Biocontrol introduction
Target pest: Paropsis charybdis (Coleoptera: Chrysomelidae), eucalyptus tortoise beetle
Agent introduced: Enoggera nassaui (Hymenoptera: Pteromalidae)
Imported:
1987, 2000
Import source:
Australia (Western Australia 1987, Tasmania 2000)
Import notes:
Cameron et al. (1989) - approximately 80 E. nassaui adults were imported from Perth, Western Australia in August 1987. They were successfully cultured for field releases.
Murphy et al. (2004) - erratic control of P. charybdis in inland regions of New Zealand suggested the Perth population of E. nassaui may not be climatically tolerant of conditions in these regions. Tasmanian E. nassaui populations could potentially provide better control in these cooler areas because of a presumably better climate match and because P. charybdis occurs in Tasmania but not Western Australia. Enoggera nassaui were collected from paropsine eggs in Tasmania during 1999/2000 and reared on Paropsis aegrota var. elliottii. Live adults and parasitised P. aegrota eggs were sent to New Zealand in May 2000, but only two strains, from the Florentine Valley and Evandale, were established in culture.
Released:
1987 (Western Australia strain), 2000 (Tasmania strains)
Release details:
Cameron et al. (1989) - in 1987-88 approximately 650 E. nassaui were released at each of Collingwood, Golden Downs and Richmond (Nelson, South Island), Longwoods (Southland, South Island), Tapanui and Kaitangata (Otago, South Island), approximately 1,000 at each of Chertsey and Rolleston (Canterbury, South Island), approximately 1,500 at each of Kaingaroa and Maketu (Bay of Plenty, North Island) and approximately 2,300 near Tokoroa (Waikato, North Island).
Kay (1990 - in Murray et al. 2008) - over 100,000 were reared and sold to forest managers throughout the country for release.
Murphy et al. (2004) - Tasmanian E. nassaui were released at four central North Island sites during November 2000 as follows: Kinleith Forest (Waikato) 1,000 Florentine Valley strain, 100 Evandale strain; Poronui Station (near Taupo, Waikato) 1,000 Florentine Valley, 1,000 Evandale; Kaingaroa Forest (Waikato/Bay of Plenty) 1,200 Florentine Valley, 800 Evandale; Rotorua (Bay of Plenty) 300 Florentine Valley, 300 Evandale. Releases consisted of approximately equal numbers of free adults and parasitised eggs hung in plastic containers from foliage.
Establishment:
Cameron et al. (1989) - Enoggera nassaui has been recovered from Maketu (Bay of Plenty, North Island) and Collingwood (Nelson, South Island). In October 1988 adults were observed ovipositing in P. charybdis eggs at Colllingwood, so the parasitoid has definitely established at least in this area.
Kay (1990 - in Murray et al. 2008) - with over 100,000 sold to forest managers throughout the country E. nassaui spread quickly.
Murphy et al. (2004) - to detect whether the Tasmanian strains released in 2000 had established, samples of parasitised P. charybdis egg batches were collected at the Poronui (Taupo) and Rotorua release sites in January 2001. The Florentine Valley strain was detected at Poronui; the Evandale strain was not detected. However, samples sizes were small.
Murray et al. (2008) - surveys in the 2007-08 summer in the Northland and Gisborne regions of the North Island and throughout the South Island found E. nassaui in seven regions in which it had previously not been detected; it has now been recovered from 20 regions in total in New Zealand. It is believed that regions where it has not been recorded represent those not yet adequately surveyed; E. nassaui is expected to be present in all eucalypt-growing areas of the country.
Withers et al. (2011) - sampling in 2010 at the Poronui (Taupo, North Island) release site indicates the Florentine Valley strain has established there; the Evandale strain was not detected and it is still unclear if latter is established. Hybrids between the Florentine Valley and the Western Australia strains were also found.
Mansfield et al. (2011) - we do not know to what extent the Tasmanian biotype has been able to establish or spread within the population of E. nassaui that is widespread throughout New Zealand. Until shown otherwise we assume that the original Perth biotype remains the dominant biotype and is still responsible for the majority of parasitism recorded on P. charybdis.
Impacts on target:
Kay (1990 - in Murray et al. 2008) - E. nassaui spread quickly to provide effective control of P. charybdis in many regions.
Cameron et al. (1993) - Enoggera nassaui is categorised as exerting “complete” control (defined as “control of the target over an extensive area so that pest outbreaks are rare or other control treatments are rarely necessary”) over P. charybdis. While there has been no analysis of the economic importance of E. nassaui, the complete control of four eucalypt pests by deliberately introduced biocontrol agents [in addition to P. charybdis being controlled by E. nassaui, the pests Eriococcus coriaceus, Gonipterus platensis and Phylacteophaga froggatti controlled by Rhyzobius ventralis + Stathmopoda melanochra, Anaphes nitens and Bracon phylacteophagus respectively - see the introduction records for these hosts/agents for details] has been particularly significant in the development of eucalypt forests and shelter.
Tribe & Cillié (2000) - Enoggera nassaui achieved initial parasitism rates (reported anonymously in 1989) of 86%, a success due to the exclusion of its hyperparasites from its native range.
Murphy and Kay (2000) - severe problems with P. charybdis defoliation can still occur in the Central North Island region of New Zealand. Enoggera nassaui may be inadequately adapted to conditions in some parts of New Zealand due to introductions originating from frost-free areas in Western Australia. Paropsis charybdis outbreaks seen in problem sites appear to result from poor spring parasitism by E. nassaui, with low parasitism (<20%) of P. charybdis eggs early in the first post-winter generation. However, high parasitism rates in the late season period (at least 80% by March) prevent a second period of larval defoliation that would otherwise occur.
Withers (2001) - the control of P. charybdis achieved by E. nassaui has been impressive, particularly throughout warmer regions of New Zealand.
Murphy (2002) - Baeoanusia albifunicle, an obligate hyperparasitoid of E. nassaui, has been detected in New Zealand for the first time. The future of E. nassaui as an effective biocontrol agent of P. charybdis in New Zealand (until now the only effective agent against this pest in this country) is now in doubt.
Jones and Withers (2003) - in 2003 in central North Island there was a 50% parasitism rate in early summer, dropping later in the season to 10% as a result of hyperparasitism by Baeoanusia albifunicle. This obligate hyperparasitoid, first detected in New Zealand in 2001, puts effective biological control of P. charybdis by E. nassaui in doubt.
Murphy et al. (2004) - erratic control by Western Australia strain of E. nassaui in inland regions of New Zealand led to release in 2000 of two Tasmanian strains to attempt expansion of the climatic range of biocontrol.
Murray et al. (2008) - the discovery of Baeoanusia albifunicle, a hyperparasitoid of E. nassaui, raised concerns over the long-term suppression of P. charybdis by E. nassaui. Field surveys in Bay of Plenty in 2003, subsequent to the self-introductions of B. albifunicle and N. insectifurax [a parasitoid of P. charybdis -see the N. insectifurax introduction record], show parasitism of P. charybdis eggs by E. nassaui declined during the season, with approximately 40% of parasitised eggs being hyperparasitised by B. albifunicle. However, N. insectifurax was parasitising 35-100% of P. charybdis eggs by late-summer. This indicates that, while B. albifunicle has the potential to severely reduce the effectiveness of E. nassaui, N. insectifurax, which is not susceptible to B. albifunicle, may play an increasingly important role in the regulation of P. charybdis with any decline in E. nassaui populations. Surveys in the 2007-08 summer in the Northland and Gisborne regions of the North Island and throughout the South Island recovered B. albifunicle from the South Island for the first time. In addition to previous North Island records in Bay of Plenty, Taupo and Coromandel, it was also located for the first time in Northland and Gisborne, as well as six South Island locations as far south as Roxburgh [Central Otago]. Baeoanusia albifunicle is expected to establish wherever E. nassaui is present in New Zealand, with the possible exception of Southland, where it has not been detected despite extensive surveys over the last three years.
Withers et al. (2011) - the apparent dominance of the Florentine Valley strain at Poronui Station (Taupo), only 10 years after release, could suggest this strain has some ecological advantage over the Western Australian strain. If so, this might benefit the biocontrol of P. charybdis elsewhere in New Zealand. It is not known if hybridisation of Florentine Valley and Western Australia strains (seen at Poronui) will improve or hinder biocontrol of P. charybdis.
Mansfield et al. (2011) - field parasitism rates monitored over three summers (2002-2005) in the Bay of Plenty and Taupo regions of the central North Island showed suppression of P. charybdis was still not consistent across both host generations although in two of the three seasons total parasitism (dominated by E. nassaui) in December was higher (up to 50%) than that reported previously (<20%, Murphy and Kay, 2000). This increase in early parasitism may reflect the introduction of the cool-adapted (Tasmanian) strain of E. nassaui or local adaptation of the parasitoid population to the prevailing climate.
Withers et al. (2018) - field work in Hawke’s Bay this year showed E. nassaui parasitising 50-75% of P. charybdis egg batches.
Withers, Todoroki et al. (2020) - current biocontrol agents (mainly the egg parasitoids E. nassaui and Neopolycystus insectifurax) have proven to be inadequate in controlling the first (spring) of two generations that P. charybdis undergoes.
Pugh et al. (2020) - P. charybdis egg parasitism was monitored at two Eucalyptus nitens plantations in the central North Island between November 2016 and April 2017. P. charybdis egg production peaked in mid‐late-November and again in early-February at both sites. The spring generation of P. charybdis escaped egg parasitism entirely. Levels of egg parasitism increased substantially from January onwards, peaking at 50-68% in March/April. Enoggera nassaui and its hyperparasitoid Baeoanusia albifunicle, as well as the P. charybdis parasitoid Neopolycytus insectifurax, were active at both sites. Enoggera nassaui was the first parasitoid to appear and remained present intermittently at low densities throughout the monitoring period. Neopolycytus insectifurax was the primary egg parasitoid in the second generation of P. charybdis.
Withers (2025) - repeated field studies have shown neither E. nassaui nor Neopolycystus insectifurax [see the N. insectifurax introduction entry] control the first spring generation of P. charybdis in New Zealand. However, E. nassaui is highly effective in mid-summer, despite being subjected to heavy hyperparasitism by the invasive Baeoanusia albifunicle, (and N. insectifurax effective in late summer) against the second P. charybdis generation. The parasitoid Eadya daenerys [see introduction entry for this species] has recently been released in New Zealand to target the spring generation of P. charybdis.
Weser et al. (2025) - previous studies have shown the egg parasitoids E. nassaui and Neopolycystus insectifurax successfully control the second (late-summer) generation of P. charybdis in New Zealand with total parasitism rates up to 100%, but only reach 0-50% parasitism in the first (spring) generation. New laboratory trials and a field trial in Marlborough, South Island in 2022-23 show that the direct and indirect (egg mortality in the absence of successful parasitism) impacts of these two parasitoids remain high, ranging from 76 to 99% mortality, indicating a successful biocontrol impact.
Impacts on non-targets:
Withers et al. (2018) - Enoggera nassaui, along with Cleobora mellyi (another biocontrol agent introduced against P. charybis), attack and kill the eggs of Paropsisterna cloelia [previously known as Paropsisterna variicollis], first detected in New Zealand in Hawke’s Bay in 2016, but have not been effective in halting the rapid population growth of P. cloelia in Hawke’s Bay. Paropsisterna cloelia has the potential to become a significant pest of eucalypts in New Zealand. Surveys this year showed E. nassaui parasitised only 1-3% of P. cloelia egg batches (compared to 50-75% of P. charybdis egg batches), and adults which emerge are small, only two thirds of the size of those that emerge from P. charybdis eggs, suggesting E. nassaui will not be an effective biocontrol agent for P. cloelia.
Weser et al. (2024) - Enoggera nassaui has been reared from Paropsisterna cloelia eggs collected in the field in New Zealand [see Withers et al. (2018) entry above in this section] but parasitism rates are generally low and P. cloelia seems to be a low-quality host, most likely due to its smaller size. Recent laboratory trials have showed that E. nassaui has a strong oviposition preference for P. charybdis over P. cloelia, though it can fully develop in P. cloelia eggs and produce viable and fertile offspring. Limited field studies to date means the impact of E. nassaui on P. cloelia egg survival in the field is largely unknown, but it is not expected to be significant.
Weser et al. (2025) - laboratory studies [see Weser et al. (2024) entry above in this section] have shown that the egg parasitoids Enoggera nassaui and Neopolycystus insectifurax, successful biocontrol agents against the eucalypt pest P. charybdis, can reproduce in the recently invasive in New Zealand eucalypt pest Paropsisterna cloelia, although the parasitoids have a strong preference for P. charybdis and with P. cloelia being a lower quality host. A 2022-23 field trial in Marlborough, South Island, where both parasitoid species and both host species were present, showed similar probabilities of P. cloelia parasitism occur in the field compared to laboratory trials. But while direct and indirect (egg mortality in the absence of successful parasitism) impacts of these two parasitoids on P. charybdis in the laboratory and field trials was high (76 to 99% mortality), impacts were considerably lower (21–68%) on P. cloelia, indicating that E. nassaui and N. insectifurax will not induce sufficient mortality in P. cloelia eggs to be effective biocontrol agents for this invasive beetle.
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.
Cameron PJ, Hill RL, Bain J, Thomas WP (1993). Analysis of importations for biological control of insect pests and weeds in New Zealand. Biocontrol Science and Technology 3(4): 387-404 https://doi.org/10.1080/09583159309355294
Jones DC, Withers TM (2003). The seasonal abundance of the newly established parasitoid complex of the eucalyptus tortoise beetle (Paropsis charybdis). New Zealand Plant Protection 56: 51-55 https://journal.nzpps.org/index.php/nzpp/article/view/6031/5859
Mansfield S, Murray TJ, Withers TM. (2011). Will the accidental introduction of Neopolycystus insectifurax improve biological control of the eucalyptus tortoise beetle, Paropsis charybdis, in New Zealand? Biological Control 56: 30-35 https://doi.org/10.1016/j.biocontrol.2010.09.008
Murphy B (2002). New insect threatens control of eucalyptus tortoise beetle. Forest Health News No. 117, April 2002 https://cdm20044.contentdm.oclc.org/digital/collection/p20044coll2/id/20/rec/9
Murphy BD, Kay MK (2000). Paropsis charybdis defoliation of Eucalyptus stands in New Zealand's Central North Island. New Zealand Plant Protection 53: 334-338 https://journal.nzpps.org/index.php/nzpp/article/view/3625/3453
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Pugh AR, Withers TM, Peters EM, Allen GR, Phillips CB. (2020). Why introducing a parasitoid of Paropsis charybdis Stål, 1860 (Coleoptera: Chrysomelidae) larvae is expected to enhance biological control of this Eucalyptus pest in New Zealand. Austral Entomology 59(4): 829-837 https://doi.org/10.1111/aen.12492
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Withers TM, Todoroki CL, Allen GR, Pugh AR, Gresham BA. (2020). Host testing of Eadya daenerys, a potential biological control agent for the invasive chrysomelid pest Paropsis charybdis, predicts host specificity to eucalypt-leaf feeding Paropsina. BioControl 65(1): 25-36. Published online: 02 November 2019. https://doi.org/10.1007/s10526-019-09978-6
