Willow Beetle Research Articles

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.

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.

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.

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.

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.

Role of Enemy‐Free Space and Plant Quality in Host‐Plant Selection by Willow Beetles

Phratora vitellinae and Galerucella lineola are two leaf beetles that feed on willows (Salix) in central Sweden. When disturbed, larvae of P. vitellinae exude droplets of a defensive secretion from dorsal glands. The secretion contains salicyl aldehyde, the precursors for which are plant—derived salicylates like salicin and other chemically similar phenolic glycosides. In contrast, larvae of G. lineola lack dorsal glands, cannot convert salicylates to salicyl aldehyde, and no not produce such a defensive secretion. We evaluate the adult oviposition pattern, larval performances, and suceptibility to predators of these two beetles on three species of willows, two rich in salicylates (Salix fragilis and S. dasyclados) and one poor in salicylates (S. viminalis). Females of G. lineola oviposited preferentially on S. viminalis and S. fragilis where larvae developed rapidly and survival was high, and avoided S. dasyclados where larval performance was poor. Variation in leaf pubescence, toughness, and nitrogen content across willow species not explain observed patterns of larval performance. However, larval performance was inversely related to the concentration of salicylates in the three willows. By contrast, the oviposition preferences of P. vitellinae did not correspond well to patterns of larval performance. Salix fragilis was by far preferred choice of oviposition, and females rarely placed eggs on either S. viminalis or S. dasyclados. The performance of P. vitellinae larvae differed markedly on the two salicylate—rich willows; larvae survived best and developed most rapidly on S. fragilis, but mortality was high and development slow on S. dasyclados. Poor larval performance on S. dasyclados was associated with high concentrations of simple phenolic compounds other than salicylates. Despite differences in performance, larvae fed these two salicylate—rich willows produced a defensive secretion which effectively repelled coccinellid predators. Larvae fed the salicylate—poor S. viminalis survived and developed well in the absence of enemies, but lacked the salicylate—based defensive secretion and were readily eaten by coccinellids. Females of P. vitellinae apparently avoided S. viminalis as an oviposition host, not because larvae performed poorly, but because larvae were defenseless against some predators when raised on this salicylate—poor willow. We argued that herbivores such as P. vitellinae obtain enemy—free space on hosts from which they sequesters plant—derived allelochemicals for defense. The result appears to be dietary specialization on host—plant species that provide these precursors for defense. Other related herbivores like G. lineola that do not employ plant—derived defensive secretions, are not so constrained and feed on a wider range of host willows.

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.

Willow Beetle – Egg to Pupa

Willow Beetle – Egg to Pupa

NOTES

Mr. F.L. Washburn, State Entomologist of Minnesota, reports the occurence at St. Anthony Park of the imported Alder and Willow Beetle, Cryptorhyncus lapathi, Linn., which was introduced in a shipment of Carolina poplars from the State of New York last spring.