315 Highlights It is well understood that damage by insect pests can have serious consequences for pasture resilience. However, the impacts of climate change on pastoral systems, the responses of insect pests, and implications for pest impact mitigation are unclear. This paper reviews pest responses to climate change, including direct impacts such as temperature and carbon dioxide levels, geographic range expansion, sleeper pests, and outbreaks resulting from disturbance such as drought and farm system changes. The paper concludes with a plea for transdisciplinary research into pasture resilience under climate change that has insect pests as an integral component – not as an afterthought. Keywords: agricultural system, biological control, insect, invertebrate Background Populations of insect pests and their impacts on pastoral farming result from multiple interacting factors including climate, pasture species, cultivars and symbiotic endophyte fungi, natural enemies, plant nutrient status, soil fertility and moisture levels, soil type, stock type and management, pasture management, cropping and pasture renovation practices and farmer awareness of pest issues (see Ferguson et al. (2019) for a substantive review of pasture insect pests). For instance, a porina (Wiseana spp.) population in an optimally fertilised, properly grazed, 5-year-old AR37 ryegrass-clover pasture established by direct drilling and not allowed to become rank when porina moths are laying eggs, will be regulated by reduced egg hatch and survival of young larvae, naturally occurring pathogens, and endophyte toxins. At the same time healthy plants will tolerate porina feeding more than if they were under nutrient stress and over grazed. This will differ substantially from a porina population in a 3-year-old AR1 pasture established after cultivation, closed to grazing during egg laying and hatch, but heavily stocked during winter, where natural population regulation will be very low, and the ryegrass unprotected by the endophyte. The latter could be further compromised ISSN 0118-8581 (Print) ISSN 2463-4751 (Online) https://doi.org/10.33584/rps.17.2021.3477 Climate change impacts on pest ecology and risks to pasture resilience Sarah MANSFIELD 1,* , Colin M. FERGUSON 2 , Philippa J GERARD 3 , David HODGES 4 , John M. KEAN 3 , Craig. B. PHILLIPS 1 , Scott HARDWICK 1 and Sue M. ZYDENBOS 1 1 AgResearch, Lincoln Science Centre, Private Bag 4749, Christchurch 8140, New Zealand 2 AgResearch, Invermay Agricultural Centre, Private Bag 50034, Mosgiel 9053, New Zealand 3 AgResearch, Ruakura Research Centre, Private Bag 3123, Hamilton 3240, New Zealand 4 DairyNZ Private Bag 3221, Hamilton 3240, New Zealand *Corresponding author: Sarah.Mansfeld@agresearch.co.nz if soil fertility is also low. Reasonable estimates of porina densities for these scenarios would be 15 and 150 larvae/m 2 , respectively. However, climate is also a key driver for pest populations, which are often strongly affected by climatic extremes, e.g., summer droughts frequently disrupt natural controls of porina and grass grub (Costelytra giveni) leading to major pest outbreaks in following years (East & Willoughby 1980; Kalmakoff et al. 1985). Despite the importance of climate, and therefore climate change, as drivers of pest populations, few studies have investigated and predicted climate change impacts on farm systems in New Zealand and none have directly addressed either the impact of climate change on New Zealand pasture insects, or their effects on future farm systems. Dynes et al. (2010) concluded that dairy farming in Manawatu had considerable adaptive capacity in relation to climate change scenarios and that the ingress of C4 grasses would potentially alter the system through declining pasture quality; this change would also provide opportunities for invasion by new pests, such as tropical grass webworm. Kalaugher et al. (2013) presented a mixed-methods framework designed to assess the adaptive potential of dairy farming systems from both bottom-up (qualitative social research with farmers and communities) and top-down (quantitative biophysical modelling) perspectives. Using this approach, Kalaugher et al. (2017) simulated climate change impacts for six pasture-based dairy farms located across New Zealand, fnding that average annual pasture production ranged from no change to an 18% decrease. While the biophysical modelling did not include potential insect pest impacts, signifcant concerns were raised through the farmer-focused analyses, particularly relating to changes in pasture species and the potential for incursion of new insect pests. Lieffering et al. (2016) modelled the impacts of climate change on two sheep and beef farming systems under six different management regimes. A key fnding was that while there was minimal impact on total annual pasture growth, there were marked changes in the seasonality of pasture production and signifcant regional differences in the farm-scale economic