When host-plant resistance to a pest leads to higher plant damage (original) (raw)
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Fungal endophytes of native grasses decrease insect herbivore preference and performance
Oecologia, 2010
Endophytic fungal symbionts of grasses are well known for their protective benefit of herbivory reduction. However, the majority of studies on endophytegrass symbioses have been conducted on economically important, agricultural species-particularly tall fescue (Lolium arundinaceum) and perennial ryegrass (Lolium perenne)-raising the hypothesis that strong benefits are the product of artificial selection. We examined whether fungal endophytes found in natural populations of native grass species deterred insect herbivores. By testing several native grass-endophyte symbiota, we examined phylogenetic signals in the effects of endophytes on insects and compared the relative importance of herbivore and symbiotum identity in the outcome of the interactions. Preference was assessed using three herbivore species [Spodoptera frugiperda (Lepidoptera), Schistocerca americana (Orthoptera), Rhopalosiphum padi (Hemiptera)] and ten native symbiota, which spanned seven grass genera. We also assessed herbivore performance in a no choice experiment for five native symbiota against S. frugiperda. We compared greenhouse and laboratory trials with natural levels of herbivory measured in experimental field populations. In all cases, we included the agronomic grass species, L. arundinaceum, to compare with results from the native grasses. Both in the field and in experimental trials, herbivores showed a significant preference for endophytefree plant material for the majority of native grasses, with up to three times lower herbivory for endophyte-symbiotic plants; however, the degree of response depended on the identity of the herbivore species. Endophyte presence also significantly reduced performance of S. frugiperda for the majority of grass species. In contrast, the endophyte in L. arundinaceum had few significant anti-herbivore effects, except for a reduction in herbivory at one of two field sites. Our results demonstrate that the mechanisms by which native symbionts deter herbivores are at least as potent as those in model agricultural systems, despite the absence of artificial selection.
Environmental Entomology, 2009
Understanding factors that affect the context dependency of species interactions has been identiÞed as a critical research area in ecology. The presence of symbionts in host plants can be an important factor inßuencing the outcome of plantÐinsect interactions. Similarly, herbivore identity can alter the outcome of plantÐsymbiont interactions. Symbiotic foliar fungal endophytes confer resistance to herbivores in economically important agronomic grasses, in part through the production of alkaloids. Although endophytes are common in nature, relatively little is known about their effects on herbivores of native, wild grass species, and a recent meta-analysis suggested that endophytes are only beneÞcial in agronomic settings. In this study, we performed choice trials for Þve insect species and a greenhouse experiment with one species to assess effects of the fungal endophyte Neotyphodium sp. on herbivores of the wild grass Festuca subverticillata. In feeding trials, endophyte presence altered the preference of all Þve insect species tested. However, the magnitude and direction of preference varied among species, with Pterophylla camellifolia (F.), Spodoptera frugiperda (J. E. Smith), and Rhopalosiphum padi L. preferring endophyte-disinfected plants and Encoptolophus costalis (Scudder) and Romalea guttata (Houttuyn) preferring endophyte-symbiotic plants. Despite reducing insect preference, the endophyte had no signiÞcant effect on S. frugiperda performance in a no-choice greenhouse experiment and did not increase plant growth in response to this herbivore. Our results show that endophyte-mediated resistance to herbivory depends strongly on herbivore identity and suggest that the Þtness consequences of endophyte symbiosis for host plants will be context dependent on the local composition of insect herbivores.
Grass–herbivore interactions altered by strains of a native endophyte
New Phytologist, 2006
Many plants support symbiotic microbes, such as endophytic fungi, that can alter interactions with herbivores. Most endophyte research has focused on agronomically important species, with less known about the ecological roles of native endophytes in native plants. In particular, whether genetic variation among endophyte symbionts affects herbivores of plant hosts remains unresolved for most native endophytes. Here, we investigate the importance of native isolates of the endophyte Epichloë elymi in affecting herbivory of the native grass host, Elymus hystrix . • Experimental fungal isolate-plant genotype combinations and endophyte-free control plants were grown in a common garden and exposed to natural arthropod herbivory.
Entomologia Experimentalis Et Applicata, 2018
Many pooid grasses (Poaceae) harbor Epichloë species (Hypocreales), endophytic fungi that often produce toxic alkaloids which may provide anti-insect protection for their hosts. Two natural populations of Achnatherum robustum (Vasey) (sleepygrass), in the Lincoln National Forest, Cloudcroft, and Weed (NM, USA), are infected with the endophyte species Epichloë funkii (KD Craven & Schardl) JF White and Epichloë sp. nov. We tested whether: (1) these endophytes affect survival, growth, and development of the insect herbivore Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae) (fall armyworm), (2) larval diets alter adult fecundity (assessed as number of larvae or eggs produced by females and number of spermatophores that males transfer to females when enclosed in pairs within each feeding group), and (3) infections affect leaf consumption in larval no-choice and choice experiments. Individual larvae were reared on Epichloë infected vs. uninfected clipped leaves from the Cloudcroft and Weed population plants. Overall, armyworm survival was not affected when fed infected sleepygrass from either population. However, larvae that fed on Weed-infected plants were smaller and had longer development than larvae that fed on uninfected and Cloudcroftinfected plants. Males fed on Weed-infected leaves had reduced mating success. Interestingly, pupal mass increased when larvae fed on either the infected leaf types. However, heavier females from both infected diets did not lay more eggs than lighter females from uninfected diets. In a no-choice test, larvae on Weed-infected plants diet consumed more leaf biomass than larvae from three other groups. In choice tests, larvae avoided feeding on leaves infected with either of the endophytes relative to uninfected leaves. Thus, the two Epichloë may provide direct protection to sleepygrass from insect herbivory by deterrence. The Weed population endophyte may provide stronger indirect protection than the Cloudcroft endophyte by reducing insect fitness or increasing risks of predation and parasitism through delayed development, even though larvae may consume more leaf biomass.
Journal of Economic Entomology, 2011
Endophytic fungi belonging to the genus Neotyphodium, confer resistance to infected host grasses against insect pests. The effect of host species, and endophtye species and strain, on feeding and survival of the corn ßea beetle, Chaetocnema pulicaria Melsheimer (Coleoptera: Chrysomelidae) was investigated. The grassÐ endophyte associations included natural and artiÞcially derived associations producing varying arrays of common endophyte-related alkaloids or alkaloid groups, peramine, lolitrem B, ergovaline, and the lolines. Preference and nonpreference tests showed that C. pulicaria feeding and survival were reduced by infection of tall fescue with the wild-type strain of N. coenophialum, the likely mechanism being antixenosis rather than antibiosis. In the preference tests, endophyte and host species effects were observed. Of the 10 different Neotyphodium strains tested in artiÞcially derived tall fescue associations, eight strongly deterred feeding by C. pulicaria, whereas the remaining two strains had little or no effect on feeding. Infection of tall fescue with another fungal symbiont, p-endophyte, had no effect. Perennial ryegrass, Lolium perenne L., infected with six strains of endophyte, was moderately resistant to C. pulicaria compared with endophyte-free grass, but four additional strains were relatively inactive. Six NeotyphodiumÐmeadow fescue, Festuca pratensis Huds., associations, including the wild-type N. uncinatumÐmeadow fescue combination, were resistant, whereas three associations were not effective. Loline alkaloids seemed to play a role in antixenosis to C. pulicaria. Effects not attributable to the lolines or any other of the alkaloids examined also were observed. This phenomenon also has been reported in tests with other insects, and indicates the presence of additional insect-active factors.
Oecologia, 1998
The eects of Acremonium alternatum Gams (Ascomycotina, Clavicipitacea) on the development and nutrition of diamondback moth larvae Plutella xylostella L. (Lepidoptera, Plutellidae) were studied in the laboratory. All experiments were conducted before the endophyte reached the green parts of the plants; thus P. xylostella, a folivore, was not in direct contact with the endophyte. Larvae feeding on leaves of previously inoculated plants suered from increased mortality, especially during the ®rst 10 days of development. Likewise, during early development surviving larvae had a reduced relative growth rate (RGR), which, however, did not result in reduced pupal or adult weight. We found sexual dierences in the food utilization eciency; female P. xylostella progeny reacted more sensitively to endophytic infection of cabbage than male larvae. Female larvae feeding on leaves of endophyte-infested plants responded to reduced eciency of conversion of ingested food (ECI) by increasing their relative consumption rate (RCR). The underlying mechanisms for these results are discussed in relation to changes in plant phytosterol metabolism which could account for reduced larval growth on inoculated cabbage plants. Our data suggest that unspecialized, soil-borne endophytic fungi, even when their association with the host plant is weak, can in¯uence aboveground herbivore development and should be considered when investigating plantinsect interactions.
A fungal endophyte of a palatable grass affects preference of large herbivores
Austral Ecology, 2017
Temperate grasses frequently acquire resistance to herbivores through a symbiosis with epichloid fungi that produces alkaloids of variable deterrent effects. However, in those cases without apparent endophyte negative effects on domestic herbivores, it is not clear whether plant consumption or preference is affected or not. We performed three experiments with 1-year-old steers (Bos taurus, Aberdeen Angus) and the annual grass Lolium multiflorum, infected or not by Epichlo€ e occultans to evaluate preference and to identify the underlying tolerance mechanisms. The first experiment evaluated steer preference for L. multiflorum cultivated in plots with three endophyte infection frequencies (low, medium and high), and investigated the role of canopy structure and plant nutritional traits on preference. The second experiment evaluated preference for chopped grass, offered in individual trays with contrasting infection frequencies (low and high), to discard possible effects associated with canopy structure and to focus on nutritional traits. The third experiment was performed with a tray + basket design that separated visual and olfactory stimuli from nutritional traits. High endophyte infection frequencies reduced consistently animal preference, even after short (~10 min) feeding events. However, we did not find significant evidence of plant structural, nutritional, visual or olfactory traits. Our results discarded several potential mechanisms; therefore, the dissuasive effect of fungal endophytes on animal consumption might be related to other mechanisms, including, likely, alkaloids and changes on grass metabolome.
Oikos, 2003
Neotyphodium coenophialum, an endophytic fungus that infects shoots of tall fescue (Festuca arundinacea), may protect its host from herbivory through production of alkaloids. Yet, the fungus can also modify plant resource allocation, regrowth dynamics, and drought tolerance, and these changes may also influence herbivores. We tested if N. coenophialum infection interacted with stress (drought or simulated herbivory) to modify plant resistance to insects. We assigned greenhouse plants to one of four treatments: 1) clipping at 3 cm above the soil surface, 2) drought stress during insect bioassays, 3) drought stress prior to insect bioassays, or 4) daily watering. Treatments were crossed with presence or absence of endophyte to give eight treatment combinations, and we assessed the performance of bird cherry‐oat aphid (Rhopalosiphum padi) and fall armyworm (Spodoptera frugiperda) feeding on plants in two separate experiments from each of the eight treatments. Aphids were placed into cl...