Susceptibility of 32 elm species and hybrids (Ulmus spp.) to the elm leaf beetle (Coleoptera: Chrysomelidae) under field conditions in Arizona

We evaluated elm leaf beetle, Pyrhalta luteola (Müller) (Coleoptera: Chrysomelidae), defoliation of 32 elm species or hybrids (taxa) established under field conditions in Holbrook, AZ. Percentage of defoliation, number of eggs, and number of larvae were estimated on randomly selected 15-cm shoot lengths annually in July, from 1996 to 2001. The following nine taxa consistently sustained 15-46% mean overall defoliation: 1) Siberian elm, U. pumila L.; 2) 'Dropmore' elm, U. pumila; 3) 'Camperdownii' elm, U. glabra Huds.; 4) 'Regal' elm, U. glabra x U. carpinifolia Gledisch x U. pumila); 5) 'Sapporo Autumn Gold' elm (U. pumila x U. japonica Sang.); 6) 'New Horizon' elm (U. pumila x U. japonica); 7) 'Charisma' elm [(U. japonica x U. wilsoniana Schneid.) x (U. japonica x U. pumila)]; 8) 'W2115-1' elm (U. parvifolia Jacq. x U. procera Salisb.); and 9) 'Homestead' elm [(U. hollandica Mill. x U. carpinifolia) x (U. pumila-racemosa Dieck x U. carpinifolia)]. Percentage of defoliation was significantly low on four Chinese elm (U. parvifolia) cultivars ('Allee', 'Athena', 'Glory'/lace bark, and 'Kings Choice'). Percentage of defoliation was also low on seven Asian elms (including U. chemnoui Cheng, U. bergmaniana Sneid., U. szechuanica Fang, and species of the U. davidiana Planch. complex [U. davidiana, U. japonica, U. wilsoniana, and U. propinqua Koidz.]) and the American elm (U. americana L.) 'Valley Forge'. Percentage of defoliation and the number of eggs or larvae per plant were highly correlated. The results of this study are generally consistent with results of past laboratory screening trials.     

Resistance of temperate Chinese elms (Ulmus spp.) to feeding by the adult elm leaf beetle (Coleoptera: Chrysomelidae)

Newly acquired Ulmus species from the temperate regions of China growing at The Morton Arboretum, Lisle, IL, were evaluated in laboratory bioassays for feeding preference and suitability for larvae and adults of the elm leaf beetle, Pyrrhalta luteola (Müller). Larval and adult no-choice and adult multiple-choice feeding studies revealed that U changii, U. lanceaefolia, U. prunifolia, U. pseudopropinqua, and U. taihangshanensis were the least suitable for feeding and reproduction by the elm leaf beetle. Ulmus wallichiana and the highly preferred U pumila were more suitable for feeding and reproduction. Suitability had no significant effect on male and female longevity. The least suitable species of U. changii, U. lanceaefolia, U. prunifolia, U. pseudopropinqua, and U. taihangshanensis show promise for future elm breeding programs.     

Anatomical and nutritional factors associated with susceptibility of elms (Ulmus spp.) to the elm leaf beetle (Coleoptera: Chrysomelidae)

A wide range of susceptibility exists across elm (Ulmus) species and hybrids to the elm leaf beetle, Pyrrhalta luteola (Müller) (Coleoptera: Chrysomelidae). We evaluated various elm species, hybrids, or cultivars (taxa) growing in an experimental plantation in the city of Holbrook, AZ, for leaf anatomical (toughness and trichome density) and nutritional (minerals and sugars) traits that may be associated with host resistance. Leaf toughness and percentage of defoliation (susceptibility) were not correlated. However, we found weak negative correlations between percentage of defoliation and density of trichomes on the leaf abaxial surface. Of the 11 leaf nutrients examined, concentrations of iron and phosphorus correlated inversely with percentage of defoliation. The remaining nine traits did not show any correlation with percentage of defoliation. We concluded that individual anatomical and nutritional traits of elm species/hybrids do not seem to create a strong barrier to elm leaf beetle defoliation. However, the results from a stepwise multiple regression analysis indicated that collectively, these traits may play an important role in determining susceptibility.     

Response of the elm leaf beetle to host plants induced by oviposition and feeding: the infestation rate matters

We investigated by olfactometry and feeding‐ and oviposition‐choice‐tests how the highly specialised elm leaf beetle, Xanthogaleruca luteola Müller (Coleoptera: Chrysomelidae), responds to conspecifically induced defences in the field elm Ulmus minor Miller (Ulmaceae). While egg deposition of the beetle induced elms to release volatiles attractive to the egg parasitoid Oomyzus gallerucae Fonscolombe (Hymenoptera: Eulophidae), feeding alone did not. In the present study, females of the elm leaf beetle showed preferences for the odours of twigs induced by low egg deposition and feeding over odours from uninfested twigs. In contrast, heavy infestation rendered elm odours less attractive to the beetles. Feeding and oviposition bioassays revealed an oviposition preference for leaves from uninfested twigs when compared to locally infested leaves. However, beetles preferred to feed upon systemically induced leaves compared to uninfested ones. The different preferences of the elm leaf beetle during host plant approach might be explained by a strategy that accounts for both gaining access to high quality nutrition and avoiding competition or parasitism.     

滤减UV-B辐射对烟叶腺毛发育和密度动态变化的影响

以烟草品种"K326"为材料,盆栽种植于自然环境条件下(CK)和覆盖不同厚度透明薄膜,分别滤减25%(T1)、50%(T2)和65%(T3)UV-B辐射的大棚中,在"K326"开花期至工艺成熟后期的4个生育期,通过扫描电镜观察了各处理烟叶腺毛形态和密度动态变化特征,并首次报道了"K326"中存在分枝腺毛。结果表明:上表皮腺毛在开花期、生理成熟期和工艺成熟前期对UV-B辐射敏感,下表皮则在开花期和工艺成熟后期对UV-B辐射敏感;T3处理腺毛密度低且延缓腺毛的发育,T1和T2处理腺毛密度较高,在工艺成熟期出现二次发育现象;各处理烟叶腺毛以长柄腺毛为主,CK、T1、T2下表皮腺毛总密度大于上表皮,而T3上、下表皮差异不大;滤减UV-B辐射有利于烟叶下表皮长柄腺毛发育,而引起腺毛二次发育的腺毛类型依处理和时期而异;适当较高强度的UV-B辐射对烟叶腺毛发育有促进作用,在研究地减弱25%～50%的UV-B辐射强度对烟叶腺毛发育较为合适。     

Development of microsatellite markers for the European white elm (Ulmus laevis Pall.) and cross‐species amplification within the genus Ulmus

Ulmus laevis Pall. is a broad‐leaved deciduous tree with a central and eastern European distribution. We describe the development of six polymorphic microsatellite markers for this species. These markers were also tested for utility in U. americana, U. glabra, U. minor and U. pumila. One additional marker gave ambiguous results in U. laevis but amplified clearly in three other species. In U. laevis, the number of alleles observed per locus ranged from two to nine. Five loci showed polymorphism in at least one of the nontarget species tested.     

Responses of ectomycorrhizal American elm (Ulmus americana) seedlings to salinity and soil compaction

American elm (Ulmus americana) seedlings were either non-inoculated or inoculated with Hebeloma crustuliniforme, Laccaria bicolor and a mixture of the two fungi to study the effects of ectomycorrhizal associations on seedling responses to soil compaction and salinity. The seedlings were grown in the greenhouse in pots containing non-compacted (0.4 g cm^?3 bulk density) and compacted (0.6 g cm^?3 bulk density) soil and subjected to 60 mM NaCl or 0 mM NaCl (control) treatments for 3 weeks. All three fungal inocula had similar effects on the responses of elm seedlings to soil compaction and salt treatment. In non-compacted soil, ectomycorrhizal fungi reduced plant dry weights, root hydraulic conductance, but did not affect leaf hydraulic conductance and net photosynthesis. When treated with 60 mM NaCl, ectomycorrhizal seedlings had several-fold lower leaf concentrations of Na⁺ compared with the non-inoculated plants. Soil compaction reduced Na⁺ leaf concentrations in non-ectomycorrhizal plants and decreased dry weights, gas exchange and root hydraulic conductance. However, in ectomycorrhizal plants, soil compaction had little effect on the leaf Na⁺ concentrations and on other measured growth and physiological parameters. Our results demonstrated that ECM associations could be highly beneficial to plants growing in sites with compacted soil such as urban areas.     

Cold tolerance and supercooling capacity in overwintering adults of elm leaf beetle Xanthogaleruca luteola (Coleoptera: Chrysomelidae)

Elm leaf beetle, Xanthogaleruca luteola (Muller) is one of the key pests of elm trees all over the world, and survives winter in reproductive diapause in sheltered locations. Seasonal variation of whole body supercooling points (SCPs), LT50 (temperature at which 50% of the test individuals die) and survival rate after exposure to subzero temperatures were determined in field collected adults during October 2008 to May 2009 and October 2009 to May 2010. The SCP of adults decreased significantly from October (median=-13.8°C) to January (median=-20.7°C) in first year, relatively similar results was observed in the second year. The lowest LT50 was observed in overwintering adults collected in January (-16.81°C) in the first year and December (-15.59°C) in the second year. Mortality at -15°C for 24 h was >70% in early autumn in both years whereas it decreased to lower than 45% in early winter, the highest mortality (100%) was observed in adults collected in May in both years. Cold acclimated adults (30 d, 5°C) in November 2008 exhibited significantly higher SCP (-12.21±0.64°C) than nonacclimated adults (-15.57±1.35°C). A 30-d exposure to 5°C caused >20% mortality in November, while <9% mortality was observed in adults collected in December and January 2008. Overwintering adults died upon freezing and the lower lethal temperatures were within the range of SCP, indicating that X. luteola is a freeze intolerant insect.     

Vessel length and conductivity of Ulmus branches: ontogenetic changes and relation to resistance to Dutch elm disease

Changes in age of the hydraulic architecture of Ulmus minor and U. minor × U. pumila juvenile wood were studied and related to tolerance to Dutch elm disease (DED). The xylem vessel dimensions and the conductivity to air of 2- to 7-year-old branches were analyzed and quantified. No obvious differences in vessel length distribution and conductivity were found to explain differences in DED tolerance among the U. minor clones, or, at the taxon level, the higher DED tolerance of U. minor × U. pumila. Among the U. minor clones, the more susceptible one had wider vessels and a higher maximum vessel diameter than the more tolerant clone. Relations between vessel lengths, vessel diameters and branch sizes were highly significant, and varied between taxa. The diameter and length of vessels increased with age, and average values stabilized 1–2 years earlier for U. minor than for U. minor × pumila. Mean maximum vessel length was significantly higher in U. minor and increased more with age and maximum vessel diameter than in U. minor × pumila. With each 0.2 m increase in height up the stem, conductivities for U. minor and U. minor × U. pumila decreased by 59 and 50 %, respectively, probably due to shortening of the vessels. The implications of xylem structure for the means of pathogen movement and resistance to DED are discussed.     

Growth inhibitory activity of Daphne gnidium L. (Thymelaeaceae) extracts on the elm leaf beetle (Col., Chrysomelidae)

Abstract:  An investigation has been performed on the activity of spurge flax ( Daphne gnidium L., Thymelaeaceae), a typical component of the Mediterranean vegetation, on the development of the elm leaf beetle ( Xanthogaleruca luteola Muller; Col., Chrysomelidae), one of the most serious defoliators of urban forests. Different concentrations of ethanolic extracts of D. gnidium leaves were added to the natural diet (elm leaf discs) of X. luteola , starting with L2 larvae, and the effects induced on the vitality, growth and phase duration of the different stages have been evaluated. A significant reduction of larval survival and adult emergence, together with an increased length of the larval period, heavy reduction of weight gain and appearance of malformations in emerged imagines were observed in presence of spurge flax extracts. These findings agree to ascribe to D. gnidium leaf extracts a growth inhibitory activity and allowed identifying what should be the optimal concentration to be applied on elm leaves to prevent heavy damages by X. luteola .     

Functional response of Tetrastichus gallerucae (Hym: Eulophidae) to different densities of the elm leaf beetle eggs,Xanthogaleruca luteola (Col: Chrysomelidae)

The elm leaf beetle is often considered as much of an indoor nuisance as a garden pest since large numbers of adults migrate into homes seeking a protected place to overwinter. Outdoors, both adults and larvae feed on the emerging leaves of virtually all species of elm trees, leaving skeleton zed foliage in their wake. Repeated severe infestations can markedly weaken a host tree, making it susceptible to other insects and diseases. The elm leaf beetle does not transmit the well-known Dutch elm disease, which is carried by another insect than elm bark beetle. The functional response of Tetrastichus gallerucae bees, that is the most important natural enemy of egg elm beetle Xanthogallerucae luteola, has been detected in Kerman province. The experiment was carried out in the growth room under conditions of 25 ± 1°C, 60 ± 5 RH and 16L:8D. Every female bee was exposed for 24 hours at densities of 2, 4, 6, 8, 10, 12, 16, 20, 30 and 40 eggs of elm leaf beetle. Every density had 10 repetitions. The results showed that T. gallerucae has the second type of functional response. The searching efficiency and the handling time of T. gallerucae was 2.63 and 0.114 on the eggs of elm leaf beetle and 2.193 and 0.112 on the eggs of hostess with diluted honey.     

Pectinase and cellulase activity in the digestive system of the elm leaf beetle,Xanthogaleruca luteola Muller (Coleoptera: Chrysomelidae)

The elm leaf beetle, Xanthogaleruca luteola, is a serious pest of elm trees in urban areas. Partial biochemical characterization of pectinases and cellulases was conducted using the larval digestive system of the pest. Midgut extracts from larvae showed optimum activity for pectinase and cellulase against pectin and carboxymethyl cellulose, respectively, under acidic conditions (pH 6). Pectinases and cellulases were respectively more stable under acidic conditions (pH 4–7) and slightly acidic conditions (pH 5–7) than under highly acidic and alkaline conditions. However, the enzymes were more stable in slightly acidic conditions (pH 6) when incubation time was increased. Maximum activity for the pectinases and cellulases incubated at different temperatures was observed at 45 and 50 °C, respectively. Mg²⁺ remarkably increased pectinase activity, and cellulase activity increased significantly in the presence of Ca²⁺ and Mg²⁺. Sodium dodecyl sulfate significantly decreased pectinase and cellulase activity. The Michaelis–Menten constant (K_M) and the maximal reaction velocity (V_max) values for pectinase were 2 mg·mL^? 1 and 0.017 mmol·min^? 1·mg^? 1 protein toward pectin, respectively. Zymogram analyses revealed the presence of one and five bands of pectinase and cellulase activity, respectively, in the larval midgut extract.     

Response of leaf water potential, stomatal resistance, and leaf rolling to water stress

Numerous studies have associated increased stomatal resistance with response to water deficit in cereals. However, consideration of change in leaf form seems to have been neglected. The response of adaxial and abaxial stomatal resistance and leaf rolling in rice to decreasing leaf water potential was investigated. Two rice cultivars were subjected to control and water stress treatments in a deep (1-meter) aerobic soil. Concurrent measurements of leaf water potential, stomatal resistance, and degree of leaf rolling were made through a 29-day period after cessation of irrigation. Kinandang Patong, an upland adapted cultivar, maintained higher dawn and midday leaf water potential than IR28, a hybrid selected in irrigated conditions. This was not explained by differences in leaf diffusive resistance or leaf rolling, and is assumed to result from a difference in root system extent.     

Biology and phenology of three leaf beetle species (Chrysomelidae) in a montane forest in southeast Brazil

The population phenology of the cassidines, Coptocycla arcuata and Omaspides trichroa, and the chrysomeline, Platyphora axillaris, was studied at Serra dos Órgãos National Park, State of Rio de Janeiro, southeast Brazil. Monthly surveys of larvae and adults were conducted between 2008 and 2011 at approximately 1000 m altitude on their respective host plants, Cordia polycephala (Boraginaceae), Ipomoea philomega (Convolvulaceae) and Solanum scuticum (Solanaceae). This is the first observation of larviparity and host record for Platyphora axillaris. Although having different life history traits, all species showed similar phenologies. They were abundant from October to March, months of high temperatures and intense rainfall, with two distinct reproductive peaks in the same season. Abundance dropped abruptly during the coldest and driest months, from May to August. Frequently none of these species were recorded during June and July. This phenological pattern is similar to other Chrysomelidae living in subtropical areas of Brazil. Temperature and rainfall appear to be the major factors influencing the fluctuation of these three species.     

Effects of environmental stress on leaf hair density and consequences for selection

We explored how five different environmental stresses and a benign environment affect the phenotypic expression of leaf hairs, and the potential for evolutionary response in this trait. To address these questions we planted full-sib families that had been selected for stress tolerance in a factorial design in which selection history was fully crossed with the current environment (eight families × six selection histories × six current environments × three blocks=864 plants). Our data suggest that leaf hair density is a complex character composed of two separable traits: leaf area and the number of hairs initiated per leaf. Leaf size is primarily controlled by the growth environment, whereas leaf hair initiation shows more genetically based variation. In the control and low water environments there was a negative linear relationship between leaf size and leaf hair density. However, within the low light and high boron treatments, leaf hair density remained constant across a range of leaf sizes, suggesting that these stresses disrupt normal leaf hair development. Selection gradient analysis showed that leaf hair density and leaf size were significantly positively associated with fitness in 4/6 of our environments. Our results suggest that environmental variation may diminish the ability of herbivores and pathogens to cause directional selection on leaf hair density.     

Host location in Oomyzus gallerucae (Hymenoptera: Eulophidae), an egg parasitoid of the elm leaf beetle Xanthogaleruca luteola (Coleoptera: Chrysomelidae)

Eggs of the elm leaf beetle Xanthogaleruca luteola are often heavily attacked by the chalcidoid wasp Oomyzus gallerucae. We studied the chemical signals mediating interactions between the egg parasitoid, its host, and the plant Ulmus campestris. Olfactometer bioassays with O. gallerucae showed that volatiles of the host-plant complex attract the parasitoid. In order to determine the source of attractive volatiles within this host-plant-complex, we tested separately the effect of odours of eggs, gravid elm leaf beetle females, faeces of the beetles and elm twigs (with undamaged leaves and leaves damaged either mechanically or by feeding of the beetles). Odours of faeces of the elm leaf beetle were attractive, whereas neither volatiles from eggs nor from gravid females acted as attractants. Volatiles from undamaged or damaged plants did not elicit a positive reaction in O. gallerucae, whereas volatiles from feeding-damaged plants onto which host eggs had been deposited were attractive. This latter result suggests that it is not feeding but deposition of host eggs onto elm leaves that induces the production of plant volatiles attractive to the egg parasitoid. Investigations of the search patterns of O. gallerucae within the habitat by laboratory bioassays revealed that the egg parasitoid encounters host eggs by chance. Contact kairomones from faeces were demonstrated to be important in microhabitat acceptance, while contact kairomones isolated from the host eggs are relevant for host recognition. Received: 12 February 1997 / Accepted: 29 April 1997     

Transcriptomic characterization of gall tissue of Japanese elm tree (Ulmus davidiana var. japonica) induced by the aphid Tetraneura nigriabdominalis

Insect galls are abnormal plant tissues induced by parasitic insect(s) for use as their habitat. In previous work, we suggested that gall tissues induced by the aphid Tetraneura nigriabdominalis on Japanese elm trees are less responsive than leaf tissues to jasmonic acid (JA), which is involved in the production of volatile organic compounds as a typical defensive reaction of plants against attack by insect pests. A comprehensive analysis of gene expression by RNA sequencing indicated that the number of JA responsive genes was markedly lower in gall tissues than in leaf tissues. This suggests that gall tissues are mostly defective in JA signaling, although JA signaling is not entirely compromised in gall tissue. Gene ontology analysis sheds light on some stress-related unigenes with higher expression levels in gall tissues, suggesting that host plants sense aphids as a biotic stress but are defective in the JA-mediated defense response in gall tissues.     

不同施钾水平对苜蓿营养物质及抗蓟马性的影响

【目的】明确施钾是否能有效提高苜蓿对蓟马的抗性以及钾-营养物质-抗虫性之间的关系。【方法】以感蓟马紫花苜蓿Medicago sativa品种甘农3号(Gannong No.3)和抗蓟马紫花苜蓿品种甘农9号(Gannong No.9)为材料,设0,6,9,12和15 g/m2(K2O)5个钾水平,在大田蓟马为害高峰期,评价和测定了不同钾水平处理下苜蓿的受害指数、虫口数量、叶片钾含量、碳氮比和游离氨基酸变化。【结果】在第2茬中,随着钾水平的升高,甘农3号和甘农9号老叶和心叶的钾含量上升,可溶性糖和碳氮比升高,游离氨基酸含量下降,虫口数量无显著性差异,受害指数显著降低(P0.05),且在9 g/m2(K2O)水平下最低。在第3茬中,甘农3号和甘农9号的受害指数、叶片钾含量、碳氮比及游离氨基酸的变化规律和第2茬相同,但虫口数量上升。第2茬和第3茬中,不同施钾水平下,苜蓿叶片钾含量与受害指数负相关但不显著(P0.05)。施钾后甘农3号的受害指数均低于未施钾甘农9号的受害指数。【结论】钾元素可通过提高苜蓿碳氮比,降低游离氨基酸的含量来提高苜蓿对蓟马的耐害性。在大田条件下,通过施钾管理来提高苜蓿品种对蓟马的耐害性是一种有效的措施。     

Variation in leaf trichomes and nutrients of Wigandia urens (Hydrophyllaceae) and its implications for herbivory

Leaf trichome variation was studied in a population of Wigandia urens (Hydrophyllaceae) in relation to water availability, diversity of herbivorous insects, and grazing rates. Plants of W. urens have glandular and urticant (stinging hairs) trichomes, and it is possible to distinguish two types of leaves: smooth leaves with only glandular trichomes and bristly leaves with both types of trichomes. Density of urticant trichomes was negatively correlated with weekly mean precipitation. Fourteen species of insects in five different orders feed on leaves of W. urens throughout the year. Grazing rates varied according to type and age of leaves. Grazing rates were lower in smooth than bristly young leaves but the rates were similar for mature leaves. Secondary metabolites, screened using qualitative methods, showed similar classes of compounds in both types of leaves. Bristly leaves had significantly higher concentrations of nitrogen, phosphorous and water and these nutritional differences were well correlated with the differences in grazing rates between bristly and smooth leaves.