Acrocera orbiculus

Kehlmaier, Christian & Almeida, Jorge Mota, 2014, New host records for European Acroceridae (Diptera), with discussion of species limits of Acrocera orbiculus (Fabricius) based on DNA-barcoding, Zootaxa 3780 (1), pp. 135-152 : 138-139

Acrocera orbiculus from Amaurobius erberi (Keyserling) (Amaurobiidae) (fig. 3)

Locality. France, Département Var, near Besse-sur-Isole, 43°19′39.60′′N 6°10′48.56′′E, Oct. 2011, leg & reared by Frits Broekhuis.

Host. Subadult Amaurobius erberi ♂ (DNA-voucher CK564). Collected between dirt and stones in a garden on 16.X.2011. The spider died on 19.X.2011 with the emergence of the acrocerid larva. The host’s barcode was compared to a set of reference barcodes comprising four of the seven Amaurobius species cited for mainland France, including a sequence of an adult male A. erberi from the same locality (DNA-voucher CK665). The latter was collected on 2.VIII.2012 and moulted twice in captivity before becoming an adult in December 2012. Both A. erberi share an identical barcode, except a single substitution, whereas the next closest species differ by an uncorrected genetic pairwise distances of 5.7% ( Amaurobius similis (Blackwall)) and 8.2% ( Amaurobius fenestralis (Stroem)) .

Parasitoid. Acrocera orbiculus ♂ (DNA-voucher CK565). The time from the emergence of the larva from its host (19.X.2011) and the eclosion of the adult fly (1.XI.2011) lasted 15 days and is documented in fig. 3.

Generally, little information is available on host specificity of Acroceridae . The most detailed host range has been documented for Ogcodes (∼100 species) with about 40 host-parasite relationships known, from at least 15 families of Araneomorphae, mostly belonging to the Lycosidae ( Schlinger 1987; Barraclough & Croucamp 1997; de Jong et al. 2000; Cady et al. 1993; Eason et al. 1967; Langer 2005; Larrivée & Borkent 2009; Kehlmaier et al. 2012; this study). In Acrocera , almost 20 host-parasite relationships are known from 7 families of Araneomorphae, mostly Lycosidae and Agelenidae ( Cady et al. 1993; Larrivée & Borkent 2009; Nielsen et al. 1999; Schlinger 1987; Toft et al. 2012; this study). Acrocera orbiculus is comparatively frequently encountered for an acrocerid (surely the most common acrocerid taxon in Europe) and has an Holarctic distribution, ranging from North America (Northwest Territories east to Ontario and Pennsylvania and south to California and Arkansas; Schlinger 1965) to the Palaearctic (from Scandinavia to North Africa, from Spain all through Russia and the Near East to China; Nartshuk 2013), possible also extending into the Afrotropics (a doubtful record from Ethiopia is listed in Nartshuk 1988). But despite this, only four rearing records from three spider families ( Amaurobiidae , Clubionidae and Lycosidae ) have been documented: Amaurobius erberi (this study), Pardosa prativaga ( Nielsen et al. 1999; Toft et al. 2012), Lycosa spec. (as A. globulus in Nielsen 1932) and Clubiona spec. (cited in Schlinger 1987; original author unknown, probably Millot 1938). The life-cycle of A. orbiculus is relatively well known. Detailed accounts include swarming, oviposition behaviour and egg morphology ( Edwards 1984; Ralley 1988) as well as larval morphology and development of early larval stages ( Nielsen et al. 1999; Toft et al. 2012) and emergence from the host to adult eclosion (this study).

Acrocerid larvae normally (but not always) leave their hosts before the spider reaches adulthood, and a morphological identification of the host to species level is often not possible. In this respect, DNA-barcoding is a potentially powerful tool for overcoming this taxonomic gap, provided that a set of morphologically identified reference barcodes of the target group is available for comparison. The obtained molecular evidence also acts as a supplementary voucher, ensuring that future nomenclatural changes to host or parasitoid taxonomy, e.g., splitting of species aggregates, will be easy to incorporate, and the use of this technique is strongly advocated in any future work focusing on host parasitoid relationships.