Willow Beetle Research Articles

Pests of energy willow and practices to control their number

Purpose. To determine the pest species composition in bioenergy willow plantations and develop practices to control their number.Methods. Field, accounting, statistical and analytical.Results. The main pests species composition of bioenergy willow plantation in different zones have been determined, namely in the zone of sufficient moisture at the Uladivka-Liulyntsi Research Breeding Station (ULRBS), in the zone of insufficient moisture at Veselyi Podil Research Breeding Station (VPRBS) and in the zone of unstable moisture at the Bila Tserkva Research Breeding Station (BTsRBS). Of the soil pests, the most harmful for sugar beet species were found May bug, June bug and marble bug, the number of which in different areas ranged from 0.1 to 0.4 (VPRBS) to 2.0 to 4.0 (ULRBS) per 1 m2. In addition to these harmful species, there were larvae of grasshoppers and Tenebrionidae, the number of which was 0.9 to 4.0 per 1 m2, as well as larvae of cereal chafer and caterpillars of winter owl moth. The density of the soil pests population somewhat exceeded the economic thresholds of harmfulness, which should be taken into account when establishing willow plantations and during the growing season. With regard to terrestrial species, the most dangerous for willow is brown willow beetle, willow aphid and apple black miner, the number of which was also not the same everywhere. Thus, the highest population density of the brown willow beetle (beetle/10 plants) was recorded in BTsRBS (3.0 to 36.0), in ULRBS (0.5 to 3.0) and VPRBS (0.2 to 3.6). The willow aphid was found in all zones at the settlement score of 1.0 to 1.5, while apple black miner was recorded only in spring in ULRBS and BTsRBS at the settlement score of 1.0. The control of the number of phytophages in willow plantation was carried out with the aid of insecticides through pre-planting soaking cuttings and spraying planted cuttings. Soaking of cuttings in solutions of systemic action insecticides contributes to a 12.9 ̶ 22.9% increase in the plant survival compared to soaking them in water. The use of insecticides for spraying cuttings during vegetation season provides a high efficiency (76.7–100.0%) of pest control.Conclusions. Energy willow is damaged by a number of soil and terrestrial pests, namely larvae of May bug, grasshopper, Tenebrionidas, cereal chafer, Carabidae (soil pests), and brown willow beetle, willow aphid and apple bark miner (terrestrial pests). The control of the number of these phytophages is carried out mainly with the aid of insecticides through pre-planting soaking cuttings or spraying planted cuttings.

Predator hunting mode and host plant quality shape attack‐abatement patterns of predation risk in an insect herbivore

AbstractGroup formation reduces individual predation risk when the proportion of prey taken per predator encounter declines faster than the increase in group encounter rate (attack‐abatement). Despite attack‐abatement being an important component of group formation ecology, several key aspects have not been empirically studied, that is, interactions with the hunting mode of the predator and how these relationships are modified by local habitat quality. In 79 cage trials, we examined individual egg predation risk in different‐sized egg clutches from the blue willow beetle Phratora vulgatissima for two predators with different hunting modes (consumption of full group [Orthotylus marginalis] vs. part group [Anthocoris nemorum]). Because these predators also take nutrients from plant sap, we could examine how the quality of alternative food sources (high‐ vs. low‐quality host plant sap) influenced attack‐abatement patterns in the presence of different hunting strategies. For the O. marginalis predator, individual egg predation risk was largely independent of group size. For A. nemorum, egg predation risk clearly declined with increasing group size. However, approximately one‐third of the grouping benefit was lost to an increase in group detectability. There were clear differences in attack‐abatement patterns between plants with high‐ vs. low‐quality sap. When O. marginalis was the predator, there was no clear change in attack‐abatement in relation to host plant quality. However, for A. nemorum there was a clear reduction in overall predation risk and a stronger attack‐abatement pattern with increasing group size when plant sap quality increased. This implies that the relative benefits of prey grouping behavior for any species might show diurnal or seasonal changes as other aspects of resource/habitat quality change for the focal predator. Modulation of attack‐abatement by bottom‐up effects such as plant‐based food resources is yet to be incorporated into general theory, despite the ubiquity of omnivorous predators and with omnivory being important for shaping food webs, ecosystem functions, and in biological control. Thus, ongoing refinement of attack‐abatement theory by focusing on bottom‐up vs. top‐down processes could have significant impacts on many important contemporary fields of study.

Weeds within willow short-rotation coppices alter the arthropod community and improve biological control of the blue willow beetle

Outbreaks of the blue willow beetle Phratora vulgatissima (L.) (Coleoptera: Chrysomelidae) threaten the yield of willow plantations that rely on biological control by natural enemies. Here we show that weed presence increases herbivore and predator/parasitoid diversity on willow shoots and causes increased predation on P. vulgatissima eggs compared to shoots within plots without weeds. We argue that, in addition to higher abundance, the community shift in favour of egg consumers and additive predator effects causes the higher predation pressure. This increase (~35 %) was apparent despite more alternative prey. Neither the willow genotype on which the predator–prey interaction occurred nor the clutch size affected egg predation levels. Our results support root’s enemy hypothesis and suggest that intensive weed control might counteract biological control in willow plantations. However, at least during the establishing phase of the plantation, increased biocontrol probably does not compensate for yield losses caused by competing weeds.

Outbreaking herbivore escapes parasitoid by attaining only a small body size

The reason why parasitoids are often unable to control insect herbivores during outbreak years has remained unclear to modern ecologists. Here I show that the blue willow beetle (Phratora vulgatissima) can escape parasitoids (Perilitus brevicollis) by reaching only a small body size during the increased competition which coincides with outbreaks. Different phases of outbreaks were simulated by allowing leaf‐beetle larvae to develop at different densities on willow. The denser the herbivore populations, the smaller body sizes they attained. In the field too, herbivore body size decreased when the level of defoliation increased. The parasitoids were clearly limited by herbivore body size, exhibiting reduced survival in parallel with decreasing herbivore size, with none of them surviving in beetles from larvae reared at the highest density. The results demonstrate how bottom‐up control of the herbivore becomes more important as outbreaks intensify, while top‐down control gradually becomes less important and collapses during the outbreak peak. Because the mechanism limiting P. brevicollis parasitoids involves herbivore body size, which is reduced at high densities, I anticipate that these parasitoids are unable to terminate herbivore outbreaks.

Plant‐sex‐biased tritrophic interactions on dioecious willow

Plant sex effects on herbivores are well studied, but little is known about these effects on predators and predator–herbivore dynamics. Here we take a holistic approach to study, simultaneously, plant sex effects on herbivore and predator preference and performance, as well as population densities and predation pressure in the field. For dioecious Salix cinerea (grey willow) we found that male plants represented higher host plant quality than females for an omnivorous predator (Anthocoris nemorum, common flower bug), while host plant quality for its herbivorous prey (Phratora vulgatissima, blue willow beetle) was not sex‐biased. The herbivore strongly preferred the host plant sex (female) that was suboptimal for the predator, which in turn followed its prey to female plants, leading to plant‐sex‐biased predation. These results provide new insight into the far‐reaching effects of plant sex on insect communities, and open up novel opportunities for improving biocontrol of the herbivore in Salix short rotation coppice.

Effects of Temperature Variation on Male Behavior and Mating Success in a Montane Beetle

Locomotion and mating ability are crucial for male reproductive success yet are energetically costly and susceptible to physiological stress. In the Sierra willow beetle Chrysomela aeneicollis, male mating success depends on locating and mating with as many females as possible. Variation at the glycolytic enzyme locus phosphoglucose isomerase (Pgi) is concordant with a latitudinal temperature gradient in these populations, with Pgi-1 frequent in the cooler north, Pgi-4 in the warmer south, and alleles 1 and 4 in relatively equal frequency in areas intermediate in geography and climate. Beetles experience elevated air temperatures during a mating season that causes differential physiological stress among Pgi genotypes, and running speeds of individuals homozygous for Pgi-4 are more tolerant of repeated thermal stress than individuals possessing Pgi-1. Here the importance of running behavior for male mating activity was examined, and differential effects of thermal stress among Pgi genotypes on male mating activity were measured. In nature, males run more than females, and nearly half of males mate or fight for a mate after running. In the laboratory, mating activity was positively correlated with running speed, and repeated mating did not reduce running speed or subsequent mating activity. Males homozygous for Pgi-4 mated longer and more frequently after heat treatment than 1-1 and 1-4 males. All heat-treated males had lower mating frequencies and higher heat shock protein expression than control males; however, mating frequency of recovering 4-4 males increased throughout mating trials, while treated 1-1 and 1-4 males remained low. These results suggest that effects of stress on mating activity differ between Pgi genotypes, implying a critical role for energy metabolism in organisms' response to stressful temperatures.

Importance of temperature for the performance and biocontrol efficiency of the parasitoid Perilitus brevicollis (Hymenoptera: Braconidae) on Salix

With the prospect of warmer temperatures as a consequence of ongoing climate change, it is important to investigate how such increases will affect parasitoids and their top-down suppression of herbivory in agroecosystems. Here we studied how the performance and biocontrol efficiency of the willow “bodyguard” Perilitus brevicollis Haliday (Hymenoptera: Braconidae) were affected at different constant temperatures (10, 15, 20, 25°C) when parasitizing a pest insect, the blue willow beetle (Phratora vulgatissima L., Coleoptera: Chrysomelidae). Parasitism did not reduce herbivory at all at 10°C, indicating poor biocontrol efficiency at low temperatures. At higher temperatures, however, parasitism reduced herbivory substantially, implying that biocontrol may be promoted by a warmer climate. Parasitoid performance (survival and development rate) generally increased with increasing temperature up to 20°C. The only exception was body size, which followed the temperature–size rule and decreased with increasing temperature. Our results indicate that a warmer climate may enhance the biocontrol of the blue willow beetle in environments that currently are cooler than the parasitoid’s optimal temperature for development.

Infection dynamic of some cultivars of shrubby willow (Salix spp.) by rust (Melampsora spp.) and willow beetle (Phratora vulgatissima L.).

Summary The aim of the study was to asses of population dynamic of Melampsora spp. and Phratora vulgatissima, the most dangerous bioenergy willows agrophags. Investigation was conducted in Research Centre for Cultivar Testing collection in years 2010–2011. First symptoms of rust infection were observed on leaves cultivars Dobkowska, Marie and Christina in first decade of July. On leaves cultivars Marcel, Marie and Christina the increase of infection at following observations was observed. On Dobkowska and Wodtur uredinia were observed in July and August. The further development of the disease and formation of new uredinia was not recognized. Depending of the willow cultivar the greatest damages caused by P. vulgatissima foraging were observed in August and September. The biggest leaf area loss was noted on Wodtur.

Plant-mediated effects of different Salix species on the performance of the braconid parasitoid Perilitus brevicollis

The blue willow beetle, Phratora vulgatissima, is considered to be the most damaging herbivorous pest in Salix short-rotation coppices throughout Europe. The braconid parasitoid Perilitus brevicollis is an important natural enemy of Phratora. As several different Salix species are used in coppices, I investigated the bottom–up (tritrophic) effects of Salix on the parasitoid. Three host plants were studied: the introduced fast-growing S. viminalis, which is highly susceptible to the beetle; S. dasyclados, which is introduced and moderately-resistant to the beetle; and the native slow-growing Salix cinerea, which is not currently used in coppices. The identity of the host-plant species had significant effects on parasitoid larval development time; parasitoids developed rapidly on the susceptible S. viminalis and slowly on the moderately resistant S. dasyclados. Increased development time resulted in reduced adult longevity. Host-plant species identity also affected larval survival; 57%, 64%, and 49% of the parasitoids successfully completed larval development in beetles fed S. viminalis, S. cinerea, and S. dasyclados, respectively. Parasitoid development was also correlated with the body size of their beetle host, but this effect was independent of the identity of the host-plant species. The results of this study suggest that the parasitoid has higher survival and growth rates when it parasitizes beetles feeding on the common coppice species S. viminalis, but the performance of the parasite is reduced when the beetle feeds on the moderately-resistant S. dasyclados. Conversely, the omnivorous biocontrol agents sometimes used in these systems appear to perform better on S. dasyclados compared to S. viminalis. The results of this study suggest that Perilitus parasitoids and omnivorous beetle predators may provide complementary protection to Salix and therefore be useful in coppice management.

Do exotic generalist predators alter host plant preference of a native willow beetle?

Abstract1 Selection can favour herbivores that choose host plants benefitting their offspring either by enhancing growth rates or by increasing larval defences against native predators. For exotic predator species that feed on herbivores, their success with invading new habitats may depend upon overcoming defences used by native prey. Whether exotic predators can alter herbivore host choice has remained unexamined. Therefore, we compared the efficacy of larval defence by Chrysomela knabi (a native beetle species) that had fed on two native willow hosts: Salix sericea (a phenolic glycoside (PG)‐rich species) and Salix eriocephala (a PG‐poor species), when attacked by exotic generalist predators. In addition, the preference and performance of C. knabi on S. sericea and S. eriocephala was examined.2 Chrysomela knabi preferred and performed better on S. sericea. In a common garden, adult C. knabi were nine‐fold more common and oviposited five‐fold more frequently on S. sericea than on S. eriocephala. In the laboratory, adult feeding preference on leaf discs and survival rates of larvae were both greater on S. sericea, and time to pupation was shorter.3 Chrysomela knabi larvae produced significantly more salicylaldehyde when fed S. sericea leaves than when fed S. eriocephala leaves. Additionally, those larvae with greater salicylaldehyde had reduced predation by two exotic generalist predators, Harmonia axyridis larvae and juvenile Tenodera aridifolia sinensis.4 The results obtained in the present study suggest that selection favoured the preference of C. knabi for PG‐rich willow plants because larvae grew and survived better and that selection by common exotic generalist predators would reinforce this preference.

Effects of Temperature on Physiology and Reproductive Success of a Montane Leaf Beetle: Implications for Persistence of Native Populations Enduring Climate Change

Understanding how climate change impacts natural systems requires investigations of the effects of environmental variation on vulnerable species and documentation of how populations respond to change. The willow beetle Chrysomela aeneicollis is ideal for such studies. It lives in California's Sierra Nevada on the southern edge of its worldwide range. Beetles experience elevated air temperatures during summertime egg laying and larval development. Exposure to these temperatures causes physiological stress, which may reduce reproductive success and endanger populations. The glycolytic enzyme phosphoglucose isomerase (PGI) is a marker of temperature adaptation in C. aeneicollis. PGI allele frequency varies across a latitudinal gradient: allele 1 is common in Rock Creek (RC), which is cooler and to the north, and allele 4 is common in Big Pine Creek (BPC), which is warmer and to the south. In populations that are intermediate in geography and climate (e.g., Bishop Creek [BC]), PGI-4 frequency increases from north to south such that alleles 1 and 4 are in relatively equal frequency in southern BC. Over the past decade, Sierra Nevada beetle populations have colonized high elevations and have become extinct at lower elevations where they were once common. In BC, the magnitude of PGI allele frequency fluctuations among life-history stages is related to maximal air temperature, with the frequency of PGI-4 increasing after the hottest part of summer. To identify mechanisms that may cause shifts in PGI allele frequency, we measured metabolic rate and fecundity for beetles collected at BC. Metabolic rate of males and females was measured at 20 degrees and 36 degrees C using flow-through respirometry. To measure laboratory fecundity, mating pairs were acclimated for 4 h each afternoon at a control temperature (20 degrees C) or at mildly elevated temperatures (26 degrees or 32 degrees C) and number of eggs laid was counted daily for 24 d, after which tissue levels of 70-kD heat shock proteins (Hsp70) were determined. Previous studies had demonstrated differences in Hsp70 expression among PGI genotypes at these temperatures. To measure field fecundity, mating pairs from BC were transplanted to similar elevations in BPC, BC, and RC and were monitored in situ for 24 d. Metabolic rate was higher for PGI 4-4 genotypes than for PGI 1-4 or PGI 1-1 individuals at 36 degrees C but not at 20 degrees C. In contrast, laboratory fecundity was greatest for females possessing PGI-1, independent of acclimation temperature. At the end of the laboratory fecundity experiment, Hsp70 expression was positively related to fecundity, suggesting minimal reproductive cost of upregulation of heat shock proteins in response to mild heat stress. In the field, fecundity was highest for PGI 1-1 and PGI 1-4 individuals in RC and PGI 4-4 individuals in BPC and was similar for all genotypes in BC. Thus, fecundity in nature was greatest for the genotypes that were most common in each area. Taken together, data reported here suggest that hot, dry summers in the Sierra Nevada may result in an increase in frequency of the PGI-4 allele and shifts to higher elevations for C. aeneicollis populations.

A Journey of Twenty-Five Years through the Ecological Biochemistry of Flavonoids

The ecological biochemistry of flavonoids, in which I have been engaged for 25 years, is summarized in this review article. The review covers (1) a survey of rare bio-active flavonoids in higher plants; (2) the fungal metabolism of prenylated flavonoids; (3) flavonoids antidoting against benzimidazole fungicides; (4) dihydroflavonol ampelopsin in Salix sachalinensis as a feeding stimulant towards willow beetles; and (5) flavones as signaling substances in the life-cycle development of the phytopathogenic Peronosporomycete Aphanomyces cochlioides, a cause of spinach root rot and sugar beet damping-off diseases. Finally recent trends in the ecological biochemistry of flavonoids are briefly described.

Phosphoglucose isomerase genotype affects running speed and heat shock protein expression after exposure to extreme temperatures in a montane willow beetle

Eastern Sierra Nevada populations of the willow beetle Chrysomela aeneicollis commonly experience stressfully high and low environmental temperatures that may influence survival and reproduction. Allele frequencies at the enzyme locus phosphoglucose isomerase (PGI) vary across a climatic latitudinal gradient in these populations, with PGI allele 1 being most common in cooler regions and PGI allele 4 in warmer ones. PGI genotypes differ in heat and cold tolerance and in expression of a 70 kDa heat shock protein. Here we examine genetic, behavioral and environmental factors affecting a performance character, running speed, for willow beetles, and assess effects of consecutive cold and heat exposure on running speed and expression of Hsp70 in the laboratory. In nature, running speed depends on air temperature and is higher for males than females. Mating beetles ran faster than single beetles, and differences among PGI genotypes in male running speed depended on the presence of females. In the laboratory, exposure to cold reduced subsequent running speed, but the amount of this reduction depended on PGI genotype and previous thermal history. Effects of exposure to heat also depended on life history stage and PGI genotype. Adults possessing allele 1 ran fastest after a single exposure to stressful temperature, whereas those possessing allele 4 ran faster after repeated exposure. Larvae possessing allele 4 ran fastest after a single stressful exposure, but running speed generally declined after a second exposure to stressful temperature. The ranking of PGI genotypes after the second exposure depended on whether a larva had been exposed to cold or heat. Effects of temperature on Hsp70 expression also varied among PGI genotypes and depended on type of exposure, especially for adults (single heat exposure, two cold exposures: PGI 1-1>1-4>4-4; other multiple extreme exposures: 4-4>1-4>1-1). There was no consistent association between alleles at other polymorphic enzyme loci and running speed or Hsp70 expression. These data suggest that variation at PGI is associated with considerable plasticity in running speed. Differences in Hsp70 expression among PGI genotypes suggest that the heat-shock response may buffer differences in thermal tolerance and performance among genotypes and help maintain the PGI polymorphism in a thermally variable environment.

The long‐term effect of partial defoliation on the yield of short‐rotation coppice willow

AbstractFive varieties of willow were planted in a randomised block design at the Northern Ireland Horticulture and Plant Breeding Station, Loughgall, County Armagh in 1997. Three treatments were applied: control (no treatment), manual defoliation and routine control (spraying) of willow beetles. The defoliation was carried out at 75% for the first 2 years and thereafter 25% up to the first harvest in January 2001. During the second production cycle, no manual defoliation was applied in order to observe the ability of the different varieties to recover from earlier damage. The variety 78112 exhibited the highest yield loss in the first cycle as a result of defoliation (∼70%), while the vigorous variety Tora suffered least yield loss (35–43%). In the recovery phase (second production cycle 2001–2003), all the varieties showed little improvement in yields in plots that had been defoliated previously, indicating a long‐term legacy of yield loss as a result of defoliation. The possible reasons for this inability to recover are discussed.

Foraging behaviour influences the outcome of predator–predator interactions

Abstract. 1. Interactions among predators may influence the total efficiency of a predator complex. The effect of intra‐ and interspecific interactions of the generalist predators Orthotylus marginalis (Heteroptera: Miridae) and Anthocoris nemorum (Heteroptera: Anthocoridae) was investigated in a laboratory experiment. Outcomes of the interactions were determined by comparing predation rates on eggs and larvae of the blue willow beetle Phratora vulgatissima of single individuals with those of two individuals of the same or different species.2. A non‐additive, antagonistic effect on predation rates due to intraspecific interactions was found between individuals of A. nemorum. No such effect was found in O. marginalis. These results are as expected as a consequence of differences in behaviour of the two predator species: A. nemorum is a much more active and mobile predator than O. marginalis.3. Contrary to expectation, interspecific interactions between A. nemorum and O. marginalis did not affect the total predation rate.4. An observation from the field corroborated the results obtained in the laboratory study; there was no negative relationship between the densities of the two predator species, indicating that the two species do not interact negatively in the field at their natural densities.5. It is concluded that the additive effect of multiple predator species is of potential value in biological control.

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.

Secondary metabolites as stimulants and antifeedants of Salix integra for the leaf beetle Plagiodera versicolora.

Plagiodera versicolora, a willow beetle living on S. sachalinensis, is found on S. integra during early June in Hokkaido Island, Japan. This insect selects several species of willows (Salix), including S. integra as host plant in Honshu Island of Japan. To determine the reasons for the limited distribution of this beetle on the willows of Hokkaido, the feeding preference of the insect to leaves of S. integra and its constituents was performed. Feeding-bioassay guided fractionation of an 80% aqueous acetone extract of fresh leaves of Salix integra to Plagiodera versicolora resulted in isolation of feeding stimulant and antifeeding constituents. Chlorogenic acid (1) and 3,5-dicaffeoyl quinic acid (2) were identified as antifeedants and 1,2-di[(9Z,12Z,15Z)-octadeca-9,12,15-trienoyl]-3-beta-D-galactopyranosyl-sn-glycerol (MGDG, 3) as feeding stimulants. The feeding test was performed by an agar disk method. The treated agar disks contained sucrose and test sample in different doses. The antifeeding activities of 1 and 2 and stimulant activity of 3 may be one of the reasons for the limited presence of P. versicolora on S. integra in Hokkaido.

Variation in thermal tolerance is linked to phosphoglucose isomerase genotype in a montane leaf beetle

Summary Sierra Nevada populations of the Willow Beetle Chrysomela aeneicollis (Schaeffer) experience extreme elevated and subzero temperatures in nature. In these populations, frequencies of phosphoglucose isomerase (PGI) alleles vary with latitude and altitude and respond to climate change. PGI genotypes differ in expression of a stress‐inducible heat shock protein (Hsp70). Here, differences in tolerance of elevated and subzero extreme temperatures were compared for field‐acclimatized and laboratory‐acclimated larvae and adults possessing three common PGI genotypes (PGI 1–1, 1–4 and 4–4). Three indices of thermal tolerance were measured – CTmax, LT50 and Hsp70 expression level. Thermal tolerance depended on life stage, prior exposure to sublethal stress and PGI genotype. Larvae were generally less tolerant of thermal extremes than adults. For both adults and larvae, prior exposure to sublethal temperatures increased survival after exposure to subsequent stress. Survival after exposure to thermal extremes was consistently related to PGI genotype (1–1 > 1–4 > 4–4), as were expression levels of Hsp70 (1–1 > 1–4 > 4–4). These results suggest that PGI genotypes differ in tolerance of thermal extremes routinely experienced by beetles in nature. A trade‐off between thermal tolerance and energy allocation may explain the persistence of the PGI polymorphism.

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.

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.