Comparison of the biology, ecology and potential pest impacts of the eucalypt-defoliating leaf beetles <i>Paropsisterna cloelia</i> and <i>Paropsis charybdis</i> (Coleoptera: Chrysomelidae) in New Zealand

Abstract

Background: Eucalypt species are grown in New Zealand for a variety of purposes. Paropsine leaf beetles (Coleoptera: Chrysomelidae) impact eucalypt plantations in Australia and other countries where eucalypts have become established. Six eucalypt-feeding paropsines from Australia have established in New Zealand to date. Paropsis charybdis Stål is currently regarded as the worst eucalypt pest. Paropsisterna cloelia (Stål) established in New Zealand in 2016 and it remains uncertain whether its potential impacts will exceed those caused by P. charybdis. Methods: In this review, we provide an update on eucalypt insect invasions in New Zealand, summarise available literature on Pst. cloelia, and compare its ecology to P. charybdis, including distribution, host preferences, phenology, and natural enemies. Finally, we identify key areas for future research and give recommendations for integrated pest management. Results: The number of specialist eucalypt-feeding insects has increased to approx. 36 species. The largely overlapping distributions of P. charybdis and Pst. cloelia in Australia indicate a similar climate tolerance; hence Pst. cloelia is likely to spread throughout New Zealand over time. Life history traits and behaviour of Pst. cloelia suggest it has a higher reproductive output and higher survival rate of immature stages than P. charybdis. This could potentially lead to severe defoliation from more frequent population outbreaks of Pst. cloelia, particularly under climatic conditions that induce growth stress in trees. Both species seem to prefer eucalypt species from different sections within the subgenus Symphyomyrtus, indicating a degree of niche separation. Paropsisterna cloelia larvae feed on both flush juvenile and adult leaves of heteroblastic eucalypt species (i.e., producing morphologically different juvenile and adult leaves), which would be of particular concern if it were to invade E. nitens plantations. Conclusions: We believe that Pst. cloelia has the potential to exceed the observed impacts from P. charybdis in New Zealand and cause growth losses in its most preferred eucalypt species. An integrated pest management approach that employs strategies, such as breeding for resistance, choice and siting of species, biological control, and/or pesticide use at set damage thresholds could result in significant economic benefits and resilience. As biocontrol is a long-term solution, other strategies need to be investigated and implemented without delay for the industry to be pre-emptive.