Adults are small sawflies, almost entirely dark brown other than pale, yellow to white legs and palps. The summer and winter generations may be distinguished by the length of the genae (Blank et al., 2010).
A. leucopoda is best detected as a feeding larva on leaves, the ‘zigzag’ browsing traces being easily recognisable as this is the only species known to produce such feeding damage on elm. Leaf-miners on elm feed within the leaf and may be mistaken for A. leucopoda, particularly the species producing more chaotic mines (e.g. Stigmella spp.), though these do not chew through the entire leaf. Once found, mature larvae can be swiftly identified by looking for T-shaped marks on thoracic legs 2 and 3 and a transversal lateral dark stripe between the stemmata. Adults are harder to find, though if captured they can be keyed out through Blank et al. (2010). The lattice-like pupal cocoons are also distinctive and can usually be found on the underside of leaves. Eggs and overwintering cocoons, particularly if the latter have fallen to the ground, are more difficult to detect. Adults are known to fly to yellow sticky panel traps often used for monitoring other sawflies, which should be a suitable method for detecting adults (Vétek et al., 2016).
Related invasive species
- Aproceros leucopoda
Related Farm Practice
- Defoliation
- Feeding
Elm zigzag sawfly is considered a minor pest within its native range in East Asia, but since first arriving in Hungary and Poland in 2003 the sawfly has spread rapidly through Europe and is continuing to expand its range. Severe localized defoliation has been recorded by the species throughout Europe on elms in a variety of situations. Most elm species are utilised as host plants, which combined with it being both parthenogenic and multivoltine means populations can build up rapidly in suitable areas. No specific predators are known, and whilst parasitoids have been described on the species in Europe no studies have investigated their efficacy at controlling elm zigzag sawfly. This species was removed from the EPPO Alert List in 2015 following no international action on the species being requested by the EPPO member countries.
Looking for the 'zigzag' feeding pattern of young A. leucopoda larvae on elm trees is the most used method for detecting the species. If found, larvae can then be keyed through using Blank et al. (2010). Older larvae often eat over the original feeding trace, obscuring it (Vétek et al., 2017). The lattice-like pupal cocoons are also distinctive, usually being found on the underside of leaves. Heavy infestations may lead to extreme defoliation, but the 'zigzags' should still be visible, along with pupal cocoons.
Reviews of elms (Ulmus spp.) in botanical gardens have revealed a number of species attacked by A. leucopoda which are only rarely planted through Europe, plus others which have not been attacked (Blank et al., 2014;Vétek et al., 2017). However, some of these records are hampered by small sample sizes (n=1 in some cases);subsequent work may find that such species are eventually attacked by A. leucopoda. Nevertheless, localized host preferences have been detected, such as an apparent aversion to Ulmus laevis in Germany (Blank et al., 2014) and in Poland (Borowski, 2018), despite this being a host tree elsewhere. Zúbrik et al. (2017) found U. laevis to be fed upon by A. leucopoda but recorded no evidence of the species on U. glabra. This may be due to climatic differences between the regions in which U. glabra grows within Slovakia, as U. glabra is an important host elsewhere (Blank et al., 2010;Csóka et al., 2012;Vétek et al., 2017). Elms can often be hard to identify to species level, which along with the genus’s complicated taxonomic history means that there may be occasional issues with host identification and differences in the names reported.
Successful development by A. leucopoda on non- Ulmus species has not been reported. Papp (2018) showed that whilst females will lay eggs on Zelkova serrata and Hemiptelea davidii (both Ulmaceae) larvae appeared not to complete development. There is thus no evidence that either species is a true host for A. leucopoda.
Significant wild hosts include Ulmus 'Lobel', Ulmus 'New Horizon', Ulmus 'Rebona', Ulmus 'Regal' and Ulmus 'Resista'.