Effects of high-temperature stress and heat shock on two root maggots, Bradysia odoriphaga and Bradysia difformis (Diptera: Sciaridae)

Bradysia odoriphaga and B. difformis (Diptera: Sciaridae) are devastating pests of vegetables, ornamentals and edible mushrooms. In Chinese chive fields, the two Bradysia species occur with similar regularities: outbreaks in spring and autumn, and population decreases in summer. Temperature may be an important factor restricting their population abundance in summer. Here, we performed a life-table study under constant high temperatures and assessed the tolerance of two Bradysia species to heat shock. Life parameters of the Bradysia species indicated slow developmental rates, and low survival rates and fecundity, when the temperature was higher than 30 °C. At 34 °C, individuals were unable to reach the adult stages from eggs. Moreover, temperatures above 36 °C showed lethal effects, decreasing their survival rates. The median lethal time (LT50) values of 4th instar B. odoriphaga and B. difformis larvae were 46.82 and 32.97 h, respectively, while the values at 38 °C were 2.12 and 1.51 h, respectively. The 4th instar larvae and pupae possessed higher thermotolerance levels than adults and eggs, indicating sensitivities to heat stress. Moreover, B. odoriphaga was more thermotolerant than B. difformis. Thus, weak thermotolerance levels may restrict their occurrences during the period of summer heat, and the difference in thermotolerance levels between the two species may be related to their regional distributions.     

DNA barcoding of Bradysia (Diptera: Sciaridae) for detection of the immature stages on agricultural crops

We investigated the usefulness of mitochondrial cytochrome c oxidase (COI) DNA barcoding of the genus Bradysia for the detection of immature stages and cryptic species complex. Although the larvae of some species in this genus are agricultural pests, immature stages are rarely identified due to the lack of key morphological characteristics. We constructed partial sequences of the COI gene for 25 species of Bradysia as a first step towards a DNA barcode. Using these data, Bradysia impatiens, B. procera and B. peraffinis were identified from larval specimens collected, respectively, from paprika, ginseng and oak sawdust beds used for cultivating shiitake. Our findings reveal a complex of three species within the B. tilicola group. These species were all identified as important pest B. ocellaris based on the morphology of male genital structures; however, the interspecific genetic divergence of the COI region was significantly greater (16.1–19.4%) than the intraspecific variation in each species. Therefore, B. ocellaris may consist of at least three species. The results demonstrate that COI DNA barcodes are useful for Bradysia species identification.     

Effects of short-term heat stress on the growth and development of Bradysia cellarum and Bradysia impatiens

Bradysia cellarum Frey and Bradysia impatiens Johansen are major pests of vegetable crops, as well as edible mushrooms and ornamental plants, and damage to hosts resulting in economic losses. Temperatures above the optimum levels for these pests have been predicted to regulate their population growth during summer. The aim of the present study was to examine the effects of both heat stress and exposure time on the growth and development of eggs, larvae and pupae for two Bradysia species. The egg stage, egg hatching rate, 4th instar larval stage, pupation rate, pupal stage and adult emergence rate were observed after exposing at high temperatures of 34°C, 37°C and 40°C for 1, 2, 4 and 6 hr. The results showed that 34°C, 37°C and 40°C for 1-, 2-, 4- and 6-hr exposure treatments prolonged the developmental stage of egg, 4th instar larva and pupa, while decreasing the egg hatching rate, pupation rate and adult emergence rate. This suggests that increasing temperature or prolonging exposure time to the heat stress could significantly affect insect survival, growth and development. Our study could provide an ecological basis for pests’ management strategy by using short-term heat stress.     

Effects of elevated water temperature on physiological responses in adult freshwater mussels

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Pest species of a fungus gnat genus Bradysia Winnertz (Diptera: Sciaridae) injuring agricultural and forestry products in Japan,with a review on taxonomy of allied species

Agricultural and forestry pest species of the Bradysia tilicola group from Japan were revised taxonomically after examination of the type specimens. A sciarid pest of Welsh onion occurred from northern Saitama, Japan since 2014 and later from south‐eastern Gunma, Japan, was identified as B. odoriphaga Yang & Zhang, 1985, sp. rev. It was removed from synonymy of B. cellarum Frey, 1948, being the first record of the species from Japan. Bradysia agrestis Sasakawa, 1978, was assigned to be a junior synonym of B. impatiens (Johannsen, 1912). Bradysia paupera Tuomikoski, 1960, sp. rev. , was removed from synonymy of B. impatiens and was recognized as a distinct species. We also compiled their host plants and fungi hitherto reported from Japan. Bradysia impatiens was here recorded from an indoor facility of cloud ear fungus, Auricularia polytricha (Montagne) Sacc., for the first time. At least 19 cultural crops belonging to 12 plant and fungal families were reported as actual and potential hosts of B. impatiens. We suggested that B. impatiens and B. paupera might have been confused in studies of mushroom production in Japan. Further survey of distribution of B. paupera in Japan needs to be done.     

Temperature × light interaction and tolerance of high water temperature in the planktonic freshwater flagellates Cryptomonas (Cryptophyceae) and Dinobryon (Chrysophyceae)

Using microcosm experiments, we investigated the interactive effects of temperature and light on specific growth rates of three species each of the phytoplanktonic genera Cryptomonas and Dinobryon. Several species of these genera play important roles in the food web of lakes and seem to be sensitive to high water temperature. We measured growth rates at three to four photon flux densities ranging from 10 to 240 μmol photon · m^?2 · s^?1 and at 4–5 temperatures ranging from 10°C to 28°C. The temperature × light interaction was generally strong, species specific, and also genus specific. Five of the six species studied tolerated 25°C when light availability was high; however, low light reduced tolerance of high temperatures. Growth rates of all six species were unaffected by temperature in the 10°C–15°C range at light levels ≤50 μmol photon · m^?2 · s^?1. At high light, growth rates of Cryptomonas spp. increased with temperature until the temperature optimum was reached and then declined. The Dinobryon species were less sensitive than Cryptomonas spp. to photon flux densities of 40 μmol photon · m^?2 · s^?1 and 200 μmol photon · m^?2 · s^?1 over the entire temperature range but did not grow under a combination of very low light (10 μmol photon · m^?2 · s^?1) and high temperature (≥20°C). Among the three Cryptomonas species, cell volume declined with temperature and the maximum temperature tolerated was negatively related to cell size. Since Cryptomonas is important food for microzooplankton, these trends may affect the pelagic carbon flow if lake warming continues.     

Molecular marker to identify the fungus gnat, <Emphasis Type="Italic">Bradysia</Emphasis> sp. (Diptera: Sciaridae), a new pest of Welsh onion and carrot in Japan

A new pest of Welsh onion and carrot, the dark-winged fungus gnat, Bradysia sp., was found in the northern region of Saitama Prefecture, Japan. DNA sequences of mitochondrial cytochrome c oxidase subunit I revealed that Bradysia sp. is identical to the Chinese chive gnat, Bradysia odoriphaga Yang and Zhang. This suggests that Bradysia sp. may be an invasive species that originates from continental East Asia. Direct sequencing analysis and PCR using a species-specific primer were found to be useful tools for discriminating Bradysia sp. from other native Japanese fungus gnats, such as Bradysia impatiens (Johannsen), Pnyxia scabiei (Hopkins), and Lycoriella ingenua (Dufour).     

Evaluation of Staphylococcus aureus DNA aptamer by enzyme‐linked aptamer assay and isothermal titration calorimetry

To monitor the specificity of Staphylococcus aureus aptamer (SA‐31) against its target cell, we used enzyme‐linked aptamer assay. In the presence of target cell, horseradish peroxidase–conjugated streptavidin bound to biotin‐labeled SA‐31 showed specific binding to S   aureus among 3 different bacteria with limit of detection of 10³ colony‐forming unit per milliliter. The apparent K _a was 1.39 μM⁻¹ ± 0.3 μM⁻¹. The binding of SA‐31 to membrane proteins extracted from cell surface was characterized using isothermal titration calorimetry, and the effect of changes in binding temperature and salt concentrations of binding buffer was evaluated based on thermodynamic parameters (K _a, ΔH , and ΔG ). Since binding of aptamer to its targets solely depends on its 3‐dimensional structure under experimental conditions used in selection process, the change in temperature and ion concentration changed the affinity of SA‐31 to its target on surface of bacteria. At 4°C, SA‐31 did not show an affinity to its target with poor heat change upon injection of membrane fraction to aptamer solution. However, the apparent association constants of SA‐31 slightly varied from K _a = 1.56 μM⁻¹ ± 0.69 μM⁻¹ at 25°C to K _a = 1.03 μM⁻¹ ± 0.9 μM⁻¹ at 37°C. At spontaneously occurring exothermic binding reactions, affinities of S  aureus aptamer to its target were also 9.44 μM⁻¹ ± 0.38 μM⁻¹ at 50mM, 1.60 μM⁻¹ ± 0.11 μM⁻¹ at 137mM, and 3.28 μM⁻¹ ± 0.46 μM⁻¹ at 200 mM of salt concentration. In this study, it was demonstrated that enzyme‐linked aptamer assay and isothermal titration calorimetry were useful tools for studying the fundamental binding mechanism between a DNA aptamer and its target on the outer surface of S  aureus .     

Surprising lack of sensitivity of biochemical limitation of photosynthesis of nine tree species to open‐air experimental warming and reduced rainfall in a southern boreal forest

Photosynthetic biochemical limitation parameters (i.e., V_cmax, J_max and J_max:V_cmax ratio) are sensitive to temperature and water availability, but whether these parameters in cold climate species at biome ecotones are positively or negatively influenced by projected changes in global temperature and water availability remains uncertain. Prior exploration of this question has largely involved greenhouse based short‐term manipulative studies with mixed results in terms of direction and magnitude of responses. To address this question in a more realistic context, we examined the effects of increased temperature and rainfall reduction on the biochemical limitations of photosynthesis using a long‐term chamber‐less manipulative experiment located in northern Minnesota, USA. Nine tree species from the boreal‐temperate ecotone were grown in natural neighborhoods under ambient and elevated (+3.4°C) growing season temperatures and ambient or reduced (≈40% of rainfall removed) summer rainfall. Apparent rubisco carboxylation and RuBP regeneration standardized to 25°C (V_cmax25°C and J_max25°C, respectively) were estimated based on AC_i curves measured in situ over three growing seasons. Our primary objective was to test whether species would downregulate V_cmax25°C and J_max25°C in response to warming and reduced rainfall, with such responses expected to be greatest in species with the coldest and most humid native ranges, respectively. These hypotheses were not supported, as there were no overall main treatment effects on V_cmax25°C or J_max25°C (p > .14). However, J_max:V_cmax ratio decreased significantly with warming (p = .0178), whereas interactions between warming and rainfall reduction on the J_max25°C to V_cmax25°C ratio were not significant. The insensitivity of photosynthetic parameters to warming contrasts with many prior studies done under larger temperature differentials and often fixed daytime temperatures. In sum, plants growing in relatively realistic conditions under naturally varying temperatures and soil moisture levels were remarkably insensitive in terms of their J_max25°C and V_cmax25°C when grown at elevated temperatures, reduced rainfall, or both combined.     

Recent CO2 rise has modified the sensitivity of tropical tree growth to rainfall and temperature

Atmospheric CO₂ (c_a) rise changes the physiology and possibly growth of tropical trees, but these effects are likely modified by climate. Such c_a × climate interactions importantly drive CO₂ fertilization effects of tropical forests predicted by global vegetation models, but have not been tested empirically. Here we use tree‐ring analyses to quantify how c_a rise has shifted the sensitivity of tree stem growth to annual fluctuations in rainfall and temperature. We hypothesized that c_a rise reduces drought sensitivity and increases temperature sensitivity of growth, by reducing transpiration and increasing leaf temperature. These responses were expected for cooler sites. At warmer sites, c_a rise may cause leaf temperatures to frequently exceed the optimum for photosynthesis, and thus induce increased drought sensitivity and stronger negative effects of temperature. We tested these hypotheses using measurements of 5,318 annual rings from 129 trees of the widely distributed (sub‐)tropical tree species, Toona ciliata. We studied growth responses during 1950–2014, a period during which c_a rose by 28%. Tree‐ring data were obtained from two cooler (mean annual temperature: 20.5–20.7°C) and two warmer (23.5–24.8°C) sites. We tested c_a × climate interactions, using mixed‐effect models of ring‐width measurements. Our statistical models revealed several significant and robust c_a × climate interactions. At cooler sites (and seasons), c_a × climate interactions showed good agreement with hypothesized growth responses of reduced drought sensitivity and increased temperature sensitivity. At warmer sites, drought sensitivity increased with increasing c_a, as predicted, and hot years caused stronger growth reduction at high c_a. Overall, c_a rise has significantly modified sensitivity of Toona stem growth to climatic variation, but these changes depended on mean climate. Our study suggests that effects of c_a rise on tropical tree growth may be more complex and less stimulatory than commonly assumed and require a better representation in global vegetation models.     

Isolation of polymorphic microsatellite loci in the clear lake gnat and two other phantom midge species of the genus Chaoborus (Diptera: Chaoboridae)

Chaoborus is of great interest to many freshwater ecologists. The adults can become pests in certain areas in North America and the larvae are an important food source for fish. In this preliminary study, we identified variable microsatellite loci in three species: Chaoborus astictopus (H_E = 0.52–0.76), Chaoborus americanus (H_E = 0.46–0.80) and Chaoborus punctipennis (H_E = 0.66–0.81). Using a biotin/streptavidin capture technique of repetitive sequences in a 96‐well format, we obtained microsatellite‐enriched genomic libraries for all three species and identified six polymorphic microsatellite markers for each species. None of the primers did yield a polymerase chain reaction fragment in a cross‐species test.     

Effect of temperature on immature development and longevity of two introduced opiine parasitoids on Bactrocera invadens

Temperature‐dependent development, parasitism and longevity of the braconid parasitoids, Fopius arisanus Sonan and Diachasmimorpha longicaudata Ashmed on Bactorcera invadens Drew Tsuruta & White, was evaluated across five constant temperatures (15, 20, 25, 30 and 35°C). Developmental rate decreased linearly with increasing temperature for both the parasitoid species. Linear and Brière‐2 nonlinear models were used to determine the lower temperature threshold at which the developmental rate (1/D) approached zero. For F. arisanus, lower thresholds to complete development estimated with the linear and nonlinear models were 10.1 and 6.9°C, respectively. The total degree‐days (DD) required to complete the development estimated by the linear model for F. arisanus was 360. In D. longicaudata, the linear and nonlinear models estimated lower thresholds of 10.4 and 7.3°C, respectively, and the total DD estimated was 282. In F. arisanus, percentage parasitism differed significantly across all temperatures tested and was highest at 25°C (71.1 ± 2.5) and lowest at 15°C (46.4 ± 1.4). Parasitoid progeny sex ratio was female biased at all temperatures except at 20°C. In D. longicaudata, percentage parasitism was highest at 20°C (52.2 ± 4.0) and lowest at 15°C (27.7 ± 2.5). Parasitoid progeny sex ratio was female biased and similar for all temperatures. Adult longevity of both parasitoids was shortest at 35°C and longest at 15°C, and females lived significantly longer than males at all temperatures tested. Our findings provide some guidance for future mass rearing and field releases of the two parasitoids for the management of B. invadens in Africa.     

Multiple generation effects of high temperature on the development and fecundity of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) biotype B

Insects are ectotherms and their ability to resist temperature stress is limited. The immediate effects of sub‐lethal heat stress on insects are well documented, but longer‐term effects of such stresses are rarely reported. In this study, survival, development and reproduction of the whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) biotype B, were compared over five consecutive generations at 27, 31 and 35 °C and for one generation at 37 °C. Both temperature and generation significantly affected the fitness of the whitefly. These impacts were more dramatic with increasing generations and temperatures. Among the experimental temperatures, the most favorable for development and reproduction were 27 °C and 31 °C. At 27 °C, survival, development and fecundity were all stable over these five generations. At 31 °C, immature survival rate was the highest in the fifth generation, but female fecundities decreased in the fourth and fifth generations. At 35 °C, egg hatching rate, immature survival rate and female fecundity decreased significantly in the fourth and fifth generations. At 37 °C, survival of B. tabaci was not adversely affected, but female fecundity at 37 °C was less than 10% of that at 27 °C or 31 °C. These results demonstrate that the lethal high temperature for B. tabaci is over 37 °C, and the whitefly population continued expanding in the five generations at 35 °C. The ability of B. tabaci biotype B to survive high temperature stress will play an important role in its population extension under global warming.     

Morphological and functional seed traits of the wild medicinal plant Dioscorea strydomiana,the most threatened yam in the world

• Morphological and functional seed traits have important roles in characterising the species regeneration niche and help to understand the reproductive biology of rare and threatened plants, which can thus support appropriate plant conservation measures.
• Seed morphometric and dispersal kinetics of the critically endangered Dioscorea strydomiana were measured and compared with those of four other Dioscorea species, and seed germination response under constant temperatures (5–35 °C) was compared with that of the congeneric and widespread D. sylvatica.
• Seed mass of D. strydomiana (ca. 14 mg) was twice that of D. sylvatica, but similar to or smaller than the other species examined. Seeds of D. strydomiana have the lowest speed of descent and lowest variability in most of the morphological traits considered, suggesting lower phenotypic plasticity but higher variance in the wing‐loading value. Seeds of D. strydomiana reached maximum germination at 15 °C (ca. 47%), which decreased slightly to ca. 37% at 25 °C and was completely inhibited at 35 °C. D. sylvatica seeds started to germinate at 10 °C (ca. 3%), reached 75–80% germination at 15–20 °C and maximum (ca. 90%) at 25–30 °C. Base temperatures for germination (T_b) were 9.3 and 5.7 °C, for D. strydomiana and D. sylvatica, respectively. Due to the higher germination percentages of D. sylvatica, ceiling and optimum temperatures could also be modelled for this species, suggesting higher sensitivity to high temperature for seeds of D. strydomiana.
• The detected poor seed lot quality of D. strydomiana suggests difficulties in reproduction from seed, highlighting the need for further investigation and conservation actions for this threatened yam species.

     

The oatmeal nematode <Emphasis Type="Italic">Panagrellus redivivus</Emphasis> survives moderately low temperatures by freezing tolerance and cryoprotective dehydration

The cold tolerance abilities of only a few nematode species have been determined. This study shows that the oatmeal nematode, Panagrellus redivivus, has modest cold tolerance with a 50% survival temperature (S ₅₀) of −2.5°C after cooling at 0.5°C min⁻¹ and freezing for 1 h. It can survive low temperatures by freezing tolerance and cryoprotective dehydration; although freezing tolerance appears to be the dominant strategy. Freezing survival is enhanced by low temperature acclimation (7 days at 5°C), with the S ₅₀ being lowered by a small but significant amount (0.42°C). There is no cold shock or rapid cold hardening response under the conditions tested. Cryoprotective dehydration enhances the ability to survive freezing (the S ₅₀ is lowered by 0.55°C, compared to the control, after 4 h freezing at −1°C) and this effect is in addition to that produced by acclimation. Breeding from survivors of a freezing stress did not enhance the ability to survive freezing. The cold tolerance abilities of this nematode are modest, but sufficient to enable it to survive in the cold temperate environments it inhabits.     

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.     

Adaptation of soil microbial growth to temperature: Using a tropical elevation gradient to predict future changes

Terrestrial biogeochemical feedbacks to the climate are strongly modulated by the temperature response of soil microorganisms. Tropical forests, in particular, exert a major influence on global climate because they are the most productive terrestrial ecosystem. We used an elevation gradient across tropical forest in the Andes (a gradient of 20°C mean annual temperature, MAT), to test whether soil bacterial and fungal community growth responses are adapted to long‐term temperature differences. We evaluated the temperature dependency of soil bacterial and fungal growth using the leucine‐ and acetate‐incorporation methods, respectively, and determined indices for the temperature response of growth: Q₁₀ (temperature sensitivity over a given 10oC range) and T_min (the minimum temperature for growth). For both bacterial and fungal communities, increased MAT (decreased elevation) resulted in increases in Q₁₀ and T_min of growth. Across a MAT range from 6°C to 26°C, the Q₁₀ and T_min varied for bacterial growth (Q_10–20 = 2.4 to 3.5; T_min = ?8°C to ?1.5°C) and fungal growth (Q_10–20 = 2.6 to 3.6; T_min = ?6°C to ?1°C). Thus, bacteria and fungi did not differ significantly in their growth temperature responses with changes in MAT. Our findings indicate that across natural temperature gradients, each increase in MAT by 1°C results in increases in T_min of microbial growth by approximately 0.3°C and Q_10–20 by 0.05, consistent with long‐term temperature adaptation of soil microbial communities. A 2°C warming would increase microbial activity across a MAT gradient of 6°C to 26°C by 28% to 15%, respectively, and temperature adaptation of microbial communities would further increase activity by 1.2% to 0.3%. The impact of warming on microbial activity, and the related impact on soil carbon cycling, is thus greater in regions with lower MAT. These results can be used to predict future changes in the temperature response of microbial activity over different levels of warming and over large temperature ranges, extending to tropical regions.     

Effects of constant and fluctuating incubation temperatures on hatching success and hatchling traits in the diamondback terrapin (Malaclemys terrapin) in the context of the warming climate

As global temperatures continue to rise, so too will the nest temperatures of many species of turtles. Yet for most turtle species, including the estuarine diamondback terrapin (Malaclemys terrapin), there is limited information on embryonic sensitivity to elevated temperature. We incubated eggs of M. terrapin at three, mean temperatures (31, 34, 37 °C) under two thermal exposure regimes (constant or semi-naturally fluctuating temperature) and measured hatching success, developmental rate, and hatchling size. Hatching success was 100% at 31 °C and 67% at 34 °C, respectively; at 37 °C, all eggs failed early in the incubation period. These values were unaffected by exposure regime. The modeled LT₅₀ (temperature that was lethal to 50% of the test population) was 34.0 °C in the constant and 34.2 °C in the fluctuating thermal regime, reflecting a steep decline in survival between 33 and 35 °C. Hatchlings having been incubated at a constant 34 °C hatched sooner than those incubated at 31 °C under either constant or fluctuating temperature. Hatchlings were smaller in straight carapace length (CL) and width after having been incubated at 34 °C compared to 31 °C. Larger (CL) hatchlings resulted from fluctuating temperature conditions relative to constant temperature conditions, regardless of mean temperature. Based upon recent temperatures in natural nests, the M. terrapin population studied here appears to possess resiliency to several degrees of elevated mean nest temperatures, beyond which, embryonic mortality will likely sharply increase. When considered within the mosaic of challenges that Maryland's M. terrapin face as the climate warms, including ongoing habitat losses due to sea level rise and impending thermal impacts on bioenergetics and offspring sex ratios, a future increase in embryonic mortality could be a critical factor for a population already experiencing ecological and physiological challenges due to climate change.     

Comparative growth and metabolism of gelatinous colonies of three cyanobacteria,Nostoc commune,Nostoc pruniforme and Nostoc zetterstedtii,at different temperatures

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