Biocontrol introduction
Target pest: Lythrum salicaria (Myrtales: Lythraceae), purple loosestrife
Agent introduced: Neogalerucella pusilla (Coleoptera: Chrysomelidae)
Release details:
Landcare Research (2025g) - the first releases of G. pusilla are planned for the spring/summer of 2025-26.
Impacts on non-targets:
Landcare Research (2023k) - host range testing for G. pusilla [referred to as Neogalerucella pusilla in Landcare Research (2023k)] was carried out prior to its introduction as a biocontrol agent into USA and Canada in the early-1990s. The 48 plant species initially tested were either taxonomically associated with L. salicaria, associated wetland plants of wildlife importance or important agricultural plants. The results indicated that G. pusilla is highly host-specific to L. salicaria. Three other test plant species supported development of G. pusilla, although only one (Lythrum alatum - not present in New Zealand) was also acceptable for oviposition and thus considered to be in the fundamental host range of the beetle. However, L. alatum was an inferior host compared to L. salicaria and considered unlikely to sustain populations of G. pusilla under natural conditions. While the host range tests concluded that normal feeding, oviposition and larval development of the beetle would be restricted L. salicaria, the results also suggested that transient spill-over feeding on certain non-target plant species in the vicinity of L. salicaria could be expected when foliage of the host plant had been depleted. Post-release studies and observations in USA and Canada support the test conclusions. Feeding has been reported on four species in the Lythraceae, and attack outside this family also documented; however, the beetle larvae do not complete development on any non-target species in the field, and the damage to these species is highly localised and of minor consequence. In New Zealand, there are no native plants and 12 exotic species (other than L. salicaria) in the family Lythraceae. Three exotic species are cultivated as ornamentals (Lythrum virgatum, Lagerstroemia indica, Lagerstroemia limii) and one, Punica granatum (pomegranate) is sporadically grown as a food plant.
General comments:
Landcare Research (2024e) - in the early-1990s, as part of their biocontrol programmes against L. salicaria, USA and Canada deployed the same four insect species that have been approved for release in New Zealand (Galerucella calmariensis, Galerucella pusilla, Hylobius transversovittatus and Nanophyes marmoratus). The agents have proven to be effective there, with populations of the weed reduced by up to 90% at some sites within the first decade. This presented an opportunity for New Zealand to piggy-back on these well-established programmes using the host range testing data and evidence from the field [see Landcare Research (2023k) entry in ‘Impacts on non-targets’ section above] to support a release application to the EPA for all four agents.
Taxonomic note (16 December 2025) - there is a lack of consensus in the scientific community on whether Neogalerucella is a genus or a subgenus of Galerucella. Prior to 1962, Galerucella pusilla was placed in the genus Galerucella. Chûjô (1962) proposed the new genus Neogalerucella. Galerucella pusilla was placed in this genus. Löbl & Smetana (2010) treated Neogalerucella as a subgenus of Galerucella in their Catalogue of Palaearctic Coleoptera and this classification was followed by Viswajyothi & Clark (2022) in their revision of the Galerucinae. Molecular phylogenetic studies by Borghuis et al. (2009) and Hambäck et al. (2013) similarly accepted Neogalerucella as a subgenus of Galerucella. However, this classification is not followed by all sources and many, particularly applied sources, continue to treat Neogalerucella as a separate genus and cite the species name Neogalerucella pusilla. BCANZ will follow Löbl and Smetana (2010) and Viswajyothi & Clark (2022) and treat Neogalerucella as a subgenus of Galerucella, i.e. this species would be cited in full as Galerucella (Neogalerucella) pusilla (Duftschmid, 1825).
EPA Applications:
EPA (2024a) - 22 August 2023: application by Horizons Regional to import and release four Coleoptera insects (Neogalerucella calmariensis, Neogalerucella pusilla, Hylobius transversovittatus, and Nanophyes marmoratus) to control purple loosestrife (Lythrum salicaria). EPA Application # APP204535, approved without controls 7 May 2024.
References
Borghuis A, van Groenendael J. Madsen O, Ouborg J (2009). Phylogenetic analyses of the leaf beetle genus Galerucella: Evidence for host switching at speciation? Molecular Phylogenetic Evolution 53(2): 361-367 https://doi.org/10.1016/j.ympev.2009.07.005
Chûjô M (1962). A taxonomic study on the Chrysomelidae (Insecta: Coleoptera) from Formosa. Part XI. Subfamily Galerucinae. The Philippine Journal of Science 91: 1-239
EPA (2024a). Application to EPA (APP204535) to import and release four Coleoptera insects (Neogalerucella calmariensis, Neogalerucella pusilla, Hylobius transversovittatus, and Nanophyes marmoratus) to control purple loosestrife (Lythrum salicaria). Environmental Protection Authority website https://www.epa.govt.nz/database-search/hsno-application-register/view/APP204535
Hambäck PA, Weingartner E, Ericson L, Fors L. Cassel-Lundhagen A, Stenberg JA, Bergste J (2013). Bayesian species delimitation reveals generalist and specialist parasitic wasps on Galerucella beetles (Chrysomelidae): sorting by herbivore or plant host. BMC Evolutionary Biology 13: 92 https://doi.org/10.1186/1471-2148-13-92
Landcare Research (2023k). Application to EPA (APP204535) to release new organisms: Neogalerucella calmariensis, Neogalerucella pusilla, Hylobius transversovittatus and Nanophyes marmoratus. Environmental Protection Authority website https://www.epa.govt.nz/assets/FileAPI/hsno-ar/APP204535/APP204535-1.-Application.pdf
Landcare Research (2024e). New EPA approvals. Weed Biocontrol: What's New? August 2024, 109: 4 https://www.landcareresearch.co.nz/publications/weed-biocontrol/weed-biocontrol-articles/new-epa-approvals/
Landcare Research (2025g). Who's who in biological control of weeds? Weed Biocontrol: What's New? August 2025, 113: 10-11 https://www.landcareresearch.co.nz/assets/Publications/Weed-biocontrol/Issue-113/weed-biocontrol-issue-113.pdf
Löbl I, Smetana A (2010). Catalogue of Palaearctic Coleoptera: Chrysomeloidea. Vol. 6. Apollo Books, Stenstrup, 924 pp. https://doi.org/10.1163/9789004260917_004
Viswajyothi K, Clark SM (2022). New World genera of Galerucinae Latreille, 1802 (tribes Galerucini Latreille, 1802, Metacyclini Chapuis, 1875, and Luperini Gistel, 1848): an annotated list and identification key (Coleoptera: Chrysomelidae) European Journal of Taxonomy 842(1): 1-102 https://doi.org/10.5852/ejt.2022.842.1945
