Instar duration, adult consumption, oviposition and nitrogen utilization efficiencies of leafhoppers feeding on different quality food (Auchenorrhyncha: Homoptera)

Abstract. 1. Plant material of Holcus lanatus L. removed from an artificially fertilized trial was used to rear leafhoppers of three feeding types: Dicrano-tropis hamata Boheman and Ebmana sulphurella Zetterstedt, (phloem feeders), Eucelis incisus Kirschbaum (xylem feeder) and Zyginidia scutellaris Herrich-Schaeffer (mesophyll feeder).
2. In the laboratory, leafhopper instar durations, adult consumption rate, oviposition rate, and nitrogen utilization efficiency were influenced by the quality of the food consumed. Adult longevity was unaffected by the level of food quality normally found in plants.
3. Z.scutellanis consumed mesophyll contents equivalent to 72% of its body weight each day but only digested about 30% of its intake. Eincicus had a low dry weight consumption rate (12% body weight/day) but digested its food more efficiently (60%) than the other feeding types. The two phloem feeders consumed mounts equivalent to 25% of their body weight each day and digested 40–50% of their intake.
4. Each species reached maximum nitrogen utilization efficiencies at different plant nitrogen levels. This suggests that leafhopper species may be associated with a particular nitrogen concentration in the grasses.     

Microbiome responses during virulence adaptation by a phloem‐feeding insect to resistant near‐isogenic rice lines

The microbiomes of phloem‐feeding insects include functional bacteria and yeasts essential for herbivore survival and development. Changes in microbiome composition are implicated in virulence adaptation by herbivores to host plant species or host populations (including crop varieties). We examined patterns in adaptation by the green leafhopper, Nephotettix virescens, to near‐isogenic rice lines (NILs) with one or two resistance genes and the recurrent parent T65, without resistance genes. Only the line with two resistance genes was effective in reducing leafhopper fitness. After 20 generations on the resistant line, selected leafhoppers attained similar survival, weight gain, and egg laying to leafhoppers that were continually reared on the susceptible recurrent parent, indicating that they had adapted to the resistant host. By sequencing the 16s rRNA gene, we described the microbiome of leafhoppers from colonies associated with five collection sites, and continually reared or switched between NILs. The microbiomes included 69–119 OTUs of which 44 occurred in ≥90% of samples. Of these, 14 OTUs were assigned to the obligate symbiont Candidatus sulcia clade. After 20 generations of selection, collection site had a greater effect than host plant on microbiome composition. Six bacteria genera, including C. sulcia, were associated with leafhopper virulence. However, there was significant within‐treatment, site‐related variability in the prevalence of these taxa such that the mechanisms underlying their association with virulence remain to be determined. Our results imply that these taxa are associated with leafhopper nutrition. Ours is the first study to describe microbiome diversity and composition in rice leafhoppers. We discuss our results in light of the multiple functions of herbivore microbiomes during virulence adaptation in insect herbivores.     

Autumnal emergence of Anagrus wasps,egg parasitoids of Empoasca vitis,from grapevine leaves and their migration towards brambles

• 1 The Anagrus‘atomus’ parasitoid group (Hymenoptera: Mymaridae), associated with Empoasca vitis (Göthe) (Homoptera: Cicadellidae), overwinters on vegetation surrounding vineyards. The emergence of parasitoid adults from grapevine leaves in autumn was studied in north‐eastern Italy, both in relation to the E. vitis egg‐laying period and to the presence of leafhoppers overwintering as eggs on Rubus bushes.
• 2 Autumnal peaks of Anagrus captured using yellow sticky traps were observed first on grapevines and then on brambles. Parasitoid captures in vineyards were observed for more than 1 month after the last first‐instar nymphs of the grape leafhoppers were noticed. Two species belonging to the A. ‘atomus’ group, Anagrus atomus and Anagrus ustulatus, were captured both on grapevines and brambles.
• 3 Parasitoids of the A.‘atomus’ group can emerge from third‐generation grape leafhopper eggs in accordance with two different development time patterns (i.e. normal or delayed). Individuals with delayed emergence required up to 2.2‐fold more time to develop from an egg to adult than individuals with normal emergence. This meant that some parasitoid adults emerged in autumn from eggs of grape leafhopper laid in August.
• 4 A delayed emergence as a result of a slower development ensures that the A.‘atomus’ parasitoid group is synchronized with the egg‐laying of leafhoppers that overwinter as eggs on Rubus spp.
• 5 Consequently, leafhoppers overwintering as eggs on brambles play a key role in the ecology of the relationship between grape leafhoppers and the A.‘atomus’ parasitoid group.

     

Do assortative mating and immigrant inviability help maintain population genetic structuring of an herbivore on a crop and a wild relative?

Population genetic structuring is common among herbivorous insects and frequently is associated with divergent host plants, such as crops and their wild relatives. Previous studies showed population genetic structuring in corn leafhopper Dulbulus maidis in Mexico, such that the species consists of two sympatric, host plant-associated populations: an abundant and widespread "pestiferous” population on maize (Zea mays mays), and a small and localized "wild" population on perennial teosinte (Zea diploperennis). a maize wild relative with a limited distribution. This study addressed whether assortative mating and immigrant inviability mediate genetic structuring of corn leafliopper by comparing the mating and reproductive successes of pestiferous and wild females that colonize their nonassociated host plants against the successes of females colonizing their associated host plants. Assortative mating was assessed by comparing mating frequencies and premating and mating times among females of each population on each host plant: immigrant inviability was assessed by comparing, across two generations, the fecundity, survival, development time, sex ratio, and population growth rate among leafhopper populations and host plants. Our results showed that on maize, and compared to resident, pestiferous females, wild females were more likely to mate, and greater proportions of their offspring survived to adult stage and were daughters;consequently, the per-generation population growth rate on maize was greater for immigrant, wild leafhoppers compared to resident, pestiferous leafhoppers. Our results suggested that wild leafhoppers emigrating to maize have a fitness advantage over resident, pestiferous leafhoppers, while immigrant pestiferous and resident wild leafhoppers on teosinte have similar fitnesses.     

Host plant dispersion, leaf hopper movement and disease transmission

Abstract.

• 1 The plant-to-plant movement of the corn leafhopper, Dalbulus maidis Delong & Wolcott, and the spread of the leafhopper-borne maize rayado fino virus were investigated in four patterns of maize (Zea mays) dispersion.
• 2 D. maidis was less abundant and the spread of the virus was slower in dense stands of maize than in sparse stands.
• 3 When plant density was held constant, leafhoppers were more abundant in maize stands with relatively equidistant plant spacing (uniform dispersion) than in stands with densely-sown rows (linear dispersion) or double-sown hills (clumped dispersion), but there was no difference in virus incidence among these plant dispersion patterns.
• 4 Leafhoppers were less likely to move to adjacent plants in uniform plant dispersion patterns than in either linear or clumped dispersion patterns. This result may explain the lack of higher virus incidence in uniform stands, despite higher leafhopper abundance.
• 5 Leafhopper movement was consistent with a simple rule: the shorter the distance to the next adjacent plant, the more likely a leafhopper is to move between plants.
• 6 These results demonstrate that host plant dispersion can affect the abundance and behaviour of highly mobile herbivorous insects even when plant density is constant.

     

Plant diversity increases herbivore movement and vulnerability to predation

Understanding how changes in plant diversity affect agroecosystem functioning remains a key challenge. We examined how intercropping alfalfa, Medicago sativa, with orchardgrass, Dactylis glomerata, affects the potato leafhopper, Empoasca fabae, its host plant (alfalfa), and the efficiency of a leafhopper predator, Nabis americoferus. In a field experiment, intercropping reduced the reproductive efficiency of the leafhopper. Nabis was more effective at reducing leafhopper abundance, and protecting alfalfa from hopperburn, in the polyculture than in the monoculture of alfalfa. In a series of laboratory experiments, we investigated mechanisms by which intercropping could enhance the efficiency of Nabis. Intercropping resulted in changes in vegetation structure and the spatial distribution of leafhoppers, but there was little evidence that these factors influenced the efficiency of Nabis. Instead, orchardgrass, a nonhost for leafhoppers, increased leafhopper movement, and Nabis captured leafhoppers more efficiently when the herbivores were more mobile. These results indicate that intercropping with nonhost plants promotes leafhopper movement and vulnerability to predation, and reveal a novel mechanism by which plant diversity can reduce herbivory.     

High Plant Richness in Prairie Reconstructions Support Diverse Leafhopper Communities

A primary reason for restoring plant communities is to increase biodiversity to previous levels. It is expected that restoring land with greater plant diversity will increase biodiversity at higher trophic levels, but high diversity seed mixes are expensive. In this study, we used one insect family, leafhoppers (Hemiptera: Cicadellidae) to assess the difference in leafhopper communities that result from establishing high compared with low plant richness restorations. We tested the hypotheses that: (1) the added effort of a high richness restoration leads to measurable increases in both diversity and richness of leafhoppers; and (2) that leafhopper community composition is more similar to remnant prairies in high richness than in low plant richness restorations. We found that higher plant richness led to 3‐ to 7‐fold increases in leafhopper and prairie‐dependent leafhopper diversity and richness in restorations. Leafhopper communities in high richness restorations were not more similar to remnant prairies, rather they were distinct among high and low richness restorations and prairie interior. Leafhopper richness and diversity correlated with plant richness, and leafhopper community composition differed among plant community assemblages, but not with the occurrence of single plant species. For our sites, species‐rich restorations provided better quality habitat for leafhoppers that was comparable to remnant prairie. Our results suggest that restorations with high plant species richness better support animal food webs.     

Ecological studies on the parasite complex associated with typhlocybine leafhoppers (Homoptera, Cicadellidae)

Abstract.

• 1 The parasite complex associated with nymphal and adult typhlocybine leafhoppers consists of the following: Dryinidae (Aphelopus species), Pipunculidae (Chalarus species) and Diapriidae (Ismarus dorsiger Curtis), the last being parasitic on species of Aphelopus.
• 2 The life cycles and temporal distribution patterns of twenty-nine species of Typhlocybinae are summarized together with the life cycles of British Aphelopus and Chalarus.
• 3 Closely related primary parasite species differ in their adult emergence times. Species differences in adult emergence times of diapausing Chalarus are correlated with species differences in host relations.
• 4 Each primary parasite genus contains both monophagous and polyphagous species. Each polyphagous species shows a distinct ‘preference’ for a particular range of hosts.
• 5 The parasite complexes of different leafhopper communities are compared, and it is concluded that it is the taxonomic composition of the leafhopper communities which is chiefly responsible for the structure and taxonomic composition of their associated parasite complexes.
• 6 Individual species of both Aphelopus and Chalarus show a degree of sensitivity to the physiology of their hosts, so achieving a high degree of synchrony.

     

Traits explain sorting of C4 grasses along a global precipitation gradient

1. Species distributions are closely associated with moisture availability, but the underlying mechanisms remain unresolved. Drought relations are especially important for plants such as C₄ grasses that dominate seasonally dry ecosystems. Here, we test the hypothesis that C₄ grass species sampled across global precipitation gradients show variation in survival under drought that can be explained by their traits.
2. Our experiment subjected 18 C₄ grass species to a lethal drought under controlled environmental conditions. The number of days until death was measured, along with root traits, senescence, and aspects of hydraulic function.
3. We identified two strategies: Drought‐avoiding species that stayed green as the water potential declined and drought‐tolerating species that senesced more quickly but could extend survival via drought‐tolerant meristems.
4. Plants that stay‐green for longer occupied drier habitats and had the longest survival under drought, facilitated by narrow root diameter and isohydric stomatal behavior. Plants that senesced quickly had thicker roots, an anisohydric strategy, and occupied wetter habitats.
5. Global distributions of C₄ grasses can be predicted by variation in rates of senescence, meristem survival, root traits, and stomatal strategy, showing the value of these traits for understanding plant distributions in relation to climate.

     

Weedy hosts and prevalence of potential leafhopper vectors (Hemiptera: Cicadellidae) of a phytoplasma (16SrIX group) associated with Huanglongbing symptoms in citrus groves

Huanglongbing (HLB) is a severe citrus (Citrus spp.) disease associated with the bacteria genus Candidatus Liberibacter, detected in Brazil in 2004. Another bacterium was found in association with HLB symptoms and characterized as a phytoplasma belonging to the 16SrIX group. The objectives of this study were to identify potential leafhopper vectors of the HLB-associated phytoplasma and their host plants. Leafhoppers were sampled every other week for 12 mo with sticky yellow cards placed at two heights (0.3 and 1.5 m) in the citrus tree canopy and by using a sweep net in the ground vegetation of two sweet orange, Citrus sinensis (L.) Osbeck, groves infected by the HLB-phytoplasma in S?o Paulo state. Faunistic analyses indicated one Agalliinae (Agallia albidula Uhler) and three Deltocephalinae [Balclutha hebe (Kirkaldy), Planicephalus flavicosta (St?l), and Scaphytopius (Convelinus) marginelineatus (St?l)] species, as the most abundant and frequent leafhoppers (Hemiptera: Cicadellidae). Visual observations indicated an association of leafhopper species with some weeds and the influence of weed species composition on leafhopper abundance in low-lying vegetation. S. marginelineatus and P. flavicosta were more frequent on Sida rhombifolia L. and Althernantera tenella Colla, respectively, whereas A. albidula was observed more often on Conyza bonariensis (L.) Cronq. and B. hebe only occurred on grasses. DNA samples of field-collected S. marginelineatus were positive by polymerase chain reaction and sequencing tests for the presence of the HLB-phytoplasma group, indicating it as a potential vector. The association of leafhoppers with their hosts may be used in deciding which management strategies to adopt against weeds and diseases in citrus orchards.     

Transmission via plants of an insect pathogenic bacterium that does not multiply or move in plants

A bacterial parasite (designated as BEV) of the leafhopper Euscelidius variegatus, which is passed transovarially to offspring, was transmitted from insect to insect via feeding of the insects in plants. The rate of bacterial infection of leafhoppers fed upon plants that had previously been exposed to BEV-infected leafhoppers declined with an increase in the time that infected leafhoppers had been off rye grass. Transmission of BEV also occurred on sugar beet and barley but not celery. The bacterium was also transmitted to and acquired from membrane-encased artificial diets. There was no evidence that the bacterium was transmitted via plant surfaces, but transmission and direct culture assays from plants indicated that the bacterium did not multiply or move within plants. This parasite-host relationship may represent a primitive stage in either the evolution of intracellular symbiosis with its insect host or to alternative parasitization of plant and insect hosts via insect transmission, as is the case for insect-vectored plant pathogens.Correspondence to: A.H. Purcell.     

Influence of plant ontogeny and abiotic factors on resistance of glandular-haired alfalfa to potato leafhopper (Hemiptera: Cicadellidae)

Laboratory experiments were conducted to characterize the trichome-based defense of glandular-haired alfalfa, Medicago sativa L., against the potato leafhopper, Empoasca fabae (Harris). Within-plant variability in leafhopper resistance was examined by caging adult leafhoppers to either basal or apical stem internodes of the leafhopper-resistant, glandular-haired M. sativa genotype G98A or the susceptible, nonglandular-haired M. sativa 'Ranger'. Young, actively secreting glandular trichomes are located on apical internodes of G98A, whereas senesced gland heads are found on older, basal internodes of G98A. After 96 h, the highest cumulative leafhopper mortality and lowest number of excretory droplets were associated with apical internodes of G98A. No difference was detected in mortality and feeding levels among insects caged to basal internodes of G98A and basal and apical internodes of Ranger. The influence of abiotic factors on leafhopper resistance was evaluated by caging adult leafhoppers to either G98A or Ranger under four combinations of low and high light (250 and 1,000 micromol s(-1) m(-2)) and temperature regimes (17 and 30 degrees C). After 96 h, the highest cumulative mortality was associated with leafhoppers confined to G98A under high light and high temperature conditions. Temperature level and plant type also had an effect on the production of excretory droplets, resulting in the highest number of excretory droplets being associated with Ranger under the high temperature regime. These results indicate that certain regions of M. sativa G98A are better protected against the potato leafhopper than others and that temperature influences resistance levels of glandular-haired alfalfa.     

Arthropod abundance in tall fescue,Lolium arundinaceum,pastures containing novel ‘safe’ endophytes

Poor livestock performance on tall fescue is linked to infection by a fungal endophyte that enhances grass resistance to stress, including herbivory, while producing ergot alkaloids toxic to vertebrate grazers. Novel ‘safe’ endophyte/grass associations produce no ergot alkaloids yet retain stand persistence, but they could be more susceptible to insect outbreaks. We tested the hypothesis that grass‐feeding insects are more abundant in novel endophyte pastures compared with those containing common endophyte. Above‐ and below‐ground herbivores were sampled across two growing seasons in pastures containing common strain endophyte (KY31), novel endophytes (MaxQ or AR584) or endophyte free. We also sampled natural enemies as an indicator of possible tritrophic effects. With a few exceptions, numbers of predatory, chewing (grasshoppers, crickets, caterpillars) or sucking insects (leafhoppers, planthoppers) were similar in common and novel endophyte pastures. Contrary to our hypothesis, Aphrodes spp. leafhoppers were more abundant in KY31 than other pasture types in 2008; their nymphs also were more abundant in KY31 than in MaxQ in 2009. Adults (but not total numbers or nymphs) of another leafhopper, Psammotettix striatus, were less abundant in KY31 than other pasture types in 2009. Popillia japonica and Cyclocephala spp. grubs did not differ in density, weight or instar among the endophyte‐containing associations. In feeding assays, armyworm (Mythimna unipuncta) survival was higher on MaxQ and NE9301, and weight gain was higher on NE9301, suggesting armyworm outbreaks could be more severe on such grasses, but that result may not be attributable solely to alkaloids because common strain and endophyte‐free grasses did not differ in either parameter. Caterpillar abundance did not differ among pasture types in the field. Our results suggest that re‐seeding common strain endophytic pastures with livestock‐safe novel endophyte/grass associations to alleviate fescue toxicosis is unlikely to promote markedly higher populations of plant‐feeding insects.     

Natural mycosis of mango leafhoppers (Cicadellidae: Hemiptera) by Fusarium sp.

Mango leafhoppers that feed on inflorescences and young shoots of mango (Mangifera indica L.) were found mycotized under natural conditions in Bangalore, India. Isolation and characterisation of the etiological agents by sequencing of the Translation Elongation Factor-1α gene, revealed 99% identity with the plant pathogenic fungus Fusarium proliferatum. This is an early report on the Fusarium associated entomopathogenicity in different mango leafhopper species.     

Small differences in root distributions allow resource niche partitioning

1. Deep roots have long been thought to allow trees to coexist with shallow‐rooted grasses. However, data demonstrating how root distributions affect water uptake and niche partitioning are uncommon.
2. We describe tree and grass root distributions using a depth‐specific tracer experiment six times over two years in a subtropical savanna, Kruger National Park, South Africa. These point‐in‐time measurements were then used in a soil water flow model to simulate continuous water uptake by depth and plant growth form (trees and grasses) across two growing seasons. This allowed estimates of the total amount of water a root distribution could absorb as well as the amount of water a root distribution could absorb in excess of the other rooting distribution (i.e., unique hydrological niche).
3. Most active tree and grass roots were in shallow soils: The mean depth of water uptake was 22 cm for trees and 17 cm for grasses. Slightly deeper rooting distributions provided trees with 5% more soil water than the grasses in a drier season, but 13% less water in a wetter season. Small differences also provided each rooting distribution (tree or grass) with unique hydrological niches of 4 to 13 mm water.
4. The effect of rooting distributions has long been inferred. By quantifying the depth and timing of water uptake, we demonstrated how even small differences in rooting distributions can provide plants with resource niches that can contribute to species coexistence. Differences in total water uptake and unique hydrological niche sizes were small in this system, but they indicated that tradeoffs in rooting strategies can be expected to contribute to tree and grass coexistence because 1) competitive advantages change over time and 2) plant growth forms always have access to a soil resource pool that is not available to the other plant growth form.

     

Relation between temporal persistence of host plants and wing length in leafhoppers (Hemiptera: Auchenorrhyncha)

Abstract.

• 1 Wing form frequencies in 255 populations of 101 species of leafhoppers (Auchenorrhyncha) in temporary and permanent habitats were documented.
• 2 The proportion of brachypterous specimens in the leafhopper assemblages on ruderal host plants in temporary habitats (median 2%, range 0–8%) was significantly lower than that on permanent host plants in undisturbed habitats (median 22%, range 0–94%).
• 3 Leafhopper species typical of temporary habitats were either monomorphic, macropterous, or wing-dimorphic with macropterous forms prevailing in both sexes.
• 4 Among the eighty-nine species recorded in permanent habitats, forty-five species were wing dimorphic. In forty-one dimorphic species, a brachypterous form prevailed. This prevalence was found for both sexes in thirty-one species, for only females in nine species and for only males in one species.
• 5 The prevalence of brachypters in males, but not in females, found in Anoscopus flavostriatus, is probably the first such documented case in Auchenorrhyncha.
• 6 The hypothesis is proposed that in temporary habitats, density-dependent production of macropters in wing dimorphic species is an adaptation to frequent habitat deterioration caused by factors independent of the density of the species.
• 7 The predominance of brachypters in permanent habitats indicates that a density-dependent decrease in fitness usually does not offset the potential decrease in fitness connected with macroptery and dispersal. Because of this inability of leafhopper populations to decrease significantly the quality of their resources, a high population density cannot be used as a predictor of future quality of these resources, which is information essential for efficient dispersal behaviour.

     

‘Sharpshooter’ in Botanic Garden: the tale of a rare plant-insect interaction

• Here we report a unique plant-insect interaction between the leafhopper Aloka depressa (tribe Phlogisini) and the host liana, Diploclisia glaucescens, from a Botanic Garden located at the southern edge of Western Ghats in India.
• Field observations and SEM micrographs were employed to derive evidences on this rare plant-insect interaction. 20-Hydroxyecdysone (20E), insect moulting hormone, was detected and quantified in the host plant D. glaucescens using HPTLC-densitometry. 20E was isolated and characterized from D. glaucescens using column chromatography, 1H-, 13C-NMR and HR-MS. 20E was also detected in A. depressa excrement using HPTLC-densitometry.
• The leafhopper A. depressa is functioning as a ‘sharpshooter’ drawing nutrients from the host liana, D. glaucescens, and flinging the waste fluid as droplets through their tail ends. SEM micrographs of A. depressa revealed its external morphological features, characteristic of a sharpshooter. We quantified 20E (0.44–1.44%, dry wt.) in various parts of D. glaucescens. 20E (1.47%, dry wt.) was also detected in the excrement of A. depressa.
• This plant (D. glaucescens)-insect (A. depressa) association crucially is not damaging the host liana. Considering the diseases caused by sharpshooting leafhoppers in the Americas, this association and the survival of the host plant (D. glaucescens) is illustrating a unique plant-insect interaction.

     

Responses and adaptation by Nephotettix virescens to monogenic and pyramided rice lines with Grh‐resistance genes

The green leafhopper, Nephotettix virescens (Distant) (Hemiptera: Cicadellidae), occasionally damages rice in Asia either directly, by feeding on the host phloem, or indirectly by transmitting tungro virus. We assessed the nature of resistance against the leafhopper in monogenic and pyramided near‐isogenic rice lines containing the resistance genes Grh2 and Grh4. Only the pyramided line was resistant to leafhopper damage. Leafhopper nymphs and adults had high mortality and low weight gain when feeding on the pyramided line and adults laid few eggs. In contrast, although there was some minor resistance in 45‐day‐old plants that possessed either Grh2 or Grh4 genes, the monogenic lines were generally as susceptible to the leafhopper as the recurrent parent line Taichung65 (T65). Resistance in the pyramided line was stable as the plant aged and under high nitrogen, and affected each of five Philippine leafhopper populations equally. Furthermore, in a selection study, leafhoppers failed to adapt fully to the pyramided resistant line: nymph and adult survival did improve during the first five generations of selection and attained similar levels as on T65, but egg‐laying failed to improve over 10 generations. Our preliminary results suggested that resistance was associated with physiological costs to the plants in some experiments. The results of this study demonstrate the success of pyramiding resistance genes through marker‐assisted breeding, to achieve a strong and potentially durable resistance. We discuss the utility of gene pyramiding and the development of near‐isogenic lines for leafhopper management.     

Effects of drought and N level on the interactions of the root hemiparasite Rhinanthus alectorolophus with a combination of three host species

• Increasing nitrogen deposition and more frequent drought events are likely to change plant interactions in natural grasslands. Both factors may also influence the interactions between hemiparasitic plants, regarded as keystone species in many grasslands, and their host species.
• We grew a combination of three suitable hosts, a grass, a forb and a legume, with and without the hemiparasite Rhinanthus alectorolophus at three levels of nitrogen (N) and two levels of water availability in a factorial design.
• Biomass of the hemiparasite and host community increased with N level and was reduced by drought to a similar degree. Larger plants in fertilised pots started to wilt earlier, and the presence of a hemiparasite further increased drought sensitivity. The hemiparasite strongly reduced biomass of the host community and overall productivity, and affected the competitive balance among host plants because it particularly reduced biomass of the dominant grass. These effects were the opposite of those of high N. The hemiparasite increased the root mass fraction of the hosts at all levels of N and water availability, indicating that the effect of the hemiparasite on the hosts was mainly due to loss of belowground resources.
• Our results indicate that hemiparasites will not always respond more strongly to increased N availability and drought than autotrophic plants, and that hemiparasites can have similarly strong effects on grassland communities as soil fertility and drought. By preferentially attacking dominant species the hemiparasites might alleviate the negative effects of nutrient enrichment on grassland diversity.

     

Differential Indirect Effects of Excluding Livestock and Rabbits from Chalk Heath on the Associated Leafhopper (Hemiptera: Auchenorrhyncha) Fauna

Preliminary results are presented of sampling the leafhopper assemblages on a field experiment designed to examine the differential effects of rabbits and livestock (mainly sheep) on the vegetation of chalk heath in southern England. Experimental plots that excluded livestock either allowed entry by rabbits or excluded them. Results were compared with those from plots grazed by both livestock and rabbits. After 7 years, exclusion of grazing herbivores had resulted in predictable increases in vegetation height, but no major changes were detected in the species composition of the vegetation. As expected, ungrazed plots had higher species richness and greater abundances of several individual leafhopper species. However, plots grazed only by rabbits had a leafhopper assemblage that was distinct from either ungrazed or mixed grazing plots. It is suggested that rabbit grazing may have subtle effects on grassland invertebrate assemblages that are not necessarily predictable from an examination of the species composition of the vegetation. Chalk heath vegetation contains an unusual mixture of calcicole and calcifuge plant species, but the leafhopper assemblage included a restricted number of calcareous grassland specialist species and only one species strongly associated with acidic grasslands; most leafhoppers recorded were generalist grassland species.