Biocontrol introduction
Target pest: Paropsis charybdis (Coleoptera: Chrysomelidae), eucalyptus tortoise beetle
Agent introduced: Neopolycystus insectifurax (Hymenoptera: Pteromalidae)
Imported:
Accidental introduction, first detected in New Zealand in 2001 [NB: a shipment of Neopolycystus imported in 1987 as N. insectifurax was subsequently determined to be N. sp., not N. insectifurax - see Cameron et al. (1989) and Berry (2003) in 'Import Notes' section.]
Import source:
Australia
Import notes:
Cameron et al. (1989) - in June 1987 approximately 400 adult Neopolycystus [considered at the time to be N. insectifurax] were received from Perth, Western Australia, successfully cultured in quarantine and the progeny released. [However, this importation was subsequently determined to be N. sp., not N. insectifurax - see Taxonomic note (2 December 2024) in 'General comments' section below.]
Jones & Withers (2003) - Neopolycystus insectifurax was first detected in the field in New Zealand in 2001, probably representing a recent accidental self-introduction. [See Taxonomic note (2 December 2024) in 'General comments' section below.]
Released: Accidental introduction, first detected in New Zealand in 2001
Release details:
Jones and Withers (2003) - following the discovery of N. insectifurax in the field in New Zealand in 2001, they were mass-reared and released in the central North Island over the summer of 2002-03 in an attempt to increase distribution.
Murray et al. (2008) - following surveys in Bay of Plenty in 2003 showing high parasitism rates of P. charybdis by N. insectifurax [see Murray et al. (2008) entry in ‘Impacts on target’ section below], inundative releases of 5,000 N. insectifurax were made in the Bay of Plenty in 2003-04.
Weser et al. (2024) - sixteen hundred N. insectifurax were released in Southland in 2003-04.
Establishment:
Jones & Withers (2003) - Neopolycystsus insectifurax has been found parasitising P. charybdis in New Zealand; these are probably the result of an accidental self-introduction [See Taxonomic note (2 December 2024) in 'General comments' section below.].
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 recovered N. insectifurax from the South Island for the first time. In addition to previous North Island records in Bay of Plenty and Coromandel, it was also located for the first time in Northland and Gisborne, as well as Marlborough, Kaikoura and North Canterbury in the South Island. Neopolycystus insectifurax is expected to establish wherever P. charybdis 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.
Weser et al. (2024) - Neopolycystus insectifurax has not been confirmed in Southland to date despite being released there in 2003-04.
Impacts on target:
Jones and Withers (2003) - Neopolycystus insectifurax parasitised 35-100% of eggs in late summer in central North Island and thus appears to be an effective second post-winter generation egg parasitoid.
Murray et al. (2008) - the discovery of Baeoanusia albifunicle, a hyperparasitoid of Enoggera nassaui [released against P. charybdis - see the E. nassaui introduction record], 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 N. insectifurax and B. albifunicle, 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. The inundative releases of N. insectifurax in Bay of Plenty in 2003-04 [see Murray et al. (2008) entry in ‘Release details’ section above] failed to improve parasitism rates in the following season and the inundative release programme ceased.
Mansfield et al. (2011) - field parasitism rates of P. charybdis eggs monitored over three summers (2002-2005) in the Bay of Plenty and Taupo regions of the central North Island showed N. insectifurax the dominant parasitoid by late summer for two of the summers. On average the parasitoid Enoggera nassaui appeared first, Baeoanusia albifunicle (a hyperparasitoid of E. nassaui) a month later, and N. insectifurax after another month. P. charybdis egg parasitism was highest towards the end of summer (usually >70%) with all three parasitoids present. However, prior to the establishment of N. insectifurax in New Zealand, parasitism by E. nassaui alone was at a similar level (>80%) at the same point in time (Murphy and Kay, 2000). Therefore, there is no strong evidence that the accidental arrival of N. insectifurax has improved biological control of P. charybdis beyond the levels achieved by E. nassaui alone because N. insectifurax has not increased parasitism during the first host generation. However the introduction of N. insectifurax was fortuitous in that it compensates for the negative effect of the hyperparasitoid's arrival (around the same time N. insectifurax arrived in New Zealand) on E. nassaui populations during the second host generation.
Withers, Todoroki et al. (2020) - current biological control agents (mainly the egg parasitoids N. insectifurax and E. nassaui) have proven to be inadequate in controlling the first (spring) of two generations that P. charybdis undergoes.
Pugh et al. (2020) - Paropsis charybdis egg parasitism was monitored at two Eucalyptus nitens plantations in the central North Island between November 2016 and April 2017. 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. Neopolycytus insectifurax, as well as the P. charybdis parasitoid Enoggera nassaui and its hyperparasitoid Baeoanusia albifunicle, 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 appeared later and became the primary egg parasitoid in the second generation of P. charybdis, providing a very useful level of control over that generation.
Weser et al. (2024) - while N. insectifurax does compensate for the reduced E. nassaui populations caused by the hyperparasitoid B. albifunicle [see entries above in this section], it is not present in all eucalypt-growing areas; it has not been confirmed in Southland to date despite being released there in 2003-04.
Withers (2025) - repeated field studies have shown neither N. insectifurax nor Enoggera nassaui [see the E. nassaui introduction entry] control the first spring generation of P. charybdis in New Zealand. However, N. insectifurax is effective in late summer (and E. nassaui highly effective in mid-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 N. insectifurax and Enoggera nassaui 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:
Weser et al. (2024) - Neopolycystus insectifurax parasitism of Paropsisterna cloelia eggs collected in the field in New Zealand has been recorded, but only on one occasion. [Paropsisterna cloelia, previously known as Paropsisterna variicollis, was first detected in New Zealand in Hawke’s Bay in 2016 and has the potential to become a significant pest of eucalypts in New Zealand (Withers et al. (2018).] Recent laboratory trials have showed that N. insectifurax has a strong oviposition preference for P. charybdis over P. cloelia, and while it can fully develop in P. cloelia eggs, offspring emerging from the eggs were small and could not produce offspring, potentially representing a population sink. Limited field studies to date means the impact of N. insectifurax on P. cloelia egg survival in the field is largely unknown, but it is not expected to be significant.
General comments:
Taxonomic note (2 December 2024) - a shipment of Neopolycystus, considered at the time to be N. insectifurax, was imported in 1987 and released in 1987-88 (Cameron et al. 1989). Neopolycystus was first detected in the field in New Zealand in 2001 (Jones & Withers 2003). Comparison of 1987-imported specimens with 2003 New Zealand field specimens showed the former were N. sp., the latter N. insectifurax (Berry 2003). It is possible that N. insectifurax established accidentally, the most probable route being inside eggs of its host on plant material (Berry 2003). Extensive monitoring of P. charybdis eggs through the 1990s failed to find Neopolycystus parasitism, supporting the conclusion that the N. insectifurax field specimens collected in 2003 represented a recent self-introduction and that the Neopolycystus released in 1987-88 failed to establish (Toni Withers, Scion, pers. comm. 2014).
References
Berry JA. (2003). Neopolycystus insectifurax Girault (Hymenoptera: Pteromalidae) is established in New Zealand, but how did it get here? New Zealand Entomologist 26: 113-114
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.
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 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
Murray TJ, Withers TM, Mansfield S and Bain J. (2008). Distribution and current status of natural enemies of Paropsis charybdis in New Zealand. New Zealand Plant Protection 61: 185-190 https://journal.nzpps.org/index.php/nzpp/article/view/6834/6662
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
Weser C, Moltchanova E, Davy MA, Pawson SM, Withers TM (2025). Established Paropsis charybdis egg parasitoids are unlikely to control the newly invaded Paropsisterna cloelia (both Coleoptera: Chrysomelidae) in New Zealand. BioControl 70: 599-612 https://doi.org/10.1007/s10526-025-10336-y
Weser C, Withers TM, Pawson SM (2024). Comparison of the biology, ecology and potential pest impacts of the eucalypt-defoliating leaf beetles Paropsisterna cloelia and Paropsis Charybdis (Coleoptera: Chrysomelidae) in New Zealand. New Zealand Journal of Forestry Science, 54 https://doi.org/10.33494/nzjfs542024x317x
Withers TM (2025). Classical biological control of defoliators in Eucalyptus plantations. In: Biological Control of Insect Pests in Plantation Forests (Eds Hurley BP, Lawson SA, Slippers B), Springer 2025, pp 205-221 https://doi.org/10.1007/978-3-031-76495-0
Withers TM, McDougal RL, Harnett M, Murray TJ (2018). Eucalyptus variegated beetle creates concern for eucalypt growers. New Zealand Tree Grower 39(2): 18-21 https://www.nzffa.org.nz/farm-forestry-model/the-essentials/forest-health-pests-and-diseases/Pests/paropsisterna-variicollis-the-eucalyptus-variegated-beetle-evb/eucalyptus-variegated-beetle-creates-concern-for-eucalypt-growers/
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
