Preferential Feeding and Occupation of Sunlit Leaves Favors Defense Response and Development in the Flea Beetle,Altica brevicollis coryletorum – A Pest of Corylus avellana

The monophagous beetle, Altica brevicollis coryletorum, is a major leaf pest of Corylus avellana (common hazel). In contrast to majority of the other studied species of shrubs, sunlit leaves are grazed to a much greater extent than shaded leaves. Since the observation of a link between leaf irradiance level and A. brevicollis feeding is unique, we hypothesized that feeding preference of this beetle species is related to the speed needed to escape threats i.e. faster jumping. We also hypothesized that sunlit leaves are more nutritious and easier to consume than the leaves of shaded shrubs. Results indicated that beetle mass was greater in beetles occupying sunlit leaves, which is consistent with our second hypothesis. The study also confirmed under laboratory conditions, that larvae, pupae and beetles that were fed full-light (100% of full light) leaves were significantly heavier than those fed with shaded leaves (15% of full light). In the high irradiance conditions (higher temperature) duration of larval development is also reduced. Further results indicated that neither the concentration of soluble phenols, leaf toughness, or the number of trichomes could explain the insect’s preference for sunlit leaves. Notably, measurements of jump length of beetles of this species, both in the field and under laboratory conditions, indicated that the defense pattern related to jumping was associated with light conditions. The jump length of beetles in the sun was significantly higher than in the shade. Additionally, in laboratory tests, beetle defense (jumping) was more strongly affected by temperature (15, 25, or 35°C for 24h) than by leaf type. The effect of sunlit, higher nutrient leaves (greater level of non-structural carbohydrates) on defense (jumping) appears to be indirect, having a positive effect on insect mass in all developmental stages.     

Influence of native and alien Prunus species and light conditions on performance of the leaf beetle Gonioctena quinquepunctata

The polyphagous beetle Gonioctena quinquepunctata Fabricius (Coleoptera: Chrysomelidae) is a serious leaf pest of the native European bird cherry, Prunus padus L., and the invasive alien black cherry, Prunus serotina Ehrh. (Rosaceae). In the shade, leaf damage is extensive in both species, whereas in full light, it is extensive in P. padus, but very low in P. serotina. We determined the influence of Prunus species and light conditions on differences in performance of both sexes of this folivore. In a laboratory experiment in which larvae were fed with leaves of a single species grown under particular light conditions, we measured larval, pupal, and adult mass, efficiency of conversion of ingested food (ECI), duration of development, total food eaten, and relative growth rate. In the field, we observed differences in beetle mass on shrubs of the two species growing under various light conditions. From the field observations, we hypothesised that leaves of the invasive P. serotina are not an equally good food source as leaves of P. padus for G. quinquepunctata, and the preference of these beetles for shaded shrubs is most favourable for their growth and development. Under laboratory conditions, we found that the beetle growth rate was not affected significantly by Prunus species or light conditions, despite the significant effect of light condition on the structure and chemical composition of Prunus seedlings. The lower ECI value for larvae feeding on sunlit leaves was compensated for by their higher level of consumption. In the field, adult insect mass was higher on P. padus than on P. serotina, and higher on sunlit shrubs of both species than on shaded ones. Under natural conditions, the mass of adult insects is probably also affected by other factors, such as predators and competition among folivores.     

Seasonal changes in photosynthesis and nitrogen allocation in leaves of different ages in evergreen understory shrub <Emphasis Type="Italic">Daphniphyllum humile</Emphasis>

Seasonal changes in photosynthetic capacity, leaf nitrogen (N) content, leaf chlorophyll (Chl) content and leaf N allocation patterns in leaves of different ages in the evergreen understory shrub, Daphniphyllum humile Maxim, growing at a forest border and an understory site were studied. In current-year leaves at the understory site, the N and Rubisco contents increased from spring to autumn although their light-saturated photosynthetic rate at 22°C (P _max²²) remained stable, indicating that their mesophyll conductance rates declined as they completed their development and/or that they invested increasing amounts of their resources in photosynthetic enzymes during this period. In contrast, seasonal changes in P _max²² in current-year leaves at the forest border site were correlated with changes in Rubisco content. In 1-year old leaves at the understory site, P _max²² and contents of Chl, leaf N, and Rubisco remained stable from spring to autumn, while these parameters decreased in 1-year-old forest border leaves, indicating that N may have been remobilized from shaded 1-year-old leaves to sunlit current-year leaves. When leaves senesced at the forest border site the Rubisco content decreased more rapidly than that of light-harvesting proteins such as LHCII, suggesting that N remobilization from Rubisco may be more efficient, possibly because Rubisco has greater N costs and is soluble, whereas the light-harvesting proteins are membrane components.     

Utilizing in situ directional hyperspectral measurements to validate bio-indicator simulations for a corn crop canopy

Two radiative transfer canopy models, SAIL and the two-layer Markov-Chain Canopy Reflectance Model (MCRM), were coupled with in situ leaf optical properties to simulate canopy-level spectral band ratio vegetation indices with the focus on the photochemical reflectance index in a cornfield. In situ hyperspectral measurements were made at both leaf and canopy levels. Leaf optical properties were obtained from both sunlit and shaded leaves. Canopy reflectance was acquired for eight different relative azimuth angles (ψ) at three different view zenith angles (θ_v), and later used to validate model outputs. Field observations of PRI for sunlit leaves exhibited lower values than shaded leaves, indicating higher light stress. Canopy PRI expressed obvious sensitivity to viewing geometry, as a function of both θ_v and ψ. Overall, simulations from MCRM exhibited better agreements with in situ values than SAIL. When using only sunlit leaves as input, the MCRM-simulated PRI values showed satisfactory correlation and RMSE, as compared to in situ values. However, the performance of the MCRM model was significantly improved after defining a lower canopy layer comprised of shaded leaves beneath the upper sunlit leaf layer. Four other widely used band ratio vegetation indices were also studied and compared with the PRI results. MCRM simulations were able to generate satisfactory simulations for these other four indices when using only sunlit leaves as input; but unlike PRI, adding shaded leaves did not improve the performance of MCRM. These results support the hypothesis that the PRI is sensitive to physiological dynamics while the others detect static factors related to canopy structure. Sensitivity analysis was performed on MCRM in order to better understand the effects of structure related parameters on the PRI simulations. LAI showed the most significant impact on MCRM-simulated PRI among the parameters studied. This research shows the importance of hyperspectral and narrow band sensor studies, and especially the necessity of including the green wavelengths (e.g., 531 nm) on satellites proposing to monitor carbon dynamics of terrestrial ecosystems.     

Pinus koraiensis twigs affect Monochamus saltuarius (Coleoptera: Cerambycidae) longevity and reproduction

This study was conducted to investigate the longevity, reproduction and ovarian development of M. saltuarius adults feeding on Pinus koraiensis twigs of three different age classes (current-year, 1-year and 2-year). Longevity and fecundity of female adults decreased with increasing twig age class (58.4, 41.9 and 35.9 days, respectively, for longevity and 43.0, 13.2 and 6.6 eggs, respectively, for fecundity). In ovarian development, the average follicle size after 1 week of feeding on current-year twigs was 3.1–3.5 times greater than those of beetles fed 1- and 2-year-old twigs. After 2 weeks of feeding, follicle size was 2.3–2.4 times greater than those of beetles fed 1- and 2-year-old twigs. These results showed that current-year twigs of P. koraiensis increase longevity and reproduction of M. saltuarius. By analyzing sugars using high performance liquid chromatography (HPLC), the quantity of fructose was found to be highest in current-year twigs and lowest in 2-year-old twigs. A sugar feeding bioassay indicated that fructose was preferred by M. saltuarius. Therefore, fructose is important to adult feeding and ovariole development in M. saltuarius.     

Size-based intraspecific variations along altitudinal gradient and follow of Bergmann’s rule in Parthenium beetle,Zygogramma bicolorata Pallister

Body size in insects is coupled with numerous physiological, life-history and ecological traits. Its variation along temperature gradient is widely studied. However, information regarding variations in body size of insects along altitudinal gradient is limited. Present study was designed considering hypothesis that there would be an increase in body size of Parthenium beetle, Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae) with increasing altitude and decreasing in temperature. To achieve the objectives, beetles were collected from three eco-climatic zones of NEPAL [Kathmandu (1400 mts, 24 °C; warm temperate zone), Chitwan (415 mts, 25 °C; upper tropical/sub-tropical zone), and Mahendranagar (229 mts, 34 °C; humid subtropical zone)], and one of INDIA [Varanasi (81 mts, 36 °C; humid subtropical zone)] for their morphometric analysis (body length and body biomass). Results revealed that the size of beetles in all eco-climatic zones increased with increasing altitude and decreasing temperature. While adults of Kathmandu were largest, followed by Chitwan and Mahendranagar, but those of Varanasi were smallest in size. The sex ratio was female-biased in Kathmandu and Varanasi, but was male-biased in Chitwan and Mahendranagar. Irrespective of temperature and altitude, females were larger than males in all eco-climatic zones. Our results affirmed our hypothesis and were in compliance with Bergmann’s rule. The findings may be helpful in understanding phenotypic plasticity and distribution pattern of Z. bicolorata adults in Indian sub-continent under global climate change scenario.     

Improving photosynthetic performance and some fruit quality traits in mango trees by shading

Excess solar radiation under hot climate can lead to decline in photosynthetic activity with detrimental effects on growth and yield. The aim of this study was to evaluate the use of a transparent plastic roof as shading for diurnal changes in photosynthetic gas exchange, chlorophyll fluorescence, fruit set and quality of mango (Mangifera indica L.) cv. ‘Nam Dok Mai’ growth in the field conditions. Fully expanded leaves were examined either shaded by the plastic roof or sunlit under natural conditions. Leaf temperature and leaf-to-air vapour pressure deficit of the shaded leaves measured on the clear day were lowered compared to those of the sunlit leaves. It resulted in increased stomatal conductance and photosynthetic rates of the shaded leaves compared to those of the sunlit leaves, especially from the morning to midday. Furthermore, the reversible decrease of the maximal quantum yield of PSII was more pronounced in the sunlit leaves than that in the shaded ones. Shading increased the total fruit number; the shaded fruits developed better external color than that of the sun-exposed fruits. Our results indicated that shading could maintain the high photosynthetic activity by reducing stomatal limitations for carbon supply and was effective in alleviating the photoinhibitory damage to PSII during bright and clear days with excessive radiation. Finally, shading could increase the number of fruits and improve mango peel color.     

Growth condition controls on G-93 parameters of isoprene emission from tropical trees

Despite its major role in global isoprene emission, information on the environmental control of isoprene emission from tropical trees has remained scarce. Thus, in this study, we examined the relationship between parameters of G-93 isoprene emission formula (C_T1, C_T2, and α), growth temperature and light intensity, photosynthesis (?, P_max), isoprene synthase (IspS) level, and 2-C-methyl-d-erythritol 4-phosphate (MEP) pathway metabolites using sunlit and shaded leaves of four tropical trees. The results showed that the temperature dependence of isoprene emission from shaded leaves did not differ significantly from sunlit leaves. In contrast, there was a lower saturation irradiance in shaded leaves than in sunlit leaves, the same as temperate plants. The photosynthesis rate of shaded leaves showed lower saturation irradiance, similar to the light dependence of isoprene emission. In most cases, the concentration of MEP pathway metabolites was of lower tendency in shaded leaves versus in sunlit leaves, whereas no significant difference was noted in IspS level between sunlit and shaded leaves. Correlation analysis between these parameters found that C_T1 of the G-93 parameter was positively correlated with the concentration of DXP and DMADP, whereas C_T2 correlated with the concentration of MEP and the average air temperature for the past 48 h. Similarly, α closely associated with the initial slope (?) of photosynthesis rate, and the basal emission factor is also linked to the photon flux of past days. These results suggest that growth conditions may control the temperature dependence of isoprene emission from tropical trees via the changes in the profiles of MEP pathway metabolites, causing alteration in the parameters of the isoprene emission formula.

     

Relative Importance of Sex,Pre-Starvation Body Mass and Structural Body Size in the Determination of Exceptional Starvation Resistance of Anchomenus dorsalis (Coleoptera: Carabidae)

In nature, almost all animals have to cope with periods of food shortage during their lifetimes. Starvation risks are especially high for carnivorous predatory species, which often experience long intervals between stochastic prey capturing events. A laboratory experiment using the common predatory carabid beetle Anchomenus dorsalis revealed an exceptional level of starvation resistance in this species: males survived up to 137 days and females up to 218 days without food at 20°C. Individual starvation resistance was strongly positively affected by pre-starvation body mass but only slightly by beetle structural body size per se. Females outperformed males even when the effect of gender was corrected for the effects of structural body size and pre-starvation body mass. The better performance of females compared to males and of beetles with higher relative pre-starvation body mass could be linked to higher fat content and lean dry mass before starvation, followed by a greater decrease in both during starvation. There was also a difference between the sexes in the extent of body mass changes both during ad libitum feeding and following starvation; the body masses of females fluctuated more compared to males. This study stresses the need to distinguish between body mass and structural body size when investigating the ecological and evolutionary consequences of body size. Investigation of the net effects of body size and sex is necessary to disentangle the causes of differences in individual performances in studies of species with significant sexual size dimorphism.     

Chemical signatures affecting host choice in the Eucalyptus herbivore,Gonipterus sp. (Curculionidae: Coleoptera)

It is well known that herbivorous insects respond to host plant volatiles. Yet details of how these insects perceive the complex profile of volatiles from different potential host plants have not been studied for most insects. Gonipterus spp. are important pests of Eucalyptus worldwide, but differ in their preference for different species of this host. In this study, we consider whether host volatiles affect the host choice for a Gonipterus sp. and we characterize the response of the female insect to the volatile profiles from these hosts in an electro-antennographic experiment. We sampled volatiles from freshly damaged leaves of three Eucalyptus species and analysed the profiles by gas chromatography coupled to electro-antennography (GC-EAD) and gas chromatography coupled to mass spectrometry. Female weevils gave a mixed range of electro-physiological responses to volatile puffs from leaves of different tree species. This suggests that differences in volatile profiles of different trees play a role in how these beetles discriminate between potential hosts. GC-EAD analysis showed that responses were as complex as the volatile chemical compositions of the leaves. A number of these chemicals were identified, and responses were mostly due to general green leaf volatiles. This was also evident from the fact that the insects showed a markedly greater response to the total volatile profile from freshly damaged leaves for all species. The females of the Gonipterus sp. can therefore detect damaged leaves, which may indicate host quality. Host specificity information is further expected to lie in the relative differences in emission ratios and synergism between different host chemical compounds, rather than specific individual compounds.     

No Effect of Host Species on Phenoloxidase Activity in a Mycophagous Beetle

Ecological immunology is an interdisciplinary field that helps elucidate interactions between the environment and immune response. The host species individuals experience have profound effects on immune response in many species of insects. However, this conclusion comes from studies of herbivorous insects even though species of mycophagous insects also inhabit many different host species. The goal of this study was to determine if fungal host species as well as individual, sex, body size, and host patch predict one aspect of immune function, phenoloxidase activity (PO). We sampled a metapopulation of Bolitotherus cornutus, a mycophagous beetle in southwestern Virginia. B. cornutus live on three species of fungus that differ in nutritional quality, social environment, and density. A filter paper phenoloxidase assay was used to quantify phenoloxidase activity. Overall, PO activity was significantly repeatable among individuals (0.57) in adult B. cornutus. While there was significant variance among individuals in PO activity, there were surprisingly no significant differences in PO activity among subpopulations, beetles living on different host species, or between the sexes; there was also no effect of body size. Our results suggest that other factors such as age, genotype, disease prevalence, or natal environment may be generating variance among individuals in PO activity.     

Lack of evolution in a leaf beetle that lives on two contrasting host plants

The interactions between plant‐eating insects and their hosts have shaped both the insects and the plants, driving evolution of plant defenses and insect specialization. The leaf beetle Trirhabda eriodictyonis (Chrysomelidae) lives on two shrubs with differing defenses: Eriodictyon crassifolium has hairy leaves, whereas E. trichocalyx has resinous leaves. We tested whether these beetles have differentiated onto the two host plants, and if not, whether the beetles prefer the better host plant and prefer mates who are from that host plant. In feeding tests, adult beetles strongly preferred eating E. trichocalyx regardless of which host they came from. In addition, females laid more eggs if they ate E. trichocalyx than E. crassifolium. So, E. trichocalyx is generally the better host. However, beetle mate preference was not in line with food choice. Males did not prefer to mate with females from E. trichocalyx. Females from E. crassifolium did prefer males from E. trichocalyx over males from E. crassifolium, but did not lay more eggs as a result of these matings. We conclude that the beetle populations we studied have not differentiated based on their host plants and may not have even adapted to the better host. Although to humans these host plant defenses differ dramatically, signs that they have caused evolution in the beetles are lacking. The case of T. eriodictyonis stands counter to many other studies that have seen the differentiation of ecotypes and/or adaptive coordination of an herbivore's life cycle based on host plant differences.     

Miniaturisation effects in larvae and adults of Mikado sp. (Coleoptera: Ptiliidae), one of the smallest free-living insects

We present the first morphological study of larvae and adults of Mikado sp. – one of the smallest known beetles and free-living insects (body length of adult is 390–455 μm). Morphological and developmental consequences of miniaturisation in Mikado and insects in general are discussed. We used histological sectioning, scanning electron microscopy, laser confocal microscopy and 3D-computer reconstruction. For the first time we report that according to the morphometric data of Mikado sp., at least some ptiliid beetles have three larval stages. We studied the muscular system of adults and larval stages. It is shown that ptiliid beetles have nearly the complete set of muscles found in larger staphyliniform beetles. Developmental and size dependent changes in the relative volume of different organs are addressed. All organ systems change allometrically in the development of Mikado sp. as well as in comparison with larger representatives of Ptiliidae and closely related groups of beetles, such as Staphylinidae. We conclude that the factors limiting miniaturisation are the size of the neural system, associated with the number and size of neurons, the mass of the skeleton, the egg size (free-living insects), and consequently the volume of the reproductive system.     

Orientation of flight for physically disturbed spotted lanternflies,Lycorma delicatula, (Hemiptera,Fulgoridae)

The spotted lanternfly, Lycorma delicatula, (Hemiptera, Fulgoridae) is an invasive pest to Korea and the United States, originating from China or Southeast Asia. Immature L. delicatula feed on a wide range of plants, but the adults are more host-selective, often preferring the tree of heaven, Ailanthus altissima. We performed field studies to evaluate adult movement in relation to A. altissima after disturbance. The Ailanthus trees were in a mixed suburban forested situated at the southern border of an open grassy field. Female adult lanternflies were manually disturbed from feeding on the trunks of large A. altissima trees. In the first experiment, insects were disturbed directly from the tree using a ballpoint pen to simulate a predatory attack. These insects usually flew initially southward away from the tree line toward a sunlit field, but turned northward back toward the tree line. In the second experiment, to simulate an initially successful predatory attack, they were manually taken from trees, and allowed to escape. The females immediately opened their wings in an apparent aposematic display. They then either immediately flew toward the sunlit open field, or remained with their wings splayed open for a prolonged period.     

Relation between age–sex classes and dietary selection of wild Japanese monkeys

Dietary selection by wild Japanese monkeys (Macaca fuscata yakui Kuroda) was examined in relation to body size. The monkeys were classified into three age–sex categories: adult males, adult females and immatures excluding suckling infants. Time spent feeding did not differ between age–sex classes, although time spent moving was longer in lighter classes. Heavier individuals fed relatively more on mature leaves, while lighter individuals fed on insects more frequently. Mature leaves were more abundant but had lower energy content than other food items in the forest. Heavier monkeys seemed to feed on greater amounts of lower quality food in this species. This finding agrees with the Jarman–Bell principle on ungulates.     

Contest dynamics for food and reproductive resources are defined by health condition in a dung beetle

Male dung beetles compete to obtain food and females, and early resource recognition and appropriation increase the probability of mating. The outcome of such encounters is expected to be defined by self‐ and the opponent’s health condition. In this study, we analyzed the effect of body condition and immune defense on the contest dynamics between males that rolled a food ball with a partner female (owner males) and intruder males of dung beetle Canthon cyanellus. Body condition was measured as body size, body dry mass, lipid mass, and muscle mass; immune defense was estimated via phenoloxidase activity. Owner males with higher lipid mass contacted the food ball significantly earlier than owner males with lower lipid mass. Individuals with lower phenoloxidase activity started to roll food balls earlier than individuals with higher phenoloxidase activity. Owner males that had higher body dry mass, compared to female partners, began to roll the food ball significantly earlier than male–female pairs with lower differences in dry mass. Heavier males won significantly more contests than lighter males. Our results suggest that the health condition is a key factor related to the dynamics and outcome of male–male contests for resources and females in C. cyanellus. Consequently, differences in individual condition are main determinants of contest outcomes in dung beetles.     

Building a Beetle: How Larval Environment Leads to Adult Performance in a Horned Beetle

The link between the expression of the signals used by male animals in contests with the traits which determine success in those contests is poorly understood. This is particularly true in holometabolous insects such as horned beetles where signal expression is determined during metamorphosis and is fixed during adulthood, whereas performance is influenced by post-eclosion feeding. We used path analysis to investigate the relationships between larval and adult nutrition, horn and body size and fitness-related traits such as strength and testes mass in the horned beetle Euoniticellus intermedius. In males weight gain post-eclosion had a central role in determining both testes mass and strength. Weight gain was unaffected by adult nutrition but was strongly correlated with by horn length, itself determined by larval resource availability, indicating strong indirect effects of larval nutrition on the adult beetle’s ability to assimilate food and grow tissues. Female strength was predicted by a simple path diagram where strength was determined by eclosion weight, itself determined by larval nutrition: weight gain post-eclosion was not a predictor of strength in this sex. Based on earlier findings we discuss the insulin-like signalling pathway as a possible mechanism by which larval nutrition could affect adult weight gain and thence traits such as strength.     

Small-scale spatiotemporal variability in body size of two common carabid beetles

Adult body size is one of the most ecologically relevant quantitative traits that underlies many other life-history traits of particular organism. In insects, there is positive intraspecific relationship between body size and female fecundity. In this study small scale temporal and spatial and space variability in structural body size of Poecilus cupreus and Anchomenus dorsalis was investigated. The beetles were collected in four fields near Prague-Suchdol in autumn 2009 and 2010, and in spring 2010, 2011 and 2012. In both species structural body size was significantly affected by sex (females were the larger sex). In A. dorsalis structural body size was also significantly affected by arable field identity, overwintering (post-overwintering individuals collected in spring were larger in comparison to pre-overwintering individuals collected in autumn), sampling year, overwintering by year and arable field by year interactions. Our results suggest that spatiotemporal variation in environmental conditions experienced by A. dorsalis during larval growth resulted in differences in adult structural body size among particular fields and particular sampling years. In addition, mean structural body size in A. dorsalis was affected by overwintering, which was probably caused by size-specific winter mortality. Moreover, effect of overwintering varied among years, probably according to the specific weather conditions during a particular winter.     

Patterns of pigment changes in apple fruits during adaptation to high sunlight and sunscald development

Reflectance spectra of four apple (Malus domestica Borkh.) cultivars were studied and chlorophyll, carotenoid, anthocyanin and flavonoid content in sunlit and shaded peel was determined. In all cases sunlit peel accumulated high amounts of phenolics (flavonoid glycosides). Adaptation to strong sunlight of an apple cultivar with limited potential for anthocyanin biosynthesis (Antonovka) was accompanied by a decrease in chlorophyll and a significant increase in total carotenoid content. The increase in carotenoids also took place in sunlit sides of the Zhigulevskoye fruits, accumulating high amounts of anthocyanins, but chlorophyll content in sunlit peel was higher than that in shaded peel. Significant increases in carotenoids and anthocyanins were detected during fruit ripening when chlorophyll content fell below 1.5–1.8 nmol cm^–2. Chlorophyll in sunlit fruit surfaces of both cultivars was considerably more resistant to photobleaching than in shaded (especially of Zhigulevskoye) sides. Induced by sun irradiation, the photoadaptive responses were cultivar-dependent and expressed at different stages of fruit ripening even after storage in darkness. The development of sunscald symptoms in susceptible apple cultivars (Granny Smith and Renet Simirenko) led to a dramatic loss of chlorophylls and carotenoids, which was similar to that observed during artificial photobleaching. The results suggest that apple fruits exhibit a genetically determined strategy of adaptation of their photoprotective pigments to cope with mediated by reactive oxygen species photodynamic activity of chlorophyll under strong solar irradiation. This includes induction of synthesis and accumulation of flavonoids, anthocyanins and carotenoids that could be expressed, if necessary, at different stages of fruit development     

Variation in shoot mortality within crowns of severely defoliated <Emphasis Type="Italic">Betula maximowicziana</Emphasis> trees in Hokkaido,northern Japan

To clarify mortality patterns of current-year shoots within the crown of Betula maximowicziana Regel after severe insect herbivory in central Hokkaido, northern Japan, we investigated the degree of defoliation, pattern of shoot development, shoot mortality, and leaf tissue-water relations. One hundred current-year long shoots growing in a B. maximowicziana plantation were observed for defoliation and mortality in June 2002. An outbreak of herbivorous insects (Caligula japonica and Lymantria dispar praeterea) occurred in the stand in mid-to-late June, and the monitored shoots were defoliated to various degrees. Within 1 month of defoliation, some of the severely defoliated shoots had produced new leaves on short shoots that had emerged from axillary buds. Stepwise logistic regression revealed that the probability that current-year long shoots would put out axillary short shoots with leaves is closely related to the degree of defoliation. To evaluate the water relations of the leaves, we determined pressure–volume curves for the leaves that survived the herbivorous insect outbreak and the new leaves that emerged after defoliation. The water potential at turgor loss (Ψ_l,tlp) and the osmotic potential at full turgidity (Ψ_π,sat) were higher for the new leaves than for the surviving leaves, indicating a lower ability to maintain leaf cell turgor against leaf dehydration in the new leaves. Of the 100 shoots, 13 died after the emergence of new leaves. Stepwise logistic regression revealed that the probability that the long shoots would die generally increased with the emergence of new leaves, with increasing shoot height. This result suggests that the combined effect of the vulnerability of newly emerged leaves and low water availability, associated with higher shoot positions within the crown, caused shoot mortality. Based on our results, some possible mechanisms for mortality in severely defoliated B. maximowicziana are discussed.