Biocontrol introduction
Target pest: Scolypopa australis (Hemiptera: Ricaniidae), passionvine hopper
Agent introduced: Centrodora scolypopae (Hymenoptera: Aphelinidae)
Imported:
1965 [Cameron et al. (1989) - prior to the 1965 introduction it was already established through self-introduction; the first record of it in New Zealand was 1961.]
Import source:
Australia
Import notes:
Cameron et al. (1989) - in February and March 1965, S. australis eggs embedded in twigs of various host plants were collected in Australia. These were transferred to a New Zealand quarantine facility and yielded two primary parasitoids, including more than 200 C. scolypopae. These were used to parasitise S. australis eggs of New Zealand origin.
Released:
Cameron et al. (1989) - there are no records of releases from the 1965 importation.
Establishment:
Cameron et al. (1989) - C. scolypopae is naturalised in New Zealand. It probably entered the country from Australia many years ago in parasitised eggs embedded in plant material.
Charles & Allen (2004) - C. scolypopae was first recorded in New Zealand in 1961. A survey in 1962 showed it present mainly in the north of the North Island with only a small population present south of Hawke’s Bay and none in Nelson. A 1999 survey found C. scolypopae in all regions surveyed (Northland, Auckland, Waikato, Bay of Plenty, Hawke’s Bay, Nelson) indicating it had spread south since 1962 and was probably present throughout the range of S. australis in New Zealand. Contrary to the suggestion C. scolypopae entered New Zealand "many years ago" its absence from earlier records indicates that it had only recently arrived in 1962.
Impacts on target:
Cameron et al. (1989) - C. scolypopae can parasitise a high proportion of S. australis eggs in New Zealand, especially in warmer climates. It is not known how this level of parasitism affects the population dynamics of the pest. A 1962 survey reported by Cumber (1966) found C. scolypopae was the most significant biological factor affecting S. australis eggs survival. Up to 87% of S. australis eggs collected north of Auckland were parasitised by C. scolypopae, with a mean of 39%. In cooler areas this proportion decreased and the parasitoid was absent from Nelson.
Charles & Allen (2004) - Cumber attributed the gradual decline in mean percent parasitism over the lower half of the North Island in the 1962 survey to the recent colonisation or absence of C. scolypopae. Data from the 1999 survey show no such difference in parasitism with a more even distribution and impact of C. scolypopae throughout the country. Parasitism in Northland and Waikato was significantly higher in 1962 than in 1999. However, S. australis egg and parasitoid populations are driven substantially by weather and can be expected to vary considerably from year to year, so apparent differences in parasitism cannot imply that there had been any long-term decline in parasitoid effectiveness between 1962 and 1999. Research by Gerard (1985) in the Waikato indicated that delayed density-dependent parasitism by C. scolypopae was the key mortality factor for S. australis. However, the evidence suggests that neither the wider distribution of C. scolypopae nor the arrival of another self-introduced aphelinid egg parasitoid (Ablerus sp.) has dramatically lowered S. australis populations over the past 15-30 years.
Logan et al. (2020) - two aphelinid egg parasitoids, Centrodora scolypopae and Ablerus sp., are thought to be the most important natural enemies of S. australis in New Zealand. Rates of egg parasitism (of both parasitoid species combined) measured during 2010–2015 in the North Island of New Zealand were about or less than 10% compared with medians of about 30–50% for historical estimates (in 1962 by Cumber, in 1981–1984 by Gerard and in 1999 by Charles and Allan). Scolypopa australis eggs laid in bracken, a favored host plant, in 2015 and 2019 were parasitised at about half the rate or less than indicated by historical measurements. The apparent decline may have been the result of asynchrony between one or both egg parasitoids and S. australis associated with warmer summer and autumn temperatures. The apparent decline in the parasitism rates broadly coincided with the arrival of Ablerus sp. in the 1990s. This species was initially considered to be a hyperparasitoid of C. scolypopae but was determined by Charles and Allan (2004) to be a primary parasitoid. Further work is needed to clarify the role of each parasitoid in S. australis population dynamics.
References
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.
Charles JG, Allan DJ. (2004). Passionvine hopper, Scolypopa australis (Walker) (Hemiptera: Ricaniidae), egg parasitism by Aphelinidae (Hymenoptera) in New Zealand. New Zealand Entomologist 27: 83-89
Logan DP, Rowe CA, Connolly PG. (2020). Long-term decline in the parasitism rate of passionvine hopper eggs (Scolypopa australis). BioControl 65: 547–558. Published online: 5 June 2020. https://doi.org/10.1007/s10526-020-10027-w
