Phratora Vulgatissima Research Articles

A comparative study of interspecies mating of Phratora vulgatissima and P. vitellinae using behavioural tests and molecular markers

AbstractThe leaf beetle genus Phratora L. (Coleoptera: Chrysomelidae) has been used to study the ecology of host plant chemicals in herbivore preference, and the evolution of host use in chemical defence. Phratora vulgatissima and P. vitellinae are sympatric species distributed widely across Europe. Their trophic niches are largely separate due to strong differences in their host feeding preference, but they have occasionally been recorded together, feeding on Salix burjatica‘Germany’ and, only in early spring, on Populus trichocarpa (Torr & A. Gray) ‘Trichobel’. Using behavioural tests and recently developed species‐specific microsatellite markers, the intra‐ and interspecific mating of both beetle species were investigated. The microsatellite markers provided evidence that interspecific mating occurred under field conditions. Interspecific mating also took place under laboratory conditions, but less frequently than mating within species. Females of both species laid fewer eggs, and fewer eggs per clutch, when isolated with an interspecific male than with a conspecific male. Female P. vulgatissima were polyandrous, as microsatellite markers showed that their larvae were the progeny of both P. vulgatissima males that had been isolated with a single female. While only 0.55% of eggs laid in interspecific pair combinations hatched, microsatellite markers provided evidence of hybridisation between beetle species; however, these larvae died within a week when reared in a Petri dish containing ‘Germany’ and P. trichocarpa leaves. It can therefore be inferred that reproductive isolation is complete. The results are discussed in relation to species integrity and the implications for diverse mixtures of short‐rotation coppice willow plantations.

Effects of host variety on blue willow beetle Phratora vulgatissima performance

Summary Phratora vulgatissima adults exhibit feeding preferences among willow varieties, yet little is known of the effects of willow variety on larval and adult performance. The effects of host variety on adult fitness and fecundity as well as on larval mortality and development were studied under laboratory conditions for 35 willow varieties. The host variety significantly affected the number of days that adults survived and the rates of weight change. On average, males lost weight and females gained weight. The total number of eggs, eggs day1, eggs clutch−1 and the length of the oviposition period were also significantly affected by willow variety. Progeny from eggs laid by adults fed on the different willow varieties showed significant differences in days to pupation and pupal weight when subsequently reared on Salix × dasyclados or on the same variety as fed to the adults. However, there was no correlation between these parameters on S. × dasyclados and the variety fed to adults. The willow variety fed to larvae significantly affected larval mortality (four varieties caused 100% mortality), the shape of larval growth curves (as measured by predicted final weight and time to half the final weight), the number of days to pupation and pupal weight. There were significant positive correlations between previously determined adult P. vulgatissima feeding preferences of the 35 willow varieties and the following: number of eggs laid, length of the oviposition period, larval mortality and development and change in adult weight. There was a considerable degree of variation in these correlations and some varieties did not follow the general trend indicated by the size or sign of particular correlations, for example, having a high feeding preference ranking yet few eggs laid, low larval weight and longer time to pupation. The differences found between varieties for adult and larval performance in conjunction with previously established feeding preferences offer great potential for utilising plant resistance to P. vulgatissima as a means of strategic control. Despite the general correlation of feeding preference and performance parameters, the results found here suggest that it appears to be possible for plant breeders to circumvent this trend.

Generalist Natural Enemies of a Willow Leaf Beetle (Phratora vulgatissima): Abundance and Feeding Habits

The natural enemies attacking eggs (and young larvae) of the willow leaf beetle Phratora vulgatissima were identified in the field. Three heteropterans were common natural enemies. The mirid Orthotylus marginalis was the most abundant and had an intermediate consumption rate in the lab, whereas the mirid Closterotomus fulvomaculatus was the least abundant but had the highest consumption rate. The anthocorid Anthocoris nemorum was intermediate in abundance but had the lowest consumption rate. However, the experimental situation (in petridish or on shoot) affected the ranking of the predators and illustrates behavioral differences. The anthocorid was very mobile and could be characterized as a “run and eat” predator, whereas the mirids were less mobile and behaved to a “find and stay” principle. Possible consequences of interspecific variation in behavior, from a biological control perspective, are discussed.

Indirect interactions between rust (Melampsora epitea) and leaf beetle (Phratora vulgatissima) damage onsalix

Willows (Salix spp.) are beneficial as a potential source of renewable energy, riparian barriers and riverbank control, yet are considered invasive weeds when they clog watercourses and lead to erosion and flooding. Interactions between willow rustMelampsora epitea (Thum.) (Uredinales: Melampsoraceae) and leaf beetlePhratora spp. (Coleoptera: Chrysomelidae) feeding damage have an impact on effective pest management and biological control. The present study investigated the effects of(a) prior mechanical leaf damage on rust development, and(b) rust infection on beetle feeding under laboratory conditions for different time intervals and levels of damage. Willow rust infection significantly reduced the amount of leaf area consumed by beetles. The result was similar when a compatible or an incompatible rust pathotype was sprayed ontoSalix viminalis (L.) ‘Mullatin’ plants. There were no overall significant effects of mechanical damage on rust development, although the lowest level of rust infection was found with the incremental damage treatment. There were, however, differences of significance for leaf position and damage status, with damaged leaves at all positions having fewer pustules and a smaller pustule area than the corresponding undamaged leaves. There was no detectable effect of possible volatile emissions from crushed willow leaves on rust infection and development, although the volatile compoundcis-3-hexenyl acetate significantly reduced pustule diameter and overall pustule area. The results are discussed in terms of the implications for pest management and biological control.

Adult beetle grazing induces willow trichome defence against subsequent larval feeding.

Induced increases in trichome density to grazing by herbivores have been suggested to increase plant resistance to future herbivore attack. In this paper we present results which show that plants of Salix cinerea L. respond to adult leaf beetle (Phratora vulgatissima L.) grazing by developing new leaves with an increased trichome density. The same plants are usually attacked again later in the season when the next generation of larvae hatches on the plants. The effect of the induced response was studied by comparing larval growth and feeding on newly developed leaves of plants exposed to different defoliation treatments. Larvae on plants previously exposed to adult grazing consumed less total leaf area and showed more dispersed feeding than larvae on plants protected from previous grazing. Larvae on plants exposed to mechanical defoliation responded intermediately. These results corresponded to the increased trichome density of defoliated plants. However, we found this larval response only in whole plant tests--when reared on single, excised leaves in petri dishes, larvae in all treatments behaved similarly. This discrepancy between the on-plant experiment and that in petri dishes highlights how experimental design may alter the conclusion of a study. We suggest that the induced response to adult grazing may act as a defence against subsequent larval feeding.

Interactions between the willow beetle Phratora vulgatissima and different genotypes of Salix viminalis

Abstract 1 Planting of species mixtures is a strategy for the non‐chemical management of willow beetles in short‐rotation coppice willows. However, the relatively susceptible Salix viminalis genotypes and their hybrids dominate current high‐yielding willows. Interactions between Phratora vulgatissima and different genotypes of S. viminalis were examined under laboratory conditions to determine if these genotypes exhibit genetic differences in susceptibility to willow beetle damage.2 Seven S. viminalis genotypes and four hybrids were tested for the feeding preference of adult P. vulgatissima, larval performance and within‐season plant response to manual defoliation (50% and 75%).3 The feeding preference of adult beetles, the growth rate of larvae, and the weight at 33 days of larvae and pupae differed significantly between genotypes. Genotypes also differed significantly in their height and weight responses to mechanical defoliation. Two genotypes were taller, with longer internodes, after defoliation than were undamaged plants. Two hybrids and their S. viminalis parent showed no significant reduction in final dry weight between 0% and 50% defoliation treatments.4 Susceptibility of genotypes to adult feeding was not correlated with their tolerance to defoliation in terms of weight or height responses; however, larval growth rate on genotypes was negatively correlated both with final height and number of leaves after 75% defoliation and with the susceptibility of genotype to adult feeding.5 Salix viminalis showed genetic differences for all parameters tested. This suggests that the planting of a mixture of these genotypes would contain genetic differences with respect to host susceptibility to P. vulgatissima. Some parameters showed similarities between a hybrid and its parent, whereas others showed differences between siblings. This offers potential for effective breeding of desirable traits.

Does host genotype diversity affect the distribution of insect and disease damage in willow cropping systems?

Summary Planting of willow genotype mixtures for biomass production has been suggested as a non‐chemical strategy for pest management. Basic information on spatial dynamics of important insects and pathogens is necessary for the effective deployment of host genotypes in a plantation. In 1998 and 1999 the degree and spatial distribution of damage by Melampsora spp. and Phratora vulgatissima were studied concurrently in a field trial containing monocultures of willow Salix genotypes with different willow rust and beetle susceptibilities, and two design mixtures (random or regular) of three or five genotypes. For both years, there was more rust and beetle damage on plants in monocultures than in mixtures. There were significant differences in the vertical distribution of beetle damage along stems between plantation designs for the 2 years, yet only in 1999 for rust. Rust severity along stems was significantly correlated between leaves, indicating localized spread of disease. In contrast, beetle damage severity along stems was weakly correlated between alternate leaves and leaves farther apart, suggesting beetle movement from tree to tree. In 1998, spatial distribution of rust was aggregated in 67% of plots studied and in 40% for beetles. There was no significant difference in the distribution of beetle damage between planting design, but rust was aggregated in 75% of mixtures and 33% of monocultures. While beetle damage distribution was similar between years, rust was aggregated in all monoculture plots but in only 8% of mixtures in 1999. The difference between years and design for rust was probably because of the later stage of rust development in 1999 and the delaying effect of mixtures on this development. In 1998, there were significant negative correlations between the extent of rust and beetle damage on individual trees. However, only 20% of plots showed a significant spatial dissociation between these two types of damage. There were fewer discernible interactions in 1999. Plantation design provides the basis for integrated control of rust and beetle damage within willow cropping systems by delaying the spread and development of both organisms. Both pest and disease can be assessed successfully simultaneously under field conditions, a major saving in human resources. Initial selection of willow mixture configuration should primarily take into account the effects of spatial design on rust development.

Factors influencing the aggregative response of the blue willow beetle, Phratora vulgatissima

AbstractFactors influencing the aggregative response of the blue willow beetle, Phratora vulgatissima (L.) (Coleoptera: Chrysomelidae), on potted plants of Salix dasyclados (Wimm) were investigated in the field. A significantly higher female beetle density was recorded on plants that had a combination of beetle‐feeding damage and conspecific beetles present as compared with control plants and plants having only damage or beetles. Volatile chemicals emitted from undamaged S. dasyclados (Wimm) leaves were found to be benzaldehyde and the green leaf volatiles (GLVs) cis‐3‐hexenyl acetate and cis‐3‐hexenol. Upon beetle‐feeding damage, there was a higher concentration of these compounds and an increase in the number of different volatile chemicals emitted. These results are discussed in relation to the behavioural ecology of the willow beetle.

Volatile compounds from Salix spp. varieties differing in susceptibility to three willow beetle species.

The volatile compounds emitted by leaves of 10 willow varieties that differ in their susceptibility to damage by blue (Phratora vulgatissima), brassy (P. vitellinae), and brown (Galerucella lineola) willow beetles were examined both before and after mechanical damage and correlated with feeding preferences of these beetles determined under laboratory conditions. Three compounds were identified from intact undamaged leaves of six willow varieties, namely cis-3-hexenyl acetate, cis-3-hexenol, and benzaldehyde. After mechanical damage, the yield and number of volatile compounds increased for all varieties. There were significant differences among willow varieties for both the concentration of cis-3-hexenyl acetate and the relative proportion of this compound to cis-3-hexenol (green leaf volatile ratio). The 10 varieties collectively showed a significant negative correlation between the relative resistance of each variety to blue and brown willow beetles and the yield of cis-3-hexenyl-acetate from damaged plants. The green leaf volatile ratio of damaged plants was also negatively correlated with the relative resistance of willow variety to these two beetle species.

Responses of the willow beetle Phratora vulgatissima to genetically and spatially diverse Salix spp. plantations

1. Phratora vulgatissima is the most serious pest of willow grown as short‐rotation coppice in Britain. The effects of genetically diverse plantations of willow on beetle density, damage and oviposition were studied in a field trial containing monocultures of willow varieties with different willow beetle susceptibility, and mixtures which differed in number and spatial configuration of varieties. In addition, P. vulgatissima adults were introduced to potted willows in cages in a glasshouse as either a monoculture or a mixture of three varieties, and damage and oviposition were recorded. 2. Beetle density, damage and oviposition in the field were generally lower in mixtures than in monocultures, especially with five varieties rather than three and random structural composition rather than regular. In the caged experiment, where beetles could not migrate, there were no significant differences between the monoculture and the mixture for mean damage or oviposition on the two susceptible varieties. 3. Over time, the average beetle density per tree in the field increased in the monocultures of susceptible varieties, yet decreased in the mixtures. The behavioural response of P. vulgatissima to vegetational diversity was consistent with the resource concentration hypothesis, with lower colonization in, and increased emigration from, mixtures compared with monocultures. 4. Genetically and spatially diverse willow mixtures provide a sound basis for pest management due to the propensity for movement by the beetles. As each movement necessitates the location of a new host plant, it is more difficult for beetles to find favourable varieties in a genetically diverse mixture than in a monoculture. 5. Adult P. vulgatissima occur in mobile aggregations, so pest and damage surveys must be intensive and cover a wide time interval. An option for pest management is a mixture of five willow varieties, at least one of which has low susceptibility to the willow beetle, grown in a random planting of varieties. The choice of variety is important, especially the susceptibility to the rust disease, as are physiological interactions between varieties that might affect beetle ecology.

Effects of leaf beetle damage on stem wood production in coppicing willow

Abstract1 The effect of defoliation by larvae of the leaf beetle Phratora vulgatissima on current‐year stem wood production of resprouting Salix viminalis was investigated for two years. Adjacent subplots with varying levels of defoliation within one large willow plantation in south Sweden were studied in the two years.2 High defoliation levels reduced stem wood production by an average of 32 and 39% in the two years, respectively.3 Medium defoliation levels reduced stem wood production by 16% in one year. In the other year, the stem wood production of medium‐defoliated stools did not differ significantly from stools exposed to low defoliation, i.e. there was full compensatory growth.4 The main difference between the year with compensatory growth and the one without was that overall productivity was higher in the year with compensation. This finding forms the basis for a mechanistic model by which compensation could be accomplished. We propose that the major contribution to full compensation comes from an increased growth among intermediate‐sized shoots of medium‐defoliated stools relative to the corresponding shoots in stools exposed to low defoliation.

Spatio‐temporal dynamics of willow beetle (Phratora vulgatissima) in short‐rotation coppice willows grown as monocultures or a genetically diverse mixture

Summary1 Phratora vulgatissima (Chrysomelidae) is the major pest of short‐rotation coppice willows in the U.K., capable of causing severe defoliation in monoculture plantations. As this beetle shows feeding preferences between willow clones, knowledge of the spatio‐temporal dynamics of P. vulgatissima is needed in order to assess the effects of mixed clonal plantings on the management of this pest.2 Distribution patterns of adult P. vulgatissima were monitored over a season at a spatial scale of every tree or every other tree in single clone plantings (monocultures) of three willow clones and in a regular row mixture of these clones.3 Distribution indices (deviation from Complete Spatial Randomness) demonstrated that P. vulgatissima adults were spatially aggregated on favourable clones in the monocultures and the mixture. The degree of aggregation (measured by the k‐parameter of the negative binomial) differed between willow clones. Beetles were highly aggregated at the start of the season, but less so later.4 Dispersal studies of P. vulgatissima adults over time showed a pattern of beetle infestation along rows of the preferred clones in a regularly structured mixture. In the monocultures, movement was less directional.5 Plantation design offers some potential for more effective non‐chemical pest management for P. vulgatissima. Monitoring of the pest must take account of our findings that adults occur in mobile aggregations.

Post hibernation dispersal of three leaf‐eating beetles (Coleoptera: Chrysomelidae) colonising cultivated willows and poplars

Summary1 We studied the spring dispersal of three common chrysomelids, from overwintering habitats into cultivated willow and poplar coppices at four sites in southern England over 2 years.2 Adult Galerucella lineola, Phratora vulgatissima and P. vitellinae overwintered under the bark of mature trees or in other niches that simulated this habitat, within a few hundred metres of the coppice plantation. Relatively few beetles remained in the coppice fields during the winter.3 Phratora vitellinae at the poplar sites emerged several weeks later than G. lineola and P. vulgatissima at the willow sites, reflecting the later leafing of poplar compared to willow. For all species, dispersal was by flight, with most activity during warm periods. Dispersal continued for several weeks for the willow‐ feeding species but was shorter for P. vitellinae. 4 All three species initially colonized the edge of the coppice field. Typically, 80% or more of the beetles colonising a plantation were within 8 m of the edge. Both Phratora spp. accumulated in the plantation edge zone for several weeks before leaving this area and colonising the crop interior.5 The patterns of dispersal and colonization identified by this study may facilitate chrysomelid management practices in infested short rotation coppice that avoid the need for insecticide applications over the entire plantation. Keywords Chrysomelidae, Galerucella lineola, Phratora vitellinae, Phratora vulgatissima, poplar, short rotation coppice, willow, winter dispersal.

The distribution of Phratora vulgatissima (Coleoptera: Chrysomelidae) on cultivated willows in Britain and Ireland

SummaryInsect samples were collected from the canopy of 24 willow short rotation coppice (SRC) sites on farmland in Britain and Ireland in 1995. The blue willow beetle Phratora (= Phyllodecta) vulgatissima (L.) (Coleoptera: Chrysomelidae), previously identified as the main defoliating pest of this crop, was recorded from 13 of these at varying levels of abundance. Data describing aspects of the environment at each site were also collected. These data were used to create potential explanatory variables for a regression analysis of beetle abundance. This analysis indicated that P. vulgatissima were most likely to occur and were more abundant at older willow sites on clay soils and at sites that bad certain free‐living willow species growing nearby. Within sites, most willow clones sampled contained P. vulgatissima, although two, Salix burjatica‘Germany’ (‘Aquatica Gigantea’) and Salix mollissima‘Q83’ (Salix triandra × Salix viminalis), were avoided. Chrysomelid pest avoidance and clonal resistance could form part of an integrated pest management strategy for SRC crops.

Life‐cycles and ecology of willow beetles on Salix viminalis in England

SummaryThe life‐cycles of three willow beetle pests, Phratora (= Phyllodecta) vulgatissima, Phratora (=Phyllodeeta) vitellinae and Galerucella lineola (Coleoptera, Chrysomelidae), were investigated during 1994–95 in a plantation of short‐rotation coppiced willows (Salix viminalis cv. Bowles Hybrid) at Long Ashton, Bristol, UK. The P. vulgatissima had one generation during the year. Overwintered adults emerged from hibernation in April and after a short feeding period, copulation and egg‐laying occurred. Larval stages were found from May–July. The new generation of adult beetles appeared in July–August and fed for a while before hibernating. Hibernating adults were found in hedgerows around the site and in the plantation on willow stools and ground vegetation. Dispersal of adult beetles between feeding and overwintering sites appeared to be fairly localized. Hence, crop management strategies that reduce the potential for overwintering in and around plantations may help to minimize spring re‐invasion and damage. Although based on limited observations, the biology of P. vitellinae and G. lineola appeared similar to that of P. vulgatissima. However, there is evidence in the literature that both these species, unlike the latter, can have a partial second generation in some years. The potential effect of insect herbivory on the growth and biomass yield of S. viminalis cv. Bowles Hybrid was investigated experimentally by artificial hand‐defoliation of pot‐grown plants. Yield losses were strongly correlated with the amount and time of defoliation. Results indicated that even slight or moderate damage by insect herbivores could have a significant impact on the biomass productivity of coppiced willows.

Susceptibility of willow clones (Salix spp.) to herbivory by Phyllodecta vulgatissima (L.) and Galerucella lineola (Fab.) (Coleoptera, Chrysomelidae)

Summary.Levels of damage by mixed natural infestations of the leaf‐feeding chrysomelid beetles, Phyllodecta vulgatissima (L.) (the blue willow beetle) and Galerucella lineola (Fab.) (the brown willow beetle), were determined in replicated field plots of 24 Salix clones at Long Ashton (Bristol, UK) during 1993–94.Over the same period, the host plant preferences of both chrysomelids were investigated in a standard multiple‐choice laboratory procedure, where beetles were enclosed in Petri dishes with leaf discs cut from young pot‐grown trees propagated from shoot cuttings taken from 20 of the 24 willow clones represented in the field study. The laboratory experiments indicated that P. vulgatissima and G. lineola had similar host plant preferences in the range of willows examined (r >0.85). In both field and laboratory, the least preferred Salix clones and hybrids were those of 5. eriocephala, followed by S. purpurea, S. burjatica, S. dasyclados and S. triandra. Clones of S. eriocephala and S. purpurea were frequently rejected altogether in laboratory tests. Most preferred were clones of S. viminalis and several hybrids of S. viminalis, S. aurita, S. caprea and S. cinerea. These results substantiate the reports that P. vulgatissima and G. lineola are deterred from feeding on willows which have relatively high concentrations of phenolic (salicylate) glucosides in the leaves. The least preferred willows, particularly S. eriocephala, S. purpurea and S. burjatica, could be of great potential value in plant breeding for resistance to these willow beetle pests.

The influence of phenolic compounds on the suitability of three Salix species as hosts for the willow beetle Phratora vulgatissima

AbstractThe phenolic glycosides salicin and salicortin were found to influence larval growth and development rates and adult feeding preference of Phratora vulgatissima in laboratory feeding studies. Salicortin was more toxic to larvae than salicin, and none of the third instar larvae fed on Salix viminalis leaves amended with 1.52% (fresh mass) salicortin pupated. Condensed tannins (proanthocyanadins) did not affect larval performance. It was concluded that Salix burjatica resistance to willow beetle is due to the high levels of salicortin which occur in leaves of this species.

The biology and population density of the willow beetle (Phratora vulgatissima [L.]) on Salix viminalis in reclaimed cutaway peat

AbstractThe life cycle and population ecology of Phratora vulgatissima (L.) were studied in Salix viminalis plots on cutaway peat at Clonsast, Co. Offaly during 1982 and 1983. Development time from the first appearance of larval instar I to ecloded adult emergence was ca 6 weeks; the duration of the pupal stage was about 2 weeks. Adults overwintered in crevices and under bark of Salix caprea in an adjacent hedgerow.Larvae were significantly more abundant on internal than on distal branches, on widely spaced than on narrowly spaced trees, and on coppiced than on uncoppiced trees. Maximal mean densities in 1982 when the trees experienced significant moisture stress were 607 larvae and 308 adults per tree. Population densities in 1983 were considerably lower (max. mean densities 154 larvae and 72 adults per tree).ZusammenfassungZur Biologie und Populationsdynamik des Weidenblattkäfers Phratora vulgatissima (L.) auf Salix viminalis in kultivierten Torfstichen in IrlandDie Untersuchungen wurden 1982 und 1983 in den Torfstichen von Klonsast, Co. Offaly, Irland durchgeführt. Die Entwicklungszeit von Phratora vulgatissima vom Larven‐ bis zum Adultenschlüpfen betrug ca. 6 Wochen, wobei auf das Puppenstadium 2 Wochen entfielen. Die Käfer überwinterten in Rindenritzen oder unter der Rinde von Salix caprea in einer angrenzenden Hecke. Die Larven waren signifikant zahlreicher auf den inneren als auf den äußeren Zweigen, auf weiter auseinander als auf dicht stehenden Bäumen und an Bäumen mit Untergebüsch als an freistehenden. Die maximale mittlere Dichte betrug 1982, als die Bäume unter stärkerem Wassermangel litten, 607 Larven und 308 Käfer pro Baum, während sie 1983 nur 154 und 72 betrug.

The invertebrate fauna of reclaimed cutaway peat in central ireland and its influence on soil fertility and plant growth

Invertebrate colonization and establishment in grassland and Salix on reclaimed cutaway peat, and the influence of invertebrates on soil fertility and plant growth, were studied. After 2 years, population densities of 74 000 Collembola, 66 000 Acari, 1400 Coleoptera and 6000 Diptera m −2 were recorded in grassland. Earthworms were scarce in recently reclaimed sites, but population densities exceeding 200 m −2 were present in older leys. Laboratory, glasshouse and field experiments demonstrated marked effects of earthworms on soil structure and grass growth. Mass loss from Salix litter was retarded by about 20% over a 6-month period when invertebrates were partially excluded. Salix burjatica was sporadically attacked by caterpillars of winter moth ( Operophtera brumata (L.)) resulting in severe defoliation and growth check in some years. Salix viminalis was severely damaged by Phratora vulgatissima (L.) (common willow beetle); Salix burjatica was unaffected by willow beetle, which was unable to complete its life cycle on this host.