Biocontrol introduction
Target pest: Scolypopa australis (Hemiptera: Ricaniidae), passionvine hopper
Agent introduced: Ablerus sp. (Hymenoptera: Aphelinidae)
Imported:
Charles & Allan (2004) - self-introduced; first report in New Zealand was from Auckland, 1995. Ablerus sp. is a distinctive species, and it is inconceivable that Cumber and Gerard would not have found it during their studies of S. australis in the 1960s and early 1980s respectively, had it then been present. Hence Harcourt’s records in 1995 probably reflected the recent arrival of Ablerus sp. in New Zealand, rather than a lack of observation in the past.
Import source:
Charles & Allan (2004) - Ablerus sp. is presumed to have arrived recently from Australia, where it has not yet been reported.
Establishment:
Charles & Allan (2004) - Ablerus sp. has dispersed since its initial discovery in Auckland in 1995 and in 1999 surveys was additionally found in the Waikato, the Bay of Plenty and Nelson. The wasp was commonly reared from S. australis eggs at some sites in those regions but not others (only two adults were reared from the Nelson samples). It appears to have spread (and be spreading) rapidly through New Zealand at a rate of approximately 125 km/year (Auckland to Nelson = 650 km in 5 years). Whether spread has been natural or with human assistance cannot be determined.
Impacts on target:
Charles & Allan (2004) - Ablerus sp. has been found in the Bay of Plenty at sites from Tauranga to Te Puke, where it can be expected to have an impact on S. australis populations that infest kiwifruit orchards. However, the ecological impact of Ablerus sp. on S australis population dynamics, or on possible alternative hosts, remains to be investigated. Currently the evidence suggests that its arrival has not dramatically lowered S. australis populations over the past 5 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.
Impacts on non-targets:
Charles & Allan (2004) - Ablerus sp. has not been found from any host other than S. australis in New Zealand.
General comments:
Charles & Allan (2004) - Ablerus sp. appears to be a thelytokous (females only), multi-voltine primary parasitoid of S. australis eggs, and not, as initially thought, a hyperparasitoid of Centrodora scolypopaea (another introduced egg parasitoid of S. australis).
References
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
