Toni Withers



Dr Withers is a expert in biological control using beneficial insects to control other pest insects and pest plants. By specialising in quantifying and interpreting insect behaviour – specifically how the biological control agent finds and recognises its host, Toni's research helps to define the host range of an agent when it is released in the field. To conduct biological control safely without endangering other taonga species requires both the in-depth understanding and scrupulous application of best practice and replicated laboratory trials. Understanding how insects interact with their hosts is also directly applicable to assessing the risk posed by new invasive insects in New Zealand. Toni has worked on the host range and ecology of a number of invasive insect pests, including Poplar Sawfly, Gum Leaf Skeletoniser, and Granulate Ambrosia Beetle.


  • Doctorate of Philosophy in Plant Health, Massey University, 1996
  • Batchelor of Science First Class Honours in Zoology, Massey University, 1991

Research capabilities

  • Entomology
  • Biosecurity
  • Invasive species management
  • Biological control
  • Integrated pest management systems
  • Pesticide trials

Career highlights

  • 1998-present: Senior Entomologist, Scion, Rotorua
  • 2018-present: President IOBC-Asia & Pacific Section
  • 1995-1998: Post-Doctoral Research Officer. CRC for Tropical Pest Management, Brisbane
  • 2012-2018: Treasurer NZ Plant Protection Society Executive Committee
  • 1999: UNESCO L'Oreal General Fellowship Overseas Study Award Recipient

Selected papers

Nahrung, HF, Lewis, ASR., Ridenbaugh, RD, Allen, GR, Reid, CAM, McDougal, RL, & Withers, TM.  2020. Expansion of the geographic range of the eucalypt pest Paropsisterna cloelia (Stål) (Coleoptera: Chrysomelidae) through synonymy and invasion. Austral Entomology, 59(2).  doi:10.1111/aen.12476.

Withers, TM, Allen, GR, Todoroki, C, Pugh, AR, & Gresham, BA 2021. Observations of parasitoid behaviour in both no-choice and choice tests are consistent with proposed ecological host range. Entomologia Experimentalis et Applicata, 169(1), 97-110.

Withers, TM, Todoroki, C, Allen, GR, Pugh, AR, & Gresham, BA 2019. Host testing of Eadya daenerys, a potential biological control agent for the chrysomelid pest Paropsis charybdis, predicts host specificity to eucalypt-leaf feeding Paropsina. BioControl, 10.1007/s10526-019-09978-6.

Peixoto, L, Allen, GR, Ridenbaugh, RD, Quarrell, SR, Withers, TM, & Sharanowski, BJ 2018. When taxonomy and biological control researchers unite: species delimitation of Eadya parasitoids (Braconidae) and consequences for classical biological control of invasive paropsine pests of Eucalyptus. PLoS ONE, 13(8), e0201276.

Withers, TM, Todd, JH, Gresham, BA, & Barratt, BIP. 2018. Comparing traditional methods of test species selection with the PRONTI tool for host range testing of Eadya daenerys (Braconidae). New Zealand Plant Protection, 71, 221-231.

Sandanayaka, WRM, Donnelly, GP, & Withers, TM 2019. Assessment of tomato potato psyllid Bactericera cockerelli (Hemiptera: Triozidae) food plant range by comparing feeding behaviour to survival of early life stages. Austral Entomology, 58(2), 387-394.

Withers, TM, & Peters, E 2017. 100 years of the eucalyptus tortoise beetle in New Zealand. New Zealand Journal of Forestry, 62(3): 16-20.

Todd JH, Barratt B, Withers TM, Berndt LA, Avila GA, Malone LA 2016. A comparison of methods for selecting non-target species for risk assessment of the biological control agent Cotesia urabae BioControl 62(1): 39-52.

Avila GA, Withers TM, Holwell GI 2016. Retrospective risk assessment reveals likelihood of potential non-target attack and parasitism by Cotesia urabae (Hymenoptera: Braconidae): A comparison between laboratory and field-cage testing results. Biological Control 103: 108-118.

Park, KC, Withers, TM, & Suckling, DM. 2016. Identification of olfactory receptor neurons in Uraba lugens (Lepidoptera: Nolidae) and their usefulness for predicting host range Journal of Insect Physiology, 78, 33-46.

Avila, GA, Withers, TM, & Holwell, GI 2016. Laboratory odour-specificity testing of Cotesia urabae to assess potential risks to non-target species. BioControl, 61(4), 365-377.

Saavedra MC, Avila GA, Withers TM, Holwell GI 2015. The potential global distribution of the Bronze bug Thaumastocoris peregrinus Carpintero and Dellapé (Hem.: Thaumastocoridae) Agricultural and forest entomology 17:375-388.

Avila, GA, Withers, TM, & Holwell, GI (2015). Olfactory cues used in host-habitat location and host location by the parasitoid Cotesia urabae. Entomologia Experimentalis et Applicata, 158(2), 202-209.

Withers TM, Carlson CA, Gresham BA 2013. Statistical tools to interpret risks that arise from rare events in host specificity testing. Biological Control 64:177-185.

Withers TM, Watson MC, Watt MS, Nelson TL, Harper LA, Hurst MRH 2013. Laboratory bioassays of new synthetic and microbial insecticides to control Eucalyptus tortoise beetle Paropsis charybdis. New Zealand Plant Protection 66: 138-147.

Withers TM, Potter K, Berndt L, Forgie S, Paynter Q, Kriticos D 2011. Risk posed by the invasive defoliator Uraba lugens (Lepidoptera: Noctuidae) to New Zealand native flora. Agricultural and Forest Entomology 13: 99-110.

Raman A & Withers TM (2003) Oviposition by introduced Ophelimus eucalypti (Hym.: Eulophidae) and morphogenesis of female-induced galls on Eucalyptus saligna in New Zealand. Bulletin of Entomological Research 93: 55-63.