Effects of the fungus Isaria fumosorosea (Hypocreales: Cordycipitaceae) on reduced feeding and mortality of the Asian citrus psyllid,Diaphorina citri (Hemiptera: Psyllidae)

The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae), is an important citrus pest primarily because it transmits bacteria putatively responsible for huanglongbing, a serious disease of citrus. We present a study on the effects of blastospore and conidial formulations of Isaria fumosorosea Wize on feeding rates and mortality of adult psyllids in laboratory bioassays. Information on quantities of honeydew droplets was used to make inferences on feeding rates. Psyllids treated with the blastospore formulation of I. fumosorosea produced fewer honeydew droplets compared to the conidial treatment and control beginning within the first 24 h after treatment. The highest daily mean number of droplets thereafter never exceeded 2.4 drops compared to 4 and 8 for the conidial treatment and control, respectively. The mean number (±SEM) of honeydew droplets produced per psyllid per day over 7 days was significantly higher in the control (5.5±0.5) compared to the blastospore treatment; however, there were no significant differences between the treatments. Psyllids treated with the conidial formulation of the pathogen showed no significant reduction in feeding activity until 4 days after treatment. One and 2 day's post-exposure, mortality of psyllids in the blastospore treatment ranged from 8 to 25% compared to 0% in the conidial and control treatments. By 7 days post-exposure, psyllid mortality reached 100% under both fungal treatments compared to none in the controls. This study documented that adult psyllids infected by I. fumosorosea (PFR 97) produce less honeydew than healthy psyllids and suggests that they may feed less, which could potentially reduce the spread of huanglongbing.     

GROWTH AND PHOTOPROTECTION IN THREE DINOFLAGELLATES (INCLUDING TWO STRAINS OF ALEXANDRIUM TAMARENSE) AND ONE DIATOM EXPOSED TO FOUR WEEKS OF NATURAL AND ENHANCED ULTRAVIOLET‐B RADIATION1

Long‐term growth response to natural solar radiation with enhanced ultraviolet‐B (UVB) exposure was examined in two species of dinoflagellates [Alexandrium tamarense (M. Lebour) Balech, At, and Heterocapsa triquetra (Ehrenb.) F. Stein, Ht], including two strains of A. tamarense, one from Spain and another from UK, and one diatom species (Thalassiosira pseudonana Hasle et Heimdal). We examined whether variable photoprotection (mycosporine‐like amino acids [MAAs] and xanthophyll‐cycle pigments) affected photosynthetic performance, phytoplankton light absorption, and growth. Growth rate was significantly reduced under enhanced UVB for the UK strain of At and for Ht (both grew very little) as well as for the diatom (that maintained high growth rates), but there was no effect for the Spanish strain of At. MAA concentration was high in the dinoflagellates, but undetectable in the diatom, which instead used the xanthophyll cycle for photoprotection. The highest cell concentrations of MAAs and photoprotective pigments were observed in the UK strain of At, along with lowest growth rates and F_v/F_m, indicating high stress levels. In contrast, the Spanish strain showed progressive acclimation to the experimental conditions, with no significant difference in growth between treatments. Increase in total MAAs followed linearly the cumulative UVB of the preceding day, and both total and primary MAAs were maintained at higher constitutive levels in this strain. Acclimation to enhanced UVB in the diatom resulted in an increase in PSII activity and reduction in nonphotochemical quenching, indicating an increased resistance to photoinhibition after a few weeks. All four species showed increased phytoplankton light absorption under enhanced UVB. Large intrastrain differences suggest a need to consider more closely intraspecific variability in UV studies.     

Establishment of <Emphasis Type="Italic">Psyllaephagus parvus</Emphasis> and <Emphasis Type="Italic">P. perplexans</Emphasis> as serendipitous biological control agents of Eucalyptus psyllids in southern California

The free-living lemon gum psyllid, Cryptoneossa triangula Taylor, and the lerp-forming spotted gum psyllid, Eucalyptolyma maideni Froggatt (Hemiptera: Psyllidae) are invasive pests of eucalypts in California. In 2007, Psyllaephagus parvus Riek (Hymenoptera: Encyrtidae) was discovered parasitizing spotted gum psyllids and Psyllaephagus perplexans Cockerell was collected from lemon gum psyllids. While neither parasitoid species was purposely introduced, presence of the parasitoids was significantly associated with reduced intensity and duration of population peaks for both psyllid species. Spring peaks were reduced more than fall peaks. We estimated minimum rates of parasitism from the ratio of mummies to live nymphs. Higher parasitism was recorded in coastal than inland locations during the spring, while parasitism was similar for coastal and inland populations in the fall. Logistic regression models suggest parasitoids were the determining factor of psyllid population densities, although physical parameters, such as irrigation, may affect psyllid or parasitoid populations.     

Genetic differentiation between eastern populations and recent introductions of potato psyllid (Bactericera cockerelli) into western North America

Although tomato psyllid, Bactericera cockerelli (Sulc) (Homoptera, Psyllidae), annually causes significant losses in potato and tomato crops in eastern Mexico and the central United States, infestations in western North America have been historically rare. However, substantial populations appeared in 2001 in western North America and caused losses in tomato production exceeding 80%; losses in 2004 reached 50%. To determine if these new outbreaks were the result of a simple range expansion or the evolution of a new B. cockerelli biotype, inter simple sequence repeat (ISSR) markers, as well as mitochondrial gene cytochrome oxidase I (COI), internal transcribed spacer 2 (ITS2), and wsp sequence data were used to characterize populations of the psyllid. Western populations from Baja, Mexico, Orange County, and Ventura County were compared with populations from central USA (Colorado and Nebraska) and eastern Mexico (Coahuila). Based on ISSR markers, the psyllid populations clustered into two groups, with one group including populations from western North America and the other group including populations from central USA and eastern Mexico. For COI comparisons, there was one base‐pair difference found in the 544 bp‐long COI fragments, but the populations again segregated along the same geographic lines. Two strains of Wolbachia were identified, the maximal differences between wsp clones from all populations was 5 bp for strain Bac1 and 23 bp for strain Bac2 out of a 555‐bp fragment. The ISSR data, therefore, were consistent in indicating the development of a new psyllid biotype that has adapted to western North America rather than a simple range expansion, but the other genetic data sets were less conclusive.     

Comparing the response of Antarctic,tropical and temperate microalgae to ultraviolet radiation (UVR) stress

The response of Antarctic, tropical and temperate microalgae of similar taxonomic grouping to ultraviolet radiation (UVR) stress was compared based on their growth and fatty acid profiles. Microalgae of similar taxa from the Antarctic (Chlamydomonas UMACC 229, Chlorella UMACC 237 and Navicula UMACC 231), tropical (Chlamydomonas augustae UMACC 246, Chlorella vulgaris UMACC 001 and Amphiprora UMACC 259) and temperate (Chlamydomonas augustae UMACC 247, Chlorella vulgaris UMACC 248 and Navicula incerta UMACC 249) regions were exposed to different UVR conditions. The cultures were exposed to the following conditions: PAR (42 μmol photons m⁻² s⁻¹), PAR + UVA (854 μW cm⁻²) and PAR + UVA + UVB (117 μW cm⁻²). The cultures were subjected to UVA doses of 46.1, 92.2 and 184.4 J cm⁻² and UVB doses of 6.3, 12.6 and 25.2 J cm⁻² by varying the duration of their exposure (1.5, 3 and 6 h) to UVR during the light period (12:12 h light-dark cycle). UVA did not affect the growth of the microalgae, even at the highest dose. In contrast, growth was adversely affected by UVB, especially at the highest dose. The dose that caused 50% inhibition (ID₅₀) in growth was used to assess the sensitivity of the microalgae to UVB. Sensitivity of the microalgae to UVB was species-dependent and also dependent on their biogeographic origin. Of the nine microalgae, the Antarctic Chlorella was most tolerant to UVB stress (ID₅₀ = 21.0 J cm⁻²). Except for this Chlorella, the percentage of polyunsaturated fatty acids of the microalgae decreased in response to high doses of UVB. Fatty acid profile is a useful biomarker for UVB stress for some microalgae. Presented at the 6th Meeting of the Asian Pacific Society of Applied Phycology, Manila, Philippines.     

Population genetic diversity of the clonal self‐incompatible herbaceous plant Linaria vulgaris along an urbanization gradient

How increasing urbanization affects biodiversity is one of the most understudied aspects of global change biology. It is, however, known that it may negatively affect plant population genetic diversity in numerous ways, for example through its negative effects on plant population size, between‐population connectivity, and reproductive success. Therefore, it is important to investigate to what extent different levels of urbanization result in these negative phenomena. Here we used microsatellite markers to investigate urbanization effects on the population genetic structure of 23 populations of the self‐incompatible, partially clonal herb Linaria vulgaris which were sampled across a gradient of urbanization. Clonal diversity as measured by the Pareto‐parameter varied between 1.11 and 2.97 and was negatively correlated to both the degree of urbanization and to population size. Urbanization and population size were not interrelated. The least clonally rich populations also experienced significantly reduced seed set. Irrespective of the degree of urbanization, L. vulgaris populations exhibited strong genetic differentiation (F_ST = 0.33) and there was no significant correlation between genetic and geographic distances, suggesting low gene flow among populations. In conclusion, we showed that urbanization negatively affected fitness of L. vulgaris populations through decreasing their clonal diversity and reproductive success, an effect that may be exacerbated by the low gene flow between populations. Although the effect was modest, the results could probably be extrapolated to bigger cities where it would be considerably more pronounced.     

Life cycle regulation in the heather psyllid Strophingia ericae : responses to temperature and photoperiod

Abstract .The response of overwintering nymphs of Strophingia ericae (Curtis) (Homoptera: Psylloidea) to long and short photoperiods over a range of temperatures was investigated to determine the interaction between these factors and winter development as a regulatory mechanism of their life cycle. Strophingia ericae was successfully reared from egg to adult in a long photoperiod (LD 18:6 h) at 10, 15 and 20°C on its host plant Calluna vulgaris. Although development time was longer at 10 than at 15 or 20°C (≈ 263 days compared with ≈ 155 and ≈ 159 days, respectively), there was no interruption in development at any of these temperatures, indicating that there was no obligatory diapause. However, short photoperiod (LD 12:12 h) inhibited development of overwintering fifth instars collected from the field in early winter. Those collected in September and kept at 15°C developed to adult in ≈ 120 days in a short photoperiod (LD 12:12 h) compared with ≈ 40 days in a long photoperiod (LD 18:6 h). Inhibition became weaker in December and disappeared by January, when fifth instars developed to adult at the same rate in both long and short photoperiods (≈ 30 days). A similar photoperiodic response was observed when the experiment was repeated at 10°C, although development times were consistently longer. The observation that insects collected from the field in early winter were able to resume development immediately on transfer to favourable conditions (15°C and LD 18:6 h photocycle) suggests that there is a photoperiodically induced quiescence (rather than a true diapause) in overwintering S. ericae, which becomes progressively reduced as winter proceeds. It was concluded that the life cycle of the upland and possibly the lowland form of S. ericae is regulated by a winter-active photoperiodic inhibition of development, which effectively synchronizes the emergence of the adult stage with higher spring temperatures and renewed host plant growth.     

The influence of the host plant on the population dynamics of Acizzia russellae (Homoptera: Psyllidae)

Abstract. 1. The role of the host plant, Acacia karroo , in the population dynamics of the indigenous non-pest psyllid, Acizzia russellae , was investigated.
2. Population levels of A.russellae in early summer were almost 10 times greater on the regenerative foliage of pruned trees (cut back in spring) than on normal trees. During late summer and winter, populations declined far more slowly on pruned trees, so that very much higher numbers of psyllids were maintained on these trees through to the next spring. This finding, and others, suggest that natural enemies and climate are not major determinants in the population dynamics of this insect under normal conditions in the field.
3. Laboratory measurements of several chemical and physical characteristics of the foliage of pruned and normal trees did not reveal any differences which would account for the observed effects.
4. Measurements of organic nitrogen concentrations in the leaves of normal A. karroo trees in the field showed significant correlations between psyllid numbers and leaf nitrogen, but only during summer in November and January.
5. Psyllid performance in the laboratory (duration of life cycle, egg production, and dry weight of emergent females) was significantly better for psyllids reared on plants containing high amino nitrogen.
6. It is suggested that the availability of quantities of suitably high quality nutrients in the leaves of pruned A. karroo trees explains the "epidemic" population levels achieved by the psyllid on pruned plants. It seems that characteristics of the host plant impose the major limitation on psyllid population growth, which may explain the permanent low endemic population levels of this insect in the field.     

Thymus vulgaris alleviates UVB irradiation induced skin damage via inhibition of MAPK/AP‐1 and activation of Nrf2‐ARE antioxidant system

Solar ultraviolet (UV) radiation‐induced reactive oxidative species is mainly responsible for the development of photoageing. Rosmarinic acid was one of the main bioactive components detected in Thymus vulgaris (TV) we extracted. In this study, UVB‐induced skin damages have been shown to be ameliorated by treatment with TV in hairless mice (HR‐1) skin, demonstrated by decreased matrix metalloproteinases (MMPs) and increased collagen production. However, the underlying molecular mechanism on which TV acted was unclear. We examined the photoprotective effects of TV against UVB and elucidated the molecular mechanism in normal human dermal fibroblasts. Thymus vulgaris remarkably prevented the UVB‐induced reactive oxygen species and lactate dehydrogenase. Dose‐dependent increase in glutathione, NAD(P)H: quinone oxidoreductase1 and heme oxygenase‐1, by TV was confirmed by increased nuclear accumulation of Nrf2. Furthermore, 5‐Methoxyindole‐2‐carboxylic acid was introduced as a specific inhibitor of dihydrolipoyl dehydrogenase (DLD). We demonstrated that Nrf2 expression was regulated by DLD, which was a tricarboxylic acid cycle‐associated protein that decreased after UVB exposure. Besides, TV significantly diminished UVB induced phosphorylation of mitogen activated protein kinases pathway, containing extracellular signal‐regulated kinase, Jun N‐terminal kinase and p38, which consequently reduced phosphorylated c‐fos and c‐jun. Our results suggest that TV is a potential botanical agent for use against UV radiation‐induced oxidative stress mediated skin damages.     

Assessment of the efficiency of different control programs to reduce Trioza apicalis Först. (Triozidae: Hemiptera) feeding damage and the spread of “Candidatus Liberibacter solanacearum” on carrots (Daucus carota ssp. sativus L.)

The control of carrot psyllid Trioza apicalis Förster largely relies on chemical measures, and the current integrated pest management (IPM) strategy is based on pest scouting. The number of active ingredients available for psyllid control will further decline in the coming years. The need for alternative control measures is therefore urgent. In this work the efficiency of different control programs including a kaolin particle film and plant-derived, crude saponin extract, chemical control, insect net and IPM (kaolin in combination with insecticides) programs to reduce psyllid feeding damage, reproduction and the spread of “Candidatus Liberibacter solanacearum” (CLso) in carrots was studied. Each year in 2016–2018, four replicates of each treatment were randomised in a row-column design on a commercial carrot farm. After the treatments were executed, the psyllid nymphs and eggs were counted. At the harvest, the carrot roots and shoots were weighed, damages assessed, and samples were taken for CLso detection from 50 plants at each replicate. Kaolin treatment alone and in combination with insecticides effectively reduced the number of psyllid nymphs and eggs in all the years studied. Saponin was applied only on the first year, since it significantly increased the number of T. apicalis eggs compared to other treatments. The insect net was superior to other treatments in all the studied aspects in all the years. Under normal weather conditions, the highest root weight was harvested under the insect net, followed by the chemical control program consisting of pyrethroids, kaolin treatment, untreated control and saponin treatment. During extreme weather conditions, chemical control programs were not effective at protecting the carrots from psyllid feeding, which was reflected as low root yield. In all years, the carrot leaf damage percent negatively correlated with the root weight. Similarly, the shoot:root ratio increased as the leaf-curling percentage rose, which was even pronounced under drought stress. The effect of climatic stress should be considered when developing IPM strategies.     

UVB radiation and 17‐hydroxygeranyllinalool diterpene glycosides provide durable resistance against mirid (Tupiocoris notatus) attack in field‐grown Nicotiana attenuata plants

Depending on geographical location, plants are exposed to variable amounts of UVB radiation and herbivore attack. Because the role(s) of UVB in the priming and/or accumulation of plant defence metabolites against herbivores are not well understood, we used field‐grown Nicotiana attenuata plants to explore the effects of UVB on herbivore performance. Consistent with previous reports, UVB‐exposed plants accumulated higher levels of ultraviolet (UV)‐absorbing compounds (rutin, chlorogenic acid, crypto‐chlorogenic acid and dicaffeoylspermidine). Furthermore, UVB increased the accumulation of jasmonic acid, jasmonoyl‐L‐isoleucine and abscisic acid, all phytohormones which regulate plant defence against biotic and abiotic stress. In herbivore bioassays, N. attenuata plants experimentally protected from UVB were more infested by mirids in three consecutive field seasons. Among defence metabolites measured, 17‐hydroxygeranyllinalool diterpene glycosides (HGL‐DTGs) showed strongly altered accumulation patterns. While constitutive HGL‐DTGs levels were higher under UVB, N. attenuata plants exposed to mirid bugs (Tupiocoris notatus) had still more HGL‐DTGs under UVB, and mirids preferred to feed on HGL‐DTGs‐silenced plants when other UVB protecting factors were eliminated by UVB filters. We conclude that UVB exposure not only stimulates UV protective screens but also affects plant defence mechanisms, such as HGL‐DTGs accumulation, and modulates ecological interactions of N. attenuata with its herbivores in nature.     

Effects of Heterogeneous Competitor Distribution and Ramet Aggregation on the Growth and Size Structure of a Clonal Plant

Spatially heterogeneous distribution of interspecific competitors and intraspecific aggregation of offspring ramets may affect the growth and size structure of clonal plant populations, but these have been rarely studied. We conducted a greenhouse experiment in which we grew a population of eight offspring ramets (plants) of the stoloniferous clonal plant Hydrocotyle vulgaris aggregately or segregately in two homogeneous treatments with or without a competing grass Festuca elata and a heterogeneous treatment with a patchy distribution of the grass. In patchy grass treatments, H. vulgaris produced markedly more biomass, ramets and stolons in open patches (without grasses) than in grass patches, but displayed lower size variations as measured by coefficient of variation of biomass, ramets and stolons among the eight plants. In open areas, H. vulgaris produced statistically the same amounts of biomass and even more stolons and showed higher size variations in patchy grass treatments than in open (no grass) treatments. In grass areas, H. vulgaris grew much worse and displayed higher size variations in patchy grass treatments than in full grass treatments. Ramet aggregation decreased the growth of H. vulgaris in open treatments and in both open and grass patches in patchy grass treatments, but had little effect in full grass treatments. Ramet aggregation had little effect on size variations. Therefore, heterogeneous distribution of competitors can affect the growth and size structure of clonal plant populations, and ramet aggregation may decrease population growth when they grow in open environments or heterogeneous environments with a patchy distribution of interspecific competitors.     

Effects of Temperature and Photorepair Radiation on a Marine Ciliate Exposed to UVB Radiation

The influences of intensity and repeated exposure to ultraviolet‐B radiation (UVB), photoreactivating repair radiation (PRR), and temperature on the scuticociliate Parauronema acutum were explored under laboratory conditions. Population growth was negatively affected after exposure to the equivalent of one sunny summer day of ambient UVB, especially in the absence of PRR. Repeated daily exposure to UVB severely compromised ciliate survival. UVB‐exposed treatments without PRR recovered slower and reached lower final abundances than treatments receiving PRR. Reducing the daily UVB exposure approximately 25% improved ciliate recovery after exposure. In the single exposure treatments, temperature effects were not consistent, except that growth was slowest for control and treatments at the lowest temperature (15 °C). These data suggest that dark repair and/or photoprotection are present in P. acutum, but photoenzymatic repair was the more effective mechanism in reversing UVB damage. Repeated exposure treatments without PRR had zero or declining growth at all temperatures (15, 20 and 25 °C), as did those with PRR at 15 °C. Significant temperature/dose differences were identified in the repeated exposure treatments; ciliates subjected to the higher UVB intensity with PRR survived only at 25 °C, while ciliate populations under reduced UVB increased at 20 and 25 °C.     

Heather-feeding psyllids of the genus Strophingia (Homoptera)

Multivariate analysis of morphological characters suggests that the genus Strophingia comprises eight distinct species, namely ericae (Curtis) [the type-species], australis sp.n., fallax Log., cinereae Hod., proxima sp.n., hispanica Hod. & Hollis, harteni sp.n., and arborea Log. Each species is fully characterized and an identification key is provided. A tentative phylogeny of the groups is proposed. Among the newly described species, australis (host plant: Erica australis) occurs in Portugal, proxima (host plant: Erica arborea and possibly Calluna vulgaris) is found throughout the Iberian peninsula, while harteni (host plant: Erica azorica) is found on the Azores.     

Effects of different temperature regimes on survival of Diaphorina citri and its endosymbiotic bacterial communities

The Asian citrus psyllid, Diaphorina citri, is a major pest of citrus and vector of citrus greening (huanglongbing) in Asian. In our field‐collected psyllid samples, we discovered that Fuzhou (China) and Faisalabad (Pakistan), populations harbored an obligate primary endosymbiont Candidatus Carsonella (gen. nov.) with a single species, Candidatus Carsonella ruddii (sp. nov.) and a secondary endosymbiont, Wolbachia surface proteins (WSP) which are intracellular endosymbionts residing in the bacteriomes. Responses of these symbionts to different temperatures were examined and their host survival assessed. Diagnostic PCR assays showed that the endosymbionts infection rates were not significantly reduced in both D. citri populations after 24 h exposure to cold or heat treatments. Although quantitative PCR assays showed significant reduction of WSP relative densities at 40°C for 24 h, a substantial decrease occurred as the exposure duration increased beyond 3 days. Under the same temperature regimes, Ca. C. ruddii density was initially less affected during the first exposure day, but rapidly reduced at 3–5 days compared to WSP. However, the mortality of the psyllids increased rapidly as exposure time to heat treatment increased. The responses of the two symbionts to unfavorable temperature regimes highlight the complex host‐symbionts interactions between D. citri and its associated endosymbionts.     

In vitro interactions between ectomycorrhizal fungi and ericaceous plants

In view of the close association between ericaceous shrubs and ectomycorrhizal trees in forest ecosystems, the interaction between ectomycorrhizal basidiomycetes and the hair roots of four typical ericoid mycorrhizal hosts was investigated in vitro. Seedlings of Vaccinium myrtillus, V. vitis-idaea, V. macrocarpon and Calluna vulgaris were inoculated with each of four ectomycorrhizal basidiomycetes from different phylogenetic groups (Laccaria bicolor, Lactarius musteus, Suillus variegatus and Tomentellopsis submollis) in a low carbon and nutrient agar-cellophane culture system. Two ericoid mycorrhizal Helotiales ascomycetes (Meliniomyces bicolor in the Rhizoscyphus ericae aggregate and a mycobiont out of the Rhizoscyphus ericae aggregate) were included for comparison. Interactions between fungi and hair roots ranged from neutral to surface attachment, and the formation of intracellular hyphal coils. Root and shoot responses to inoculation were different between the host/fungus combinations. The ectomycorrhizal fungus L. bicolor formed extensive intracellular colonization, spreading cell-to-cell with multiple hyphal entry points and intracellular hyphal coils with single entry points in C. vulgaris and V. macrocarpon epidermal cells respectively, however, no significant effects on plant growth were detected. Meliniomyces bicolor formed intracellular hyphal coils in the epidermal cells of V. myrtillus and V. macrocarpon but not the other host spp. The M. bicolor isolate stimulate V. myrtillus root length about 2.5 times. Interestingly, although the unknown ascomycete strain out of the Rhizoscyphus ericae aggregate formed intracellular hyphal coils in epidermal cells of all host plants, it suppressed the growth of C. vulgaris, V. myrtillus, and V. vitis-idaea but not to V. macrocarpon. Further and more detailed experimentation under more ecological realistic conditions for a longer period of time is needed.     

Solar ultraviolet-B radiation affects plant-insect interactions in a natural ecosystem of Tierra del Fuego (southern Argentina)

We examined the effects of solar ultraviolet-B radiation (UVB) on plant-herbivore interactions in native ecosystems of the Tierra del Fuego National Park (southern Argentina), an area of the globe that is frequently under the Antarctic “ozone hole” in early spring. We found that filtering out solar UVB from the sunlight received by naturally-occurring plants of Gunnera magellanica, a creeping perennial herb, significantly increased the number of leaf lesions caused by chewing insects. Field surveys suggested that early-season herbivory was principally due to the activity of moth larvae (Lepidoptera: Noctuidae). Manipulative field experiments showed that exposure to solar UVB changes the attractiveness of G. magellanica leaf tissue to natural grazers. In a laboratory experiment, locally caught moth caterpillars tended to eat more tissue from leaves grown without UVB than from leaves exposed to natural UVB during development; however, the difference between treatments was not significant. Leaves grown under solar UVB had slightly higher N levels than leaves not exposed to UVB; no differences between UVB treatments in specific leaf mass, relative water content, and total methanol-soluble phenolics were detected. Our results show that insect herbivory in a natural ecosystem is influenced by solar UVB, and that this influence could not be predicted from crude measurements of leaf physical and chemical characteristics and a common laboratory bioassay. Received: 4 December 1997 / Accepted: 12 May 1998     

Effects of UVB Radiation on the Initial Stages of Growth of Gigartina Skottsbergii, Sarcothalia Crispata and Mazzaella Laminarioides (Gigartinales, Rhodophyta)

The effects of UVB radiation on the growth of macroalgal thalli were evaluated using tetrasporophytic fronds of the Rhodophytes Gigartina skottsbergii, Sarcothalia crispata and Mazzaella laminarioides. The tetrasporophytic fronds were collected from nature and the tetrasporophyte sporelings grown in a temperature regulated chamber at 8 ± 2 ^∘C with a 12L:12D (Light: Dark) photoperiod, Photosynthetically Active Radiation (PAR) of 55 μmol photons m⁻² s⁻¹ and seawater enriched with 20 mL L⁻¹ of Provasoli medium. We exposed the thalli of these macroalgae to PAR (55 μmol photons m⁻² s⁻¹) and three treatments using a combination of PAR with three different levels of UVB radiation (0.10, 0.15 and 0.23 W m⁻² for G. skottsbergii and S. crispata and 0.02, 0.05 and 0.10 W m⁻² for M. laminarioides) during a period of 71 days. Growth of thalli was quantified by measuring their length using digitized photographs of samples.Important differences were detected in the growth of individuals cultured under the effects of UVB radiation, when compared to the control (i.e. plants exposed to PAR only). In the case of G. skottsbergii and S. crispata higher levels of UVB radiation resulted in slower growth of thalli. In nearly all measurements for the first two species, UVB radiation levels of 0.1 W m⁻² induced differences in thallus growth, while for M. laminarioides levels of UVB radiation of 0.1 W m⁻² were effective only after a prolonged period of exposure.Differential effects of UVB radiation on G. skottsbergii, S. crispata and M. laminarioides could interfere with the natural populations of these economically important macroalgal species in southern Chile, where they occur under the annual influence of the Antarctic Ozone Hole and the general thinning of the ozone layer.     

Effects of temperature on phenological synchrony and altitudinal distribution of jumping plant lice (Hemiptera: Psylloidea) on dwarf willow (Salix lapponum) in Norway

Summary.

• 1 The geographical distributions of three species of jumping plant lice (psyllids) along an altitudinal transect (988–1300 m a.s.l.) in southern Norway were restricted within the range of their host plant Salix lapponum. One species, Cacopsylla propinqua, occurred at all sampling locations between 988 and 1222 m, whereas C.palmeni was confined to higher altitudes (1153–1222 m) and C.brunneipennis was more abundant at lower altitudes (988–1101 m).
• 2 C.brunneipennis and C.palmeni developed only on female catkins. Development times of catkins and psyllids were similar (approximately 50 days) and successful psyllid development depended on close phenological synchrony with catkins.
• 3 Thermal requirements for development of female catkins were greater at low altitude (988 m) compared with higher altitude (1222 m), showing local adaptation of S.lapponum to altitude. In general, thermal requirements of psyllids were less than those of catkins at the same location. C.brunneipennis had higher thermal requirements than C.palmeni.
• 4 Field experiments, using polythene enclosures to elevate temperatures at two sites at different altitudes (by 0.6–1.4 deg. C), showed that insects had an enhanced relative rate of development under elevated temperatures compared with their host plants.
• 5 Indices of phenological synchrony were calculated from thermal requirements of psyllids and catkins. Under elevated temperatures, phenological synchrony decreased at both sites. This resulted in the subsequent development of smaller adult insects at low altitude, although at higher altitude, insects developing under elevated temperatures were larger and had a higher survival rate compared with controls.
• 6 Effects of temperature on phenological synchrony may explain the limits to the geographical range of psyllids. The consequences of climate change on psyllid populations will depend on the effects of decreased phenological synchrony on insect development and this may differ within the insect's geographical range.

     

The effects of population and thermal acclimation on the growth,condition and cold responsive mRNA expression of age-0 lake sturgeon (Acipenser fulvescens)

In Manitoba, Canada, wild lake sturgeon (Acipenser fulvescens) populations exist along a latitudinal gradient and are reared in hatcheries to bolster threatened populations. We reared two populations of lake sturgeon, one from each of the northern and southern ends of Manitoba and examined the effects of typical hatchery temperatures (16°C) as well as 60-day acclimation to elevated rearing temperatures (20°C) on mortality, growth and condition throughout early development. Additionally, we examined the cold shock response, which may be induced during stocking, through the hepatic mRNA expression of genes involved in the response to cold stress and homeoviscous adaptation (HSP70, HSP90a, HSP90b, CIRP and SCD). Sturgeon were sampled after 1 day and 1 week following stocking into temperatures of 8, 6 and 4°C in a controlled laboratory environment. The southern population showed lower condition and higher mortality during early life than the northern population while increased rearing temperature impacted the growth and condition of developing northern sturgeon. During the cold shock, HSP70 and HSP90a mRNA expression increased in all sturgeon treatments as stocking temperature decreased, with higher expression observed in the southern population. Expression of HSP90b, CIRP and SCD increased as stocking temperature decreased in northern sturgeon with early acclimation to 20°C. Correlation analyses indicated the strongest molecular relationships were in the expression of HSP90b, CIRP and SCD, across all treatments, with a correlation between HSP90b and body condition in northern sturgeon with early acclimation to 20°C. Together, these observations highlight the importance of population and rearing environment throughout early development and on later cellular responses induced by cold stocking temperatures.