The megadiverse parasitoid wasp family Ichneumonidae (Hymenoptera) is classically considered an exception to the extensively studied latitudinal diversity gradient: the majority of ichneumonid species are described from temperate regions. The gradient has been hypothesized to be dependent on the biology of the wasps, but recently questions of sampling and description biases have been raised. Here, we show with primary data that the species richness of Ichneumonidae is markedly underestimated in tropical areas and that latitudinal diversity patterns in the family remain uncharacterized. We discovered a startling 177 likely undescribed orthocentrine species with relatively low sampling effort in the forests of Central America and Amazonian Ecuador, over three times the previously known orthocentrine diversity in the world's tropics. Species accumulation curves reveal that we are just beginning to unveil the true extent of tropical orthocentrine diversity. We also found evidence for cryptic species; our DNA analysis revealed additional species not easily distinguishable using morphological characteristics. The difficulty in establishing species richness patterns of Ichneumonidae probably follows from the relative lack of taxonomic expertise and the low density of ichneumonid species throughout the landscape.

Abstract. 1. Previous studies have found the parasitoid wasp family Ichneumonidae (Hymenoptera) to have an exceptional latitudinal species richness gradient that peaks at mid-latitudes instead of the tropics; however, insufficient tropical sampling and species description may have biased the conclusions. It has been unclear which subfamilies might be species rich in tropical lowland rain forests.2. This study reports the subfamily abundance composition of a large ichneumonid data set (>30 000 individuals in 20 subfamilies) collected by Malaise traps and insecticidal canopy fogging in Amazonian Ecuador and Peru and suggests which subfamilies would be important for future study.3. Relative abundance data from one Peruvian site are compared to similar lowland samples from Costa Rica and Georgia (USA).4. Contrary to a common assumption, a number of ichneumonid subfamilies are very abundant and presumably species rich in western Amazonia. Cryptinae and Orthocentrinae are noticeably the two most abundant subfamilies, and a number of koinobiont lepidopteran parasitoids, which are generally thought to be scarce in the tropics, are also surprisingly abundant (e.g. Anomaloninae, Banchinae and Cremastinae). However, the subfamilies whose primary hosts are rare in the tropics (e.g. Ctenopelmatinae, Tryphoninae) can still be expected to be more diverse in the temperate than in tropical zone.5. Further research on the latitudinal species richness gradient within different ichneumonid subfamilies is encouraged to help understand what factors determine macroecological species richness patterns and what is the total number of ichneumonid species on earth.

Utilising short‐term but geographically extensive sampling in Guatemala, Honduras, and Nicaragua, we examined altitudinal trends in species richness and diversity of ichneumonid parasitoid wasps. This study covered 19 subfamilies, including four globally large subfamilies that have not yet been taxonomically revised in the Neotropics. Sampling was done at 25 sites classified into three elevational categories on the basis of the average elevation of traps at each site (low 34–659 m a.s.l., middle 1033–1709 m a.s.l., and high 1930–2565 m a.s.l.). A total of 2847 ichneumonid individuals were captured and sorted into 751 morphospecies, most of which were identified to the genus level. We found a clear compositional gradient in ichneumonid communities along the elevational gradient, as the majority of species were restricted to either one elevational zone or two adjacent zones. In our data, mid‐ and high‐elevation sites had generally higher ichneumonid species richness and diversity than low‐elevation sites. These trends were largely similar to those found in larger scale Mesoamerican ichneumonid studies. Yet, the low ichneumonid richness at low elevations may partly be a sampling artefact. This provides a new piece of evidence for the suggestion that extensive sampling is needed for uncovering the real diversity of ichneumonids in tropical lowland forests, and that the reputation of Ichneumonidae as a notable example of a reversed latitudinal diversity gradient may be undeserved.

Xanthopimpla Saussure, 1892 is one of the largest genera of the family Ichneumonidae. Th e genus is very species rich in Indo-Australia but poorly represented in the Neotropical region. In this paper two morphologically very distinctive species of the genus, X. amazonica sp. n. Gómez, Sääksjärvi & Veijalainen, and X. jussilai sp. n. Veijalainen, Sääksjärvi & Broad, are described and illustrated. Th e new species have been collected in the Peruvian and Ecuadorean Amazonia. A revised key to the Neotropical species of the genus is provided. Xanthopimpla aurita Krieger is recorded for the fi rst time from Peru.