Target pest: Hyperomyzus lactucae (Hemiptera: Aphididae), sowthistle aphid
Agent introduced: Aphidius sonchi (Hymenoptera: Braconidae)
Stufkens & Farrell (1994) - sowthistle aphid (Hyperomyzus lactucae) mummies containing developing A. sonchi were collected from numerous sites in southeast Australia and imported into quarantine at Lincoln, Canterbury in 1992 and 1993. Emerging adult parasitoids were used to found a culture on sowthistle aphids.
Stufkens & Farrell (1995) - batches of 1,000-18,000 mummified hosts and adult parasitoids were released between February and November 1994 on sowthistle in blackcurrant crops or market gardens at one or two sites in the following regions: Waikato, Hawkeâ€™s Bay and Manawatu in the North Island; Nelson, North Canterbury, Mid Canterbury, South Canterbury and Southland in the South Island.
Stufkens & Farrell (1995) - surveys of sowthistle for establishment were undertaken at release sites and sites in Bay of Plenty (in the North Island) and Marlborough (in the South Island) in November 1994 and May 1995. By May 1995, A. sonchi was found at all surveyed sites except South Canterbury and Southland. Substantial rates of parasitism were recorded in November 1994 in Bay of Plenty and Marlborough, where no releases were made, indicating that A. Sonchus was established in these regions prior to the releases.
Impacts on target:
Stufkens & Farrell (1995) - surveys of blackcurrants at two Nelson sites and two Mid Canterbury sites in November 1994 yielded few (total 44) mummies of H. lactucae in dense aphid populations. No parasitism was found in dissections of 1,056 sexual forms collected from blackcurrants at these sites in May 1995, when 16-68% parasitism was found in H. lactucae on adjacent sowthistles. In New Zealand, H. lactucae alternates between sowthistle and blackcurrant [with the sexual forms infesting blackcurrant (Stufkens & Farrell 1994)]. Sexual forms of H. lactucae were parasitised by A. sonchi in the laboratory; blackcurrant foliage may be unattractive to A. sonchi and a further study of factors limiting parasitism in blackcurrants is required.
Impacts on non-targets:
Stufkens & Farrell (1994) - host range testing was carried out in quarantine at Lincoln. Twenty-three aphid species (including five of the seven known native species) were exposed to A. sonchi in choice and no-choice tests. Several exotic aphid species other than H. lactucae were parasitised. None of the native species were parasitised, nor any of the seven exotic species closely related to natives.
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.
Stufkens & Farrell (1994) - permission to release A. Sonchus was requested on the grounds that Hyperomyzus species are the only known hosts in the field and that in laboratory trials no native species or exotic species closely related to natives were attacked [see â€˜Impacts on non-targetsâ€™ section]. Permission to release was given in early-1994.
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
Stufkens MW, Farrell JA (1994). Quarantine host range tests on two exotic parasitoids imported for aphid control. Proc. 47th New Zealand Plant Protection Conf. :149-153
Stufkens MW, Farrell JA (1995). Release and establishment of Aphidius sonchi, a parasitoid of the sow thistle aphid in New Zealand. Proc. 48th New Zealand Plant Protection Conf. 343-344