Severe Insect Pest Impacts on New Zealand Pasture: The Plight of an Ecological Outlier

Abstract

New Zealand’s intensive pastures, comprised almost entirely introduced Lolium L. and Trifolium L. species, are arguably the most productive grazing-lands in the world. However, these areas are vulnerable to destructive invasive pest species. Of these, three of the most damaging pests are weevils (Coleoptera: Curculionidae) that have relatively recently been controlled by three different introduced parasitoids, all belonging to the genus Microctonus Wesmael (Hymenoptera: Braconidae). Arguably that these introduced parasitoids have been highly effective is probably because they, like many of the exotic pest species, have benefited from enemy release. Parasitism has been so intense that, very unusually, one of the weevils has now evolved resistance to its parthenogenetic parasitoid. This review argues that New Zealand’s high exotic pasture pest burden is attributable to a lack of pasture plant and natural enemy diversity that presents little biotic resistance to invasive species. There is a native natural enemy fauna in New Zealand that has evolved over millions of years of geographical isolation. However, these species remain in their indigenous ecosystems and, therefore, play a minimal role in creating biotic resistance in the country’s exotic ecosystems. For clear ecological reasons relating to the nature of New Zealand pastures, importation biological control can work extremely well. Conversely, conservation biological control is less likely to be effective than elsewhere.

Towards Post-Pandemic Sustainable and Ethical Food Systems

“…Meanwhile, trade globalization (and climate change) have introduced new pest and disease species into ecosystems without resident natural enemies and this is adversely impacting food production and environmental quality (e.g., Cock et al 2012;Ferguson et al 2018). Despite integrated pest management systems, which limit the use of pesticides through biological control and breeding for plant resistance (e.g., Goldson et al 2020), food systems remain vulnerable to further disruption through the arrival of yet more transported pest species.…”

Pre‐emptive host‐specificity testing of Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae) reveals high parasitism levels against the endemic New Zealand alpine shield bug in laboratory no‐choice tests

“…Semiochemicals associated with plants and potential hosts are important cues which parasitoids use to make decisions about which hosts to search for and, ultimately, which hosts to parasitise (Godfray 1994;Hilker & McNeil 2008;Colazza & Wajnberg 2013;Meiners and Peri 2013). Scelionid egg parasitoids are known to use kairomones associated with adult hosts, and the adhesive material surrounding eggs, as important host location and acceptance cues (Strand & Vinson 1982;Bin et al 1993;Conti et al 2003;Tognon et al 2018).…”

“…Classical biological control programmes can be safe and cost-effective ways to manage the impacts of pests below economically acceptable thresholds (Caltagirone 1981;Cock et al 2015;Goldson et al 2020). However, the introduction of a biological control agent (BCA) into a novel environment brings with it the risk of non-target effects (Follett & Duan 2000;Lynch & Thomas 2000;Louda et al 2003;De Clercq et al 2011).…”

Genetic Diversity in Invasive Populations of Argentine Stem Weevil Associated with Adaptation to Biocontrol

“…A biocontrol system has been in use since the 1990s to manage a destructive, invasive pest of New Zealand pastures, the Argentine stem weevil (ASW; Listronotus bonariensis Kuschel) (Coleoptera: Curculionidae). New Zealand pastures are highly modified, based on a very low number of introduced Palearctic plant species, and are particularity susceptible to pest impacts [ 5 ]. This susceptibility is due to low plant and animal diversity, resulting in low biotic resistance to invasive species [ 5 ].…”

“…New Zealand pastures are highly modified, based on a very low number of introduced Palearctic plant species, and are particularity susceptible to pest impacts [ 5 ]. This susceptibility is due to low plant and animal diversity, resulting in low biotic resistance to invasive species [ 5 ]. In New Zealand, adult ASW populations can reach densities of 700 adults m-2 and cause economic impacts of up to NZ$200M per annum [ 6 , 7 , 8 ].…”