Effect of maize stunting mollicutes on survival and fecundity of Dalbulus leafhopper vectors

The effect of corn stunt spiroplasma (CSS) on survival and fecundity of three Dalbulus leafhopper species was determined. CSS significantly reduced the survival, as measured by the time to 50% (t₅₀) and 25% (t₂₅) survival, and by the scale parameter (b) of the Weibull model, for D. elimatus and D. gelbus. Fecundity of these two species, as measured by the net and gross reproductive rates, was also reduced by CSS. CSS did not significantly affect the corn leafhopper, D. maidis. In a separate experiment, maize bushy stunt mycoplasma (MBSM) reduced the survival and fecundity of D. maidis at temperatures from 20 to 29 °C. The effect of MBSM on D. maidis survival was less severe than CSS on D. elimatus and D. gelbus; t₂₅, but not t₅₀, was reduced by MBSM. Survival times and the cohort generation time generally declined with increasing temperature. Fecundity, however, generally increased with increasing temperature.     

温度和食物浓度对三品系萼花臂尾轮虫实验种群动态的影响

应用个体培养方法,研究了温度(20、25和30℃)和藻类食物浓度(1．5×10^6、3．0×10^6、6．0×10^6和9．0×10^6cells·ml^-1)对青岛、芜湖、广州三品系萼花臂尾轮虫种群动态的影响．结果表明,温度仅对轮虫的世代时间和种群内禀增长率有显著影响,而品系对所有生命表参数均无显著影响．轮虫种群的内禀增长率随培养温度的升高而增大,世代时间则随培养温度的升高而缩短．食物浓度仅对轮虫的生命期望值和平均寿命有显著影响,品系对轮虫的净生殖率、世代时间、生命期望值和平均寿命也有显著影响．三品系间,以广州品系轮虫的净生殖率、世代时间、生命期望值和平均寿命最大,芜湖品系最短．当食物浓度为3．0×10^6cells·ml^-1时,轮虫的生命期望值和平均寿命最长,9．0×10^6cells·ml^-1时最短．各品系轮虫的净生殖率、世代时间、总生殖率、生命期望值和平均寿命均随培养温度的升高而减小,广州品系的净生殖率除外．轮虫种群的内禀增长率和广州品系轮虫的总生殖率则随培养温度的升高而增大．青岛和广州品系轮虫的各生命表参数,均与食物浓度呈曲线相关,但芜湖品系仅世代时间、平均寿命和生命期望值随食物浓度的增大而缩短．     

温度和食物浓度对三品系萼花臂尾轮虫实验种群动态的影响

应用个体培养方法,研究了温度(20、2和30 ℃)和藻类食物浓度(1.5×10₆、3.0×10₆、6.0×10₆和9.0×10₆ cells·ml^-1)对青岛、芜湖、广州三品系萼花臂尾轮虫种群动态的影响.结果表明,温度仅对轮虫的世代时间和种群内禀增长率有显著影响,而品系对所有生命表参数均无显著影响.轮虫种群的内禀增长率随培养温度的升高而增大,世代时间则随培养温度的升高而缩短.食物浓度仅对轮虫的生命期望值和平均寿命有显著影响,品系对轮虫的净生殖率、世代时间、生命期望值和平均寿命也有显著影响.三品系间,以广州品系轮虫的净生殖率、世代时间、生命期望值和平均寿命最大,芜湖品系最短.当食物浓度为3.0×10₆ cells·ml^-1时,轮虫的生命期望值和平均寿命最长,9.0×10₆ cells·ml^-1时最短.各品系轮虫的净生殖率、世代时间、总生殖率、生命期望值和平均寿命均随培养温度的升高而减小,广州品系的净生殖率除外.轮虫种群的内禀增长率和广州品系轮虫的总生殖率则随培养温度的升高而增大.青岛和广州品系轮虫的各生命表参数,均与食物浓度呈曲线相关,但芜湖品系仅世代时间、平均寿命和生命期望值随食物浓度的增大而缩短.     

The influence of stage-dependent dispersal on the population dynamics of three amphipod species

In metapopulations, the maintenance of local populations can depend on source–sink dynamics, where populations with positive growth rate seed populations with negative growth rate. The pattern and probability of successful dispersal among habitats can therefore be crucial in determining whether local populations will become rare or increase in abundance. We present here data on the dispersal strategy and population dynamics of three marine amphipods living in pen shells (Atrina rigida) in the Gulf of Mexico. The three amphipod species in this study disperse at different life stages. Neomegamphopus hiatus and Melita nitida disperse as adults, while Bemlos unicornis disperses as juveniles. The two species that disperse as adults have the highest initial population sizes when a new shell becomes available, likely caused by the arriving females releasing their brood into these recently occupied shells. This dispersal pattern results in initially higher population growth, but fewer occupied shells, as noted by their clumped distribution. In contrast, the species that disperses as juveniles accumulates more slowly and more evenly across habitats, eventually dominating the other two in terms of numerical abundance. The metapopulation dynamics of the three species seems to be highly dependent on the life history stage involved in dispersal. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Differential acquisition of chrysanthemum yellows phytoplasma by three leafhopper species

Chrysanthemum yellows (CY) phytoplasma has been transmitted with three leafhopper species: Euscelidius variegatus (Kirschbaum), Macrosteles quadripunctulatus (Kirschbaum) and Euscelis incisus (Kirschbaum): the first two species are reported as CY phytoplasma vectors for the first time. Leafhoppers were allowed to acquire the pathogen from the following source plants: Apium graveolens L., Catharanthus roseus L., Chrysanthemum carinatum Schousboe L. and C. frutescens L. DNA extracted from healthy or inoculative leafhoppers-exposed plants were analyzed by dot-blot and Southern hybridizations with a molecular probe constructed onto a fragment of European aster yellows phytoplasma DNA. The three leafhopper species were able to transmit CY phytoplasma after acquisition on chrysanthemum, but only M. quadripunctulatus and E. variegatus transmitted after feeding on periwinkle, and none acquired it from celery. All plant species tested were susceptible to CY, but while chrysanthemum and periwinkle were suitable for both inoculation and acquisition, celery did not seem to be a good source of phytoplasma for further inoculations. It is concluded that host plants influence leafhoppers' vectoring ability, possibly due to the different feeding behaviour of the insects on diverse plant species. Since CY, like several other phytoplasmas, can be transmitted by different insect species, it is likely that a close transmission specificity probably does not exist between phytoplasmas and their leafhopper vectors.     

Inoculation and acquisition of maize bushy stunt mycoplasma by its leafhopper vector Dalbulus maidis

Maize bushy stunt mycoplasma (MBSM), a mycoplasma-like organism, is transmitted in a persistent manner by the corn leafhopper, Dalbulus maidis, to maize (Zea mays). The influence of the duration of acquisition access and inoculation access periods on the transmission of MBSM by D. maidis was investigated. The proportion of plants infected by D. maidis increased significantly from 0 to 0.51 as the inoculation access time to a plant increased from 10 min to 72 h (X²= 101.5, P < 0.001). Likewise, the proportion of insects acquiring MBSM from infected plants increased from 0 to 0.19 as the acquisition access time to the source plant increased from 10 min to 72 h (X²= 53.2, P < 0.001). The data were fitted to a loglinear regression model. No significant association was found between the sex of the insects and vector ability.     

Acquisition and transmission of corn stunt spiroplasma by its leafhopper vector Dalbulus maidis

As the acquisition access period of Dalbulus maidis on infected maize increased from 15 min to 7 days, the incubation period of corn stunt spiroplasma (CSS) in the insect decreased from 27 days to 8 days and the final proportion of transmitting insects increased from 5% to 100%. After 7 days access the median incubation period (IPsO) was 14.3 days (IP₅₀ females = 12.9 days: IP₅₀ males =16.8 days), while the proportion of transmitting insects increased from 4. 3% (9 days after the start of acquisition access) to a maximum of 93% (after 22 days), before decreasing. Females started transmitting significantly earlier and a greater proportion transmitted each day than males, until day 22 when both sexes transmitted equally. Of the insects which transmitted CSS, 29% did so continuously until death; 66% failed to transmit during the last 1–3 days, and 5% transmitted intermittently towards the end of their life. During daily transfer, females were more likely to infect plants consecutively (up to 25) than males, and females infected the higher proportion of test plants. As the transmission access period was increased from 1 h to 72 h, the proportion of transmitting insects increased from 22.5% to 97.3% and the incubation period in maize decreased.     

Vector status of three leafhopper species for Australian lucerne yellows phytoplasma

Abstract   The leafhoppers Orosius argentatus (Evans), Austroagallia torrida (Evans) and Batracomorphus angustatus (Osborn) were used in transmission tests to determine their vector status for the phytoplasma associated with Australian lucerne yellows (ALuY). Caged, seed-grown lucerne plants were monitored for foliar symptom expression after feeding by leafhoppers transferred from ALuY symptomatic lucerne plants. Twelve of 25 plants developed phytoplasma disease-like symptoms including stunting and yellowing. The most pronounced foliar symptoms were displayed by five plants that had been fed on by O. argentatus and four plants that had been fed on by A. torrida. One plant, fed on by O. argentatus , showed the distinctive root symptoms of ALuY . A phytoplasma was identified by electron microscopy in two plants fed on by O. argentatus and one by A. torrida. For each group of plants that had been fed on by a single leafhopper species, one plant was phytoplasma positive as determined by the polymerase chain reaction (PCR) using universal primers. The phytoplasma detected by PCR in the plant fed on by A. torrida was identified by restriction fragment length polymorphism (RFLP) analysis as the tomato big bud (TBB) phytoplasma. The PCR product from two plants fed on by B. angustatus and O. argentatus were too faint for RFLP analysis. PCR assays were conducted on DNA extracted from the head and thorax of each leafhopper species from transmission tests and from field-collected insects, but no phytoplasma DNA was detected. These findings suggest O. argentatus is a vector of the ALuY pathogen and A. torrida is a vector of the TBB phytoplasma.     

Effect of temperature and host plant on the development of the blackfaced leafhopper

Population dynamics of the blackfaced leafhopper, Graminella nigrifrons (Forbes) (Homoptera: Cicadellidae), was studied at five temperatures (18, 21, 24, 27, & 30°C) in the laboratory on seedling maize (Zea mays L.), oats (Avena sativa L.), and the perennial johnsongrass (Sorghum halepense (L.) Pers.). Effects of temperature and host plant on egg to adult mean development time, adult size and weight, and fecundity were determined. Leafhoppers on all three hosts developed fastest at the highest temperature tested (21.3 days), and slowest at the lowest temperature tested (73.2 days). The duration from first to last adult eclosion was shortest at 30°C, (11.5 days) and longest at 18°C (43 days). The sex ratio of males to females did not differ from 1:1, but males developed an average of 1.2 days faster than females on all three hosts. Mean percent development/day ranged from 1.4% at 18°C to 4.7% at 30°C. The relationship of this development rate and temperature was determined using both a linear model and a variable parameter biophysical model. Based on these models, the developmental threshold is estimated at 12–15°C. The lowest temperature yielded larger and heavier adults (312 g, dry weight) than did the highest temperature (225 g). Fewer leafhoppers developed on the perennial than the annuals at 30°C and fewer on the annuals than the perennial at 18°C. Our results suggest that early in the season johnsongrass and perhaps other perennials are the superior developmental hosts for this leafhopper, whereas in midsummer when temperatures are highest, annuals are the better hosts.

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Résumé La dynamique des populations (durée de développement de l'uf à l'adulte, poids et taille des adultes, fécondité) de G. nigrifrons Forbes (Homop. Cicadellidae) a été étudiée au laboratoire à 5 températures sur plantules de maïs (Zea mays L.), avoine (Avena sativa L.) et sorgho vivace (Shorgum halepense (L.) Pers.). Sur les 3 plantes, les mâles se développent en moyenne 1,2 j plus vite que les femelles. Les relations entre vitesse de développement et température ont été déterminées en utilisant à la fois un modèle linéaire et le modèle biophysique à 2 paramètres de Sharpe & DeMichele (1977).Les températures plus basses donnent des adultes des 2 sexes plus gros et plus lourds. Moins de G. nigrifrons se sont développés sur la graminée vivace que sur les 2 graminées annuelles à la température la plus élevée (30°C), tandis qu'à la température la plus basse (18°C) moins de cicadelles se sont développées sur les graminées annuelles. La température semble jouer un rôle significatif en déterminant l'adéquation des plantes comme hôtes convenant au développement de G. nigrifrons. Le potentiel de ponte de cette cicadelle avait été sous-estimé par les étudies précédentes.

     

The parasitoid Gonatopus bartletti reduces presence of plant-pathogenic Spiroplasma kunkelii within the leafhopper vector Dalbulus maidis

Homopteran vectors (e.g., leafhoppers) of plant pathogens are vessels for reproduction of cell wall‐free bacteria. These vectors also serve as hosts for larval parasitoid dipterans, hymenopterans, and strepsipterans. However, no study has explored the relationship among these wall‐free bacteria and parasitoid larvae within the insect host. We studied the corn stunt spiroplasma (CSS), Spiroplasma kunkelii Whitcomb (Mycoplasmatales: Spiroplasmataceae), a bacterium that originated from secondary symbionts that cause corn stunt disease in maize, Zea mays L., and its reproduction in the haemolymph of the corn leafhopper, Dalbulus maidis (Delong and Wolcott) (Homoptera: Cicadellidae). We also studied the dryinid parasitoid Gonatopus bartletti Olmi (Hymenoptera: Dryinidae), the larva of which feeds in the corn leafhopper haemolymph. Our results showed that when CSS and the wasp coexisted in D. maidis, the development of the parasitoid was not affected by S. kunkelii. Parasitoid development was successfully completed when leafhoppers acquired S. kunkelii before or after parasitism and when CSS had median (10 days) and long (20 days) incubation periods in the leafhopper before parasitization. The presence of S. kunkelii did not affect parasitoid development to the adult stage. However, polymerase chain reaction showed that the presence (survival) of S. kunkelii in the leafhopper was negatively affected by the parasitoid larva. Fewer leafhoppers had CSS before and after parasitization compared with leafhoppers that only acquired the CSS. This negative effect helps to explain the high parasitism rate by G. bartletti in D. maidis and the low presence of S. kunkelii in the corn leafhopper when CSS and the wasp parasitoid overlap throughout their geographic distribution. The parasitoid larva may negatively affect S. kunkelii by (1) producing antibacterial peptides that are toxic to CSS; (2) producing teratocytes that take nutrients from the host for larval development, but these nutrients are required by CSS; (3) affecting, indirectly, CSS through other symbiotic microorganisms; and (4) producing proteins with antibacterial activity that are present in the venom of the wasp parasitoid.     

Effect of the epizoic rotifer Brachionus rubens on the population growth of three cladoceran species

Using population densities and growth rates as criteria, we studied interactions between the epizoic rotifer Brachionus rubens and each of three cladoceran species differing in size and reproductive rates — Daphnia carinata, Moina macrocopa and Ceriodaphnia rigaudi. In all mixed — species experiments, B. rubens existed in both the epizoic mode, attached to the cladoceran host, and in the free-swimming mode. Rotifer population growth rates were significantly depressed in the presence of M. macrocopa, presumably as a consequence of exploitative and interference competition. The largest cladoceran, D. carinata probably did not suppress B. rubens, because the epizoic component of the rotifer population escaped from the deleterious effects of mechanical interference. Peak population numbers and initial population growth rates reached by all three cladocerans were lower in the presence of B. rubens, probably because of the adverse effects of the epizoic infestation, which was maximal on D. carinata and least on C. rigaudi. In mixed-species cultures of D. carinata and M. macrocopa, the presence of B. rubens helped D. carinata coexist with M. macrocopa, which otherwise would have suppressed the Daphnia.     

Effects of acorn masting on population dynamics of three forest-dwelling rodent species in Hokkaido,Japan

The effects of the abundance of acorns of the oak, Quercus crispula, on the population dynamics of three rodent species (Apodemus speciosus, A. argenteus, and Clethrionomys rufocanus) were analyzed using time series data (1992–2006). The data were obtained in a forest in northern Hokkaido, Japan, by live trapping rodents and directly counting acorns on the ground. Apodemus speciosus generally increased in abundance following acorn masting. However, the clear effect of acorn abundance was not detected for the other two rodent species. Acorns of Q. crispula contain tannins, which potentially have detrimental effects on herbivores. Apodemus speciosus may reduce the damage caused by acorn tannins with tannin-binding salivary proteins and tannase-producing bacteria, whereas such physiological tolerance to tannins is not known in the other two rodent species. The differences in the effects of acorns between the three species may be due to differences in their physiological tolerance to tannins.     

The effect of temperature on asexual population growth of three species of Naididae (Oligochaeta)

The population growth rates of monospecific cultures of asexually reproducingNais variabilis, N. elinguis andPristina aequiseta were determined under laboratory conditions at 8 °C, 12 °C and 20 °C. Two different agar-based culture media were used to promote bacterial populations as a food for the worms. The exponential growth rate (r) of the worm populations was dependent upon species, temperature and culture medium. Highest r-values recorded were forN. variabilis andP. aequiseta at 20 °C (mean population doubling time about 3 days) and the lowest r-value recorded was forP. aequiseta at 8 °C (mean population doubling time about 22 days). The r-values forN. elinguis were generally lower than expected, possibly because conditions in the experimental cultures were less suitable for this species. Temperature, culture medium and species identity also affected the carrying capacity of the cultures. Carrying capacity increased with increase in temperature over the experimental range.P. aequiseta cultures supported significantly higher carrying capacities than theNais cultures at all temperatures.     

Effect of photoperiod and temperature on the development of frost hardiness in three Alnus species

The influence of short day and low temperature on cold acclimation of A. crispa (Ait.) Pursh, A. glutinosa (L.) Gaertn. and A. rubra Bong, was investigated. Two clones of each species originating from in vitro propagation were exposed to three daylength/temperature treatments. Periodically plantlets were exposed to controlled freezing temperature in order to evaluate their level of frost hardiness.
Short day (SD) and cold temperature (CT) and long day (LD) and cold temperature (CT) were the most effective treatments for the development of frost hardiness in shoots and roots of the three species tested. Short day (SD) and warm temperature (WT) induced a significant increase in hardiness in shoots of all three species. However, this treatment did not trigger root hardening. A. crispa was found to be the hardiest species followed by A. glutinosa and A. rubra . Intraspecific variation was observed between the two A. glutinosa clones. A glutinosa clone AG8, a Russian provenance, showed a greater freezing resistance than A. glutinosa clone AG2, a German provenance.     

Effects of temperature on the development,performance and fitness of the corn leafhopper Dalbulus maidis (DeLong) (Hemiptera: Cicadellidae): implications on its distribution under climate change

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