Biological control of an alien tree, Acacia cyclops, in South Africa: impact and dispersal of a seed-feeding weevil, Melanterius servulus

Several Australian Acacia species have become highly invasive in a number of ecologically sensitive areas of South Africa. Many have useful attributes that, to an extent, have hampered biocontrol efforts by restricting potential agents to those reducing seed production whilst not affecting vegetative growth. The outcome of the introduction of a seed-feeding weevil, Melanterius servulus, against Acacia cyclops in 1994, was assessed by investigating the plant’s reproductive phenology, as well as levels of damage caused by the beetles. The study provided essential information on host/agent interactions and, on the build up and spread of populations of the agent. Seed damage is commonly as high as 90% (exceptionally it reaches 100%), and dispersal rates of the beetles on average is almost 2 km per year. The consistently high levels of seed damage achieved hold promise for the future of the program, however, its ultimate success will be further enhanced through the integration of biological control with other manual clearing operations that are currently employed on a large scale in South Africa.     

Morphology and phenology of seeds and whole fruit eaten by Milne-Edwards’ sifaka,Propithecus diadema edwardsi,in Ranomafana National Park,Madagascar

Although it is an anatomical folivore, the diet of the Milne-Edwards’ sifaka (Propithecus diadema edwardsiA. Grandidier, 1871) in Ranomafana National Park contained 35% seeds, 30% whole fruit, and 28% leaves. Plant species used as seed sources differed from those used as whole fruit sources in terms of temporal variation in consumption, taxonomic affiliation, morphology, and phenology. Although seeds were destroyed in both exploitation styles used by the sifakas—seed and whole fruit-eating—the gross morphology of species used as seed sources conformed to the complex of traits typical for fruits experiencing seed predation, while species used as whole fruit sources conformed to traits typical for fruits that do not experience predispersal predation. Many of the 19 plant species from which the seed was extracted and eaten contained a single seed with moderate testa thickness, and fruits containing this type of seed were medium-sized with dry or fibrous flesh, moderate skin thickness, and a dull color. In contrast, brightly colored, juicy fruits with minimally protected seeds were characteristic of the 38 plant species from which both pericarp and seed were eaten. Compared to transectwide measures of fruit availability or patterns restricted to whole fruit sources, fewer species of seed sources produced fruit per month and fruiting activity was more seasonal.     

Is one parasitoid enough? A test comparing one with a pair of parasitoid species in the biological control of arrowhead scales

In classic biological control using natural enemies, the question of whether a single species or multiple species should be introduced has been a matter of debate. The introduction of two parasitoids, Aphytis yanonensis and Coccobius fulvus (Hymenoptera: Aphelinidae), to control the arrowhead scale, Unaspis yanonensis (Hemoptera: Diaspididae), which is a serious pest in Japanese citrus orchards, has been one of the most successful biological control projects in Japan. The success of this program may be explained by two alternative hypotheses: (1) the parasitoid species work complementarily, or (2) only one of them plays a major role. To test which hypothesis is applicable to this host-parasitoid system, we conducted caging experiments and observed temporal changes in the proportion of the parasitisms and the densities of arrowhead scales enclosed with one of the following combinations of parasitoids: (1) A. yanonensis and C. fulvus together, (2) A. yanonensis alone, (3) C. fulvus alone, or (4) neither parasitoid. Parasitisms in the cohorts with A. yanonensis and C. fulvus together and C. fulvus alone rapidly increased to approximately 70%; parasitism with A. yanonensis alone also increased slightly, although it remained consistently lower that those with A. yanonensis and C. fulvus together and C. fulvus. At the end of the experiment, parasitisms with A. yanonensis and C. fulvus together and C. fulvus alone were significantly higher than that with A. yanonensis alone. Parasitism by C. fulvus constituted most of (74%) the parasitism in the cohort with A. yanonensis and C. fulvus together. Further, only C. fulvus suppressed the population growth rates of scales significantly. These results suggest that C. fulvus alone successfully suppresses scale populations as efficiently as both species together do.     

Mesocosm experiment on the impact of invertebrate predation on zooplankton of a tropical lake

Invertebrate predation on zooplankton was investigated in mesocosms in the shallow tropical Lake Monte Alegre, São Paulo State, Brazil, in the summer of 1999. Two treatments were applied: one with natural densities of prey and the predators Chaoborus brasiliensis and the water mite Krendowskia sp. (Pr+), and another without predators (Pr-). Three enclosures (volume: 6.6 m³ of water per enclosure) per treatment were installed in the sediment of the deepest area of the lake (5.0 m). At the beginning, Chaoborus larvae were present in Pr- enclosures, because of technical difficulties in preventing their entrance, but they virtually disappeared in the course of the experiment. Water mites were almost absent in Pr- enclosures. Chaoborus predation negatively influenced the Daphnia gessneri population, but not the populations of the copepods Tropocyclops prasinus and Thermocyclops decipiens and the rotifers Keratella spp. Death rates of Daphnia were generally significantly higher in the Pr+ treatment; Daphnia densities increased after the disappearance of Chaoborus in Pr-. Copepod losses to predation in the experiment may be compensated by higher fecundity, shorter egg development time, and lower pressure on egg-bearing females, resulting in a lower susceptibility to Chaoborus predation. The predation impact of water mite on microcrustaceans and rotifers in the experiment was negligible.     

Post-dispersal predation and scatterhoarding of Dipteryx panamensis (Papilionaceae) seeds by rodents in Panama

In tropical rain forests of Central America, the canopy tree Dipteryx panamensis (Papilionaceae) fruits when overall fruit biomass is low for mammals. Flying and arboreal consumers feed on D. panamensis and drop seeds under the parent or disperse them farther away. Seeds on the ground attract many vertebrate seed-eaters, some of them potential secondary seed dispersers. The fate of seeds artificially distributed to simulate bat dispersal was studied in relation to fruitfall periodicity and the visiting frequency of diurnal rodents at Barro Colorado Island (BCI), Panama. The frequency of visits by agoutis is very high at the beginning of fruitfall, but in the area close (<50 m) to fruiting trees (Dipteryx-rich area) it declines throughout fruiting, whereas it remains unchanged farther (>50 m) away (Dipteryx-poor and Gustavia-rich area). Squirrels were usually observed in the Dipteryx-rich area. Along with intense post-dispersal seed predation by rodents in the Dipteryx-rich area, a significant proportion of seeds were cached by rodents in the Dipteryx-poor area. Post-dispersal seed predation rate was inversely related to hoarding rate. A significantly greater proportion of seeds was cached in March, especially more than 100 m from the nearest fruiting tree. This correlates with the mid-fruiting period, i.e. during the height of D. panamensis fruiting, when rodents seem to be temporarily satiated with the food supply at parent trees. Hoarding remained high toward April, i.e. late in the fruiting season of D. panamensis. Low survival of scatterhoarded seeds suggests that the alternative food supply over the animal's home-ranges in May–June 1990 was too low to promote survival of cached seeds. Seedlings are assumed to establish in the less-used area of the rodents' home-range when overall food supply is sufficient to satiate post-dispersal predators.     

Determinants of spatial distribution in a population of the subalpine butterfly Oeneis chryxus

Summary This paper describes temporally varying determinants of the spatial distribution of adults in an insect population and the relationship between that distribution and the mating system. Male Oeneis chryxus butterflies were distributed nonrandomly throughout a sloping Colorado meadow divided horizontally by a dirt road into an upper and lower slope. Over an eight-year period of intensive study, the proportion of males located on the road, the upper slope, and the lower slope varied as a function of population size and sex ratio. In each year, more than half of the male population aggregated on sections of the road in a distinct and recurring pattern that was not correlated with the distribution of any food resource or thermal regime. Females were usually extremely scarce and not distributed in any pattern apparent from the few observations of them. Areas densely occupied by males were associated with visual landmarks. We hypothesize that the male distribution is determined by a pattern of movement of receptive females toward these landmarks. The road offers a thermally favorable environment with an unobstructed view in which to await the passage of scarce females. The mating system in this population has several lek-like features and supports the prediction that landmark mating is a favored strategy under conditions of female scarcity and wide dispersal of resources.     

沙生植物倒披针叶虫实在古尔班通古特沙漠的分布

倒披针叶虫实(Corispermum lehmannianum)在古尔班通古特沙漠广泛分布,重要值仅次于该沙漠建群种白梭梭(Haloxylon persicum),对沙面的稳定起着非常重要的作用。采用固定样方法对自然条件下该植物的分布特征和种群数量动态进行了研究。结果表明:1)倒披针叶虫实在沙丘各坡位均占有较高重要值,尤其活化程度较高的中部和上部优势度更明显;2)生长季节的不同阶段,除坡顶外,其他各坡位种子主要分3批萌发出苗,不同时期种子萌发出苗数量存在差异,3月份有大量种子萌发出苗,4月份种子萌发出苗数最多,5月份萌发出苗量逐渐减少。而坡顶3月份种子萌发出苗量最多,4月至5月均无种子萌发出苗。因此,除坡顶外,种子萌发出苗数量和种群密度在其他各坡位呈先增后减的趋势。生长季结束时各坡位种群密度表现为:中部和上部底部和丘间顶部;3)成熟植株单位面积种子产量为:中部和上部丘间和底部顶部,且中部和上部单位面积种子数量极显著多于丘间、坡底和坡顶(P0.01);4)通过对0—5 cm和6—10 cm土壤种子库密度研究发现,沙丘中部和上部种子库密度显著高于其他坡位。综合以上研究表明,倒披针叶虫实在沙面较活化的中部和上部呈优势分布,对沙漠环境具有良好适应性。因此,该植物是一种极具开发潜力的沙生植物。     

Impact of selective predation by Mesocyclops pehpeiensis on a zooplankton community: experimental analysis using mesocosms

Predation by cyclopoid copepods is an important factor affecting zooplankton communities in freshwater habitats. Experiments provide strong evidence of the role of selective predation by cyclopoid copepods in structuring zooplankton communities. To assess the predation impact of a cyclopoid copepod, Mesocyclops pehpeiensis, we conducted a mesocosm experiment using 20-l polyethylene tanks in which the density of the predator and the food available to herbivorous zooplankton varied. M. pehpeiensis had a notable but selective effect on the zooplankton community. The population of a small cladoceran, Bosmina fatalis was affected negatively, but M. pehpeiensis did not have any apparent impact on the population dynamics of another Bosmina species, B. longirostris. On the other hand, the population of small rotifers responded positively to the presence of M. pehpeiensis, and their densities increased in mesocosms with a high density of M. pehpeiensis. It seems that suppression of B. fatalis by M. pehpeiensis predation indirectly affected rotifers by releasing them from competition with B. fatalis. The results suggest that copepod predation is a powerful factor regulating zooplankton communities directly and indirectly.     

Biological properties of the endemic and threatened shrub in Iberia Vella pseudocytisus subsp. paui Gómez Campo (Cruciferae) and implications for its conservation

We present new data about chorology, seed bank, dispersal, seedling biology and population structure of the threatened endemic shrub Vella pseudocytisus subsp. paui Gómez Campo in Spain. In addition, we investigate human activities that are linked with the fine-scale distribution of the taxon to offer conservation recommendations.Currently, the plant occurs in two populations close to the city of Teruel (East central Spain), growing in an open shrubby community on patches of gypsum substrate surrounded by agricultural landscape. The plant has disappeared from two reported locations dated from early 20th Century likely due to human activities.The seed bank seems to be poor. A ballistic dispersal mechanism appears to move seeds between 0 and 4 m. We did not find a clear seasonal pattern of seedlings emergence although spring cohorts are the largest. Also, this period was where leaf seedling growth was more prominent. During the 3 years of our survey, the cumulative mortality was 94.2% of all seedlings plants. Plants are estimated to remain in the seedling stage for approximately 5 years. The demographic structure of both populations shows no apparent gaps in the distribution of size classes. Adult plants greater than 200 dm³ represent the most important stage for seed production and persistence.We point out two key factors for conservation purposes, first the weakness of some of the plant biological properties for natural establishment and second its ability to colonise artificial environments. We propose a mitigation of clonal spread in those sites and the protection of juvenile stages in more natural locations.     

树兰原球茎内生细菌群落多样性及功能分析

【目的】通过分析树兰原球茎内生细菌群落组成、多样性特征和促生功能,探究树兰种子萌发相关的核心细菌类群及生物学功能。【方法】以树兰原球茎(树兰种子在树皮基质上共生萌发、在树叶基质上共生萌发、在MS1培养基上非共生萌发)和共生萌发基质(松树皮、腐熟树叶)共5个样本为研究材料,采用高通量测序技术分析不同萌发条件下原球茎内生细菌的16S rRNA基因多样性,比较分析细菌群落多样性和物种组成特征,通过传统的内生细菌分离方法获得共生萌发原球茎内生细菌菌株,并进行促生潜力评价。【结果】从5个研究样本中共获得2 735个可操作分类单元(operational taxonomic unit, OTU),属于41门453科876属,其中变形菌门(Proteobacteria)和放线菌门(Actinobacteria)为优势门。主坐标分析(principal coordinates analysis, PCoA)结果表明,树兰原球茎与萌发基质细菌群落结构存在差异,非共生萌发原球茎与在树皮基质上共生萌发原球茎内生细菌群落结构最为接近。功能预测表明,在树叶基质上共生萌发的原球茎内生细菌固氮功能显著高于其他萌发条件。通过分离培养,共获得内生细菌19株,分属12属16种,其中鞭毛膨胀芽孢杆菌(Tumebacillus flagellatus)、Bradyrhizobium cenepequi和人参腐殖土魏茨曼氏菌(Weizmannia ginsengihumi)为共生萌发原球茎共有种;韩国假单胞菌(Pseudomonaskoreensis)和 W. ginsengihumi兼具有溶磷、产吲哚乙酸(indole-3-acetic acid, IAA)和铁载体的潜在能力。【结论】在不同环境中萌发的树兰原球茎均有丰富的内生细菌群落定殖;从共生萌发原球茎中分离的内生细菌具有固氮、溶磷、产IAA和铁载体等促生功能。本研究为兰科植物种子萌发相关微生物资源挖掘及兰科植物与微生物互作研究提供科学依据。     

Azteca protection of Cecropia: ant occupation benefits juvenile trees

Summary In this 15 month investigation I experimentally demonstrated that sapling Cecropia aff. obtusifolia in lowland western Ecuador grow more vigorously when occupied by the ant Azteca constructor than when the ants have been removed. Thus the interaction is directly beneficial to Cecropia juveniles. The difference in growth is associated with differences in herbivory and vine cover. Removal of ants significantly increases nocturnal Coleoptera herbivory on unoccupied plants. In contrast to the influence on beetle numbers, Azteca are ineffective against Homoptera and cecidomyiid gall flies. Although ant-occupied saplings had less chewing herbivore damage throughout the study, the ants were more effective protectors in the dry season than in the rainy season, when herbivore pressure increased. In addition to reducing herbivory, Azteca efficiently remove vines from occupied saplings.     

珍稀濒危植物紫纹兜兰的种群结构和数量动态

通过对广东省河源市紫金县白溪省级自然保护区紫纹兜兰(Paphiopedilum purpuratum)进行样方调查,运用种群生命表、存活曲线、种群生存函数值和时间序列预测分析方法,研究紫纹兜兰种群的动态变化过程,揭示各龄级植株的数量动态和变化规律。结果表明,紫纹兜兰龄级以幼龄为主,幼龄阶段占整个种群的54.73%,年龄结构为稳定型。种群年龄结构的动态指数V_(pi)为0.33、V_(pi)'为0.07,均大于0,紫纹兜兰的存活曲线更接近Deevey-Ⅱ型,表明该种群目前属于稳定型种群。累计死亡率函数和危险率函数上升,生存率函数下降,死亡密度函数波动较大。从时间序列预测分析表明,种群具备一定的恢复能力,但是种群整体数量随时间的增加,成年植株逐渐增加,幼苗减少。平均开花和结实率仅为16.94%和3.29%,种子没有胚乳而营养不足,在自然环境下很难发育成幼苗,主要靠分蘖植株繁殖,因此对紫纹兜兰幼苗的保护很关键。     

Acid stress in Rumex hydrolapathum (Polygonaceae) and its influence on the phytophage Lycaena dispar (Lepidoptera; Lycaenidae)

Summary The relationship of insect growth to host condition was tested on host plants grown by hydroculture with a standard nutrient solution, but under different acidities, ranging from pH 3.5–7.5. The indirect effect of the host on the development of the phytophage was tested in the pupal stage. The host plant Rumex hydrolapathum had its highest nitrogen content in the range pH 5.5–6.5; pupal weight of Lycaena dispar was correlated with nitrogen concentration, ash weight and water content. There is a remarkable difference in element concentration between young and old leaves of the host, which varies with acidity of the rooting substrate.In this experiment a negative relationship was detected between reproduction of the phytophage and stress of the host.     

Metapopulation genetic structure of two coexisting parasitoids of the Glanville fritillary butterfly

We investigated the metapopulation genetic structure of two specialist parasitoids, Cotesia melitaearum and Hyposoter horticola, attacking the Glanville fritillary butterfly (Melitaea cinxia) in the Åland Islands south-western Finland. The host butterfly persists as a classic metapopulation in a network of 4,000 small habitat patches within an area of 50 by 70 km . The two parasitoids are known to differ greatly in their population dynamics and spatial pattern of occupancy in local host populations. Analysis of genetic population structure using F_ST and clustering of multilocus genotypes revealed a distinct large-scale spatial structure in C. melitaearum but a very weak pattern in H. horticola. This result is consistent with the known difference in the dispersal range (much longer in H. horticola) and population size (much greater in H. horticola) of the two parasitoids.     

Population dynamic aspects of chironomid larvae of the littoral zone of Lake Maarsseveen I

Population dynamics of chironomid larvae in the littoral zone of Lake Maarsseveen I were investigated to a depth of 6 m. No essential differences in the composition and density between various sampling stations in the shallow sand flats were found. Two species,Cladotanytarsus mancus andStictochironomus sticticus, were found to be the main components of the chironomid population to a depth of 4 m. The density ofCladotanytarsus, which occurred predominantly to a depth of 1 m, increased from June to a maximum in December. In May and June, the entireCladotanytarsus population emerged.Stictochironomus had its peak of abundance in June. From this cohort, a part, differing in size for each of the various years, emerged in August. The remainder of this population, together with the offspring of the August adults, emerged in May. The size of the August midges, and the number of its eggs was smaller than that of the May midges. At depths greater than 4 m,Tanytarsus bathophillus was found to be the dominant chironomid.In summer the abundance of the small (second and third instars)Stictochironomus was primarily affected by water mite predation. In autumn and winter,Cladotanytarsus was the main food source for water mites. In autumn, whenStictochironomus larvae have molted into the fourth instar, predation by bream decreased the density of these larvae. In winter, the impact of this fish is negligible.     

Effects of Light on the Tritrophic Interaction Between Kidney Bean Plants, Two-Spotted Spider Mites and Predatory Mites, Amblyseius Womersleyi (Acari: Phytoseiidae)

By analyzing the volatiles from Tetranychus urticae-infested kidney bean plants (Phaseolus vulgaris) at different times for two days, we found that they were mainly produced in the light. Tetranychus urticae showed a higher oviposition rate and spent more time feeding during the day (in the light) than at night (in the dark). Infested leaves placed in the light attracted the predatory mite Amblyseius womersleyi, whereas those that were placed in the dark for at least 2h in daytime did not. This indicates that presence or absence of light affects the production of herbivore-induced plant volatiles. Amblyseius womersleyi dispersed more frequently and consumed more T. urticae eggs during the day (in the light) than at night (in the dark), whereas their oviposition rate did not differ between day and night. Presence or absence of herbivore-induced plant volatiles in the surroundings did not affect dispersal, predation or oviposition rates of A. womersleyi. These results show that A. womersleyis behavior coincides with the production pattern of herbivore-induced plant volatiles.     

Does the Number of Diapausing Eggs Laid on Bark Affect the Population Dynamics of the Spider Mite Panonychus mori?

We studied the relationship between number of diapausing eggs produced by the spider mite Panonychus mori and the subsequent population trend for a period of 3 years. Panonychus mori showed a single population density peak on its host plant moonseed, Cocculus trilobus. The position and height of this peak were correlated with the density of diapausing eggs around the moonseed leaf buds produced the winter before. In 1994 the density of diapausing eggs measured in February was 4.3/bud, which was 6–14 times higher than the density of diapausing eggs for the same period in 1995 (0.3/bud) and 1996 (0.7/bud). The subsequent population density peak in 1994 occurred in mid June and was about 2.5 times higher than the peaks in 1995 and 1996, which both occurred early September. Thus, the present study showed a positive correlation between the density of diapausing eggs on the host plant and the start and the extend of the population increase the next growing season. Predators associated with the spider mite population were phytoseiid mites, especially Amblyseius eharai was well synchronized with the spider mite density in 1994. Field observations revealed that P. mori produced diapausing eggs in response to short photoperiod in early October each year, which corresponded with the timing predicted by the critical photoperiod around 13 h at 18°C, as assessed in laboratory trials. Diapause ended by early April when egg hatchability attained about 50% and eggs took 9 days to hatch at 25°C and a 16L:8D photoperiod. Hatching in early April was twice faster than in late February.     

金沙江流域4种特有植物野生资源现状及受威胁等级评估

物种受威胁状况的及时评估是调整物种濒危状态,继而实施有效保护措施的重要依据。该文以金沙江流域特有植物贯叶马兜铃(Aristolochia delavayi)、旱地木槿(Hibiscus aridicola)、云南百部(Stemona mairei)和白魔芋(Amorphophallus albus)为调查评估对象,通过多年野外调查,依据《IUCN物种红色名录等级和标准:3.1版》和《使用指南:15.1版》对4物种的濒危现状进行了重新分析和评估。结果表明,在现有野生种群资源下贯叶马兜铃被列为易危(VU),旱地木槿和白魔芋被列为濒危(EN),云南百部为近危(NT)。与4物种现行濒危等级的比较表明,贯叶马兜铃的濒危等级由濒危降级为易危,旱地木槿由易危上调为濒危,白魔芋由近危上调为濒危,云南百部的濒危状态则维持不变。这为4种特有植物的野生资源现状了解、濒危状态更新以及适时调整有效保护策略提供了科学参考。