Target pest: Acaena anserinifolia (Rosales: Rosaceae), piripiri
Agent introduced: Ucona acaenae (Hymenoptera: Tenthredinidae), sawfly
Cameron et al. (1989) - between 1928 and 1940, one shipment of eggs and larvae, and 16 shipments of prepupae of U. acaenae were received from Chile under the name Antholcus varinervis [see entry in the 'General comments' section]. A total of 26,407 insects were sent, from which 11,692 sawflies emerged, 94.6% of which were females. An unidentified fungus destroyed many of the prepupae sent and 184 parasitoids were isolated in quarantine.
Cameron et al. (1989) - the first releases were made in June 1936 when 440 sawflies were liberated near Wanganui (central North Island) and a further 5,600 were released near Hunterville, Wanganui and Eltham (all central North Island). Releases were made in June and July of each succeeding year until 1948, including at Nelson, Marlborough and Otago in the South Island. A total of 30,000 sawflies were released from imported and reared material.
Cameron et al. (1989) - by 1938, it was reported that U. acaenae was increasing in numbers and although population build-up was slow, observations at two North Island populations suggested the insect was well established. These populations were not monitored after 1940 and U. acaenae has not been recorded there since. Observations were made at a release site near Nelson for a further two years, during which time the sawfly caused conspicuous damage to the weed. Unfortunately, the site was destroyed in 1942 and the insect was never recorded again. It is still possible that U. acaenae populations survive in New Zealand, but since it as not been recorded since 1942, this seems very unlikely. The reasons the sawfly did not establish are uncertain. Some claim the larvae were heavily preyed on by birds, but this is unsubstantiated. Fungus was common in the rearing colony and fungal disease may have caused a decline in field populations, but this is speculation.
Paynter et al. (2016) - persisted for four years at Mackay's Bluff, Nelson, until the site was destroyed by fire.
Impacts on target:
Cameron et al. (1989) - was observed causing conspicuous damage to A. anserinifolia at a site near Nelson until that site was destroyed in 1942; U. acaenae has not been recorded in New Zealand since.
Impacts on non-targets:
Cameron et al. (1989) - trials in New Zealand showed U. acaenae did not lay eggs on the foliage of blackberry, raspberry, rose, strawberry or the native Rubus australis. Larvae fed on strawberry leaves but could not complete development on this host. Foliage of the other test species was not attacked.
Smith (1973) - in the 1920s, an Acaena-feeding sawfly was found in Chile and imported into New Zealand in 1928 under the name Antholcus varinervis as a biocontrol agent. However, it is evident from the description of A. varinervis by Spinola, the author of the species, that it is not the Acaena-feeding sawfly introduced to New Zealand. The sawfly imported into New Zealand represents a new genus and species and is described here as Ucona acaenae.
Cameron PJ, Hill RL, Bain J, Thomas WP (1989). A Review of Biological Control of Invertebrate Pests and Weeds in New Zealand 1874-1987. Technical Communication No 10. CAB International Institute of Biological Control. DSIR Entomology Division. 424p.
Paynter QE, Fowler SV, Gourlay AH, Peterson PG, Smith LA and Winks CJ. (2016). The influence of agent rearing success and release size on weed biocontrol programs in New Zealand. Biological Control 101: 87-93
Smith DR (1973). Sawflies of Chile: a new genus and species and key to genera of Tenthredinidae (Hymenoptera: Symphyta). Proceedings of the Entomological Society of Washington 75(4): 402-408 https://www.researchgate.net/profile/David-Smith-38/publication/260798492_Sawflies_of_Chile_A_new_genus_and_species_and_key_to_genera_of_Tenthredinidae_Hymenoptera_Symphyta/links/5602b9f608ae849b3c0e52a5/Sawflies-of-Chile-A-new-genus-and-species-and-key-to-genera-of-Tenthredinidae-Hymenoptera-Symphyta.pdf
Valentine EW (1970). A list of the phytophagous Hymenoptera in New Zealand New Zealand Entomologist: 4(4) 52-52