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Both adults and larvae of Listronotus bonariensis damage ryegrass (Lolium spp.), a dominant component of New Zealand pasture. Damage can be reduced by Epichloë festucae var. lolii, a biotrophic fungal symbiont of ryegrass, through the production of alkaloids with deterrent and/or toxic effects to insect herbivores including L. bonariensis. Here we report results from two pot trials and a field trial comparing endophyte strains with different alkaloid profiles that have been introduced to reduce or eliminate adverse effects on stock. Adult L. bonariensis feeding scars, number of eggs and the proportion of tillers with larval damage and the severity of that damage were recorded. Samples of pseudostem and leaf blades were analysed for alkaloids. AR1 endophyte reduced adult feeding, oviposition, and larval damage whereas AR37 had no effect on adults but was highly effective in reducing larval damage. Reduction in adult feeding and oviposition by different NEA strains was governed by concentrations of peramine and ergovaline. For plants infected with AR37, alkaloid concentrations that determined the extent of larval damage were influenced by host species and ploidy; tetraploid L. perenne was more severely damaged than its diploid equivalent; L. multiflorum cultivars were more susceptible than the L. hybridum and L. perenne cultivars. [ABSTRACT FROM AUTHOR]

Aphids are major pests of cereal and pasture grasses throughout the world, vectoring disease and reducing plant production. There are few control options other than insecticides. Epichloë endophytes that produce loline alkaloids in their hosts provide a possible mechanism of control, with both meadow fescue and tall fescue naturally infected with loline-producing endophytes showing a resistance to Rhopalosiphum padi. We screened Elymus spp. naturally infected with endophytes that produced loline alkaloids at concentrations known to affect aphids on fescue but found no effect on these insects infesting Elymus. A synthetic loline-producing endophyte association with rye also had no effect on the aphids. After hypothesizing that the lolines were being translocated in the xylem in Elymus and rye rather than the phloem, we tested the rye and meadow fescue infected with loline-producing endophytes against a xylem feeding spittlebug. The endophyte in rye inhibited the feeding of the insect and reduced its survival, whereas the endophyte-infected meadow fescue had no effect on the spittlebug but reduced the number of aphids. Lolines applied to the potting medium of endophyte-free and endophyte-infected rye, ryegrass, and tall fescue resulted in a decrease in the aphid populations on the endophyte-free pasture grasses relative to the untreated controls but had no effect on aphid numbers on the rye. We tentatively conclude that lolines, produced in both natural and synthetic association with Elymus and rye, are partitioned in the xylem rather than the phloem, where they are inaccessible to aphids. [ABSTRACT FROM AUTHOR]

Cerodontha australis Malloch (wheat sheath miner) is a leaf mining fly native to New Zealand and eastern Australia that feeds on grasses and cereals. It is thought to have limited economic impact despite being one of the most widespread and common insects in New Zealand pastures. In this study, data on C. australis were gathered over an 18‐month period from field plots of endophyte‐free Lolium perenne. Observations from pot trials on parasitism and other leaf miner species are also presented. Larval numbers were highest in late spring to early summer. One distinct peak per year of eggs and pupae indicated that this species may not be multivoltine, contradicting previous literature. Damage levels were high in spring/summer, with leaf mining in up to 53% of tillers sampled and, in mid‐summer, extending into the pseudostem in up to 41% of sampled tillers. Measurement of cephaloskeleton lengths confirmed that this species has three larval instars. Generally, only one larva per tiller survives to pupation, indicating density dependent regulation of populations, and larval/ pupal parasitism can reach high levels in summer. This study provides new information on the seasonal biology of C. australis, and its potential impact on L. perenne pastures in Waikato, New Zealand. [ABSTRACT FROM AUTHOR]

Argentine stem weevil adults (ASW, Listronotus bonariensis) feed on the leaves of agricultural grasses and their larvae mine the pseudostem, causing extensive damage that can result in plant death. Plants emit volatiles that serve as signals to host-searching insects and these odours can be altered by both herbivory and fungal endophyte-infection. This study investigated whether ASW adults utilise olfaction to identify their host plants, perennial ryegrass (Lolium perenne), and if conspecific herbivory or the presence of Epichloë festucae var. lolii fungal endophytes (strain wild-type or AR1) influenced such responses. Results from olfactometer bioassays established that ASW adults were able to utilise their olfactory response to orient towards volatiles released by perennial ryegrass and further, the weevils displayed a preference for plants previously damaged by conspecific weevils. However, there was no evidence that weevils had the ability to distinguish between endophyte-infected and endophyte-free plants using olfaction alone. Using a push–pull extraction technique, thirteen volatile compounds were identified in the blend released by perennial ryegrass. Endophyte and herbivory were found to alter these volatile compounds and quantities emitted by this forage grass. This study suggests that despite observing differences in the plant volatile blend, ASW do not perceive endophyte (wild-type and AR1) using olfaction alone and must rely on other cues, e.g. contact chemoreception or post-ingestional malaise, to detect the presence of a bioactive endophyte in an otherwise acceptable host plant. [ABSTRACT FROM AUTHOR]

Grasses have developed a wide range of morphological and physiological mechanisms to resist herbivory. For instance, they accumulate silicon (Si) in tissue, as physical defence, and associate symbiotically with foliar Epichloë‐endophytes that provide chemical defence via antiherbivore alkaloids. Recent evidence showed that some Epichloë‐endophytes increase foliar Si in forage grasses; however, whether this impacts insect herbivores is unknown. Furthermore, while Si is primarily a physical defence, it also affects production of plant defensive secondary metabolites; Si supply might therefore affect Epichloë‐alkaloids, although this remains untested.We grew endophyte‐free (Nil) and Epichloë‐infected tall fescue and perennial ryegrass in a factorial combination with or without Si supplementation, in the absence or presence of Helicoverpa armigera. Epichloë‐endophyte strains were AR584 for tall fescue, and AR37, AR1 or Wild‐type (WT) for perennial ryegrass. We assessed how Si supply and Epichloë‐endophytes in interaction with herbivory affected foliar Si and mutualist‐derived alkaloid concentrations. Subsequently, their effects on H. armigera relative growth rates (RGRs) were evaluated.Endophytes generally increased Si concentrations in Si‐supplied plants. In tall fescue AR584 and perennial ryegrass AR37, endophytes increased constitutive (herbivore‐free) and induced (herbivore‐inoculated) Si concentrations by at least 25%; in contrast, in perennial ryegrass, the AR1 endophyte only increased constitutive levels. Si supply did not affect alkaloids produced by AR584 or AR1/WT endophytes; however, in the presence of herbivory, Si supply decreased the induction of alkaloids produced by AR37 endophytes by 33%. For tall fescue, Si supply reduced H. armigera RGR by at least 76%, regardless of endophytic status, whereas, endophyte‐alkaloids played a secondary role only reducing herbivore growth in the absence of Si supply. Conversely, in perennial ryegrass, both Si and endophyte‐alkaloids (regardless of Si supply) reduced herbivore RGR although not synergised.Novel interactions between constitutive and induced Si‐ and alkaloid‐based antiherbivore defences in grasses were observed. Overall, Si had a greater effect on the folivore than endophytes in both grasses. Endophyte defences contributed more to herbivore resistance in perennial ryegrass than tall fescue. We demonstrate that Si and endophytes were not antagonistic and highlight that the protective nature of their interaction varies with the grass‐endophyte species tested. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Climate change is anticipated to lead to an increase in the occurrence and intensity of drought and fluctuations in insect cycles that will challenge modern pasture systems. Feeding by root aphids such as Aploneura lentisci Pass. can be a significant challenge to pastures. These below-ground living aphids are commonly found in New Zealand and Australia, feeding year-round on the roots of graminaceous plants such as perennial ryegrass (Lolium perenne L.). Some strains of the fungal endophyte Epichloë festucae var. lolii in perennial ryegrass can provide protection against root aphids and greater resilience under drought, contributing to higher persistency and growth than endophyte-free plants. However, the interaction between insect pressure and drought is not understood. This study examined the effect of drought on root aphid populations and plant performance in perennial ryegrass plants relative to endophyte status (±) and endophyte strain (AR37, NZCT) in a glasshouse experiment. Plants were cloned across the drought and well-watered treatments, and half of the plants were inoculated with root aphids, whilst half of the plants were treated with insecticide. Endophyte infection with strain NZCT and AR37 reduced root aphid numbers. Aphid populations were significantly higher in drought-stressed than in well-watered plants in both endophyte-infected and endophyte-free treatments. Under drought conditions, root aphid populations were increased 4-fold in NZCT and 8-fold in AR37 and endophyte-free plants in comparison with their well-watered counterparts. Root aphids reduced shoot dry weight by 16% in drought-exposed and 26% in well-watered plants in comparison with their insecticide-treated counterparts whilst reducing root biomass by 49%. Our results suggest that root aphids are likely able to exploit the higher availability of amino acids in the plant sap of drought-exposed plants. This study provides evidence that climate change-mediated impacts of root aphids could reduce production in perennial ryegrass-dominant pastures. However, field trials would be necessary to determine whether this effect is seen in situ, where numerous additional factors will be operating at the same time. [ABSTRACT FROM AUTHOR]

New Zealand's economically vital exotic pastures are unique in their low complexity making them highly susceptible to invasive pest species such as the Argentine stem weevil Listronotus bonariensis. This field-based contribution further examined the ecology of the adult weevil and its parasitoid control agent Microctonus hyperodae. This included factors that affect field sampling accuracy, interpretation of population density and parasitism estimates. Compared to adult population estimates measured via turf flotation, suction sampling (G-vac) showed c.30% under-estimation of population densities while parasitism rates were over-estimated by c.26%. The bionomic implications of the sampling biases are discussed as they relate to the recently observed sharp declines in L. bonariensis parasitism. The weevil's field parasitism rates showed no relationship to population density again confirming the parasitoid's very high host searching efficiency. This study also coincided with meteorological conditions (>30°C) that resulted in a very large L. bonariensis 'swarming' event. The mass emigration from the experimental plots left only a low residual population of parasitised weevils that typically do not fly. Therefore, measured L. bonariensis populations and their M. hyperodae parasitism levels cannot always be presumed to be solely the result of population dynamics in situ. [ABSTRACT FROM AUTHOR]

The wheat sheath miner, Cerodontha australis Malloch (Diptera: Agromyzidae), is a small leaf‐ and stem‐mining fly that is native to New Zealand and eastern Australia where it feeds on grasses and cereals. Although not considered to be a major insect pest of pastures in New Zealand, it can be abundant during spring and summer in Waikato, New Zealand, and infests tillers of the introduced pasture plant, perennial ryegrass, Lolium perenne L. (Poaceae). Cerodontha australis is not deterred from feeding on L. perenne infected with commercially available strains of the fungal endophyte Epichloë festucae var. lolii, which have been shown to provide protection from a range of other insect pests. In this study, three‐pot trials and periodic examination over 18 months of field‐collected L. perenne tillers showed that two Epichloë endophyte strains, AR47 and AR48, reduced the survival and feeding damage by C. australis larvae, but there was no evidence of an effect on adult female feeding or oviposition. Compared to other strains of E. festucae var. lolii endophytes tested, plants infected with AR47 and AR48 had fewer and smaller larvae and less larval mining. The number of tillers with mining was reduced in AR47 relative to endophyte‐free (Nil) by 57.1% (ranging from 25.0 to 92.5% across trials) and in AR48 by 67.1% (26.3–100%). Larvae in AR47 and AR48 were found further from the base of the tiller where they were less likely to damage the meristem and cause tiller death. The number of larvae and pupae in pseudostems was reduced in AR47 and AR48 compared with Nil by 78.4 and 82.0%, respectively, in the field trial. Very few larvae survived to pupation in AR47 and AR48 plants, with a reduction compared to Nil of over 81.5% in AR47 and over 97% in AR48 in each of the four trials presented here. [ABSTRACT FROM AUTHOR]

In identifying endophytes for use in pastures in New Zealand there have been two strategies used, either exclusion of ergopeptine and lolitrem alkaloids or, retaining some ergopeptine expression to enhance the stability of natural defences against invertebrate pests. Both have their strengths and weaknesses. It is a matter of balancing these to ensure the end-user has access to a product that satisfies their needs – a persistent pasture with low to nil animal toxicity in terms of animal production and welfare. The range and intensity of ergot alkaloids in grazed pasture on both pasture and ruminants is reviewed, with emphasis on New Zealand. Ergot alkaloids associated with pasture are produced by associations between certain Epichloë endophyte strains and temperate grasses. Ergot alkaloids have been shown to improve persistence of pasture through providing resistance/deterrence to insect pests as well as deterring grazing animals. However, ergovaline is toxic to grazing animals. Some commercially available ryegrass-endophyte associations can produce ergovaline concentrations close to those found in associations between ryegrass and the standard endophyte. It is feasible to eliminate ergot alkaloids from pasture grasses in New Zealand as endophyte strains are commercially available that do not express ergovaline and yet still provide excellent pest resistance. [ABSTRACT FROM AUTHOR]

The dairy industry provides an important contribution to the Australian economy, but its productivity relies on grass pastures that suffer significant damage from invertebrate pests. Managing these pests remains a challenge as information on their abundance and impact is only available for a handful of taxa in a few Australian dairy regions. In this study, we undertook an extensive survey of above‐ and below‐ground pest communities across seven dairy regions in south‐eastern Australia by repeatedly sampling 57 paddocks in 2017 and 2018. We then applied energetic models to estimate the amount of metabolisable energy produced by pastures that are potentially consumed by pests. Our survey indicates that dairy farmers encounter a similar composition of above‐ground pests in most sampled regions, with a few pests, especially Sminthurus viridis (lucerne flea) and Rhopalosiphum padi (bird cherry‐oat aphid), dominating pest communities. Below‐ground pests were more variable between regions and are more likely to require region‐specific control strategies. Our energetic modelling suggests that pests consume a threefold greater percentage of metabolisable energy produced by pastures during autumn than spring. S. viridis and R. padi were among the most economically important pests across all regions and seasons, while other pests, including several species of scarabs and the small pointed snail, Prietocella barbara, were predicted to be particularly damaging in specific regions. Together, our field survey and energetic modelling provide baseline information to assist dairy farmers manage invertebrate pests and help guide future research in the Australian dairy industry. [ABSTRACT FROM AUTHOR]