Colonization, riparian habitat selection and home range size in a reintroduced population of European beavers in the Loire

1. Colonization in a reintroduced population of European beavers in the Loire Valley was studied between 1974 and 1999. It followed a discontinuous remoteness model and a scattered distribution, beavers occupying only 25% of the river system over the 2800 km explored.
2. After 5 years, the colonization rate reached 104.2% year^–1 of new sites occupied (SD 75% year^–1), before dropping over the next 20 years. Nevertheless, the number of new colonies per km (0.125) remained stable throughout the years.
3.  Populus nigra , Salix alba and Fraxinus angustifolia were the dominant woody species in beaver sites, often associated with some herbaceous species.
4. The length of willow grove dominated by S. alba and P. nigra ( x ) was the best predictor of beaver home range ( y ), fitting the equation y =−0.742 x  + 5.9. Long-term maintenance of the population requires a minimum of 1.79-km of willows per colony.
5. In cutting tree trunks, beavers stimulate shoot development from the remaining stumps. They rejuvenate riparian forests, increase the number of tree stems and help stabilize the banks. Their effect on woody plant morphogenesis may have consequences for the helophyte communities used as food or habitat by other aquatic species.     

Trait‐mediated indirect interactions: Moose browsing increases sawfly fecundity through plant‐induced responses

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Defoliation tolerance affects the spatial and temporal distributions of larch sawfly and natural enemy populations

1. The monophagous larch sawfly, Pristiphora erichsonii, requires larch, Larix spp., shoots for oviposition and foliage for larval development. The hypothesis that chronic defoliation reduces shoot availability for adult females, causing shifts in host use within plantations of L. decidua and L. leptolepis , was evaluated over a 3-year period.
2. Larch productivity and sawfly abundance varied six- to 10-fold among individual trees within each plantation. Sawflies concentrated oviposition on the most rapidly growing trees, and had a marginal impact on shoot production. Consequently, sawfly herbivory on individual trees remained relatively constant for 3 years, failing to support the hypothesis that P. erichsonii defoliation causes shifts in host use.
3. Pristiphora erichsonii larval performance varied 20–30% among individual host trees. The oviposition event did not significantly affect larval performance or foliar nutrient content.
4. The relationship between cocoon survival and natural enemy abundance was evaluated among fifteen L. leptolepis trees. Parasites and predators killed over 65% of the 18 315 cocoons sampled. The proportion of cocoons killed by parasitoids declined significantly with P. erichsonii density, while predation rates increased under heavily infested trees. Overall, the proportion of cocoons killed by parasitoids and predators did not vary with sawfly density.
5. Results indicate that components of host vigour, herbivore performance and natural enemy guilds exhibit substantial spatial heterogeneity among trees within plantations of exotic Larix trees. Moreover, individual larch can tolerate repeated oviposition and herbivory without a rapid loss in shoot production. The potential for host plant physiological tolerance to herbivory to interact with natural enemy population dynamics and behaviour so as to stabilize herbivore population patterns is discussed.     

Beaver herbivory on aquatic plants

Herbivores have strong impacts on marine and terrestrial plant communities, but their impact is less well studied in benthic freshwater systems. For example, North American beavers (Castor canadensis) eat both woody and non-woody plants and focus almost exclusively on the latter in summer months, yet their impacts on non-woody plants are generally attributed to ecosystem engineering rather than herbivory. Here, we excluded beavers from areas of two beaver wetlands for over 2 years and demonstrated that beaver herbivory reduced aquatic plant biomass by 60%, plant litter by 75%, and dramatically shifted plant species composition. The perennial forb lizard’s tail (Saururus cernuus) comprised less than 5% of plant biomass in areas open to beaver grazing but greater than 50% of plant biomass in beaver exclusions. This shift was likely due to direct herbivory, as beavers preferentially consumed lizard’s tail over other plants in a field feeding assay. Beaver herbivory also reduced the abundance of the invasive aquatic plant Myriophyllum aquaticum by nearly 90%, consistent with recent evidence that native generalist herbivores provide biotic resistance against exotic plant invasions. Beaver herbivory also had indirect effects on plant interactions in this community. The palatable plant lizard’s tail was 3 times more frequent and 10 times more abundant inside woolgrass (Scirpus cyperinus) tussocks than in spatially paired locations lacking tussocks. When the protective foliage of the woolgrass was removed without exclusion cages, beavers consumed nearly half of the lizard’s tail leaves within 2 weeks. In contrast, leaf abundance increased by 73–93% in the treatments retaining woolgrass or protected by a cage. Thus, woolgrass tussocks were as effective as cages at excluding beaver foraging and provided lizard’s tail plants an associational refuge from beaver herbivory. These results suggest that beaver herbivory has strong direct and indirect impacts on populations and communities of herbaceous aquatic plants and extends the consequences of beaver activities beyond ecosystem engineering.     

Effects of three stressors on vegetation in an oligohaline marsh

1. When multiple stressors have interactive effects they can lead to important changes in ecosystem function. We examined how three stressors affected the plant community in an oligohaline marsh in southeastern Louisiana, U.S.A. These stressors included herbivory (mostly by the introduced rodent Myocastor coypus ), disturbance (herbicide application) and nutrient enrichment (three levels of N–P–K fertilizer). Sampling was conducted six times over 4 years.
2. Recovery after disturbance was slow, such that after 26 months biomass in disturbed plots was 36% that of controls. Slow recovery appeared to be due to herbivory, as exclusion of herbivores for 14 months led to much more biomass compared to non-excluded plots. Exclusion did not, however, aid recovery of species richness; this recovery required 51 months in total.
3. Nutrient enrichment increased biomass by 41% and decreased species richness by c. 20% in later sampling periods. Decreased species richness was due primarily to a reduced ability of dominant species to co-exist (as determined with Hill's diversity number N1). Nutrient enrichment did not interact with the other treatments.
4. Disturbance favoured two grasses ( Echinochloa crus-galli and Leptochloa fascicularis ), while lack of disturbance favoured two herbs ( Sagittaria lancifolia and Polygonum punctatum ) and two vines ( Ipomoea sagittata and Cuscuta pentagona ). Nutrient enrichment positively affected abundance of two species ( C. pentagona and L. fascicularis ). Herbivory did not affect species composition.
5. The effect of one stressor (experimental disturbance) on plant biomass depended on the strength of another stressor (herbivory). Nutrient enrichment was also important in affecting the plant community, but only as a single stressor. All effects changed over time, and it was clear that to understand properly the effects of multiple stressors, long-term, manipulative field experiments are necessary.     

Community structure of insect herbivores in a hybrid system: examining the effects of browsing damage and plant genetic variation

Abstract.  1. Using three genetic classes of willows, Salix eriocephala , Salix sericea , and their interspecific F1 hybrid, the influence of browsing damage and the importance of genetic class on insect community structure were evaluated.
2. Three-year-old plants grown from seeds generated from controlled crosses were placed in a common garden after a damage treatment was imposed on them (plants were either left undamaged during the previous winter or they had 50% of the previous year's growth removed). Clipping damage caused large increases in mean shoot length for plants.
3. The abundance of eight species of insect herbivores was determined for every plant to evaluate community structure for three genetic classes across the two damage levels. Based on manova , damage treatment had a modest effect on the relative abundance of herbivores (i.e. their proportional representation). In contrast, dramatic differences were detected among genetic classes for relative abundance; in cases where damage treatment influenced relative abundance of herbivores, the importance of genetic class was at least 20-fold greater than that of damage treatment. No interaction between genetic class and browsing treatment was detected for community structure.
4. The weak response of the herbivore community to clipping damage, contrasted to the large response to genetic class, was very surprising because mean shoot length was greatly altered by damage treatment. These findings, coupled together with previous research, suggest that plant genetic differences can act as the primary basis for herbivore community structure, while the effects of browsing may not be as common.     

Ants and plant size shape the structure of the arthropod community of Hirtella myrmecophila, an Amazonian ant-plant

Abstract.  1. To investigate the influence of plant size and the presence of resident ants on the arthropod community associated with the ant-plant Hirtella myrmecophila , ants ( Allomerus octoarticulatus ) were experimentally removed from plants of various sizes, with a second group of similar-sized plants remaining as controls. The abundance and diversity of arthropods on these plants were determined at 45-day intervals for 7 months. Collected arthropods were assigned into one of three predetermined groups: herbivores, spiders (mostly web-building spiders), or 'tourists' (mostly non-resident ants, hemipterans, dipterans, or scarabeid beetles).
2. Ant removal had a positive influence on the abundance and diversity of herbivores, but no measurable effects on the abundance and diversity of 'tourists', while the effect on spider abundance was significant only when data from Dipoena sp. nov. were removed from the analysis. While A. octoarticulatus had a negative effect on most spiders, it favoured Dipoena sp. nov., which was found to be a specialist predator of A. octoarticulatus .
3. Plant size positively affected the abundance and diversity of 'tourists' in plants with and without ants, but for herbivores and spiders this effect was dependent on ant treatment. In ant-maintained plants the per-plant abundance of herbivores and spiders was independent of plant size, whereas in ant-removed plants it was not.
4. These results suggest that A. octoarticulatus affects all arthropods found on its host plant, except those presenting an occasional and temporary association with the plant, and that the magnitude of ant effects on the susceptible guilds increases as plant size increases.     

Avian Density and Nest Survival on the San Pedro River: Importance of Vegetation Type and Hydrologic Regime

Abstract: Lowland riparian vegetation in the southwestern United States is critically important for maintaining a high richness and density of breeding birds. Further investigation is needed within riparian corridors, however, to evaluate the relative importance of vegetation type and hydrologic regime for avian density and nest survival as targets for regional conservation or restoration efforts. We estimated the densities of 40 bird species and for species grouped on the basis of nest height and dependence on surface water in gallery cottonwood–willow (Populus spp.–Salix spp.) forests, saltcedar (Tamarix spp.) shrub lands, and terrace vegetation types along a gradient in the hydrologic regime of the San Pedro River, Arizona, USA. We also assessed nest survival for shrub-nesting insectivores and herbivores. Canopy-nesting birds as a group and 14 individual bird species reached their greatest densities in cottonwood forests regardless of the hydrologic regime. Water-dependent birds as a group reached their highest density in both intermittent- and perennial-flow cottonwood stands, but certain species occurred almost exclusively in perennial-flow sites. Two shrub-nesting species and the brown-headed cowbird (Molothrus ater) were most abundant in saltcedar shrub lands, and the brown-headed cowbird was most abundant in saltcedar stands with intermittent flows. Mesquite (Prosopis spp.) and big sacaton (Sporobolus wrightii) grassland each maintained the highest densities of certain species within ≥1 hydrologic regime. Shrub-nesting insectivores had the greatest nest survival in cottonwood, including Arizona Bell's vireo (Vireo bellii arizonae), and also had lower proportions of nests parasitized and preyed upon, although 95% confidence intervals among vegetation types overlapped. Nest survival for both shrub-nesting insectivores and herbivores was lowest in intermittent-flow saltcedar, although, again, confidence intervals overlapped. Nest survival was lower in parasitized than nonparasitized nests in mesquite and across vegetation types for Arizona Bell's vireo and in cottonwood for Abert's towhee (Pipilo aberti). Riparian management that maintains heterogeneous riparian vegetation types, including floodplain vegetation comprising cottonwood–willow gallery riparian forests with some stretches of perennial flow, are important for maintaining the high diversity and abundance of breeding birds on the San Pedro River and probably across the region. Cottonwood stands also appear to maintain highest nest survival for some shrub-nesting birds.     

Prioritising potential guilds of specialist herbivores as biological control agents for prickly acacia through simulated herbivory

Understanding plant response to herbivory facilitates the prioritisation of guilds of specialist herbivores as biological control agents based on their potential impacts. Prickly acacia ( Acacia nilotica ssp. indica ) is a weed of national significance in Australia and is a target for biological control. Information on the susceptibility of prickly acacia to herbivory is limited, and there is no information available on the plant organ (i.e. leaf, shoot and root in isolation or in combination) most susceptible to herbivory. We evaluated the ability of prickly acacia seedlings, to respond to different types of simulated herbivory (defoliation, shoot damage, root damage and combinations), at varying frequencies (no herbivory, single, two and three events of herbivory) to identify the type and frequency of herbivory that will be required to reduce the growth and vigour. Defoliation and shoot damage, individually, had a significant negative impact on prickly acacia seedlings. For the defoliation to be effective, more than two defoliation events were required, whereas a single bout of shoot damage was enough to cause a significant reduction in plant vigour. A combination of defoliation + shoot damage had the greatest negative impact. The study highlights the need to prioritise specialist leaf and shoot herbivores as potential biological control agents for prickly acacia.     

Plant resistance, plant traits, and host plant choice of the leaf-folding sawfly on the arroyo willow

Abstract. 1. The hypotheses that genetic variation in host plant resistance of the arroyo willow affected leaf folder ( Phyllocolpa sp.) (Hymenoptera: Tenthredinidae) density and that genetic variation in shoot length and leaf length was correlated with resistance were tested.
2. Willows grown in pots and exposed to ovipojsition by the leaf folding sawfly in cages had significantly different densities among clones, indicating variation in resistance caused by genetic differences among conspecific host plants.
3. There was a general correspondence between leaf folder density on potted cuttings and on the plants in the field that were the sources of cuttings.
4. In behavioural choice experiments, susceptible clones (with highest leaf fold densities) had the highest oviposition activity of female leaf folders compared to clones that were resistant to the leaf folder.
5. Clones differed significantly in shoot length and leaf length among clones grown in pots, among clones in the field, and between shoots with galls and shoots without galls on clones in the field.
6. Leaf folder density was significantly positively correlated with mean shoot length on field clones in 1985 and 1986, but was not correlated with leaf length, although leaf length and shoot length were correlated.
7. Leaf length variation among willow clones accounted for a significant portion of the variation in resistance of potted willows, but shoot length was unimportant.     

Plant-attracted ants affect arthropod community structure but not necessarily herbivory

Abstract.  1. The effectiveness of ants as plant defenders is equivocal for plants that attract ants via extrafloral nectaries (EFNs).
2. This study focused on the myrmecophilic savannah tree Pseudocedrela kotschyi that attracts ants to EFNs and on the arthropod fauna associated with P. kotschyi . Herbivory and arthropod community composition were compared between trees that were dominated by one of three congeneric ant species, Camponotus acvapimensis , C. rufoglaucus , and C. sericeus , and between trees where ants were experimentally excluded and untreated control trees.
3. Short-term ant-exclusion experiments failed to demonstrate a consistent effect of ants on herbivory.
4. Plants dominated by different ant species differed significantly in leaf damage caused by herbivorous insects. The relative ranking of herbivory levels of the trees dominated by different ant species was persistent in three consecutive years.
5. Ants significantly reduced the abundance of different arthropod groups (Araneae, Blattodea, Coleoptera, Homoptera, non-ant Hymenoptera). Other groups, including important herbivores, seemed not to be affected (Lepidoptera, Orthoptera, Thysanoptera, Heteroptera).
6. The study suggests that the presence of ants only benefits plants when specific ant species are attracted, and protection by these ants is not counterbalanced by their negative effect on other beneficial arthropods.     

Habitat edges as a potential ecological trap for an insect predator

Abstract.  1. Ecological traps, where animals actively select poor habitat for reproduction over superior habitat, are generally associated with birds at forest edges. This study examines oviposition preference, predation, and parasitism rates in the mantid Stagmomantis limbata to determine the potential generality of this phenomenon.
2. Egg case (oothecae) densities were measured across two edge types (cottonwood and desert scrub) within desert riparian ecosystems. A positive edge effect in oothecae density was found with an approximate three-fold increase in density at cottonwood ( X _edge = 0.05 oothecae/100 m² vs. X _interior = 0.015 oothecae/100 m²) and desert scrub ( X _edge = 0.20 oothecae/100 m² vs. X _interior = 0.06 oothecae/100 m²) edges ( P  < 0.01).
3. Rates of bird predation were significantly higher for oothecae at desert scrub edges and showed a trend of higher predation rates at cottonwood edges, suggesting that riparian habitat edges may be acting as an ecological trap for this mantid species. There was no effect of edges on oothecal parasitism rates.
4. These results provide an example of the effect of habitat edges on a generalist insect predator and indicate that an ecological trap may exist with respect to one of its natural enemies.     

The deleterious effects of salinity stress on leafminers and their freshwater host

Abstract.  1. Salinity is an important cause of abiotic stress in wetland communities yet little is known about its consequences for freshwater plants and their insect herbivores. The goal of this study was to test the effect of salinity on a leafmining insect, Cerodontha iridiphora , and its herbaceous host plant, Iris hexagona .
2. Leafminer performance was evaluated on irises grown in control and saline treatments, and the effects of salinity and herbivory on leaf quality and mortality was measured.
3. Leafminer density and size were significantly lower on irises grown in saline water compared with freshwater.
4. Both salinity and herbivory accelerated leaf senescence and mortality, and their combined effects increased tissue loss by an order of magnitude compared with controls.
5. Leafminers acted as nutrient sinks. The undamaged regions of mined leaves contained 40% less nitrogen than unmined leaves, providing a mechanism for the premature leaf mortality.
6. Salinity was detrimental to the performance and survival of both the iris leafminer and its host plant. We propose that glycophytic host plants and their insect herbivores will suffer more than halophytic communities from environmental salinity because they lack the adaptive mechanisms to tolerate this potent physiological stress.     

Lowland boreal forests characterization in Algonquin Provincial Park relative to beaver (Castor canadensis) foraging and edaphic factors

Beaver (Caster canadensis) foraging and edaphic conditions can modify the vegetational characteristics of woody plant community in lowland boreal forests. Effective management of these areas requires an understanding of the relative contribution of these factors in shaping the woody plant community structure. Our objective was to quantify the effects of herbivory by beavers and edaphic conditions on woody plant community organization of lowland boreal forests surrounding beaver ponds. Woody vegetation and soils were sampled at 15 ponds occupied by beavers and one other pond abandoned by them in southern Algonquin Park, Ontario. We measured spatial variation in plant diversity, foraging rates and sapling recruitment of trees and shrubs along gradients of beaver foraging intensity and soil moisture, P, K, Mg, and pH. Beavers fed preferentially on a small number of deciduous species and the number of cut stems declined sharply with increasing distance from ponds. Conifers increased in relative dominance to deciduous species in the presence of beavers. Plant species richness and stem and basal area diversity peaked at intermediate distances (about 25 m) from ponds. Sapling recruitment by non-preferred species was positively related to foraging intensity. Total stem abundance and basal area and sapling recruitment by four preferred species (Populus tremuloides, Acer rubrum, Acer saccharum and Corylus cornuta) were negatively related to foraging intensity. However, by including Alnus rugosa and Salix bebbiana (also preferred by beavers) these patterns changed, becoming positively related to foraging intensity. There was also a pronounced gradient in soil moisture, which also decreased with distance from ponds. The other measured edaphic variables did not vary consistently with distance from ponds. Sapling recruitment in mesic versus xeric species varied consistently with hydrid conditions along the moisture gradient, such that variation in moisture also could produce the observed pattern of plant diversity. Diversity patterns changed three years after beaver abandonment of a pond, though sapling recruitment patterns in preferred and non-preferred species around the abandoned pond were similar to the occupied ponds. These observations suggest spatial variation in woody plant richness and diversity could be determined by combined effects of both herbivory (disturbance by beavers) and variable responses of different species to edaphic conditions.     

Unintended Consequences of Invasive Predator Control in an Australian Forest: Overabundant Wallabies and Vegetation Change

Over-abundance of native herbivores is a problem in many forests worldwide. The abundance of native macropod wallabies is extremely high at Booderee National Park (BNP) in south-eastern Australia. This has occurred because of the reduction of exotic predators through an intensive baiting program, coupled with the absence of other predators. The high density of wallabies at BNP may be inhibiting the recruitment of many plant species following fire-induced recruitment events. We experimentally examined the post-fire response of a range of plant species to browsing by wallabies in a forest heavily infested with the invasive species, bitou bush Chrysanthemoides monilifera. We recorded the abundance and size of a range of plant species in 18 unfenced (browsed) and 16 fenced (unbrowsed) plots. We found the abundance and size of bitou bush was suppressed in browsed plots compared to unbrowsed plots. Regenerating seedlings of the canopy or middle storey tree species Eucalyptus pilularis, Acacia implexa, Allocasuarina littoralis, Breynia oblongifolia and Banksia integrifolia were either smaller or fewer in number in grazed plots than treatment plots as were the vines Kennedia rubicunda, Glycine tabacina and Glycine clandestina. In contrast, the understorey fern, Pteridium esculentum increased in abundance in the browsed plots relative to unbrowsed plots probably because of reduced competition with more palatable angiosperms. Twelve months after plots were installed the community structure of the browsed and unbrowsed plots was significantly different (P = 0.023, Global R = 0.091). The relative abundance of C. monilifera and P. esculentum contributed most to the differences. We discuss the possible development of a low diversity bracken fern parkland in Booderee National Park through a trophic cascade, similar to that caused by overabundant deer in the northern hemisphere. We also discuss its implications for broad scale fox control in southern Australian forests.     

Interactions among elk, aspen, galling sawflies and insectivorous birds

Using two years of observational and experimental data, we examined the hypothesis that browsing by elk on aspen indirectly affects the distribution of a leaf-galling sawfly, which in turn affects insect diversity and foraging patterns of insectivorous birds. We found that: i) in an analyses of 33 arthropod species, the presence of sawflies significantly increased arthropod richness and abundance by 2 X and 2.5 X, respectively. ii) browsing by elk reduced sawfly gall abundance such that 90% of the galls were found on unbrowsed aspen ramets. iii) insectivorous birds attacked 60–74% of the galls on unbrowsed shoots compared to 11% on browsed shoots. When leaf-galler abundance was experimentally held constant on browsed and unbrowsed shoots, predation by insectivorous birds did not differ significantly. This result suggests that browsing affects the patterns of avian predation by altering the distribution of a galling insect. These data argue that bottom-up, top-down, and lateral factors can act in concert to affect the distribution of a galler, structure arthropod communities and affect predation by insectivorous birds.     

Effects of below- and above-ground herbivores on plant growth,flower visitation and seed set

Separate and combined effects of root and leaf herbivores on plant growth, flower visitation and seed set were tested in a factorial experiment using potted mustard, Sinapis arvensis, at an old fallow field. A 50% leaf removal by cabbageworms (Pieris rapae) when the seedlings had their first four leaves reduced plant height and shoot mass, and delayed the onset of flowering. Root herbivory by two wireworms (Agriotes sp.) over the whole experiment changed flower visitation; the number of flower visitors per plant was higher in plants with root herbivores than in plants without root herbivores. Combined leaf and root herbivory affected flowering period, number of fruits per plant and number of seeds per fruit. Plants attacked by leaf and root herbivores had a shorter flowering period and produced fewer fruits per plant than plants with root herbivores only. Although the experimental plants faced major herbivore-induced growth changes, plant reproduction (seed set and weight per plant) was similar in all treatments, documenting their ability to effectively compensate for leaf and root herbivory.     

Experimental evidence that the ecosystem effects of aquatic herbivory by moose and beaver may be contingent on water body type

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Feeding by Hessian fly [Mayetiola destructor (Say)] larvae does not induce plant indirect defences

Abstract.  1. Recent research has addressed the function of herbivore-induced plant volatiles in attracting natural enemies of feeding herbivores. While many types of insect herbivory appear to elicit volatile responses, those triggered by gall insects have received little attention. Previous work indicates that at least one gall insect species induces changes in host-plant volatiles, but no other studies appear to have addressed whether gall insects trigger plant indirect defences.
2. The volatile responses of wheat to feeding by larvae of the Hessian fly Mayetiola destructor (Say) (Diptera: Cecidomyiidae) were studied to further explore indirect responses of plants to feeding by gall insects. This specialist gall midge species did not elicit a detectable volatile response from wheat plants, whereas a generalist caterpillar triggered volatile release. Moreover, Hessian fly feeding altered volatile responses to subsequent caterpillar herbivory.
3. These results suggest that Hessian fly larvae exert a degree of control over the defensive responses of their host plants and offer insight into plant-gall insect interactions. Also, the failure of Hessian fly larvae to elicit an indirect defensive response from their host plants may help explain why natural enemies, which often rely on induced volatile cues, fail to inflict significant mortality on M. destructor populations in the field.     

Can intra‐specific genetic variation in arbuscular mycorrhizal fungi (Glomus etunicatum) affect a mesophyll‐feeding herbivore (Tupiocoris notatus Distant)?

Abstract.  1. Arbuscular mycorrhizal fungal (AMF) infection can have negative, positive or neutral effects on insect herbivore populations, but patterns are difficult to predict.
2. Intra-specific genetic variation in nutrient uptake ability between fungal isolates may also have indirect effects on insect herbivores due to changes in plant quality. In preliminary studies mirid ( Tupiocoris notatus ) populations were significantly reduced on tobacco ( Nicotiana rustica ) colonised by AMF but it was unknown if same-species fungal isolates differed in their effect.
3. An experiment was performed as a first test of the effect of intra-specific genetic variation in the mycorrhizal fungus Glomus etunicatum on mirid nymphal population structure, dynamics, and growth rate.
4. Mirid nymphal populations were lower on mycorrhizal fungal-infected plants. Population size, however, did not differ between the mycorrhizal isolates. While no statistical difference in population between isolates was found, one isolate consistently had 1.7–2.4 times lower mirid populations compared with the controls, indicating that the magnitude of effect is different between mycorrhizal isolates.
5. The significantly negative effect of AMF on mirid populations likely resulted from AMF-induced changes in plant quality (e.g. increased defence). This study lends further support to recent demonstrations that below-ground symbionts significantly influence above-ground processes. In addition, mycorrhizal fungi can affect insect population structure, which may have consequences for future herbivory.