Subfamily Composition of Ichneumonidae (Hymenoptera) from Western Amazonia: Insights Into Diversity of Tropical Parasitoid Wasps
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Insect Conservation and Diversity (2012) doi: 10.1111/j.1752-4598.2012.00185.x Subfamily composition of Ichneumonidae (Hymenoptera) from western Amazonia: Insights into diversity of tropical parasitoid wasps ANU VEIJALAINEN,1 ILARI E. SA¨ A¨ KSJA¨ RVI,1 TERRY L. ERWIN,2 1 3 ISRRAEL C. GO´ MEZ and JOHN T. LONGINO 1Department of Biology, Section of Biodi- versity and Environmental Science, University of Turku, Turku, Finland, 2Department of Entomology, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA and 3Department of Biology, University of Utah, Salt Lake City, UT, USA 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 ichneumo- nid 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 low- land 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 Or- thocentrinae 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 Cremas- tinae). However, the subfamilies whose primary hosts are rare in the tropics (e.g. Cte- nopelmatinae, 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 ich- neumonid subfamilies is encouraged to help understand what factors determine mac- roecological species richness patterns and what is the total number of ichneumonid species on earth. Key words. Abundance, canopy, idiobiont, koinobiont, Neotropics, parasitoid wasps, tropical rain forest. Introduction temperate zones have fewer kinds of animals and plants, and the Arctic and Antarctic regions by comparison are stark and bar- One of the most striking biogeographical and ecological patterns ren (Wallace, 1878; Hawkins, 2001). A classical exception to the is the gradient of increasing species diversity from the poles to regular latitudinal pattern is the apparent anomalous species the equator (Gaston, 2000; Hillebrand, 2004). The earliest richness gradient of the large family Ichneumonidae (Hymenop- explorer-naturalists noticed that the tropics teem with life, the tera; e.g. Willig et al., 2003). Most ichneumonids are parasitoids that develop feeding in (endoparasitoids) or on (ectoparasitoids) other arthropods, Correspondence: Anu Veijalainen, Zoological Museum, FI-20014 finally killing the host. Koinobiont species generally allow the University of Turku, Turku, Finland. E-mail anuvei@utu.fi host to continue its development after oviposition, and they have Ó 2012 The Authors Insect Conservation and Diversity Ó 2012 The Royal Entomological Society 1 2 Anu Veijalainen et al. become specialised to tolerate the host’s immunological and undescribed arthropod species (Erwin et al., 2005; Erwin & Ge- chemical defences, whereas the more generalist idiobionts para- raci, 2009). Amazonian ichneumonids remained basically unex- lyse the host permanently or even kill it to circumvent its plored up until 10 years ago when the first (and so far only) immune system (see Askew & Shaw, 1986; Santos & Quicke, long-term Malaise trap project was carried out in north-eastern 2011). Unlike most other groups of organisms (Gaston, 2000), Peru (Sa¨ a¨ ksja¨ rvi, 2003). Gradually, the ichneumonids at the An- several studies have failed to demonstrate an increase in ichne- dean and Andean–Amazonian interface are also becoming bet- umonid species richness from temperate latitudes towards the ter known (Palacio et al., 2007; Broad et al., 2011; Castillo tropics (Owen & Owen, 1974; Janzen, 1981; Skillen et al., 2000; et al., 2011). A lack of knowledge on the South American ichne- but see Gauld, 1987). This is puzzling, because many arthropod umonid fauna restricts our understanding about the family’s glo- groups that ichneumonids utilise as hosts show their highest spe- bal distribution and diversity; thus, the situation needs serious cies richness in tropical regions (Robbins & Opler, 1997; Ho¨ fer attention. & Brescovit, 2001; Erwin et al., 2005; but see Kouki et al., Parasitoids play an important role in tropical trophic interac- 1994). Despite their proclaimed poor representation in the tro- tions and food web dynamics (Lewis et al., 2002; Tylianakis pics, Ichneumonidae has still been estimated to be possibly the et al., 2007; Dyer et al., 2010), and thus, it is important to have a largest animal family on earth (Gauld et al., 2002: over 100 000 clear understanding of their diversity. Tropical biodiversity is species; Yu et al., 2005: ca. 23 300 described species). As a result, disappearing at an alarming rate owing to human activities (Bass their global distribution has prompted discussion and multiple et al., 2010), accentuating the need for accurate assessment of hypotheses to explain the supposed latitudinal species richness parasitoid diversity. Shaw and Hochberg (2001) even question gradient anomaly (see Sime & Brower, 1998; Santos & Quicke, the utility of conservation initiatives that do not take parasitic 2011). wasps into account. A recent review by Santos and Quicke (2011) explores the As the family is of enormous size and encompasses a great possibility that some large-scale patterns of parasitoid insects variety of parasitoid life history strategies (Gauld, 2000), it seems may be artefacts owing to biases in species sampling and descrip- best to investigate the latitudinal species richness gradient with tion, and they explain that much of the current overall picture smaller clades or functional groups within the family. The main can follow from differential latitudinal representation of differ- aim of this study is to show which subfamilies might have a regu- ent subfamilies. However, it has not been demonstrated which lar latitudinal species richness gradient in the Western Hemi- subfamilies might be more species rich in the tropics than in tem- sphere. We hypothesise that some ichneumonid subfamilies are perate regions. Indeed, the lowland tropics have been under- very abundant in the Neotropics – even more abundant than sampled compared to the temperate zone, and the studies in the they are in extra-tropical samples from southern USA. This tropics have not embraced multiple collecting methods, time study reports the subfamily abundance composition of a data periods or habitats. Species accumulation curves and propor- set collected in the lowland rain forests of Ecuador and Peru. tions of undescribed species per sample still suggest that a major- The results of one of the Peruvian sites is compared to published ity of tropical lowland ichneumonid species are yet to be data from Central American lowland rain forest (La Selva, discovered (Horstmann et al., 1999; van Noort, 2004; Sa¨ a¨ ksja¨ rvi Costa Rica) and North American temperate forest (Hitchiti et al., 2004). Certain ichneumonid subfamilies and tribes, for Experimental Forest, Georgia, USA). example some idiobionts (Pimplinae, Rhyssinae and Cryptini) and nocturnal koinobionts (Ophioninae), have in fact been observed to be at their richest in tropical regions (Gauld, 1986, Material and methods 1987; Sa¨ a¨ ksja¨ rvi et al., 2004; Zu´ n˜iga Ramirez, 2004). Whether these are the only groups more diverse in the tropics is still open Field sampling was carried out at three study sites in western to debate. For example, Santos and Quicke (2011) highlight the Amazonia (Fig. 1), under the aegis of three separate biodiversity Orthocentrinae, a koinobiont subfamily typically associated inventory projects. The sampling was carried out by ground- with fungivorous dipteran hosts (but see Yu et al., 2005 for other level Malaise traps in Peru and insecticidal canopy fogging in host taxa), whose tropical fauna might be neglected because of Ecuador during 1994–2006. the species’ small body size. The Neotropical region is the focus of this study. The Costa Rican Ichneumonidae are relatively well documented (Gauld, Ecuador, Orellana: Onkone Gare and Tiputini 1991, 1997, 2000; Gauld et al., 1998, 2002). Taxonomic papers have also been published on the Mexican and Cuban faunas In eastern Ecuador, TLE and his research team used insecti- (Kasparyan & Ruı´z Cancino, 2005, 2008; Ferna´ ndez Triana cidal canopy fogging to sample arthropods near Yasunı´ et al., 2006; Gonza´ lez-Moreno, 2011). Elsewhere in the Neo- National Park, Department of Orellana, from the rain forest tropics, studies are scattered and few (see Yu et al., 2005). Data canopy (see Lucky et al., 2002; Erwin et al., 2005). The team for Amazonian Ichneumonidae are still markedly wanting. The worked at two study sites, Onkone Gare (OG; 0°39¢25.685¢¢S, largest rain forest area in the world spreads across the Amazon 76°27¢10.813¢¢W) and Tiputini Biodiversity Station (TBS; River