Biocontrol introduction
Target pest: Lythrum salicaria (Myrtales: Lythraceae), purple loosestrife
Agent introduced: Hylobius transversovittatus (Coleoptera: Curculionidae)
Release details:
Landcare Research (2025g) - the first releases of H. transversovittatus are planned for the spring/summer of 2025-26.
Impacts on non-targets:
Landcare Research (2023k) - host range testing for H. transversovittatus was carried out prior to its introduction as a biocontrol agent into USA and Canada in the early-1990s. The 48 plant species tested were either taxonomically associated with L. salicaria, associated wetland plants of wildlife importance or important agricultural plants. The results indicated that H. transversovittatus is highly host-specific to L. salicaria. Two other plant species, Lythrum alatum and Decodon verticillatus (both in the family Lythraceae and neither present in New Zealand) were potential hosts for the weevil, but they were inferior hosts compared to L. salicaria and neither were accepted for oviposition by H. transversovittatus in field trials in the presence of L. salicaria, i.e. when given a choice. In Europe, 13 Lythrum species co-occur with L. salicaria, yet the only reported host plant of the weevil is L. salicaria. Since the release of H. transversovittatus in USA and Canada in 1992 there have been no records of attack on non-target plant species in those countries. 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 (Neogalerucella calmariensis, Neogalerucella 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.
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
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
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
