. The region’s ctenopelmatine fauna is very poorly known – there are only 69 described species from South America, Central America and Mexico (Cresson 1874, Townes 1970, Lanfranco 1980, Graf et al. 1991, Barron 1994, Gauld et al. 1997, Reshchikov 2011). In the most recent large study on Neotropical ctenopelmatines, 42 species from Costa Rica belonging to 14 genera were reported (Gauld et al. 1997).

In the present study, we describe a new species of Lathrolestes Foerster from Ecuadorian Amazonia. Lathrolestes is a large genus of the ctenopelmatine tribe Perilissini with 85 described species including 4 species from Costa Rica (Yu et al. 2012). The new species, Lathrolestes gauldi sp. n., was collected by canopy fogging in the lowland rainforests of Ecuadorian Amazonia. This represents the first record of the subfamily Ctenopelmatinae from Ecuador and the Neotropical rainforest canopy. We also provide a key to four species of Lathrolestes occurring in the Neotropical region and six closely related species from the southern United States and Mexico.

The holotype specimen was collected by Dr. Terry L. Erwin and his research team from the canopy of a lowland tierra firme rainforest at Onkone Gare, Department of Orellana, Ecuador, on the 2nd of July, 1995. The site is located near the Yasuní National Park 216 m.a.s.l. in primary rainforest where the vegetation is old and diverse. The annual precipitation exceeds 2500 mm and the temperature always remains above 10 degrees Celsius. For a more specific description of the study site, see Lucky et al. 2002 and Erwin et al. 2005.

The lateral illustration (Fig. 1) of Lathrolestes gauldi shows the habitus and coloration of the species. In addition, we provide more detailed illustrations of the face (Fig. 2), propodeum (Fig. 3), ovipositor (Fig. 4) and areolet of the fore wing (Fig. 5) of the holotype specimen. All digital pictures were taken using an Olympus SZX16 stereomicroscope attached to an Olympus E520 digital camera and combined using the CombineZP program created by Alan Hadley (http://www.hadleyweb.pwp.blueyonder.co.uk/index.htm). The key below is modified from the one presented in Gauld et al. (1997). The morphological terminology follows mainly that of Gauld et al. (1997), wing vein nomenclature is based on Ross (1936).

Only one specimen of Lathrolestes gauldi sp. n. has been found despite the large sampling effort taking place in many Amazonian study localities (see Veijalainen et al. 2012). However, this is a normal situation with rainforest ichneumonids which are relatively difficult to sample, even by using long-term sampling programs (Sääksjärvi et al. 2004). Thus, Lathrolestes gauldi sp. n. seems to be a rare species, and further sampling is needed to clarify its distribution in the Western Amazonia.