Abstract:

Objective: Acer truncatum is a precious economic forest tree species in China, and its seed oil contains rich nervonic acid and other substances, which is vital for preventing and treating human neurological diseases. However, in recent years, we have found that A. truncatum seeds have been severely damaged by the larvae of a Cecidomyiid species, Acumyia sp. (Diptera). The present study aims to investigate and identify the natural enemies of Acumyia sp. for environmentally friendly pest management. Method: Through field investigations in Beijing and Inner Mongolia, as well as indoor rearing, a chalcid wasp that parasitizes and preys on the larvae and pupae of Acumyia sp. was discovered. A taxonomic study was subsequently conducted, revealing the parasitoid as a new species, Systasis aceri Yang, Liu et Cao sp. nov., which belongs to the genus Systasis (Hymenoptra, Chalcidoidea, Pteromalidae). In this paper, the new species is described in detail, and color photos are provided. Additionally, the biology of this wasp is reported and compared with other related species. Result: This new species is similar to a parasitic wasp in China, Systasis obolodiplosis Yao et Yang, also a Cecidomyiid parasitoid, but can be distinguished by the following characters: the new species has a golden-green body color, with female body length of 3.4–3.6 mm and male body length of 1.8–2.4 mm (whereas the latter has a blue body with a purple metallic tint; female body length of 2.1 mm and male body length of 1.3 mm); the clypeus shape is square-like with width 1.4 times its height (the latter’s clypeus is much wider, with a width 2.0 times its height); the gaster is long, with a length 2.7 times of its own width (the latter’s gaster is shorter, with a length only 1.8 times its width). Xiao & Huang revised the species of the genus Systasis in China and provided a key to nine species. Using this key, the new species was initially misidentified as Systasis procerula Xiao et Huang. However, the female of the new species differs in other characteristics: post-marginal vein length is 1.4 times the stigmal vein (the latter’s post-marginal vein is shorter than the stigmal vein); antenna is shorter, with the length of pedicel plus flagellum being 1.15 times the head width (the latter is 1.4 times the head width); gaster is much longer, with a length 2.7 times its own width (the latter’sgaster is shorter, with a length only 1.5 times its width). Additionally, the biology of the new species is discussed. The parasitism rate of the new species on the larvae and pupae of Acumyia sp. was about 36%. Its 1st–2nd instar (when they were young and smaller) larvae were parasitic, while the 3rd instar (when they grew larger) and later larvalstages became predatory, capable of preying on 35?52 Acumyia sp. larvae (or puparium) within a single seed. Usually there were 60?126 individuals of the cecidomyiid larvae fed in a single seed and 4?6 parasitoid larvae parasitized/preyed. However, only 1?3 wasps finally emerged. The wasp occurs 2 generations per year and is a preliminary natural enemy of Acumyia sp. Conclusion: The discovery of this natural enemy provides an excellent biological control agent for the Acer seed pest Acumyia sp. This finding is important for protecting the precious tree species A. truncatum and its seed oil resources, offering a potential technique for future biological control of the seed pest.

Key words: Acer truncatum, Acumyia sp., Systasis aceri Yang, Liu et Cao, parasitoid and predatory natural enemy, biological control