Phylogeny and taxonomy of powdery mildew on Viburnum species.

The phylogeny and taxonomy of powdery mildew on Viburnum species is evaluated and discussed. Morphological and phylogenetic analyses revealed two new species and demonstrated that Erysiphe hedwigii and E. viburni should be reduced to synonymy and are referred to herein as E. viburni. The two new species, E. viburniphila and E. pseudoviburni, previously hidden under E. viburni (including E. hedwigii), is described on the basis of European, North American, and East Asian powdery mildew collections on Viburnum edule, V. tinus, V. odoratissimum var. awabuki, and V. sieboldii. The sexual morph of E. viburniphila is similar to that of E. viburni; however, morphological differences exist in their asexual morphs. Analyses of sequences from the internal transcribed spacer (ITS) and 28S genomic regions of Erysiphe species obtained on Viburnum species (and other closely allied Eryisphe species) throughout the world reveled that E. viburniphila and E. pseudoviburni are in two different monophyletic groups that are separate from all other Erysiphe species. Erysiphe hedwigii and E. viburni on Viburnum species have often been recognized as separate species based on morphological differences in the size of their chasmothecia and the number of chasmothecial appendages. Taxonomic conclusions based on these morphological distinctions within these species are unreliable (these characters are rather variable and often have overlapping ranges). The present phylogenetic analyses suggest that E. hedwigii has to be reduced to synonymy with E. viburni. To fix the application of the species names E. hedwigii and E. viburni, epitypes have been designated for these taxa with ex-epitype sequences. Additionally, the Asian species E. miranda is phylogenetically confirmed as a species of its own, described in detail and discussed.

The Effect of Leaf Wetness on Phytophthora ramorum Zoospore Infection of Rhododendron 'Cunningham's White' and Viburnum tinus.

We performed studies using zoospore inoculum combined from nine isolates of Phytophthora ramorum and determined the effect of leaf wetness on infection of whole plants of Rhododendron 'Cunningham's White' and Viburnum tinus. The mean percentage of infected leaves for both host species increased gradually across a dew chamber moisture period of 1 to 6 h, reaching approximately 80% infection by 6 h. We also evaluated the effect of a postinoculation drying period on infectivity of the two host species with zoospore inoculum. With a 30-min postinoculation drying period, Rhododendron 'Cunningham's White' sustained less than 40% infected leaves, whereas V. tinus had an infection rate of almost 75% infected leaves. Disease percentages for both host species declined sharply with drying periods longer than 30 min. Knowledge of infectivity parameters for P. ramorum will provide a better understanding of epidemic development and lead to improved recommendations for control.

[Diurnal rhythm of Viburnum awabuki and Betula luminifera volatiles and electroantennogram response of Batocera horsfieldi].

By the method of Tenax-TA absorbent adsorption combined with GC-MS, this paper analyzed the changes of the diurnal rhythm of the volatiles in the healthy branches and Batocera horsfieldi-damaged branches of Viburnum awabuki and Betula luminifera, and electroantennogram technique was used to perform a comparative analysis on the electroantennogram (EAG) responses of unmated male and female B. horsfieldi to the volatiles. After the feeding by B. horsfieldi, there was a decrease in the contents of limonene, nonanal, hexadecane, butyl acrylate, and 3-methyl-butanoic acid in damaged branches of V. awabuki and in the neohexane and hexadecane contents in damaged branches of B. luminifera. Simultaneously, new materials such as permethyl 99A, octyl alcohol, iodo, decanal, hexanal, and bioallethrin etc. were newly synthesized in the damaged branches. The EAG response values of unmated male and female B. horsfieldi adults to the volatiles in the damaged branches of B. luminifera were the highest, being 1.23 mV and 1.38 mV, while to the healthy branches of V. awabuki were the lowest, being 0.95 mV and 1.01 mV, respectively. As for the time period, the EAG response values of the adults to the volatiles were the lowest from 12:00 to 14:00, which accorded with the feeding behaviors of the adults, i. e., taking food in the field in early morning or at dusk.

Do plant mites commonly prefer the underside of leaves?

The adaxial (upper) and abaxial (lower) surfaces of a plant leaf provide heterogeneous habitats for small arthropods with different environmental conditions, such as light, humidity, and surface morphology. As for plant mites, some agricultural pest species and their natural enemies have been observed to favor the abaxial leaf surface, which is considered an adaptation to avoid rain or solar ultraviolet radiation. However, whether such a preference for the leaf underside is a common behavioral trait in mites on wild vegetation remains unknown. The authors conducted a 2-year survey on the foliar mite assemblage found on Viburnum erosum var. punctatum, a deciduous shrub on which several mite taxa occur throughout the seasons, and 14 sympatric tree or shrub species in secondary broadleaf-forest sites in Kyoto, west-central Japan. We compared adaxial-abaxial surface distributions of mites among mite taxa, seasons, and morphology of host leaves (presence/absence of hairs and domatia). On V. erosum var. punctatum, seven of 11 distinguished mite taxa were significantly distributed in favor of abaxial leaf surfaces and the trend was seasonally stable, except for Eriophyoidea. Mite assemblages on 15 plant species were significantly biased towards the abaxial leaf surfaces, regardless of surface morphology. Our data suggest that many mite taxa commonly prefer to stay on abaxial leaf surfaces in wild vegetation. Oribatida displayed a relatively neutral distribution, and in Tenuipalpidae, the ratio of eggs collected from the adaxial versus the abaxial side was significantly higher than the ratio of the motile individuals, implying that some mite taxa exploit adaxial leaf surfaces as habitat.

Predation by Podisus maculiventris (Say) (Hemiptera: Pentatomidae) on viburnum leaf beetle, Pyrrhalta viburni (Paykull) (Coleoptera: Chrysomelidae), under laboratory and field conditions.

To evaluate the potential of Podisus maculiventris (Say) (Heteroptera: Pentatomidae) as a biological control agent against viburnum leaf beetle, Pyrrhalta viburni (Paykull) (Coleoptera: Chrysomelidae), laboratory trials were conducted to measure prey consumption of P. maculiventris over nymphal development. Field trials tested the impact of augmentative releases of P. maculiventris nymphs on populations of P. viburni, using both open shrubs and caged branches of Viburnum trilobum. In the laboratory, P. maculiventris nymphs successfully developed while preying on P. viburni larvae and adults. Each nymph consumed an average of 100.6 larvae or 16.9 adults. Immature development duration was comparable between nymphs feeding on P. viburni adults and those given Galleria mellonella (L.) (Lepidoptera: Pyralidae) larvae as prey. In field trials, inundative releases of 30 P. maculiventris nymphs on naturally infested V. trilobum shrubs significantly reduced pest defoliation on shrubs infested with < 3,000 larvae but had no effect on shrubs with heavier infestations. On caged branches, individual nymphs successfully developed when feeding only on P. viburni larvae. These results show that P. viburni larvae and adults are suitable prey for P. maculiventris and this predator could potentially be developed as a biological control agent against P. viburni.

Plant defense elicitors fail to protect Viburnum dentatum from herbivory by viburnum leaf beetle (Coleoptera: Chrysomelidae).

Pyrrhalta viburni (Paykull) (Coleoptera: Chrysomelidae), a new landscape pest in the United States, feeds in both the larval and adult stages on foliage of plants in the genus Viburnum. A field trial was conducted from 2004 to 2006 to examine the impact of several elicitors of plant defense on ability of arrowwood viburnum (Viburnum dentatum L.) to resist attack by P. viburni in both larval and adult stages. The treatments included jasmonic acid (JA), harpin, and paclobutrazol. For comparison, imidacloprid and untreated controls were included in the trial. The soil-applied treatments (paclobutrazol and imidacloprid) were applied once during the trial (spring 2004), and the foliarly applied treatments (JA and harpin) were applied each spring. Herbivory by viburnum leaf beetle larvae and adults was measured yearly in spring and summer, respectively, and plant height was recorded at the end of each growing season. The only treatment that decreased feeding by viburnum leaf beetle was imidacloprid; these plants were virtually untouched throughout the duration of the trial. Plants treated with JA and harpin actually suffered greater feeding damage at the end of the second growing season; other than this observation, the elicitors had no impact on viburnum leaf beetle. As expected, plant height was decreased for the shrubs treated with paclobutrazol, a plant growth regulator, and unaffected by JA and harpin. Plant height was increased for the shrubs treated with imidacloprid. These shrubs also seemed to be protected from viburnum leaf beetle after residues dropped below lethal levels.

Ovipositional biology of Viburnum leaf beetle, Pyrrhalta viburni (Coleoptera: Chrysomelidae).

Pyrrhalta viburni Paykull, a new landscape pest in the United States, feeds in both the larval and adult stages on foliage of plants in the genus Viburnum. We measured lifetime oviposition capacity of mated and unmated females reared in the laboratory versus field-collected females, as well as ovipositional response to physical characteristics of the host plant. Both mated and unmated females produced eggs, but at different rates. Field-collected females and mated females reared in the laboratory laid similar numbers of egg masses containing similar numbers of eggs, but unmated females laid approximately one half as many eggs, the result primarily of smaller clutch size. Mated females reared in the laboratory had a preovipositional period of 11.4 +/- 1.7 versus 29 + 11.7 d for unmated females, and unmated females lived significantly longer than mated females. The angle and diameter of stems of V. trilobum, a very susceptible host, both greatly influenced oviposition; females laid most eggs on vertically oriented stems, and those of smallest diameter; when these factors were combined, stem diameter predominated. Females also had a very strong geotactic response, preferring to lay eggs on portions of stems toward gravity, even when stems were at fairly shallow angles.