China has a rich diversity of forage plants comprising 2581 species in 364 genera and 65 families, including 57 grass species in 28 genera and 56 legume species in 24 genera. Of these, 14 species are commonly cultivated (Yan et al. 2008). The main commercial forage crops grown in China include L. chinensis, of which 1.31 M tonnes are produced per annum (p.a.), M. sativa (1.43 M tonnes p.a), Zea mays L. (silage corn) (0.53 M tonnes p.a.) and Lolium spp. (0.30 M tonnes p.a.) along with Avena sativa L. (Oats) (0.47 M tonnes p.a.) (Yun and Song 2017).

In Inner Mongolia and western northeast China, awnless brome (Bromus inermis Leyss.) is grown in a range of environments, including forest edge meadows, hill country and riverside roads. The grass has high nutritional value, good palatability, is tolerant to grazing and is cold hardy. It is also used to stabilise erosion-prone sandy areas. Fescue (Festuca spp. L.) is grown in alpine meadows, hillside grasslands, forests, thickets and sandy soils at an altitude of 2200-4400 metres above sea level, to provide forage for cattle, sheep and horses. The Xilin River system represents a typical inland river found in Inner Mongolia grassland. Originating in the Keshiketen Banner of Chifeng City, the river flows southeast to northwest, finally feeding into the Chagan Naoer wetland. The Xilin River Basin covers an area of approximately 10,000 km² with distinct landscape form and diverse plant communities (Tong et al. 2004). The dominant grass species are L. chinensis and Stipa grandis P. Smirn, along with Agropyron cristatum (L.) Gaertn, Achnatherum sibiricum (L.) Keng ex Tzvelev, Koeleria cristata (Linn.) Pers., C. squarrosa and Carex korshinskyi Kom. (Zhang et al. 2014).

In improved dairy and sheep grasslands in China, the main grass species are Z. mays, perennial ryegrass L. and annual ryegrass, Elymus dahuricus Turcz. ex Griseb and E. sibiricus L., Bromus inermis Leyss. and cocksfoot (Dactylis glomerata L.). The predominant legumes are M. sativa, erect milkvetch (Astragalus adsurgens Pall.), common sainfoin (Onobrychis viciaefolia Scop.), T. repens, T. pratense and common vetch (Vicia sativa L.). Oats Avena sativa L., sudan grass (Sorghum sudanense (Piper) Stapf.) and sorghum (S. bicolor (L.) Moench) are also grown for forage. While the economic value of these main forage plant species is not available, the area grown and yields are shown in Suppl. material 1: Table S1.

Alfalfa is perennial leguminous forage, valued in China as a high-quality feed for livestock and poultry. Since 2000, China has been returning farmland to forest and grassland to reduce water and wind erosion in areas prone to these phenomena (Zao et al. 2012). As a result, the area planted in alfalfa has successively expanded as it is regarded as an important part of the restoration of regional ecological environments and because it is seen as integral to the transformation of traditional agricultural, by increasing farmers’ income and promoting social and economic development (Zao et al. 2012; Li 2019).

Native grasses in New Zealand, while of some benefit for livestock grazing, are increasingly valued as iconic grassland landscape species (Mark et al. 2013). The main areas of native grasslands are found in the central North Island, but more extensively in the South Island high country (Figure 2). There are 157 grass species endemic to New Zealand with an additional 31 indigenous species with a shared distribution in Australia and other Pacific Islands (Edgar and Connor 2010). These include silver tussock (Poa cita Edgar), fescue tussock (Festuca novae-zelandiae (Hack.) Cockayne), several Chionochloa spp. (e.g. C. rigida (Raoul) Zotov, C. rubra Zotov, C. flavescens Zotov and C. pallens Zotov) and Carex spp. (e.g. C. buchananii Bergg. and C. dipsacea Bergg.). Tussock grasslands deliver a wide range of important ecosystem services that provide many tangible benefits to human well-being but have generally not been quantified or evaluated (Mark et al. 2013). In addition, these biomes support endemic invertebrate communities that may be unable to adapt to modified grasslands and face displacement by exotic invaders, for example, 25 of New Zealand’s 26 terrestrial amphipod species are endemic with evidence that they are being displaced in areas where an Australian invader, Arcitalitrus sylvaticus (Haswell) is present (Duncan 1994; Lowry and Myers 2019).

Figure 2.

Map of New Zealand, showing the geographic distribution of the grassland and crop, land use classes. Land use classes sourced from the New Zealand Land Cover Database (LCDB), using New Zealand’s 1:50,000 topographic database (https://www.linz.govt.nz/land/maps/topographic-maps/topo50-maps). Reference: Thompson S, Gruner I, Gapare N (2003) New Zealand Land Cover Database Version 2: Illustrated Guide to Target Classes, Version 5.0_January 2020, 126 pp.

Based on 2018 data, New Zealand’s agricultural production utilises 13.7 M ha (7.5 M ha in grassland and 2.4 M ha in native tussock or Rytidosperma), of which 8.8 M ha supports sheep and beef farming and 2.4 M ha dairy farming and 0.26 M ha deer farming (Anon 2020). Total agricultural exports in 2018-19 had an estimated value of NZ$34.16 B (Free On Board (FOB)) of which pastoral exports were worth an estimated $24.4 B (FOB) (Anon 2020). However, this is impacted, on average, by estimated losses to insect pests of NZ$2.3 B p.a. (Ferguson et al. 2019).

Intensively developed New Zealand pastures consist of combinations of plant species predominantly based on a grass/legume mix. The most extensively used species are perennial, short rotation hybrid and annual ryegrasses (Lolium spp.) and white clover. Other pasture species are tall fescue (Schedonorus phoenix), cocksfoot, timothy (Phleum pratense), red clover, chicory (Chicorium intybus) and plantain. In less developed pastures, browntop (Agrostis capillaris L.) is heavily utilised.

Alfalfa is an important dryland species used for grazing and stored winter forage. It is particularly valuable to farmers in environments where conventional ryegrass-white clover plant species cannot persist (Avery et al. 2008; Moot 2012). Alfalfa is grown across 200,000 ha producing approximately 12 tonne/ha and additionally fixing 30 kgN/tonne of legume grown. Animal production from alfalfa is approximately 700 kg of red meat per ha (D. Moot, Lincoln University, pers. communication). Other pasture legumes also grown in New Zealand for dryland farming, but on a limited scale, are Caucasian clover (T. ambiguum) and subterranean (T. subterraneum) and balansa (T. michelianum) clovers (Moot 2012).

Supplementing grazing pastures, fodder brassicas (Brassica rapa, B. napus and B. olearacea), fodder beet (Beta vulgaris) and ryecorn (Secale cereale) are sown for specialised winter grazing, while maize is greatly utilised for silage. Cereals (wheat Triticum spp, barley (Hordeum vulgare) and oats, although predominantly grown as grain crops, are also produced for silage. The value of the main forage plant species to New Zealand is shown in Suppl. material 2: Table S2.

Much of the research on grassland pests has focused on the Inner Mongolian Plateau (Le et al. 2007) and, to a lesser extent, the Tibetan Plateau (Wang and Fu 2004). In Inner Mongolian native grasslands, the herbivorous insect species complex is dominated by 96 species of grasshoppers and locusts (Orthoptera: Acrididae) and these comprise the major pest group. The key pests are Oedaleus asiaticus Bey-Bienko, Calliptamus abbreviates Ikonn and Dasyhippus barbipes (Fischer-Waldheim) (Tu et al. 2015), especially on L. chinensis, oats and fescue in the Inner Mongolia, Xinjiang and river valleys in the eastern Qinghai-Tibet Plateau. In recent years, O. asiaticus has shown gregarious and migrating behaviour similar to that of the oriental migratory locust (Locusta migratoria manilensis (Meyen)) and has become one of the most damaging pests in northern China, at times accounting for over 90% of all grasshopper populations. On average, grasshoppers damage over 20 M ha of rangeland and forage crops p.a., consuming 1.6 M tonnes DM p.a. at an estimated cost of US$80 M p.a. (Zhu 1999) (equivalent to US$124 M in 2020 (813 M CNY or NZ$172M)). Another assessment by Hong et al. (2014) estimated losses attributable to grassland locusts at 1.6 B CNY p.a. from 2003 to 2012. On the Qinghai-Tibetan Plateau, larvae of a species complex of the genus Gynaephora (Lepidoptera: Lymantridae) (Yuan et al. 2015), are significant pests of grasslands (Yan et al. 2006; Zhang and Yuan 2013). In 2003, an outbreak in the Qinghai Province was estimated to cover an area of 1 M ha², leading to a loss of over 90 M CNY (Zhang and Yuan 2013). In addition, the presence of cocoons in the litter can cause skin irritations and blisters to livestock (Yan et al. 2006).

Larvae of several other Lepidoptera also damage grasslands. These include the beet webworm (or meadow moth) (Loxostege sticticalis (L.), the northern armyworm (Mythimna separata Walker and the fall armyworm (Spodoptera frugiperda (J.E. Smith). Loxostege sticticalis is a widely distributed, polyphagous, migratory species (Wei et al. 1987; Sun et al. 1995) that can cause significant losses in grasslands and forage crops during outbreak years (Hong et al. 2013; Tu et al. 2015). A list of key pest species in grassland and alfalfa in China can be found in Suppl. material 3: Table S3.

For alfalfa, the main pests are aphids and thrips, followed by alfalfa weevil (Hypera postica (Gyllenhal) (Coleoptera: Curculionidae), but published literature lists between 55 (Zhang et al. 2016) and 269 (Zhang et al. 2018) pest species, in a range of taxa and which attack all stages of the plant. Aphids and thrips are the most widespread taxa throughout the alfalfa growing regions, while H. postica is significant in the Ningxia and Xinjiang regions. Other pests include: Heliothis viriplaca (Hufnagel) (= Heliothis dipsacea) (He et al. 1997) and beet webworm (Loxostege sp.) (Zhang et al. 2005a). Both aphids and thrips reduce the yield and nutritional value of damaged alfalfa (Zhang et al. 2005b; Wu et al. 2013; Zhang et al. 2017) and also vector viral plant diseases. Aphids have been reported to transmit alfalfa mosaic virus (AMV), alfalfa leaf curl virus (ALCV) and bean mosaic virus (Garran and Gibbs 1982; Roumagnac et al. 2015; Ryckebusch et al. 2020) and recently two viruses (AMV and Medicago sativa alphapartitivirus 1 (MsAPV1)) have been identified in thrips (Li et al. 2021). The main aphid pest species are the blue alfalfa aphid (Acyrthosiphon kondoi Shinji), cowpea aphid (Aphis craccivora Koch), pea aphid (Acyrthosiphon pisum (Harris)) and spotted alfalfa aphid (Therioaphis trifolii (Monell)). The major thrips species is Odontothrips loti (Haliday) while Thrips tabaci Lindeman, Frankliniella occidentalis (Perg.) and Frankliniella intonsa (Trybom) also cause damage.

The area sown in alfalfa is expanding year by year and the most recent data showed that, in 2017, 4.15 M ha of alfalfa were being grown with a yield of 29.3 M tonnes (National Animal Husbandry Service 2017). As the area sown in alfalfa increases, so too do the incidence and impact of insect pests. Based on 2017 data, it is estimated that alfalfa pests cause at least 20% yield loss, with an average direct economic loss of 9.144 B CNY p.a (2.03 B NZD p.a.) (Li et al. 2020). Large scale outbreaks of T. trifolii have been estimated to cause economic losses to growers of between 0.151 to 1.127 B USD (Wu et al. 2013). Currently, H. postica is considered a major constraint on alfalfa production, as currently there are no effective control measures available (Zhang 2015).

In New Zealand tussock grasslands, severe damage to plants by indigenous insects is uncommon although occasionally observed, for example, grass grub (Costelytra giveni Coca-Abia & Romero-Samper), several species of the moth commonly called porina (Wiseana spp.) and striped chafer beetle (Odontria striata White) (Campbell 1982; Barratt et al. 1988). Similarly, the impact of exotic insects within these systems seems low, although Argentine stem weevil (Listronotus bonariensis) Kuschel (Coleoptera: Curculionidae) (ASW) is widespread (Murray et al. 2003) and has been shown to feed on seedling blue tussock (Poa colensoi Hook.f.), F. novae-zelandiae and narrow-leaved snow tussock (Chionochloa rigida (Raoul) Zotov) and, potentially, could impact on seedling survival (Barratt et al. 2016). Indigenous insects have been shown to feed on exotic plants in areas where native vegetation is largely intact; for example, the native weevils Chalepistes spp. (formerly Irenimus spp., Brown 2017) and Nicaeana spp. (Barratt and Johnstone 1984; Barratt et al. 1992) will feed on and damage clover and seedlings. Similarly, the same genera can be common within cultivated and sown pastures consisting of entirely exotic pasture plants, but are not known to cause significant damage to these.

Insect pests are a persistent and significant economic cost to improved grassland and forage production systems in New Zealand (e.g. Zydenbos et al. 2011; Jackson et al. 2012; Ferguson et al. 2019), with a small number having a major impact on production and longevity of pastures (Suppl. material 4: Table S4). The major pests in improved grasslands are the endemic grass grub and porina, especially W. cervinata (Walker) and W. copularis (Meyrick) (Richards et al. 2017), along with the exotic ASW, clover root weevil (Sitona obsoletus, Gmelin) (CRW) and African black beetle (Heteronychus arator) (F.) (Ferguson et al. 2019). The estimated annual costs to agriculture are shown in Table 1.

Several lesser, or locally significant, pests also impact on production and persistence: black field cricket (Teleogryllus commodus) (Walker) (Orthoptera: Gryllidae), clover flea (Sminthurus viridis) (L.) (Collembola: Sminthuridae) and African black beetle are recurrent pests in the warmer areas of North Island, while Tasmanian grass grub (Accrosidius tasmaniae (Hope)) is widespread and locally damaging.

In part, the significant impact caused by endemic species, such as grass grub and porina, can be attributed to the high nitrogen and low fibre content of the exotic plant species compared to the native plant hosts (e.g. Atijegbe et al. 2020). Endemic scarabs that can have significant impacts locally include species from the genera Odontria (e.g. O. striata (White)) (Ferguson et al. 2019) and Pyronota (e.g. P. festiva F. and P. setosa (Given)) (Townsend et al. 2018). Endemic Orthopteran species, also found in improved grasslands, include the small field cricket (Bobilla spp.) and grasshopper (Phaulacridium marginale) (Walker). Neither is considered pests.

With the relatively recent increased use of the herb, narrow leaf plantain (Plantago lanceolata), in improved pasture (Stewart 1996), two previously insignificant, native Lepidoteran species Scopula rubraria (Doubleday) and Epyaxa rosearia (Doubleday) have emerged as pests, particularly when plantain is grown as a monoculture (Ferguson and Phillip 2014). Other pests that can specifically affect pasture seedling establishment include several lepidopteran species, including Eudonia sabulosella (Walker) and E. submarginalis (Walker) (both referred to as sod webworm) and Agrotis ipsilon (Hufnagel) (greasy cutworm). The wheat bug, Nysius huttoni White, is an endemic species often found both in native and improved grasslands and is also an invasive species (Lay-Yee et al. 1997; Aukema et al. 2005). Nysius huttoni has a wide host range which includes Triticum aestivum (wheat), several Brassica and Poaceae spp., M. sativa, T. repens and T. pratense (EPPO 2006) and can have significant impacts on seedling survival (e.g. Gurr 1957; Ferguson 1994).

Alfalfa in New Zealand is grown either as a monoculture, destined to be harvested for stored winter feed and, to a lesser extent, for feed pellet production or as grazing alfalfa, either as a monoculture or in combination with grass, often tall fescue. It has only a few major pests, but the key species are all exotic and comprise Sitona discoideus Gyllenhal (in New Zealand called lucerne weevil) and three aphid species (A. kondoi, A. pisum and T. trifolii). The introduction of A. kondoi and A. pisum to New Zealand was also associated with an increase in the incidence of AMV in alfalfa stands (Forster et al. 1985). Lesser pests are white fringed weevil (Naupactus leucoloma (Boheman)) (King et al. 1982) and the little fringed weevil (Atrichonotus taeniatulus (Berg)) (Barratt et al. 1998).

In grasslands, insects, entomopathogens and birds play an important role in naturally controlling pest populations. Insect biological control agents include dipteran species within Bombyliidae, Calliphoridae, Asilidae and Syrphidae, a range of coleopteran species of Carabidae (e.g. Tenebrionidae, Cicindelidae and Coccinellidae), neuropterans within the Chrysopidae and parasitoids. Entomopathogens include Metarhizium anisopliae (Metchnikoff) Sorokin, locust microsporidia (Nosema locustae Canning), Beauveria bassiana (Balsamo) Vuillemin, Bacillus thuringiensis Berliner and Entomo poxviruses (EPV). The former two are used extensively for grasshopper control, while B. bassiana and B. thuringiensis were mainly used for controlling soil pests, such as scarab larvae or lepidopteran larvae on foliage. These are usually applied to forage crops including maize and M. sativa.

Particularly in the control of locusts, pathogenic fungi and microsporidia are important in preventing the occurrence of outbreak populations. Strains of M. anisopliae and B. bassiana, specific to locusts, were introduced into China in 1990s and different formulations, such as an oil base, baits and wettable powder have been explored to optimise control in various grassland conditions. Since then, approximately 100 M hectares have been treated with B. bassiana (Zhang et al. 2000; Nong et al. 2007; Bian et al. 2009).

Locust microsporidium, isolated from Locusta migratoria migratoriodies (Reiche & Fairmaire) in the 1950s, has been shown to infect over 100 locust species and other orthopterans. It significantly reduces food intake, activity, fecundity and viability of eggs and causes insect death after 15 to 20 days (Wang and Yan 1999; Wu et al. 2000; Zhang and Yan 2008). Locust poxvirus is mainly used for locust control in Xinjiang, north-west of China, where Calliptamus italicus L., Gomphocerus sibiricus sibiricus (L.) and Dociostaurus spp. are the dominant locust species (Wang 1994).

Rosy starling (Pastor roseus L., formerly Sturnus roseus), hens (Gallus gallus domesticus L.) and ducks (Anatidae) are also used for localised control of grassland pests, especially grasshoppers and locusts (Lu et al. 2006). Rosy starlings have been shown to be an effective predator, with artificial nesting boxes used extensively to support populations (China Grassland Statistics 2018). The starlings feed both during the locust breeding and growth periods, with each adult starling shown to consume 120 to 180 locusts per day. Two studies carried out in the Xinjiang Region, showed that over a breeding season, rosy starlings were able to significantly decrease grasshopper densities (Guo 2005; Ji et al. 2008). Furthermore, starlings have been shown to follow locust swarms ensuring ongoing control (Guo 2005; Yu and Ji 2007). The use of poultry by farmers for pest control mainly occurs in Inner Mongolia and Xinjiang (China Grassland Statistics 2018).

A selection of insect biocontrol agents, both native and introduced and found in grassland and alfalfa in China, is shown in Table 2.

In natural New Zealand grasslands, several native natural enemies provide natural population regulation of significant endemic pests, particularly grass grub and porina. However, this breaks down in improved grasslands under agricultural management, primarily due to the disruption of soil-borne pathogens following cultivation. Some natural entomopathogens do regulate populations of these insects in older pastures, but they do not prevent pest outbreaks in young pastures (Jackson et al. 2012). Other natural enemies, for example, Procissio cana Hutton (Diptera: Tachinidae) which can parasitise up to 20% of third-instar grass grub larvae, are uncommon in highly modified pastures (Merton 1982). The introduction of several exotic biocontrol agents targeting these endemic pests failed (Cameron et al. 1989) and any similar attempts are now very unlikely to gain approval from New Zealand’s Environmental Protection Authority.

Two endemic entomopathogenic bacteria, S. proteamaculans (Paine and Stansfield 1919), Grimont et al. 1978 and Serratia entomophila Grimont et al. 1988 (both Enterobacteriaceae), have been found to suppress larval populations of grass grub (Hurst et al. 2000; Hurst et al. 2018). The former is the only endemic biopesticide that has been commercially developed for use against pasture pests in New Zealand, but since its availability in 1990, uptake has been low. Serratia proteamaculans also has activity against mānuka beetle (Pyronota spp.) larvae. In addition, laboratory trials where mānuka beetle larvae were treated with the entomopathogenic fungi Beauveria brongniartii (Saccardo) Petch, produced high rates of larval mortality (Townsend et al. 2010), although formal field trials to determine efficacy have not been undertaken. Several porina-active microbial pathogens have been identified, including fungi, protozoa, viruses and nematodes (Bourner et al. 1996). The fungus, M. anisopliae, can cause infrequent epizootics of larvae (Latch and Kain 1983). The entomopathogenic bacterium, Yersinia entomophaga Hurst et al., 2011, isolated from grass grub has been shown in laboratory and field trials to have high levels of pathogenicity against larvae of two species of porina: W. cervinata and W. copularis (Hurst et al. 2019). However, attempts to commercially produce formulations of indigenous pathogens, targeting these pests, are largely thwarted by the small market size and the relatively high cost of development (Glare and O’Callaghan 2019).

Three braconid parasitoids from the genus Microctonus have been introduced to provide biological control of three exotic weevil pests. Microctonus aethiopoides Loan (Moroccan ecotype) was released to control the alfalfa pest S. discoideus (Stufkens and Farrell 1980), M. hyperodae Loan for ASW (Goldson et al. 1992) and M. aethiopoides (Irish ecotype) for CRW (Gerard et al. 2006). All introductions were successful in suppressing damaging weevil populations, with both M. aethiopoides ecotypes providing natural control of what would otherwise have been major pests. An economic analysis of biological control of CRW in one region of New Zealand, found that control returned NZD14.78/ha/year and NZD6.86/ha/year for dairy and sheep & beef farms, respectively (Basse et al. 2015). Conversely, while M. hyperodae initially provided effective control of ASW (Barker and Addison 2006), recent evidence points to a breakdown in parasitoid efficiency and resurgence of weevil damage (Tomasetto et al. 2018).

The adult stage of L. bonariensis is susceptible to the entomopathogens Microsporidium itiiti Malone and B. bassiana (Barker et al. 1989), although they do not seem to provide effective control on the pest in the field. Isolates of B. bassiana have shown high levels of virulence against S. obsoletus (Nelson et al. 2015), but preliminary field trials showed limited success in the field (e.g. Brownbridge et al. 2006). Conversely, recent field trials of Y. entomophaga have demonstrated very good control of the adult stage of African black beetle (Mansfield et al. 2020).

An important strategy for protecting grasses (fescue and ryegrass) from insect pests in New Zealand is the development and use of fungal endophytes. Several Epichloë endophyte strains, producing different ranges of toxins that deter herbivorous insect feeding or oviposition (Schardl et al. 2013), are commercially available and their use is ubiquitous (Rodriguez et al. 2009; Schardl 2010). Such endophytes are effective in combatting ASW, African black beetle and porina, root aphids and pasture mealy bug (Popay and Hulme 2011) and show activity against grass grub (Ferguson et al. 2019).

Several biological control agents have been introduced and established in New Zealand for control of insect pests in improved grassland and alfalfa and are shown in Table 3. The list is compiled both from the Biological Control Agents Introduced to New Zealand (BCANZ) database, initially compiled from Cameron et al. (1989) and regularly updated as an online resource (Ferguson et al. 2007), along with published journal literature. It does not include predators, such as spiders (Vink et al. 2013), lacewings and ladybirds (e.g. Coccinella undecimpunctata L. (11 spotted ladybirds)), that may have some impact in improved grasslands, but which were not specifically introduced for that purpose. Feeding by the common starling (Sturnus vulgaris L.), an exotic bird species introduced to New Zealand during European colonisation, has been shown in some instances to reduce grass grub populations by 40–60%, with predation able to reduce larval populations below levels that caused yield losses (East and Pottinger 1975). However, the authors concluded that the effectiveness of control depended on the presence of high starling numbers, with only localised control achievable.