Biocontrol introduction
Target pest: Therioaphis trifolii (Hemiptera: Aphididae), spotted alfalfa aphid
Agent introduced: Trioxys complanatus (Hymenoptera: Braconidae)
Imported:
1982-1984
Import source:
Cameron et al. (1989) - Australia (where it was introduced in 1977).
Import notes:
Cameron et al. (1989) - six shipments, each of 200-300 individuals, was received from CSIRO (Canberra and Melbourne) from May 1982 to April 1984.
Released:
1983
Release details:
Cameron et al. (1989) - over 50,000 parasitoids were released between January 1983 and April 1985. Releases, all in the North Island, were mainly in Auckland (Tapora 5,000, Helensville 13,500, Mt Albert 6,200, Whitford 1,300, Pukekohe 19,000) with smaller releases in Waikato (Huntly 1,500, Hamilton 1,600), Bay of Plenty (Te Puke 2,000) and Hawke's Bay (Hastings 170).
Establishment:
Cameron et al. (1989) - recovered only from Pukekohe, Helensville and Tapora. At the latter two sites it was only recovered only in 1983; at Pukekohe parasitism levels averaged 16% in the 1984/85 season, peaking at 38% in March, but the parasitoid was not detected after April 1985. Although it has not been recovered since April 1985 it may still persist at very low levels.
Impacts on target:
Cameron et al. (1989) - with the widespread use of lucerne cultivars resistant to T. trifolii this aphid does not a have a significant impact on New Zealand agriculture. Against the background of a small and declining population of T. trifolii it is hard to evaluate the impact of T. complanatus. The rates of parasitism recorded at Pukekohe during spring and late-autumn in the 1984/85 season averaged 30% and over. If T. complanatus persists in New Zealand it may limit any subsequent population increases of T. trifolii.
Impacts on non-targets:
Bulman et al. (2021) - to identify Aphidiinae parasitoids [the subfamily of family Braconidae to which Trioxys 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.
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.
