Biocontrol introduction
Target pest: Acyrthosiphon pisum (Hemiptera: Aphididae), pea aphid
Agent introduced: Aphidius eadyi (Hymenoptera: Braconidae)
Imported: 1977
Import source: Morocco via USA
Import notes:
Cameron et al. (1981) - a Moroccan strain was imported from the University of California at Riverside, USA, in May 1977. It was imported as Aphidius urticae but since described as Aphidius eadyi [see 'General comments' section].
Released:
1977
Release details: Cameron et al. (1989), 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. 1,580 individuals were released at Helensville near Auckland in the North Island in May 1977. Following the rapid establishment and spread of A. aedyi, 5,000 individuals were redistributed, between 1977 and 1979, to the Rotorua, Taupo and Manawatu areas of the North Island, and to Lincoln (Mid Canterbury) in the South Island.
Establishment:
Cameron et al. (1981) - Aphidius eadyi has now successfully overwintered and has dispersed sufficiently that establishment can be claimed. It was first recovered from a mummified pea aphid in December 1977 at the Phillips release site near Helensville, Auckland (where it was released in September 1977). Within 2 months parasitised pea aphids were common up to 5 km from the initial release site and in one year had dispersed 120 km northward to Ruakaka and a similar distance southward to Hamilton.
Cameron et al. (1989), Cameron & Walker (1989) - all releases led to recovery and establishment. Spread throughout the South Island appears to have resulted from the single release at Lincoln. By the end of 1986 it was established in all lucerne growing areas of New Zealand. Although easy to establish compared to Aphidius ervi (released for control of Acyrthosiphon pisum and Acyrthosiphon kondoi), 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 (A. eadyi is monophagous on A. pisum) 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. (1981) - comparison of areas with and without parasites, in space and time, indicates that A. eadyi has reduced Acyrthosiphon pisum populations.
Cameron et al. (1989), Cameron & Walker (1989) - since the establishment of the polyphagous Aphidius ervi, this parasitoid has partly displaced A. eadyi from A. pisum (upon which A. eadyi is monophagous), although the overall rate of parasitism of A. pisum (30-40%) has not changed. In 1984-85, with both parasitoids present, A. eadyi produced low rates of parasitism in A. pisum, averaging 7% and never exceeding 20%. 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.
Impacts on non-targets:
Teulon et al. (2008) - 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.
General comments:
Starý et al. (1980) - laboratory and field evidence has indicated that "A. urticae Hal. auct.", a common parasitoid of the pea aphid, is in fact a new species, described here as Aphidius eadyi sp. n. This species is known to only parasitise pea aphid; the whole "A. urticae-group" is under current investigation and, for the meantime at least, A. urticae Hal. has become restricted solely to the material reared from the original host, Microlophium evansi on the stinging nettle, Urtica dioica.
References
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
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.
Cameron PJ, Walker GP (1989). Release and establishment of Aphidius spp. (Hymenoptera: Aphidiidae), parasitoids of pea aphid and blue green aphid in New Zealand. New Zealand Journal of Agricultural Research 32: 281-290 https://doi.org/10.1080/00288233.1989.10423463
Cameron PJ, Walker GP, Allan DJ (1981). Establishment and dispersal of the introduced parasite Aphidius eadyi (Hymenoptera: Aphidiidae) in the North Island of New Zealand, and its initial effect on pea aphid. New Zealand Journal of Zoology 8(1): 105-112 https://doi.org/10.1080/03014223.1981.10427947
Starý P, González D, Hall JC (1980). Aphidius eadyi sp.n. (Hymenoptera: Aphidiidae), a widely distributed parasitoid of the pea aphid, Acyrthosiphon pisum in the Palearctic. Insect Systematics & Evolution 11(4): 473-480 https://doi.org/10.1163/187631280794710079
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. 421–430. USDA, Forest Service, Morgantown, WV. https://www.cabi.org/ISC/FullTextPDF/2009/20093074320.pdf
