Target pest: Acyrthosiphon pisum (Hemiptera: Aphididae), pea aphid
Agent introduced: Aphidius ervi (Hymenoptera: Braconidae)
Cameron et al. (1989) - 1977 Japan via University of California, Riverside; 1977 Israel via University of California Riverside; 1977 Greece via University of California, Riverside; 1977 Tashkent (USSR) via University of California, Riverside; 1977 Belgium via University of California, Riverside; 1979-1980 Tasmania; 1981 Rothamstead, UK.
Cameron et al. (1989) - this species was obtained from three sources and was imported over a period of nearly four years [see 'Import source' section]. Three strains obtained from Riverside (Japan, Tashkent, Belgium) were reared individually and released in significant numbers. The Israel and Greece strains were released in very small numbers and cultures were not maintained. The material from Tasmania included a strain which originated in Japan, as well as a naturalised Tasmanian strain. The Tasmanian material was reared individually as well as in combination with the Belgian strain.
Cameron et al. (1989), Cameron & Walker (1989) - Japan strain 1977-78, Israel 1977-78, Greece 1977-78, Tashkent 1977-79, Belgium 1977-81, Tasmania 1979-81, Belgium x Tasmania 1979-81, Rothamsted 1981.
Cameron & Walker (1989) - parasitoids were released as mummies harvested from plants, or as mummies and parasitised aphids on potted plants. Usually, harvested mummies were released into field cages which were removed after emergence of adult parasitoids, but occasionally they were scattered over lucerne at the release site. Releases were made as follows: Japan strain - released in the Auckland and Hawkeâ€™s Bay regions, 1977-78 (1,840 parasitoids released); Belgium strain - Auckland, Waikato, Taupo, Wanganui, 1977-81 (25,290); Tashkent strain - Auckland, Marlborough, Nelson, Mid Canterbury, Dunedin, 1977-79 (1,090); Tasmania strain - Auckland, Taupo, Wanganui, 1977-81 (26,380); Belgium strain x Tasmania strain - Auckland, Taupo, Wanganui, 1977-81 (10,840); UK strain - Taupo, 1981 (1,600).
Cameron et al. (1989), Cameron & Walker (1989) - Aphidius ervi was recovered in the first phase of rearing and release (March 1977 to June 1979) but did not persist at many sites; only the Tashkent strain persisted, and this only in the South Island. Following releases of Tasmanian and Tasmanian x Belgian A. ervi from 1979 to 1981, recoveries were made in the Wairakei-Reporoa area (near Taupo) and the spread of this population appears to be responsible for the establishment of this species in the North Island. By 1986, A. ervi was present from north of Auckland to the Manawatu in the North Island, with separate populations in Canterbury and Otago in the South Island. Although difficult to establish compared to Aphidius eadyi (released for control of Acyrthosiphon pisum, and monophagous on this aphid), A. ervi has replaced A. eadyi as the predominant parasitoid of Acyrthosiphon spp. in the North Island. This dominance may result from its polyphagous nature which allows it to utilize both Acyrthosiphon spp. (A. pisum and A. kondoi) in lucerne, as well as alternative hosts in adjacent crops.
Impacts on target:
Cameron et al. (1989), Cameron & Walker (1989) - Aphidius ervi has been slower to establish and spread than Aphidius eadyi (released for control of Acyrthosiphon pisum, and monophagous on this aphid) but has become dominant over A. eadyi. Rearing from mixed Acrythosiphon populations (A. pisum and A. kondoi) in New Zealand has shown A.ervi prefers A. kondoi and has also partly displaced A. eadyi from A. pisum. With the establishment of A. ervi the overall rate of parasitism of A. pisum has not increased, but A. kondoi is now parasitised as well, at a rate similar to combined parasitism by both parasitoids on A. pisum. In 1984-85, A. ervi parasitism frequently exceeded 40% in A. kondoi and rarely exceeded 20% in A. pisum. Hyperparasitioids have been reared from an average of 47% of Aphidius mummies and may reduce the impact of the parasitoids. However, a clear change occurring in lucerne in New Zealand over the period of parasitoid introduction and establishment has been the decline in aphid density, although other factors may have contributed to this decline.
Cameron et al. (1993) - Aphidius ervi is categorised as exerting â€śpartialâ€ť control (defined as â€śadditional control remains commonly necessary butâ€¦pest outbreaks occur less frequentlyâ€ť) over Acyrthosiphon pisum and A. kondoi.
Impacts on non-targets:
Carver (2000) - a new indigenous aphid, Aphis cottieri sp. nov. is described. One specimen from Mid Canterbury (South Island) was parasitised by Aphidius sp. near ervi. The recorded parasitoid is conspecific with or closely related to Aphidius ervi, which, as known, is a selectively polyphagous species with a preference for Acyrthosiphon spp. in pastures and Metopolophium and Sitobion spp. in cereal crops, but not for Aphis sp. The situation warrants further investigation.
Teulon et al. (2008) - a specimen considered to be A. ervi was identified in New Zealand in 1963 from Aulacorthum solani (glasshouse potato aphid, an exotic pest) on Histeropteris excelsa (a fern). DNA sequencing of parasitoids attacking New Zealand native aphids, from collections made since 1998, mostly in the South Island, found a range of braconid and aphelinid species. While some species have yet to be fully characterised and may be New Zealand native parasitoids new to science and other species need to be verified using morphological characters, one Aphidius sp. attacking Aphis healyi is a putative introduced species.
Bulman et al. (2021) - to identify Aphidiinae parasitoids [the subfamily of family Braconidae to which Aphidius belongs] of native New Zealand aphids, native aphids were collected throughout the South Island between 2006 and 2018. Aphidiinae parasitism was rare; in total, parasitism was observed from eight native aphid species at 16 locations. All cases of parasitism were by phylogenetically related native Aphidiinae, and it seems reasonable to conclude that this is the predominant parasitoid threat that these aphids experience. The total number of parasitoids located was low due to the rarity of the aphid hosts themselves, so the possibility of infrequent interactions between biocontrol agents and endemic aphids cannot be eliminated. However, over the 14-year collection period of this study, no examples of native aphid parasitism by introduced Aphidiinae was found. Among the native aphids, parasitism of Aphis cottieri was of particular interest because a parasitoid from this host was previously described as Aphidius ervi or a closely related species [see Carver (2000) above]. Although it was the most easily located and abundant endemic aphid species, parasitism of A. cottieri in the wild was rarely observed during this study. The few examples observed were by native aphidiines. These observations are consistent with prior evidence suggesting that A. ervi should not parasitise Aphis spp. It seems highly likely that the previously observed A. cottieri parasitoid was a native species detected in this study and not A. ervi.
Bulman S, Drayton GM, Cameron PJ, Teulon DAJ, Walker GP (2021). Endemic New Zealand aphids (Hemiptera: Aphididae) parasitised by native Aphidiinae (Hymenoptera: Braconidae), not biological control parasitoids. Austral Entomology 60(4): 713-721 https://doi.org/10.1111/aen.12564
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Carver M (2000). A new indigenous species of Aphis Linnaeus (Hemiptera: Aphididae) on Muehlenbeckia (Polygonaceae) in New Zealand. New Zealand Entomologist 22: 3-7 https://doi.org/10.1080/00779962.1999.9722049
Teulon DAJ, Drayton GM, Scott IAW (2008). Exotic introductions of primary parasitoids of aphids in New Zealand: the good and the bad. In: Proceedings of the Third International Symposium on Biological Control of Arthropods (eds PG Mason, DR Gillespie & C Vincent), pp. 421â€“430. USDA, Forest Service, Morgantown, WV. https://www.cabi.org/ISC/FullTextPDF/2009/20093074320.pdf