Damage and recovery from UV-B exposure in conidia of the entomopathogens Verticillium lecanii and Aphanocladium album

We evaluated the effects of exposure to doses supplied at an environmentally realistic intensity of UV-B radiation (800 mW m(-2) weighted irradiance) on the culturability and germination of selected strains of the entomopathogenic Hyphomycetes Verticillium lecanii and Aphanocladium album. Increased UV-B exposure decreased relative percent culturability for all strains. Four hours of exposure to UV-B were sufficient to reduce the culturability close to zero. The LT(50) (50% lethal time) ranged from 120 ± 5 min for the V. lecanii strain ARSEF 6430 to 86 ± 14 min for the A. album strain ARSEF 6433. A strong delay in the germination of surviving conidia was observed. To determine the occurrence of photoreactivation in these two genera, we evaluated the effect of exposure to visible light after exposure to UV-B radiation. There was no significant difference in relative culturability between conidia exposed to visible light after UV-B exposure compared to those incubated in the dark after UV-B exposure. This indicates that photoreactivation, if it occurs, must have limited importance in the repair of the damage induced by UV-B radiation in these two genera.     

Variability in conidial thermotolerance of Metarhizium anisopliae isolates from different geographic origins

Notable variability in thermotolerance was found among conidia of 16 isolates of the insect-pathogenic fungi Metarhizium anisopliae var. anisopliae and one M. anisopliae var. acridum isolated from latitudes 61 degrees N to 54 degrees S. Conidial suspensions were exposed to 40 or 45 degrees C for 2, 4, 8, and 12 h. Most of the isolates tolerated 40 degrees C very well, with relative germination (germination relative to unheated controls) above 90% after 12 h of exposure. Exceptions were three isolates originating from high latitude, viz., ARSEF 2038 (38 degrees N, South Korea), 4295 (54.4 degrees S, Australia), and 5626 (61.2 degrees N, Finland) that had approximately 80% germination. High variability, however, was observed among isolates at 45 degrees C; viz., after 2 h exposure, relative germination was above 80% for six isolates, between 50 and 70% for three isolates, and between 0 and 30% for eight isolates. After 8 and 12 h at 45 degrees C, only two M. anisopliae isolates pathogenic to grasshoppers, viz., ARSEF 324 (latitude 19 degrees S, Australia) and 3609 (15 degrees N, Thailand), had high relative germination (91.6 and 79.4%, respectively, for 8 h exposures; and 90 and 47.1%, respectively, for 12 h). These isolates also were the most tolerant to UV-B radiation [J. Invertebr. Pathol. 78 (2001) 98-108]. The median lethal dose (LD50) for isolate ARSEF 324 was 49.4 and 47.9 degrees C, for 2 and 4 h of exposures, respectively. Exposure of conidia to wet-heat greatly delayed germination of some isolates. In general, isolates from higher latitudes demonstrated greater heat susceptibility than isolates from nearer the equator. Dry conidia tolerated 50 degrees C better than 45 degrees C in aqueous suspension.     

Enzyme activities associated with oxidative stress in Metarhizium anisopliae during germination, mycelial growth, and conidiation and in response to near-UV irradiation

Metarhizium anisopliae isolates have a wide insect host range, but an impediment to their commercial use as a biocontrol agent of above-ground insects is the high susceptibility of spores to the near-UV present in solar irradiation. To understand stress responses in M. anisopliae, we initiated studies of enzymes that protect against oxidative stress in two strains selected because their spores differed in sensitivity to UV-B. Spores of the more near-UV resistant strain in M. anisopliae 324 displayed different isozyme profiles for catalase-peroxidase, glutathione reductase, and superoxide dismutase when compared with the less resistant strain 2575. A transient loss in activity of catalase-peroxidase and glutathione reductase was observed during germination of the spores, whereas the intensity of isozymes displaying superoxide dismutase did not change as the mycelium developed. Isozyme composition for catalase-peroxidases and glutathione reductase in germlings changed with growth phase. UV-B exposure from lamps reduced the activity of isozymes displaying catalase-peroxidase and glutathione reductase activities in 2575 more than in 324. The major effect of solar UV-A plus UV-B also was a reduction in catalase-peroxidases isozyme level, a finding confirmed by measurement of catalase specific activity. Impaired growth of M. anisopliae after near-UV exposure may be related to reduced abilities to handle oxidative stress.     

Effects of UV-A (320 to 399 Nanometers) on Grazing Pressure of a Marine Heterotrophic Nanoflagellate on Strains of the Unicellular Cyanobacteria Synechococcus spp

In the open ocean, where turbidity is very low, UV radiation may be an important factor regulating interactions among planktonic microorganisms. The effect of exposure to UV radiation on grazing by a commonly isolated marine heterotrophic nanoflagellate, Paraphysomonas bandaiensis, on two strains of the cyanobacteria Synechococcus spp. was investigated. Laboratory cultures were exposed to a range of irradiances of artificially produced UV-B (290 to 319 nm) and UV-A (320 to 399 nm) for up to 10 h. At a UV-B irradiance of 0.19 W m, but not 0.12 W m, grazing mortality of Synechococcus spp. and nanoflagellate-specific grazing rates were reduced compared to mortality and grazing rates with UV-A treatment. Within 6 h of exposure, UV-A alone suppressed grazing mortality at irradiances as low as 3.02 W m. The extent to which grazing mortality and nanoflagellate-specific grazing rates were suppressed by UV-A increased with both irradiance and duration of exposure. Over a 6-h exposure period, differences in grazing mortality were largely attributable to differential survival of nanoflagellates. Over a longer period of exposure, there was impairment by UV-A alone of nanoflagellate-specific grazing rates. Rates of primary productivity of Synechococcus spp. were also reduced by UV-A. The extent to which Synechococcus productivity was reduced, compared to the reduction in Synechococcus grazing mortality, depended on the duration of UV-A exposure. These results support the hypothesis that UV-A alone influences the composition and biomass of marine microbial communities by affecting predator-prey interactions and primary production.     

Variations in UV-B tolerance and germination speed of Metarhizium anisopliae conidia produced on insects and artificial substrates

Solar ultraviolet radiation (UV-A and UV-B) is a major factor in failure of programs using the insect pathogenic fungus Metarhizium anisopliae as a biological control agent. Studies were conducted to determine if growth conditions, viz. artificial (agar media or rice grain) or natural (infected insects) substrates for conidial production affect two traits that directly influence performance of conidia after field application: tolerance to UV-B radiation and conidial germination speed. Conidia of two isolates (ARSEF 23 and ARSEF 2575) of M. anisopliae var. anisopliae produced on potato dextrose agar plus yeast extract (PDAY) or on fungus-killed larvae of two insect species, Galleria mellonella and Zophobas morio, were inactivated by exposure to UV-B radiation. Conidia of both isolates when produced on insect cadavers were significantly more sensitive to UV-B radiation than conidia produced on PDAY. Also, conidia from insect cadavers germinated slower than those from PDAY cultures. A comparison of conidia from artificial substrates showed that conidia produced on Czapek's and Emerson's YpSs agar media or rice grains had higher tolerance to UV-B radiation and germinated faster than conidia raised on PDA and PDAY. Accordingly, the growth substrate and nutritional environment in which conidia are produced influences M. anisopliae conidial UV-B tolerance and speed of germination; and manipulation of these variables could be used to obtain conidia with increased tolerance to UV-B radiation and shorter germination times.     

Inhibition of photosynthetic activity by UV-B radiation in radish seedlings

Inhibition of primary photosynthetic reactions by UV-B radiation (280 nm-320 nm) was demonstrated in radish leaves ( Raphanus sativus cv. Saxa Treib). Detached radish cotyledons from 10-day-old seedlings were irradiated with continuous white light and increasing UV-B irradiances using cut-off filters with increasing transmission for shorter wavelengths (WG 360, WG 345, WG 320, WG 305, WG 295, WG 280). Photosynthetic activity measured in terms of chlorophyll fluorescence induction (Kautsky effect) after 2, 4, 6, 8 and 24 h irradiation decreased in a wavelength dependent way with increasing UV-B irradiance and irradiation time.
Radish seedlings grown for 10 days from the time of germination under the same UV-B irradiation conditions exhibited similar reductions of the variable fluorescence as detached cotyledons irradiated for short time periods. They additionally had lower initial fluorescence at high UV-B radiation levels, although the chlorophyll content per leaf area increased. In contrast to short term experiments, the plastoquinone and flavonoid content increased with increasing UV-B irradiance when based on leaf area.     

Variability in susceptibility to simulated sunlight of conidia among isolates of entomopathogenic Hyphomycetes

The influence of simulated sunlight on survival of conidia of 4 species of entomopathogenic Hyphomycetes was investigated. Conidia from 65 isolates ofBeauveria bassiana, 23 ofMetarhizium anisopliae, 14 ofMetarhizium flavoviride and 33 isolates ofPaecilomyces fumosoroseus were irradiated by artificial sunlight (295 to 1,100 nm at an ultraviolet-B irradiance of 0.3 W m^–2) for 0, 1, 2, 4 and 8 h. Survival was estimated by comparing the number of colony forming units (CFU) produced by conidia exposed to irradiation to the number of CFUs produced by an unexposed control. Survival decreased with increased exposure to simulated sunlight; exposure for 2 h or more was detrimental to all isolates tested. Overall, isolates ofM. flavoviride were the most resistant to irradiation followed byB. bassiana andM. anisopliae. Conidia ofP. fumosoroseus were most susceptible. In addition to the large interspecies differences in susceptibility to irradiation, there was also an intraspecies variation indicating that strain selection to irradiation tolerance may be important in the development of microbial control agents where increased persistence in an insolated environment is desirable.Abbreviations CFU Colony forming units - UV-B ultraviolet radiation-B     

UV-B辐射对植物花粉萌发率和花粉管生长的累积效应

研究了19种植物花粉在不同UV－B辐射强度和辐照时间下其萌发率和花粉管伸长的变化,结果表明,UV－B辐射增加显著抑制大多数植物花粉的萌发率和花粉管生长;与对照相比,较高强度的UV－B对花粉的抑制作用大于较低强度;几个种的花粉萌发率及花粉管生长对UV－B增强不敏感,甚至被UV－B辐射所促进;辐射时间越长,对花粉抑制作用愈大,说明具有辐射累积效应,由此可知,植物花粉的萌发过程对UV－B的敏感性变化在自然条件下将会产生严重的生态学后果。     

Effects of UV-A (320 to 399 Nanometers) on Grazing Pressure of a Marine Heterotrophic Nanoflagellate on Strains of the Unicellular Cyanobacteria Synechococcus spp.

In the open ocean, where turbidity is very low, UV radiation may be an important factor regulating interactions among planktonic microorganisms. The effect of exposure to UV radiation on grazing by a commonly isolated marine heterotrophic nanoflagellate, Paraphysomonas bandaiensis, on two strains of the cyanobacteria Synechococcus spp. was investigated. Laboratory cultures were exposed to a range of irradiances of artificially produced UV-B (290 to 319 nm) and UV-A (320 to 399 nm) for up to 10 h. At a UV-B irradiance of 0.19 W m⁻², but not 0.12 W m⁻², grazing mortality of Synechococcus spp. and nanoflagellate-specific grazing rates were reduced compared to mortality and grazing rates with UV-A treatment. Within 6 h of exposure, UV-A alone suppressed grazing mortality at irradiances as low as 3.02 W m⁻². The extent to which grazing mortality and nanoflagellate-specific grazing rates were suppressed by UV-A increased with both irradiance and duration of exposure. Over a 6-h exposure period, differences in grazing mortality were largely attributable to differential survival of nanoflagellates. Over a longer period of exposure, there was impairment by UV-A alone of nanoflagellate-specific grazing rates. Rates of primary productivity of Synechococcus spp. were also reduced by UV-A. The extent to which Synechococcus productivity was reduced, compared to the reduction in Synechococcus grazing mortality, depended on the duration of UV-A exposure. These results support the hypothesis that UV-A alone influences the composition and biomass of marine microbial communities by affecting predator-prey interactions and primary production.     

Cold activity and tolerance of the entomopathogenic fungus Tolypocladium spp. to UV-B irradiation and heat

Studies on the stress resistance of insect-pathogenic fungi are very important to better understand the survival of these organisms in the environment. In this study, we examined the cold activity (8 ± 1 °C for 7 days), UV-B tolerance (Quaite-weighted UV-B irradiance at 847.90 mW m⁻² for 1, 2, 3, and 4 h), and wet-heat tolerance (45 °C for 1, 2, 3, and 4 h) of two isolates of Tolypocladiumcylindrosporum (ARSEF 3392 and 5558), one isolate of Tolypocladium geodes (ARSEF 3275), and two isolates of Tolypocladium inflatum (ARSEF 4772 and 4877) based on their germination, compared with Metarhizium robertsii (ARSEF 2575). After 3 h of UV-B exposure, T. cylindrosporum germinated at a greater rate than the other Tolypocladium species and had similar viability to that of the M. robertsii. Most Tolypocladium isolates, however, were less UV-B tolerant than M. robertsii. The T.cylindrosporum isolates were also the most thermotolerant, with similar tolerance to the M. robertsii. The isolates of T. inflatum and T. geodes, which had similar heat tolerance, were the least heat tolerant compared with the isolates of T. cylindrosporum and M. robertsii. After 4 h of heat exposure, the germination of T. inflatum and T. geodes isolates was not significantly different. For cold activity, both T.cylindrosporum isolates germinated to ca. 100% in only 3 days. Approximately 50% of the two T. inflatum isolates germinated, and less than 5% of T. geodes germinated after 3 days. All fungal isolates, however, completely germinated by the seventh day, except M.robertsii. The isolates of T. cylindrosporum, therefore, were the most heat and UV-B tolerant, and had the highest cold activity compared to the other species. The tolerance of M. robertsii to UV-B radiation and heat was similar to that of T.cylindrosporum.     

Influence of growth environment on tolerance to UV-B radiation, germination speed, and morphology of Metarhizium anisopliae var. acridum conidia

We previously reported wide variability in UV-B tolerance among different Metarhizium anisopliae isolates [Braga, G.U.L., Flint, S.D., Miller, C.D., Anderson, A.J., Roberts, D.W., 2001a. Variability in response to UV-B among species and strains of Metarhizium isolated from sites at latitudes from 61 degrees N to 54 degrees S. J. Invertebr. Pathol. 78, 98-108] as well as wide phenotypic variability in some of these isolates in response to alterations in their growth environments [Rangel, D.E.N., Braga, G.U.L., Flint, S.D., Anderson, A.J., Roberts, D.W., 2004. Variations in UV-B tolerance and germination speed of M. anisopliae conidia produced on artificial and natural substrates. J. Invertebr. Pathol. 87, 77-83]. Studies on other biological systems have demonstrated that strong selective pressure for tolerance to a stress factor may reduce the phenotypic variability of this trait. In the present study, conidia of the isolate most tolerant to radiation and heat, ARSEF 324, presented very little phenotypic variability in UV-B tolerance in response to production on either artificial culture medium or infected insects. The phenotypic plasticities in two other traits (conidial morphology and germination speed), however, were considerably higher.     

Effect of Temperature on Germination, Radial Growth and Virulence of Metarhizium anisopliae and Beauveria bassiana on Megalurothrips sjostedti

The effect of temperature on germination, radial growth and pathogenic activity of two strains of Beauveria bassiana and four strains of Metarhizium anisopliae on the legume flower thrips, Megalurothrips sjostedti , was studied in the laboratory. Germination, radial growth and pathogenic activity was low for all strains at 15 C. Optimum temperature for germination, radial growth and pathogenic activity ranged between 25-30 C. The fastest growing strain at 25-30 C was M. anisopliae strain ICIPE 69. Compared to other strains, ICIPE 69 also appeared to have a broad temperature range of pathogenic activity against the pest. The significance of these findings in relation to control of M. sjostedti is discussed.     

Do panther chameleons bask to regulate endogenous vitamin D3 production?

Basking by ectothermic vertebrates is thought to have evolved for thermoregulation. However, another beneficial effect of sunlight exposure, specifically the ultraviolet B (UV-B) component, includes endogenous production of vitamin D(3). In the laboratory, panther chameleons exhibited a positive phototaxis to greater visible, ultraviolet A (UV-A) and UV-B light. However, with equivalent high irradiances of UV-A or UV-B, their response to UV-B was significantly greater than it was to UV-A. Exposure of in vitro skin patches of panther chameleons to high UV-B (90 microW/cm(2)) for 1 h significantly enhanced vitamin D(3) concentration. Voluntary exposure to higher UV-B irradiance (70 vs. 1 microW/cm(2)) resulted in greater circulating 25-hydroxyvitamin D(3) in female panther chameleons (604 vs. 92 ng/mL). Depending on dietary intake of vitamin D(3), chameleons adjusted their exposure time to UV-B irradiation as if regulating their endogenous production of this vital hormone. When dietary intake was low (1-3 IU/g), they exposed themselves to significantly more UV-producing light; when intake was high (9-129 IU/g), they exposed themselves to less. Vitamin D(3) photoregulation seems to be an important additional component of the function of basking.     

Evaluation of the different levels of variability in the underwater light field of a shallow estuary

The underwater light climate of a shallow estuary located at the southern coast of the Baltic Sea has been investigated, with special emphasis on the spectral irradiance composition and on short-term irradiance fluctuations caused by vertical mixing and wave focussing. The inherent optical properties of the water body were dominated by phytoplankton pigment absorption in the long-wavelength range and by coloured, dissolved organic matter (cDOM) absorption in the wavelength range <500 nm, including ultraviolet-A (UV-A) and ultraviolet-B radiation (UV-B). Pronounced particulate scattering combined with the absorption values to give very high attenuation coefficients, especially for the shorter wavelengths of UV-B radiation. Photosynthetically active radiation (PAR) was found to be reduced to 1% of the surface value within 0.8 m in the inner, hypertrophic end of the estuary and within 1.9 m in the outer, eutrophic parts of this system, with corresponding 1% penetration depths for UV-B of 0.13 and 0.31 m. During late winter and early spring, the period when reduced atmospheric ozone concentrations and enhanced UV-B have been reported over northern Europe, the irradiance levels in the water column were greatly reduced, due to strong attenuation by ice cover and overlying snow. cDOM concentration of the water was also found to remain at a high level during these periods, and indeed throughout the year, thus reducing the exposure of organisms to UV-R and PAR still further. A complex irradiance regime was found in this system, with irregular and high amplitude fluctuations caused by wind-induced vertical mixing and wave focussing being superimposed upon the solar-angle-dependent seasonal and daily cycles. The methods used to quantify the short-term fluctuations are described, and their relevance to phytoplankton physiology is discussed. The wave-focussing effect is unique to the aquatic environment, and measurements showed that average subsurface irradiances could be increased by up to 5 times for periods lasting for <1 s. The highest irradiances recorded during wave-focussing events reached over 9,000 μmol photons m^–2 s^–1. Received in revised form: 7 April 2000 Electronic Publication     

Impact of ultraviolet radiation on cell structure, UV-absorbing compounds, photosynthesis, DNA damage, and germination in zoospores of Arctic Saccorhiza dermatodea

Stratospheric ozone depletion leads to enhanced UV-B radiation. Therefore, the capacity of reproductive cells to cope with different spectral irradiance was investigated in the laboratory. Zoospores of the upper sublittoral kelp Saccorhiza dermatodea were exposed to varying fluence of spectral irradiance consisting of photosynthetically active radiation (PAR, 400-700 nm; =P), PAR+UV-A radiation (UV-A, 320-400 nm; =PA), and PAR+UV-A+UV-B radiation (UV-B, 280-320 nm; =PAB). Structural changes, localization of phlorotannin-containing physodes, accumulation of UV-absorbing phlorotannins, and physiological responses of zoospores were measured after exposure treatments as well as after 2-6 d recovery in dim white light (8 mumol photon m(-2) s(-1)). Physodes increased in size under PAB treatment. Extrusion of phlorotannins into the medium and accumulation of physodes was induced not only under UVR treatment but also under PAR. UV-B radiation caused photodestruction indicated by a loss of pigmentation. Photosynthetic efficiency of spores was photoinhibited after 8 h exposure to 22 and 30 mumol photon m(-2) s(-1) of PAR, while supplement of UVR had a significant additional effect on photoinhibition. A relatively low recovery of photosystem II function was observed after 2 d recovery in spores exposed to 1.7 x 10(4) J m(-2) of UV-B, with a germination rate of only 49% of P treatment after 6 d recovery. The amount of UV-B-induced DNA damage measured as cyclobutane-pyrimidine dimers (CPDs) increased with the biologically effective UV-B dose (BED(DNA)). Significant removal of CPDs indicating repair of DNA damage was observed after 2 d in low white light. The protective function of phlorotannins has restricted efficiency for a single cell. Within a plume of zoospores, however, each cell can buffer each other and protect the lower layer of spores from excessive radiation. Exudation of phlorotannins into the water can also reduce the impact of UV-B radiation on UV-sensitive spores. The results of this study showed that the impact of UVR on reproductive cells can be mitigated by protective and repair mechanisms.     

Exposure to low irradiances favors the synthesis of 9-cis beta, beta-carotene in Dunaliella salina (Teod.)

We examined the effect of irradiance on the synthesis of beta-carotene and its isomers by Dunaliella salina. Growth irradiance had a marked effect both on growth of the alga (which was suppressed at both low and high irradiances) and on the accumulation of beta-carotene. The accumulation of beta-carotene but not alpha-carotene was closely linked to an increase in irradiance. Growth at low irradiances (20-50 micromol m(-2) s(-1)) promoted a high ratio of 9-cis to all-trans beta-carotene (>2:1), while exposure to high irradiances (200-1,250 micromol m(-2) s(-1)) resulted in a large reduction in this ratio (to <0.45:1). A similar pattern was seen for the geometric isomers of alpha-carotene, with exposure to low irradiance favoring the accumulation of the 9-cis form. The carotenoid biosynthesis inhibitors 4-chloro-5(methylamino)-2-(alpha-alpha-alpha-trifluoro-m-tolyl)-3-(sH )-pyridazinone and 2-(4-chlorophenylthio)triethylamine caused the accumulation of the precursors phytoene and lycopene, respectively, in D. salina. High-performance liquid chromatography and infrared analysis showed that phytoene adopted the 15-cis and all-trans forms (as in higher plants), and that lycopene primarily adopted the all-trans form. This indicates that isomerization of beta-carotene takes place during or after cyclization.     

Diverse responses to UV-B radiation and repair mechanisms of bacteria isolated from high-altitude aquatic environments

Acinetobacter johnsonii A2 isolated from the natural community of Laguna Azul (Andean Mountains at 4,560 m above sea level), Serratia marcescens MF42, Pseudomonas sp. strain MF8 isolated from the planktonic community, and Cytophaga sp. strain MF7 isolated from the benthic community from Laguna Pozuelos (Andean Puna at 3,600 m above sea level) were subjected to UV-B (3,931 J m-2) irradiation. In addition, a marine Pseudomonas putida strain, 2IDINH, and a second Acinetobacter johnsonii strain, ATCC 17909, were used as external controls. Resistance to UV-B and kinetic rates of light-dependent (UV-A [315 to 400 nm] and cool white light [400 to 700 nm]) and -independent reactivation following exposure were determined by measuring the survival (expressed as CFU) and accumulation of cyclobutane pyrimidine dimers (CPD). Significant differences in survival after UV-B irradiation were observed: Acinetobacter johnsonii A2, 48%; Acinetobacter johnsonii ATCC 17909, 20%; Pseudomonas sp. strain MF8, 40%; marine Pseudomonas putida strain 2IDINH, 12%; Cytophaga sp. strain MF7, 20%; and Serratia marcescens, 21%. Most bacteria exhibited little DNA damage (between 40 and 80 CPD/Mb), except for the benthic isolate Cytophaga sp. strain MF7 (400 CPD/Mb) and Acinetobacter johnsonii ATCC 17909 (160 CPD/Mb). The recovery strategies through dark and light repair were different in all strains. The most efficient in recovering were both Acinetobacter johnsonii A2 and Cytophaga sp. strain MF7; Serratia marcescens MF42 showed intermediate recovery, and in both Pseudomonas strains, recovery was essentially zero. The UV-B responses and recovery abilities of the different bacteria were consistent with the irradiation levels in their native environment.     

Effects of UV-B radiation on Gelidium floridanum (Rhodophyta, Gelidiales): germination of tetraspores and early sporeling development

The increased incidence of UV-B radiation, particularly in southern South America, has sparked more interest in its effects on marine organisms. Here we describe the effects of UV-B on the early life stages of Gelidium floridanum, an agar-producing species abundant on rocky coasts in southern Brazil. Treated samples were submitted to 0.12 W?m^?2 of artificial UV-B radiation for 2 h per day over a 15-day period. UV-B exposure induced impairment of tetraspore germination and germling development. We observed a delay in germination, a reduced growth rate of tetrasporelings, and morphological changes, such as a different length-to-width ratio, twisted thallus, loss of pigmentation, and differentiation of more than one apical cell, all leading to a different growth pattern in sporelings that survived treatment. Results indicated a great susceptibility of early-developing Gelidium to UV-B, even at low irradiance and short exposure time.     

In vivo study on combined toxicity of Metarhizium anisopliae (Deuteromycotina: Hyphomycetes) strain ESC-1 with sublethal doses of chlorpyrifos, propetamphos, and cyfluthrin against German cockroach (Dictyoptera: Blattellidae)

The effect of Metarhizium anisopliae (Metschnikoff) Sorokin strain ESC-1 alone and in combination with sublethal doses of commercial formulations of chlorpyrifos, propetamphos and cyfluthrin on mortality of CSMA strain of German cockroach, Blattella germanica (L.), was determined by conducting in vivo studies that included 3 bioassays. Spores of M. anisopliae cultured on SDAY media had germination of >90%. Based on bioassay 1, doses ranging from 0.5 to 300 ppm of chlorpyrifos and propetamphos, and 0.05 to 40 ppm of cyfluthrin were selected for bioassays 2 and 3. Cockroach mortality ranged from 5 to 20% for insecticides alone and 48 to 70% for insecticides + M. anisopliae in bioassay 2. In bioassay 3, mortality ranged from 15 to 60% for insecticides and 57.5 to 92.5% for insecticides + M. anisopliae. Percentage of cockroach mortality resulting from insecticide + M. anisopliae combinations was significantly higher than insecticide alone. Mortality was also significantly higher in certain insecticide + M. anisopliae combinations than M. anisopliae alone. There was no significant interaction between M. anisopliae and insecticides with their concentrations in bioassay 2, indicating an additive effect. But in bioassay 3, a significant interaction was observed when M. anisopliae was combined with multiple insecticide concentrations. The interaction indicated an additive effect for chlorpyrifos and cyfluthrin, and a synergistic effect for propetamphos. There were significant differences in LT50 among various treatment combinations. M. anisopliae alone or insecticide + M. anisopliae combinations did not affect body weight in treated German cockroaches.     

感染松墨天牛的金龟子绿僵菌菌株的初步筛选

松墨天牛是松材线虫病的主要媒介昆虫,本文对分离自松墨天牛的6株金龟子绿僵菌,以及从光肩星天牛、大蜡螟、伊藤厚丝角叶蜂和土蝽上分离的各1个菌株,共10个菌株的产孢情况、孢子萌发率进行研究;在此基础上选出金龟子绿僵菌1291、1349和2049三个菌株及球孢白僵菌F-263菌株,采用成虫跗节接种法和幼虫浸渍法进行室内松墨天牛及大蜡螟的毒力测定比较。结果表明,供试绿僵菌菌株对松墨天牛幼虫在接种15天后的感染僵虫率为76.9％～93.1％(1×10⁷孢子/mL);成虫在接种20天后的僵虫率亦达57.9％～75.0％(6.5×10⁵～3.4×10⁶孢子/成虫);2049菌株表现尤其突出;对应的球孢白僵菌F-263对幼虫和成虫的僵虫率分别是96.3％(1×10⁷孢子/mL)和55％(9.7×10⁵孢子/成虫)。但这3个金龟子绿僵菌菌株对大蜡螟的毒力较低,存在较明显的寄主专化性。这3个菌株今后在防治松墨天牛方面具有较大开发应用价值。