Argentine Stem Weevil Research Articles

Feeding Performance of Argentine Stem Weevil Is Reduced by Peramine from Perennial Ryegrass Infected with Endophyte Fungus.

One of the primary supports for extensive agriculture is pasture, which can suffer severe damage from insects including the Argentine stem weevil, Listronotus bonariensis. The main control method has been the infection of ryegrass with an endophyte fungus, forming a symbiotic association that produces alkaloids. In this study, we evaluated the impact of endophyte and peramine production on the weight of L. bonariensis across seven unnamed lines (LE161-LE167), and two Lolium perenne cultivars: Jumbo and Alto AR1. L. bonariensis adults fed on leaves from LE164, LE166, and ALTO AR1 showed weight losses of 13.3%, 17.1% and 18.2%, respectively. Similarly, the corresponding alkaloidal extract from LE164, LE166, and ALTO AR1 exhibited an antifeedant effect on L. bonariensis adults in laboratory assays, as observed through weight loss or low weight gain (-12.5%, 8.8% and 4.9%, respectively). Furthermore, one alkaloid, peramine, also elicited an antifeedant effect when incorporated into an artificial diet. Liquid chromatographic analysis of the alkaloid extract revealed that peramine was present in LE164, LE166 and ALTO AR1 in amounts ranging from 46.5-184.2 ng/g. Peramine was not detected in Jumbo and the remaining experimental lines. These data suggest that L. bonariensis were susceptible to peramine produced from endophyte infection in experimental lines LE164 and LE166, as well as ALTO AR1, affecting their feeding behavior.

Immune system modulation & virus transmission during parasitism identified by multi-species transcriptomics of a declining insect biocontrol system

BackgroundThe Argentine stem weevil (ASW, Listronotus bonariensis) is a significant pasture pest in Aotearoa New Zealand, primarily controlled by the parasitoid biocontrol agent Microctonus hyperodae. Despite providing effective control of ASW soon after release, M. hyperodae parasitism rates have since declined significantly, with ASW hypothesised to have evolved resistance to its biocontrol agent. While the parasitism arsenal of M. hyperodae has previously been investigated, revealing many venom components and an exogenous novel DNA virus Microctonus hyperodae filamentous virus (MhFV), the effects of said arsenal on gene expression in ASW during parasitism have not been examined. In this study, we performed a multi-species transcriptomic analysis to investigate the biology of ASW parasitism by M. hyperodae, as well as the decline in efficacy of this biocontrol system.ResultsThe transcriptomic response of ASW to parasitism by M. hyperodae involves modulation of the weevil’s innate immune system, flight muscle components, and lipid and glucose metabolism. The multispecies approach also revealed continued expression of venom components in parasitised ASW, as well as the transmission of MhFV to weevils during parasitism and some interrupted parasitism attempts. Transcriptomics did not detect a clear indication of parasitoid avoidance or other mechanisms to explain biocontrol decline.ConclusionsThis study has expanded our understanding of interactions between M. hyperodae and ASW in a biocontrol system of critical importance to Aotearoa-New Zealand’s agricultural economy. Transmission of MhFV to ASW during successful and interrupted parasitism attempts may link to a premature mortality phenomenon in ASW, hypothesised to be a result of a toxin-antitoxin system. Further research into MhFV and its potential role in ASW premature mortality is required to explore whether manipulation of this viral infection has the potential to increase biocontrol efficacy in future.

Epichloë fungal endophyte strains and their Lolium hosts affect resistance to Listronotus bonariensis (Coleoptera: Curculionidae)

ABSTRACT 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.

Different parasitoid species elicit varied Argentine stem weevil, Listronotus bonariensis avoidance responses

ABSTRACT Importation biological control can create new host-natural enemy responses that are different from those behaviours elicited in native ranges of the agent, and/or the pest. This possibility was investigated with the Argentine stem weevil (Listronotus bonariensis) in the presence of three endoparasitoid species with different levels of affinity to the weevil in New Zealand pasture. The question posed was whether the weevil exhibits species-specific or generic responses to the three parasitoids. The first parasitoid was Microctonus hyperodae which has a coevolutionary history with L. bonariensis. The second, was Microctonus aethiopoides, which has similar ecological and behavioural characteristics to M. hyperodae. The third parasitoid was Aphidius colemani, which attacks pasture aphids and is phylogenetically remote from the Microctonus spp. Microcosms were used to examine and compare the L. bonariensis responses when confronted by each of these parasitoids. L. bonariensis showed strong behavioural responses when confronted by M. hyperodae and similar, but very much reduced responses when exposed to M. aethiopoides. The weevil exhibited no measured reaction to A. colmani. Therefore, L. bonariensis showed a species-specific response to M. hyperodae rather than a generic response. The implications of the L. bonariensis behavioural responses to all three parasitoids are discussed in terms of the species’ phenotypic closeness and centres of origin.

Behaviour drives contemporary evolution in a failing insect-parasitoid importation biological control programme

Biological control of pests continues to become more important in agriculture as pesticides are being withdrawn. However, successful control can be compromised by contemporary evolution. Recent work in New Zealand has shown that the once-successful biological control programme of the sexually reproducing grassland weevil pest Listronotus bonariensis by the asexual parasitoid Microctonus hyperodae has now failed. To explain the mechanisms associated with this, weevil parasitism rates were intensively monitored between 1994 and 2019. Frequent sampling took place at widely dispersed New Zealand sites spanning the warmer northern regions to the cooler south. Based on elapsed heat accumulation above the parasitoid’s development temperature threshold of 10.2°C degree-day (DD), the results over c. 25 years indicated that the extent of parasitism decline at a given location was directly related to the accumulated DD. The latter, in turn, was taken to be indicative of parasitoid activity and selection pressure. Accordingly, laboratory microcosm experiments measuring the response of weevils collected from the North–South distribution to a common population of parasitoids showed that the weevils from the warmer northern region showed higher rates of avoidance of the searching parasitoids than those from the cooler south. This strongly supported the hypothesis that the weevil resistance mechanism is related to levels of parasitoid avoidance behaviour arising from long-term parasitoid selection pressure. This study of the behaviourally based acquisition of resistance to a biological control agent illustrates a general need to consider the potential capability of an exotic target host to develop resistance to imported biological control agents. This includes identifying existing host adaptations that selection pressure could potentially act upon that may compromise otherwise successful biological control programmes. Such a requirement points to the need for long-term monitoring of biological control systems and understanding of parasitoid/host dynamics.

Plant-Mediated Behavioural Avoidance of a Weevil Towards Its Biological Control Agent.

New Zealand pastures largely comprising Lolium ryegrass species (Poales: Poaceae) are worth $19.6B and are subject to major pest impacts. A very severe pest is the Argentine stem weevil Listronotus bonariensis (Kuschel) (Coleoptera: Curculionidae). This has been previously suppressed by the importation biological control agent, Microctonus hyperodae Loan (Hymenoptera: Braconidae). However, this suppression has recently declined and is subject to investigation. It has been hypothesised that grass type influences the parasitism avoidance behaviour by the weevil and thus parasitism rates. This study explored the hypothesis using three common pasture grasses: a diploid Lolium perenne x Lolium multiflorum hybrid ryegrass (cv. Manawa), a tetraploid Italian ryegrass L. multiflorum Lam. (cv. Tama), and a diploid perennial ryegrass L. perenne L. (cv. Samson). The described laboratory-based microcosm methodology determined the extent of weevil avoidance behaviour on each of these three grasses when subjected to the parasitoid. Such reaction was gauged by the extent of reduced weevil on-plant presence and feeding compared to the control populations. In the absence of the parasitoid, the hybrid cv. Manawa ryegrass is as highly favoured by the weevil as the tetraploid cv. Tama. On diploid cv. Samson, feeding is considerably less. In the presence of the parasitoid, weevils on the tetraploid cv. Tama plants showed little avoidance activity in response to the parasitoid and it can be argued that the benefits of staying on this plant outweighed the possibility of parasitism. Conversely and surprisingly, in the parasitoid’s presence, weevils on diploid cv. Manawa showed very strong avoidance behaviour leading to levels of exposure similar to those found on the less-preferred diploid cv. Samson. These findings reflect how weevil parasitism rates have declined in most Lolium grasses, particularly diploids, since the 1990s, but not in the tetraploid L. multiflorum. This contribution supports the hypothesis that the decline in weevil parasitism rates has been the result of rapid evolution arising from parasitoid-induced selection pressure and the countervailing effect of the nutritional quality of the host plants.

Implications of sampling bias and population behaviour in the study of parasitoid-based biocontrol of Listronotus bonariensis in New Zealand’s exotic pasture ecosystems

ABSTRACT 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.

Analytical purity of old New Zealand forage seed samples and detection of fungal and insect contaminants including ryegrass endophyte and Argentine stem weevil

ABSTRACT Pasture seed samples that were harvested around 1917 in New Zealand were analysed for purity, Epichloë endophyte and insects. Samples consisted of 13 packets of seed varying from 2.2 to 15.0 g and comprising, Chewings fescue (Festuca rubra L.), cocksfoot (Dactylis glomerata L.), oat (Avena sativa L.), perennial ryegrass (Lolium perenne L.) and red clover (Trifolium pratense L.). These findings show that in the period prior to modern seed testing laboratories only four of the 13 samples (31%) could possibly have met today’s seed certification standards as it relates to seed purity. When compared with published purities and weed content of seed of the era these samples appear typical. Endophyte testing on the four ryegrass seed samples and the ryegrass contaminants found in the Chewings fescue and cocksfoot samples showed sample-to-sample variation in endophyte infection from nil to 91%. One cocksfoot sample, most likely harvested from the Banks Peninsula, contained an Argentine stem weevil. Subsequent checking of entomological collection records also revealed specimens being present in the Wellington region from 1916. Together these occurrences precede the earliest published record for the species in New Zealand by ten years and suggest that it may have been widespread at that time.

The effects of clover and nitrogen fertiliser on the presence of pasture pests in dairy pastures

A comprehensive dataset obtained from sampling four trials investigating interactions between perennial ryegrass and white clover under two levels of applied nitrogen (N) has highlighted different effects of pasture composition and N use on pasture pests.• For swards with white clover, presence of clover root weevil, whitefringed weevil and grass grub increased under low N by 36%, 11% and 5%, respectively, compared with high N treatments.• High N increased the presence of both Argentine stem weevil and root aphid by 7%.• Unexpectedly, clover reduced the presence of two grass feeders, Argentine stem weevil and black beetle, by 7% and 11% respectively.• Presence of grass grub was 17-30% lower under tetraploid ryegrasses than under diploids.• More clover and reduced N fertiliser inputs could reduce the frequency of black beetle and Argentine stem weevil with environmental benefits.

The role of Epichloë grass endophytes during pasture renewal

The literature on the importance of Epichloë grass endophytes during pasture renewal is reviewed. Perennial ryegrass endophyte strains such as AR1, NEA2, and Standard Endophyte (SE) as well as tall fescue and meadow fescue endophytes, significantly increase seedling survival at establishment under insect pressure, for example from adult Argentine stem weevil, grass grub, and African black beetle. However, in endophyte-infected ryegrass, insect-derived plant damage increases 10–43 days after sowing despite the presence of endophyte. Insecticidal seed treatments can mitigate the vulnerability to insect predation during this time.

Olfactory responses of Argentine stem weevil to herbivory and endophyte-colonisation in perennial ryegrass

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.

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

Modified, agricultural landscapes are susceptible to damage by insect pests. Biological control of pests is typically successful once a control agent has established, but this depends on the agent’s capacity to co-evolve with the host. Theoretical studies have shown that different levels of genetic variation between the host and the control agent will lead to rapid evolution of resistance in the host. Although this has been reported in one instance, the underlying genetics have not been studied. To address this, we measured the genetic variation in New Zealand populations of the pasture pest, Argentine stem weevil (Listronotus bonariensis), which is controlled with declining effectiveness by a parasitoid wasp, Microctonus hyperodae. We constructed a draft reference genome of the weevil, collected samples from a geographical survey of 10 sites around New Zealand, and genotyped them using a modified genotyping-by-sequencing approach. New Zealand populations of Argentine stem weevil have high levels of heterozygosity and low population structure, consistent with a large effective population size and frequent gene flow. This implies that Argentine stem weevils were able to evolve more rapidly than their biocontrol agent, which reproduces asexually. These findings show that monitoring genetic diversity in biocontrol agents and their targets is critical for long-term success of biological control.

Sampling to determine density of arthropods in intensively grazed grasslands

AbstractArthropod population field studies undertaken to understand the impacts and population dynamics of the target organism rely on sampling methods that provide accurate measurements of population density. Unsuitable methods may underestimate or provide widely variable measures of population density. The suitability of three vacuum sampling methods: a domestic vacuum cleaner, Vortis™, and blower‐vac (G‐vac), plus heat extraction of turves were compared for sampling common species in an intensively grazed irrigated dairy pasture. Each method used a different approach to sampling with the number of samples per method based on protocols that had been used in grasslands. Overall, for adults of the weevil Listronotus bonariensis, no method provided a consistently high mean density, while for adults of the weevil Sitona obsoletus, the vacuum cleaner and turf heat extraction methods gave generally higher mean densities. For predatory beetles and lacewings, heat extraction was the most effective for density measurements, while for ladybirds and spiders, the Vortis™ provided the best estimate of mean density. Increasing pasture dry matter (kg Dm/ha) generally had a significant negative effect on S. obsoletus density but not for L. bonariensis. While no method was consistently superior than another, the vacuum cleaner and heat extraction methods generally provided higher mean densities. The G‐vac generally produced the lowest density estimates, but the sampling protocol meant a larger collection area per unit effort and therefore the probability of detection was higher compared with the three other methods. In conclusion, the study showed that the optimal sampling method depends on the taxa targeted, and more than one method may be required to measure density and diversity of species in both natural and modified grasslands.

Biological Control Success of a Pasture Pest: Has Its Parasitoid Lost Its Functional Mojo?

Sustainable and integrated pest management often involves insect parasitoids. However, the effectiveness of parasitoids biocontrol has often failed, frequently for obscure reasons. A parasitoid’s success is partly due to its behavioral response to pest density, i.e. its consumer functional response. For many years in New Zealand, a braconid parasitoid, Microctonus hyperodae successfully suppressed a severe ryegrass weevil pest, Listronotus bonariensis. However, there is now evidence that this has severely declined, but that the extent of decline can depend on the pasture species. Here, we tested whether the current functional responses of M. hyperodae to L. bonarensis in two of the most common New Zealand pasture grasses (Lolium multiflorum and L. perenne) reflect observed differences in field parasitism and whether this functional response has changed over time. Our analysis involved data both from 1993 and 2018. We found a type I functional response in L. multiflorum in both years, but the slope of the relationship declined over time. There was no evidence for any type of functional response in L. perenne. This lack of response in the L. perenne coincided with consistently found lower parasitism rates on this host plant than in L. multiflorum; both in the field and laboratory. Here, we found that apparently declining searching efficiency was correlated with the decline in parasitism. This observation supports the hypothesis that parasitism decline could be the result of evolution of resistance based on enhanced evasive behaviour by L. bonariensis.

Complex Interactions among Sheep, Insects, Grass, and Fungi in a Simple New Zealand Grazing System.

Epichloë fungi (Ascomycota) live within aboveground tissues of grasses and can have important implications for natural and managed ecosystems through production of alkaloids. Nonetheless, vertebrate herbivores may possess traits, like oral secretions, that mitigate effects of alkaloids. We tested if sheep saliva mitigates effects of Epichloë alkaloids on a beetle pest of perennial ryegrass (Lolium perenne L.) in a New Zealand pasture setting. Plants with one of several fungal isolates were clipped with scissors, grazed by sheep, or clipped with sheep saliva applied to cut ends of stems. We then assessed feeding damage by Argentine stem weevils on blade segments collected from experimental plants. We found that clipping plants induced synthesis of an alkaloid that reduces feeding by beetles and that sheep saliva mitigates this effect. Unexpectedly, the alkaloid (perloline) that explains variation in beetle feeding is one produced not by the endophyte, but rather by the plant. Yet, these effects depended upon fungal isolate. Such indirect, complex interactions may be much more common in both managed and natural grassland systems than typically thought and could have implications for managing grazing systems.

Breakdown in classical biological control of Argentine stem weevil: a matter of time

Earlier study at a national scale has shown that insect pests in agriculture can develop resistance to natural enemies following ongoing expansion and simplification of agricultural systems. Here, we used 25 years of field-sampling data segmented into three distinct ecoregions in New Zealand to show that parasitism rate of a key pasture pest (Listronotus bonariensis, Argentine stem weevil) by the introduced parasitoid Microctonus hyperodae has significantly declined. However, this decline has not happened simultaneously in all three ecoregions but with a one year time-lag. The variation in parasitism rate trends might be attributed to subsets of the weevil populations that became resistant to their biocontrol agent once having been exposed to seven years selection pressure (ca. 14 generations) since the parasitoid releases. This result supports the hypothesis that adaptation leading to resistance might have similarly occurred in different parts of the country indicating that the genetic variation needed for the acquisition of resistance was equally present everywhere.

Pest categorisation of Listronotus bonariensis.

The Panel on Plant Health performed a pest categorisation of Listronotus bonariensis (Coleoptera: Curculionidae), the Argentine stem weevil, for the EU. L. bonariensis is a well‐defined species, recognised as a serious pest of pasture grasses, especially Lolium spp. and Poa annua, in New Zealand, and a rare pest of cereals in Argentina, Brazil and New Zealand. Larvae feed within the tillers and stems of grasses; adults can cut emerging cotyledons although they usually graze on leaves. Larval damage is most serious. Larval feeding causes a reduction in pasture quality that impacts on the production of grazing animals. L. bonariensis is not known to occur in the EU and is listed in Annex IIAI of Council Directive 2000/29/EC. L. bonariensis established in New Zealand via imported grass seeds and has been intercepted on grass seeds entering the EU. Considering the climatic similarities of the regions where the pest occurs and the very great extent to which hosts are grown across the EU, L. bonariensis has the potential to establish within the EU with two or three generations possible per year. Impacts could occur in grassland pastures and perhaps occasionally in cereals. In New Zealand, endophytic fungi occurring on potential hosts deter L. bonariensis from ovipositing on leaves and are toxic to larvae. Whether endophytic fungi on grasses in Europe could provide some resistance to L. bonariensis is uncertain. Phytosanitary measures are available to reduce the likelihood of introduction of this weevil. L. bonariensis fits all of the criteria assessed by EFSA to satisfy the definition of a Union quarantine pest. L. bonariensis does not meet the criterion of occurring in the EU territory for it to be regarded as a Union regulated non‐quarantine pest.

Ploidy in <i>Lolium</i> spp. cultivars affects Argentine stem weevil parasitism by <i>Microctonus hyperodae</i>


 
 
 A laboratory study was conducted to: (1) advance earlier work to determine the susceptibility of Listronotus bonariensis (Argentine stem weevil) to its parasitoid biological control agent, Microctonus hyperodae, in the presence of diploid ryegrasses such as Lolium multiflorum or Lolium perenne; and (2) determine whether or not plant orientation (i.e. horizontal vs. vertical) had any effect on parasitism rates. No significant differences in parasitism rates were found in the Listronotus bonariensis populations in the two grasses. However, combining and analysing these data with those from an earlier experiment conducted in the same way showed that parasitism rates were significantly lower in diploid Lolium multiflorum cultivars than in tetraploid Lolium multiflorum. This is the first clear evidence of a ploidy effect on parasitism rates in the presence of Lolium multiflorum. Tetraploid Lolium multiflorum has fewer, more robust and larger tillers than the diploid Lolium spp. so higher parasitism rates may be related to the lack of hiding places for an evasive genetically-driven behaviourally-based resistance by Listronotus bonariensis.
 
 

Impact of Epichloë endophytes on adult Argentine stem weevil damage to perennial ryegrass seedlings

AbstractIn New Zealand, the fungal endophyte Epichloë festucae var. lolii Latch, Christensen & Samuels (Hypocreales) is widely used to enhance productivity and survival of mature perennial ryegrass, Lolium perenne L. (Poaceae) plants. These endophytes produce alkaloids that reduce damage by insect pests, such as Argentine stem weevil (ASW), Listronotus bonariensis (Kuschel) (Coleoptera: Curculionidae). However, knowledge of the effect of these fungi on seedlings is limited. High concentrations of grass‐endophyte‐derived alkaloids occur in endophyte‐infected seed and can be translocated into seedlings to provide early protection from insect herbivory. A glasshouse experiment was conducted in which adult ASW were given a choice between perennial ryegrass cultivar ‘One50’ without endophyte (Nil) or containing endophyte strains AR1, AR37, or NZCT, and cv. ‘Trojan’ containing strain NEA2, in three post‐sowing time periods. ASW feeding damage was assessed together with plant survival and dry weight production. Plant survival and dry matter production was reduced in all treatments with mortality highest in endophyte‐free and AR37 treatments, especially in the first and second time period. Strongest adult ASW deterrence occurred on seedlings infected with endophyte strains that produce peramine (AR1, NZCT, and NEA2). Strain NZCT was virtually undamaged in the third time period whereas damage initially increased in AR1 and NEA2 up until day 50–53 post‐sowing and then declined. Endophyte‐free and AR37 treatments were significantly more damaged than AR1, NZCT, and NEA2. This research indicated there is a period of seedling vulnerability to adult ASW attack during germination, even for strains producing peramine. Possible explanations for these results are discussed.

Argentine stem weevil: farmer awareness and the effectiveness of different ryegrass/endophyte associations

Abstract Argentine stem weevil (ASW) is a highly destructive pest of ryegrass that has recently been associated with increased incidences of field damage. A survey of farmer awareness and management practices in relation to this pest was carried out. Many (47%) farmers sowed favoured plant hosts such as short-term and tetraploid ryegrasses. A field trial, undertaken near Hamilton, compared the effects on ASW larval damage of 10 different ryegrass/endophyte associations in comparison with an endophyte-free control with and without seed treatment. U2 endophyte in a diploid perennial festulolium and AR37 endophyte in a hybrid tetraploid, an Italian diploid and a tetraploid perennial ryegrass had significantly less damage (42%). NEA2 endophyte in a diploid perennial ryegrass and AR1 endophyte in short-term ryegrasses failed to protect plants from severe damage by this pest. Farmers need to be aware of the risks of ASW damage to short-term and tetraploid ryegrasses. Keywords: ploidy, short-term ryegrasses, larval damage, endophyte strains, pasture management