Paraulax Kieffer and Cecinothofagus Nieves-Aldrey & Liljeblad (Cynipidae: Paraulacini) were long supposed to be gall-makers on southern beeches (Nothofagus, Nothofagaceae). Dissections of galls on Nothofagus Blume, suggested that Cecinothofagus could be instead either endoparasitoid or inquiline of Aditrochus larva (Chalcidoidea). We sequenced the universal COI barcode and Ultra-Conserved Elements (UCEs) from young larvae of Aditrochus collected from galls on Nothofagus and highlighted that one of them also contained DNA from Cecinothofagus ibarrai Nieves-Aldrey & Liljeblad. So far, when galls attributed to Aditrochus were dissected in early development stages they all contained only a single larva and no remains of other larvae. Conversely, when Cecinothofagus ibarrai was reared from galls on Nothofagus, remains of the host larva were observed inside the larval chamber. Altogether, biological observations and molecular results suggest that Cecinothofagus ibarrai is likely an endoparasitoid of Adritrochus. This result confirms the tribe Paraulacini as being entomophagous and supports the hypothesis of an ancestral parasitoid lifestyle for Cynipoidea.

Biology, Cynipoidea, Chalcidoidea, Nothofagus

Paraulacini is a tribe of Cynipidae that contains two closely related genera, Paraulax Kieffer and Cecinothofagus Nieves-Aldrey & Liljeblad (Nieves-Aldrey et al. 2009). Unlike most Cynipidae that are found in the Northern Hemisphere, the six species described in Paraulacini occur in southern South-America (Argentina and Chile; Nieves-Aldrey et al. 2009). Our lack of biological knowledge on Paraulacini would have been anecdotal if the tribe was not recovered sister to all other Cynipoidea in a recent phylogenomic hypothesis proposed by Blaimer et al. (2020). Acquiring knowledge on their biology has thus become crucial to accurately infer the ancestral lifestyle of Cynipoidea.

Paraulax and Cecinothofagus were long supposed to be gall-makers on southern beeches (Nothofagus, Nothofagaceae) (Dalla Torre and Kieffer 1910; De Santis et al. 1993; Ronquist 1999; Csóka et al. 2005), probably by analogy with the Cynipidae of the northern hemisphere that induce gall on many plant lineages (Ronquist 1999). As of today, the biology of Paraulax remains unknown. Dissections of galls on Nothofagus suggested that Cecinothofagus could be instead either endoparasitoid or inquiline of larva of Aditrochus Rübsaamen (Chalcidoidea) (Nieves-Aldrey et al. 2009). Along with the genera Espinosa Gahan and Plastobelyta Kieffer, Aditrochus belongs to the tribe Melanosomellini (Pteromalidae, Ormocerinae) that only occurs in southern South America (Bouček 1988; De Santis et al. 1993). As for Paraulacini, the biology of Aditrochus is poorly known. Aditrochus is indeed supposed to be a gall-maker (Bouček 1988), while Espinosa and Plastobelyta have been considered inquilines or parasitoids of gall-makers (Bouček 1988).

In the course of a project to infer the tree of life of Chalcidoidea, we sequenced the universal COI barcode and Ultra-Conserved Elements (UCEs) from larvae of Aditrochus and highlighted that one of them contained DNA from another species that was identified as Cecinothofagus ibarrai. We discuss the implication of such result in the light of biological data to infer the most likely trophic relationships between Aditrochus and Cecinothofagus (Fig. 1).

Figure 1. 

Adults of Aditrochus coihuensis (above) and Cecinothofagus ibarrai wasps (under) showing their different size. Photograph J.L. Nieves-Aldrey.

Cynipids reared from galls on Nothofagus (Paraulax and Cecinothophagus) have long been supposed to be gall inducers (Dalla Torre and Kieffer 1910; De Santis et al. 1993; Ronquist 1999; Csóka et al. 2005). Gall dissection by Nieves-Aldrey et al. (2009) (see also Figs 3, 4) suggested that species of Cecinothofagus were instead parasitoids or lethal inquilines within galls induced by species of Aditrochus.

Figure 3. 

Cross section of galls of Aditrochus species on Nothofagus showing the central larval chamber and the gall inducer Aditrochus larva (note the absence of remains of other larvae inside the chamber). A, B Aditrochus coihuensis C Aditrochus fagicolus D–F Aditrochus coihuensis larva paralyzed by an endoparasitoid (likely Cecinothofagus ibarrai). Photographs J.L. Nieves-Aldrey.

Figure 4. 

Cross sections of galls of Aditrochus species on Nothofagus showing emergences of the gall inducer Aditrochus adult and the endoparasitoid Cecinothofagus adult A, B Cecinothofagus ibarrai (Cynipidae) (note the remains of the host larva inside the larval chamber) C Cecinothofagus ibarrai emerged from a gall of Aditrochus gnirensis on Nothofagus antarctica D Adult Aditrochus coihuensis emerged from its gall on Nothofagus dombeyi. Red arrows show the remains of the host larva. Photographs J.L. Nieves-Aldrey.

Larvae assigned to Aditrochus were observed by one of us (JLNA) in dozens of dissected galls collected on Nothofagus species in Chile in field campaigns from the years 2005, 2006, 2012, 2013 and 2014. In all cases, the galls dissected in early development stages contained only a single larva occupying the central larval chamber in the gall (Fig. 3). Furthermore, no remains of other larvae were present which confirmed that the larvae were gall inducers and not parasitoids. Here we confirm that these larvae belong to Chalcidoidea on the basis of morphology and both DNA barcoding and sequencing of UCEs. Although the biology of Melanosomellini is poorly known (only half of the 30 genera have reliable host records; Noyes 2019), most of them are considered to be gall makers (Noble 1941). Trichilogaster acaciaelongifoliae (Froggatt, 1892) has even been used to control the invasive Acacia longifolia (Andr.) Willd. in South Africa. Melanosomellini are associated with eight plant families that originated in the southern hemisphere: Myrtaceae (7 genera), Fabaceae Mimosoideae (5), Fagales [Nothofagaceae (3) and Casuarinaceae (2)], Malvales [Malvaceae (2) and Elaeocarpaceae (1)], Celastraceae (1) and Apocynaceae (1). However, Brachyscelidiphaga appears to be an inquiline in galls of Apiomorpha Rübsaamen (Hemiptera, Eriococcidae) on Eucalyptus L’Hér. (Bouček 1988). Therefore, our results are in agreement with the most common biology found in Melanosomellini.

Conversely, when Cecinothofagus ibarrai was reared from galls on Nothofagus, remains of the host larva were observed inside the larval chamber (Fig. 4). Here, we show that one larva of A. coihuensis (JRAS07470_0104) also hosted the DNA of Cecinothofagus ibarrai. From all these results, we can conclude that Cecinothofagus ibarrai was likely an endoparasitoid of this larva. This result confirms that the early evolution of cynipoids may be entomophagous in nature (Blaimer et al. 2020). In this study where the ancestral lifestyle of Cynipoidea was estimated to be either inquiline or parasitoid, our results may contribute to remove ambiguity.

To conclude, our study demonstrated that the usual trophic interactions observed in northern hemisphere on Fagaceae (cynipids are gall makers and pteromalids are parasitoids) is reversed in the southern hemisphere on Fagaceae (pteromalids are gall makers and cynipids are parasitoids or inquilines) … … a bit like water drains the other way Down Under!