Grazing-driven shifts in soil bacterial community structure and function in a typical steppe are mediated by additional N inputs.

Herbivore grazing and nitrogen (N) fertilization affect soil microbial diversity and community composition both in direct and indirect pathways (e.g., via alterations in soil microenvironment and plant communities); however, their combination effects are still largely unexplored. We carried out a field study to investigate how soil abiotic properties, plant community composition and functional traits altered soil bacterial community structure and function in response to a long-term herbivore grazing (17-year sheep grazing with four stocking rates) and anthropogenic N inputs (6-year N addition with four levels) experiment. We show that a high stocking rate of 8.7 sheep ha-1 (SR8.7) decreased soil bacterial α- and ß-diversity, while α- and ß-diversity showed hump-shaped and saddle-shaped responses, respectively, with increasing N addition rate, reaching tipping points at the N application rate of 10 g N m-2 year-1 (N10). The synergistic effects of grazing and N addition induced the highest soil bacterial α-diversity at SR2.7 with N10. The contrasting effects of grazing and N addition induced higher soil bacterial ß-diversity at SR8.7 with N20. Plant factors (e.g., aboveground biomass of Stipa bungeana and community-weighted mean carbon [CWM_C]), edaphic factors (e.g., soil moisture, pH, NO3--N, and C:nutrients ratios) and their interactions were the most significant factors affecting the diversity and community composition of bacteria. Our structure equation model (SEM) shows that grazing-induced negative effects on soil pH and plant community composition indirectly increased the ß-diversity of soil bacteria, while grazing-induced decreased CWM_C had positive effects on bacterial α-diversity and community structure. However, N addition indirectly increased ß-diversity of soil bacteria via changes in soil NO3--N and plant community composition, while N addition had negative impacts on bacterial α-diversity and community structure via variations in CWM_C. The interaction of grazing and N addition increased the complexity and stability of the bacterial network. Based on the KEGG database, grazing and N addition could accelerate the soil functional potential of C and N cycling. Our findings suggest that N application at a rate of <10 g N m-2 year-1 with a stocking rate of <5.3 sheep ha-1 could maintain the development of soil bacteria in supporting the most important ecosystem functions and services. Complex responses of soil microbes to grazing and N addition indicate the need for deeper investigations of the impacts of global change on microbial involvement in biogeochemical cycles.

UAV Assisted Livestock Distribution Monitoring and Quantification: A Low-Cost and High-Precision Solution.

Grazing management is one of the most widely practiced land uses globally. Quantifying the spatiotemporal distribution of livestock is critical for effective management of livestock-grassland grazing ecosystem. However, to date, there are few convincing solutions for livestock dynamic monitor and key parameters quantification under actual grazing situations. In this study, we proposed a pragmatic method for quantifying the grazing density (GD) and herding proximities (HP) based on unmanned aerial vehicles (UAVs). We further tested its feasibility at three typical household pastures on the Qinghai-Tibetan Plateau, China. We found that: (1) yak herds grazing followed a rotational grazing pattern spontaneously within the pastures, (2) Dispersion Index of yak herds varied as an M-shaped curve within one day, and it was the lowest in July and August, and (3) the average distance between the yak herd and the campsites in the cold season was significantly shorter than that in the warm season. In this study, we developed a method to characterize the dynamic GD and HP of yak herds precisely and effectively. This method is ideal for studying animal behavior and determining the correlation between the distribution of pastoral livestock and resource usability, delivering critical information for the development of grassland ecosystem and the implementation of sustainable grassland management.

Reproductive plasticity in response to the changing cluster size during the breeding period: a case study in a spider mite.

Animals living in clusters should adjust their reproductive strategies to adapt to the social environment. Theories predict that the benefits of cluster living would outweigh the costs of competition. Yet, it is largely unknown how animals optimize their reproductive fitness in response to the changing social environment during their breeding period. We used Tetranychus ludeni Zacher, a haplodiploid spider mite, to investigate how the ovipositing females modified their life-history traits in response to the change of cluster size (i.e., aggregation and dispersal) with a consistent population density (1 ♀/cm2). We demonstrate that (1) after females were shifted from a large cluster (16 ♀♀) to small ones (1 ♀, 5 and 10 ♀♀), they laid fewer and larger eggs with a higher female-biased sex ratio; (2) after females were shifted from small clusters to a large one, they laid fewer and smaller eggs, also with a higher female-biased sex ratio, and (3) increasing egg size significantly increased offspring sex ratio (% daughters), but did not increase immature survival. The results suggest that (1) females fertilize more larger eggs laid in a small population but lower the fertilization threshold and fertilize smaller eggs in a larger population, and (2) the reproductive adjustments in terms of egg number and size may contribute more to minimize the mate competition among sons but not to increase the number of inhabitants in the next generation. The current study provides evidence that spider mites can manipulate their reproductive output and adjust offspring sex ratio in response to dynamic social environments.

Male larval experience of cues from adult rivals alters lifetime sperm investment patterns in a sperm heteromorphic moth, Ephestia kuehniella.

Male animals may adjust their resource allocations for reproduction and other fitness functions in response to cues from rivals. For instance, adult males increase their investment in sperm for a higher paternity share when they perceive sperm competition risk in their surroundings. In nature, both juveniles and adults may coexist spatially and temporally. Yet, it is not clear how juvenile males of different ages respond to cues from adult rivals and fine-tune their lifetime investment in sperm production and ejaculation in any insect. Here we used the Mediterranean flour moth, Ephestia kuehniella, which produces both fertile eupyrene and infertile apyrene sperm, to explore this question. We demonstrate that the late, but not early, instar larvae are sensitive to adult male cues. As a response, they produce more sperm before emergence and their resultant adults have shorter mating latency and ejaculate more sperm in the first few matings. When the juvenile stage produces more eupyrenes, the adult stops making these sperm, but regardless of the number of apyrenes produced during the juvenile stage, the adult continues to make them. These findings suggest that the number of spermatogonia for eupyrenes may be limited and that for apyrenes may be flexible. Our results show that the insect does not trade off survival, mating frequency, body size, or testis size for sperm production in response to adult males during the larval stage. Knowledge created in the present study offers insight into the stage-dependent sensitivity of juvenile males to cues from adult rivals and subsequent lifetime resource allocations.

Temperature-dependent development and reproduction of Tarsonemus confusus (Acari: Tarsonemidae): an important pest mite of horticulture.

The tarsonemid mite Tarsonemus confusus Ewing has become an economically important pest in orchards in China. This study investigated the temperature-dependent development and reproduction of T. confusus at 15, 20, 25, 30, 33 and 35 °C. Eggs failed to hatch at 35 °C. When temperature increased from 15 to 30 °C, the developmental rate of eggs, larvae and quiescent larvae and that from egg to adulthood of both sexes significantly increased, and the time period required by females to commence oviposition significantly decreased. The lower temperature threshold (T0) for the development of eggs, larvae and quiescent larvae was between 9.3 and 12.0 °C and both sexes required about 60 degree days (DD) to complete a life cycle. Females were expected to start oviposition at 12.9 °C. The number of eggs laid, the number of female offspring produced and the egg hatch rate were significantly higher at 20, 25 and 30 °C than at 15 and 33 °C. Increasing temperature shortened the longevity of both sexes but increased the intrinsic rate of increase (rm) and finite capacity for increase (λ) with significantly shorter generation time (T) and doubling time (DT) within a temperature range of 15-30 °C. The net reproductive rate (R0) was highest at 25 °C. Results of this study may improve our knowledge of fundamental biology and ecology in genus Tarsonemus in general and in T. confusus in particular. Based on the local climate conditions, the applications of these results in predicting the seasonal population dynamics of T. confusus and timing the pest management are discussed.

Pathogenicity of Beauveria bassiana PfBb and Immune Responses of a Non-Target Host, Spodoptera frugiperda (Lepidoptera: Noctuidae).

Exploring the pathogenicity of a new fungus strain to non-target host pests can provide essential information on a large scale for potential application in pest control. In this study, we tested the pathogenicity of Beauveria bassiana PfBb on the important agricultural pest Spodoptera frugiperda (Lepidoptera: Noctuidae) by determining the relative activities of protective enzymes and detoxifying enzymes in different larval instars. Our results show that the B. bassiana PfBb strain could infect all six larval instars of S. frugiperda, and its virulence to S. frugiperda larvae gradually increased with an increase in spore concentration. Seven days after inoculation, the LC50 of B. bassiana PfBb was 7.7 × 105, 5.5 × 106, 2.2 × 107, 3.1 × 108, 9.6 × 108, and 2.5 × 1011 spores/mL for first to sixth instars of S. frugiperda, respectively, and the LC50 and LC90 of B. bassiana PfBb for each S. frugiperda instar decreased with infection time, indicating a significant dose effect. Furthermore, the virulence of B. bassiana PfBb to S. frugiperda larvae gradually decreased with an increase in larval instar. The activities of protective enzymes (i.e., catalase, peroxidase, and superoxide dismutase) and detoxifying enzymes (i.e., glutathione S-transferases, carboxylesterase, and cytochrome P450) in S. frugiperda larvae of the first three instars infected with B. bassiana PfBb changed significantly with infection time, but such variations were not obvious in the fifth and sixth instars. Additionally, after being infected with B. bassiana PfBb, the activities of protective enzymes and detoxification enzymes in S. frugiperda larvae usually lasted from 12 to 48 h, which was significantly longer than the control. These results indicate that the pathogenicity of B. bassiana PfBb on the non-target host S. frugiperda was significant but depended on the instar stage. Therefore, the findings of this study suggest that B. bassiana PfBb can be used as a bio-insecticide to control young larvae of S. frugiperda in an integrated pest management program.

A haplodiploid mite adjusts fecundity and sex ratio in response to density changes during the reproductive period.

Population density is one of the main socio-environmental factors that have critical impacts on reproduction of animals. Consequently, they need to adjust their reproductive strategies in response to changes of local population density. In this study we used a haplodiploid spider mite, Tetranychus ludeni Zacher (Acari: Tetranychidae), to test how population density dynamics during the reproductive period altered female reproductive performance. We demonstrate that females produced fewer eggs with a significantly higher female-biased sex ratio in dense populations. Reducing fecundity and increasing daughter production in a dense environment could be an advantageous strategy to minimise the intensity of local food competition. However, females also reduced their fecundity after arrival in a new site of larger area from a dense population, which may be associated with higher web production costs because females need to produce more webs to cover the larger area. There was no trade-off between egg number and size, and egg size had little impact on reproductive fitness. Therefore, T. ludeni females could adapt to the shift of population density during their reproductive period by manipulating the fecundity and offspring sex ratio but not the egg size.

An Improved Method for Monitoring Multiscale Plant Species Diversity of Alpine Grassland Using UAV: A Case Study in the Source Region of the Yellow River, China.

Plant species diversity (PSD) is essential in evaluating the function and developing the management and conservation strategies of grassland. However, over a large region, an efficient and high precision method to monitor multiscale PSD (α-, ß-, and γ-diversity) is lacking. In this study, we proposed and improved an unmanned aerial vehicle (UAV)-based PSD monitoring method (UAVB) and tested the feasibility, and meanwhile, explored the potential relationship between multiscale PSD and precipitation on the alpine grassland of the source region of the Yellow River (SRYR), China. Our findings showed that: (1) UAVB was more representative (larger monitoring areas and more species identified with higher α- and γ-diversity) than the traditional ground-based monitoring method, though a few specific species (small in size) were difficult to identify; (2) UAVB is suitable for monitoring the multiscale PSD over a large region (the SRYR in this study), and the improvement by weighing the dominance of species improved the precision of α-diversity (higher R 2 and lower P values of the linear regressions); and (3) the species diversity indices (α- and ß-diversity) increased first and then they tended to be stable with the increase of precipitation in SRYR. These findings conclude that UAVB is suitable for monitoring multiscale PSD of an alpine grassland community over a large region, which will be useful for revealing the relationship of diversity-function, and helpful for conservation and sustainable management of the alpine grassland.

Seasonal Variation in Soil and Herbage CO2 Efflux for a Sheep-Grazed Alpine Meadow on the North-East Qinghai-Tibetan Plateau and Estimated Net Annual CO2 Exchange.

The Qinghai-Tibetan Plateau is a vast geographic area currently subject to climate warming. Improved knowledge of the CO2 respiration dynamics of the Plateau alpine meadows and of the impact of grazing on CO2 fluxes is highly desirable. Such information will assist land use planning. We measured soil and vegetation CO2 efflux of alpine meadows using a closed chamber technique over diurnal cycles in winter, spring and summer. The annual, combined soil and plant respiration on ungrazed plots was 28.0 t CO2 ha-1 a-1, of which 3.7 t ha-1 a-1occurred in winter, when plant respiration was undetectable. This suggests winter respiration was driven mainly by microbial oxidation of soil organic matter. The winter respiration observed in this study was sufficient to offset the growing season CO2 sink reported for similar alpine meadows in other studies. Grazing increased herbage respiration in summer, presumably through stimulation of gross photosynthesis. From limited herbage production data, we estimate the sustainable yield of these meadows for grazing purposes to be about 500 kg herbage dry matter ha-1 a-1. Addition of photosynthesis data and understanding of factors affecting soil carbon sequestration to more precisely determine the CO2 balance of these grasslands is recommended.

Reproductive Strategies That May Facilitate Invasion Success: Evidence From a Spider Mite.

With significant surge of international trade in recent decades, increasingly more arthropod species have become established outside their natural range of distribution, causing enormous damage in their novel habitats. However, whether a species can colonize its new environment depends on its ability to overcome various barriers which may result in establishment failure, such as inbreeding depression and difficulty to find mates. Here, we used a haplodiploid pest, Tetranychus ludeni Zacher (Acari: Tetranychidae), which is native to Europe but now cosmopolitan, to investigate whether its reproductive strategies have facilitated its invasion success, providing knowledge to develop programs for prediction and management of biological invasions. We show that inbreeding had no negative influence on female reproductive outputs and longevity over 11 successive generations, allowing mother-son and brother-sister mating to occur at the invasion front without adverse consequences in fitness. Virgin females produced maximum number of sons in their early life to ensure subsequent mother-son mating but later saved resources to prolong longevity for potential future mating. Females maximized their resource allocation to egg production immediately after mating to secure production of maximum number of both daughters and sons as early as possible. Furthermore, mated females with mating delay increased proportion of daughters in offspring produced to compensate the loss of production of daughters during their virgin life. We suggest that the lack of inbreeding depression in successive generations and the ability to adjust resource allocations depending whether and when mating occurs may be the key features that have facilitated its invasion success.

Mating Delay Reduces Reproductive Performance but not Longevity in a Monandrous Moth.

Age at mating is one of the most important factors that affect mating success and reproductive fitness in insects. The present study investigated how the age of the two sexes at mating determined mating success, reproductive fitness and longevity in Phauda flammans (Walker) (Lepidoptera: Phaudidae), a serious pest of Ficus spp. trees in South and Southeast Asia. The study may provide basic knowledge for the development of mating disruption programs using sex pheromones to control this pest. The species is monandrous and its adults live for only 4-5 d. We show that delayed mating significantly lowered mating success in both sexes, with males being more severely affected than females. Mating delay also reduced reproductive outputs of both sexes but females were more negatively affected than males. We did not find any effect of delayed mating on longevity of either sex. Our findings suggest that mating disruption with sex pheromones can be an effective method to delay mating in P. flammans, reducing reproductive success and thus limit population growth.

Sex-Specific Allometry of Morphometric and Reproductive Traits in Oriental Fruit Flies (Diptera: Tephritidae).

The oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), is a highly invasive and polyphagous pest of many horticultural crops in the world, and is currently present in Asia, Africa, and Oceania. To provide essential knowledge for quality control in mass-rearing programs for sterile insect technique against the pest, we investigated how adult body weight and hind-tibial length were correlated in each sex and how body size of each sex affected lifetime reproductive fitness . We show that body weight and hind-tibial length were significantly positively correlated in both sexes, indicating that either trait can be used as an index of body size. However, the weight-tibial length relationships were sex specific, with females gaining disproportionally more weight than males with the increase of hind-tibial length. Body size was not significantly correlated with longevity of either sex, but males lived significantly longer than females. Larger females laid significantly more eggs regardless of body size of the male partner, suggesting that male size has no effect on fecundity. However, body size of both sexes had a significant effect on fertility. We conclude that selection on body size-reproductive fitness relations operates in different directions for the two sexes of B. dorsalis , with larger females and average males having highest reproductive fitness.

Flirtation reduces males' fecundity but not longevity.

Theory predicts that due to limited resources males should strategically adjust their investment in reproduction and survival. Based on different conceptual framework, experimental designs, and study species, many studies support while others contradict this general prediction. Using a moth Ephestia kuehniella whose adults do not feed and thus have fixed resources for their lifetime fitness, we investigated whether males adjusted their investment in various life activities under dynamic socio-sexual environment. We allowed focal males to perceive rivals or additional females without physical contact. We show that males do not adjust the number of sperm they transfer to mates in a given copulation at different immediate or both immediate and mean sperm competition levels. Contradictory to general predictions, our results demonstrate that cues from additional females increase males' investment in courtship and reduce their lifetime number of copulations and sperm ejaculated, whereas cues from rivals have no effect on these parameters. Males have similar longevity in all treatments. We suggest that the sex pheromone produced by multiple females overstimulate males, increasing males' costly flirtations, and reducing their lifetime copulation frequency and fecundity. This finding offers a novel explanation for the success of mating disruption strategy using sex pheromones in pest management.

Phenological dynamics of Dasineura mali (Diptera: Cecidomyiidae) and its parasitoid Platygaster demades (Hymenoptera: Platygasteridae) in apple orchards.

The midge Dasineura mali Kieffer (Diptera: Cecidomyiidae) is an important pest of apple (Malus domestica Borkh.) and a potential fresh fruit contaminant, causing quarantine concerns. The phenological dynamics of D. mali and its egg parasitoid Platygaster demades Walker (Hymenoptera: Platygasteridae) were studied in the field in Palmerston North, New Zealand, for 2 yr. Both shoot infestation rate by D. mali and D. mali density per shoot sharply increased in the second generation, reaching approximately 65% and 100-200 eggs, respectively. However, although the infestation rate in the third generation remained as high as in the second generation, the pest density per shoot significantly decreased to 40-60 eggs in the third generation. In the fourth generation, both infestation rate and pest density per shoot decreased to approximately 30% and 10 eggs. Due to the simultaneous decline of the apple shoot number and D. mali density in the third and fourth D. mali generations, the absolute number of D. mali in the orchard also has declined proportionally during the same period. The parasitism and superparasitism rates significantly increased as the season progressed, from 45 to 55 and 37% in the first generation to 87 and 82% in the fourth generation, respectively. Our results suggest that P. demades contributes to the continuous decline of D. mali numbers in the field; it is a good searcher, particularly when its hosts become increasingly scarcer over the season, and it avoids overshooting the host population later in the season by increasing superparasitism. The frequency of P. demades aestivation increases from late spring to midsummer and then decreases during the late summer and early autumn. Although the emergence of P. demades was approximately 2 to 3 wk behind that of D. mali in each generation, the increasing parasitism rates from the first to the fourth generations indicate that P. demades is synchronized with D. mali in the field.

Biased sex ratio and low population density increase male mating success in the bug Nysius huttoni (Heteroptera: Lygaeidae).

Demographic factors such as operational sex ratio (OSR) and local population density (LPD) are temporally and spatially dynamic in the natural environment but the influence of these variables on male mating success and the mechanisms behind it are still poorly understood and highly controversial. Here, we manipulated the OSR and LPD of a seed bug, Nysius huttoni, and carried out a series of mating trials to test how these variables affected male mating success. The two demographic factors had no significant interactions, suggesting that they affect male mating success independently in N. huttoni. In this species male mating success was significantly higher in both male- and female-biased OSR than in even OSR. It is suggested that, in male-biased OSR, the increased intensity of competition and interference does not result in lower male mating success; rather, males may make more effort in courting and females may have more chance to encounter better males, resulting in higher male mating success. In female-biased OSR, females may become less choosy and less likely to reject male mating attempt, leading to the higher male mating success. Lower male mating success in N. huttoni in high LPD may be due to increased interference between males and/or delayed female receptiveness for mating. OSR had a stronger effect on male mating success than LPD in N. huttoni, suggesting that OSR and LPD affect mating success in different ways and intensities.

Mate location and recognition in Glenea cantor (Fabr.) (Coleoptera: Cerambycidae: Lamiinae): roles of host plant health, female sex pheromone, and vision.

Glenea cantor (Fabricius) is an important pest of kapok trees [Bombax ceiba L.=Gossampinus malabaricus (DC.) Merr.] in southern China and Vietnam, and its adults are diurnally active. We carried out both field and laboratory experiments to examine the mechanisms that brought G. cantor sexes together from a long distance and facilitated mate location and recognition in a close range. Long-range sex pheromones are not involved in mate location. Mutual attraction of sexes to weakened kapok trees where adult feeding, mating, and oviposition occur plays the key role in mate location from a long distance. In a close range, vision and a female sex pheromone that operates over a short distance (3-3.5 cm) and/or by contact are major cues males use for mate location and recognition. Males seem to use combined chemical and visual cues to achieve mating. Male antennae, particularly the terminal five segments, are critical for males to detect and recognize females. Removal of male palpi has no significant effect on mate location and recognition by males.