害虫防治决策的复序贯分析方法及抽样技术研究

复序贯抽样决策技术实际应用的受限 ,原因在于截止限序贯抽样模型的缺乏。本文在检验昆虫种群空间格局回归模型的基础上 ,推导出了目前国内常用检验回归模型的截止限序贯抽样模型 ,并将其运用于复序贯分析决策过程中。实例分析表明 ,对于同一种生物种群 ,在一定的精度 (D)和置信水平(tα)要求下 ,复序贯抽样决策技术可以大幅度地节约抽样成本     

Downy mildew (Plasmopara viticola) epidemics on grapevine under climate change

As climate is a key agro‐ecosystem driving force, climate change could have a severe impact on agriculture. Many assessments have been carried out to date on the possible effects of climate change (temperature, precipitation and carbon dioxide concentration changes) on plant physiology. At present however, likely effects on plant pathogens have not been investigated deeply. The aim of this work was to simulate future scenarios of downy mildew (Plasmopara viticola) epidemics on grape under climate change, by combining a disease model to output from two general circulation models (GCMs). Model runs corresponding to the SRES‐A2 emissions scenario, characterized by high projections of both population and greenhouse gas emissions from present to 2100, were chosen in order to investigate impacts of worst‐case scenarios, among those currently available from IPCC. Three future decades were simulated (2030, 2050, 2080), using as baseline historical series of meteorological data collected from 1955 to 2001 in Acqui Terme, an important grape‐growing area in the north‐west of Italy. Both GCMs predicted increase of temperature and decrease of precipitation in this region. The simulations obtained by combining the disease model to the two GCM outputs predicted an increase of the disease pressure in each decade: more severe epidemics were a direct consequence of more favourable temperature conditions during the months of May and June. These negative effects of increasing temperatures more than counterbalanced the effects of precipitation reductions, which alone would have diminished disease pressure. Results suggested that, as adaptation response to future climate change, more attention would have to be paid in the management of early downy mildew infections; two more fungicide sprays were necessary under the most negative climate scenario, compared with present management regimes. At the same time, increased knowledge on the effects of climate change on host–pathogen interactions will be necessary to improve current predictions.     

Dispersal of plant fragments in small streams

1. Streams are subject to frequent natural and anthropogenic disturbances that cause sediment erosion and loss of submerged vegetation. This loss makes downstream transport and retention of vegetative propagules on the streambed very important for re‐establishing vegetation cover. We measured dispersal and retention of macrophyte stem fragments (15–20 cm long) along 300 m long reaches of four small to medium sized Danish lowland streams. 2. The number of drifting stem fragments declined exponentially with distance below the point of release. This finding makes the retention coefficient (k, m⁻¹) in the exponential equation a suitable measure for comparisons among different macrophyte species, and between stream reaches of different hydrology and vegetation cover. 3. Buoyancy of macrophyte tissue influenced retention. Elodea canadensis stems drifted below the water surface, and were more inclined to be retained in deeper water associated with submerged plants and obstacles in the streambed. Ranunculus peltatus stems were more buoyant, drifted at the water surface, and were more inclined to be trapped in shallow water and in riparian vegetation. 4. The retention coefficient of drifting stems increased with the relative contact between the flowing water and streambed, bank and vegetation. Thus, the retention coefficients were highest (0.02–0.12 m⁻¹) in shallow reaches with a narrow, vegetation‐free flow channel. Here there were no significant differences between E. canadensis and R. peltatus. Retention coefficients were lowest (0.0005–0.0135 m⁻¹) in deeper reaches with wider vegetation‐free flow channels. Retention of E. canadensis was up to 16 times more likely than retention of R. peltatus. 5. Overall, the longitudinal position in the stream system of source populations of species capable of producing numerous stems, the species‐specific retention coefficients of stems, and the retention capacity of stream reaches should be important for species distribution in perturbed stream systems. Retention of stems is probably constrained in headwaters by the small downstream flux of stem fragments because of the restricted source area, and constrained in downstream reaches by small retention coefficients. Macrophyte retention may, consequently, peak in medium‐sized streams.     

Coevolutionary genetics of plants and pathogens

Summary The genetic polymorphism maintained by host-pathogen coevolution is analysed in a multilocus model. The model assumes gene-for-gene interactions of the type commonly observed between host plants and their fungal pathogens. Unstable (epidemic) systems maintain more resistance genes, fewer virulence genes, and less overall genetic diversity than stable (endemic) diseases. The stability of the system depends primarily on demographic parameters, such as the pathogen's intrinsic rate of increase, rather than genetic parameters, such as the costs of resistance and virulence. At equilibrium the model predicts that the number of resistance alleles in each host plant follows a binomial distribution that depends on the cost to the pathogen for carrying virulence alleles. Similarly, the number of virulence alleles in each pathogen spore follows a binomial distribution that depends on one minus the cost to the host for carrying resistance alleles. Data from wild populations match the predicted binomial distributions.     

Comparison of the predicted impact of a screwworm fly outbreak in Australia using a growth index model and a life-cycle model

Abstract. The spatial population dynamics of an Old World screwworm fly, Chrysomya bezziana Villeneuve (OWS), outbreak in Australia have been modelled in two ways. The first model uses weekly growth indices derived from climatic data to predict the adult female population. The second is a detailed cohort life-cycle model. Due to technical and time constraints, the growth index model is preferred as the biological component of a much larger bioeconomic model because of its smaller program size and faster execution. In deciding whether adoption of the growth index model would be at the expense of scientific accuracy, the life-cycle model was developed as a yardstick. We showed that the growth index model was a practical and adequate substitution for the OWS life-cycle model and a novel spatial/temporal modelling approach with generic qualities. We elaborate on the previously reported growth index model, describe the life-cycle model and compare the results of both models. In the event of an OWS incursion in northern or eastern Australia, given average climatic conditions, both models predict that most of the suitable range (some 2.3M km²) will be colonized within 4–5 years if an eradication campaign is not attempted. Much of its permanent range would be in tropical and subtropical extensive grazing regions. Where computer or funding resources are restrictive, models incorporating growth indices may prove adequate for spatial population studies of some species.     

Study of plants visited by honeybees (Apis mellifera L.) in the Central Rif Region (N. Morocco) using pollen analysis

Quantitative pollen analyses of Moroccan honey samples provided by amateur beekeepers from the Central Rif region demonstrates that nectar is generally the main honey source, and that most honeys have a medium‐low presence of botanical elements. However, two samples reached values as high as 1.08–1.83 qualifying as honeydew honeys. Qualitative results yielded 60 pollen types belonging to 33 families. Ammi visnaga L., Mentha pulegium L., M. rotundifolia (L.) Hudson, Eucalyptus camaldulensis Dehnh. and Rubus ulmifolius Schott. were the main nectar sources, and Cistaceae, Poaceae, Cannabis sativa L. and grasses were exploited as a pollen source. When compared to the parent vegetation honeydew and mint sources are widely exploited, but other sources such as eucalyptus and heather are underutilised.     

Using virtual 3-D plant architecture to assess fungal pathogen splash dispersal in heterogeneous canopies: a case study with cultivar mixtures and a non-specialized disease causal agent

Background and Aims

Recent developments in plant disease management have led to a growing interest in alternative strategies, such as increasing host diversity and decreasing the use of pesticides. Use of cultivar mixtures is one option, allowing the spread of plant epidemics to be slowed down. As dispersal of fungal foliar pathogens over short distances by rain-splash droplets is a major contibutor to the spread of disease, this study focused on modelling the physical mechanisms involved in dispersal of a non-specialized pathogen within heterogeneous canopies of cultivar mixtures, with the aim of optimizing host diversification at the intra-field level.

Methods

Virtual 3-D wheat-like plants (Triticum aestivum) were used to consider interactions between plant architecture and disease progression in heterogeneous canopies. A combined mechanistic and stochastic model, taking into account splash droplet dispersal and host quantitative resistance within a 3-D heterogeneous canopy, was developed. It consists of four sub-models that describe the spatial patterns of two cultivars within a complex canopy, the pathway of rain-splash droplets within this canopy, the proportion of leaf surface area impacted by dispersal via the droplets and the progression of disease severity after each dispersal event.

Key Results

Different spatial organization, proportions and resistance levels of the cultivars of two-component mixtures were investigated. For the eight spatial patterns tested, the protective effect against disease was found to vary by almost 2-fold, with the greatest effect being obtained with the smallest genotype unit area, i.e. the ground area occupied by an independent unit of the host population that is genetically homogeneous. Increasing both the difference between resistance levels and the proportion of the most resistant cultivar often resulted in a greater protective effect; however, this was not observed for situations in which the most resistant of the two cultivars in the mixture had a relatively low level of resistance.

Conclusions

The results show agreement with previous data obtained using experimental approaches. They demonstrate that in order to maximize the potential mixture efficiency against a splash-dispersed pathogen, optimal susceptible/resistant cultivar proportions (ranging from 1/9 to 5/5) have to be established based on host resistance levels. The results also show that taking into account dispersal processes in explicit 3-D plant canopies can be a key tool for investigating disease progression in heterogeneous canopies such as cultivar mixtures.     

Spatial pattern analysis of the incidence of aster yellows disease in lettuce

The degree of aggregation of lettuce plants infected by aster yellows phytoplasma (AYP) was investigated in 12 fields from three experiments. Position of diseased and healthy plants was mapped in a 6–9×12-m section of each field; for most analyses, fields were divided into 10-plant quadrats. Mean disease incidence (p) ranged from 0.01 to 0.30. The frequency of diseased plants was described by the beta-binomial distribution, with an index of aggregation (θ) ranging from 0 to 0.17, positively correlated withp, and generally increasing over time within a field. Distance-class analysis revealed a core-cluster size of only a few plants. However, spatial autocorrelations ofp between quadrats were not significant, indicating that the scale of spatial pattern was small, generally less than 10 plants. An overall measure of aggregation was given by the slope parameter of the binary form of the power law, in which the log of the calculated variance is regressed on the log of the theoretical variance for a binomial distribution. The slope was 1.18 and significantly different from 1. Results for this “simple-interest” disease are interpreted in relation to the persistent transmission of AYP by its aster leafhopper vector.     

北京地区红脂大小蠹空间分布型与抽样技术研究

对北京地区红脂大小蠹Dendroctonus valens LeConte空间分布型进行了研究。结果表明红脂大小蠹成聚集分布,其聚集原因是由红脂大小蠹本身的聚集行为或聚集行为与环境的异质性共同作用引起。同时,应用Iwao统计方法,提出了最适理论抽样数和最佳序贯抽样模型。