Search

The main objective of this study was to evaluate two restoration techniques, “stone rows” and “stone rows + tree planting” on soil organic carbon (SOC) sequestration and structure in terms of water stable aggregates as well as the time required to restore soil fertility. The Carbon, Aggregate and Structure Turnover (CAST) model was used to model the changes of SOC content and water stable aggregate formation under the two restoration techniques. Field experiments used for calibration of the model were conducted using a randomized block design. Soil samples were class fractionated followed by a micro-aggregate isolation procedure. The two restoration techniques contributed significantly to improving soil total carbon content. By running five year simulation of the “stone rows”, the estimated total carbon input was 27 Mg ha-1 of which 6.1 Mg ha-1 were sequestered in the soil and 20.7 Mg ha-1 were released as CO2. In “stone rows + planting”, the total SOC content after five years was estimated to be 22.96 Mg ha-1, which was broken down to 15.43 Mg ha-1 aggregated carbon and 26.60 Mg ha-1 CO2. Fifty-year simulations showed a SOC increase to 54.8 Mg ha-1 in “stone rows”, and to 86.0 Mg ha-1 in “stone rows + planting”. This means that natural grassland vegetation slowly improves soil carbon content and soil quality, but with trees behind stone rows, the result will be about 50% higher.

In order to improve forecasting of pest epidemics, it is important to know the spatial scale at which specific forecasts are reliable. To investigate the spatial scale of aphid outbreaks, we have developed a spatio-temporal stochastic aphid population growth model, and fitted the model to empirical spatial time-series aphid population data using a Bayesian hierarchical fitting procedure. Furthermore, detailed spatial data of the initial phases of population growth was investigated in a semivariogram. Our results suggest that there is limited spatial variation in the initial occurrence probability at a spatial scale of 10 km. Consequently, the results support the hypothesis that initial aphid population sizes and outbreaks may be predicted in fields within a 10 km radius. For farmers, this may imply that they can rely their decision of whether to spray against aphids on observations made by other nearby farmers or by the consultancy service.

Oecophylla spp. are used as biocontrol agents for many types of insect pests. A large and stable population is essential for effective control of pests. Colonies of Oecophylla spp. can be transplanted from wild habitats into orchards. Transplanted colonies can only survive in the presence of egg laying queens. It is difficult to locate nests with egg laying queens in large colonies that may sometimes contain more than 100 nests. Therefore, the need to explore and develop methods for rearing newly mated queens in nurseries may not be over emphasized, hence the current study. In the first experiment, we tested three rearing methods on queen survival and colony establishment. In the second experiment, we compared feeding techniques of different weaver ants on young colony growth. We observed that queens were best reared under continuous, indirect access to water. The first workers emerged earlier (32 days on average) in indirect and direct continuous access to water methods than on limited access to water (sprinkled) (38 days on average). Moreover, rearing mated queens under continuous indirect access and continuous direct access to water methods saved labour and time, because of limited attendance to the colonies. Availability of water, sugar solution and different sources of protein throughout improved the growth of young colonies. Likewise, the number of workers increased rapidly. Therefore rearing mated queens in nurseries is possible and would minimize hustles in hunting for the colonies and their queens in the wilderness.

The larvae of Hermetia illucens are known to successfully bio-convert a vast range of organic substrates into high protein and fat biomass, but little is known about the larval instars. During this research, larval head capsules and biomass growth were measured daily and the specific metabolic rate of larger instars were considered. The head capsule measurements revealed that H. illucens pass through 6 actively feeding larval stadia before entering the last nonfeeding but migrating 7th stadium. Larval growth follows a sigmoid curve with slowly accelerating growth in the earlier stadia and decelerating growth in the latest stadia. In contrast, development was fast until reaching stadium 6 and then slowed down. Accordingly, the specific metabolic rate was high in instars 3, 4 and 5 and reduced in instars 6 and 7.

Bumblebee queens look for an abandoned, well-insulated mouse nest to start a family, where temperatures can be 15 degrees warmer than outside

In order to improve forecasting of aphid epidemics, it is important to know the spatial scale at which specific forecasts are reliable. To investigate the spatial scale of aphid epidemics, we have developed a spatio-temporal stochastic aphid population growth model, and fitted the model to empirical spatial time-series aphid population data using a Bayesian hierarchical fitting procedure. Furthermore, detailed spatial data of the initial phases of epidemic development was investigated in a semivariogram. Our results suggest that there is limited spatial variation in the initial occurrence probability at a spatial scale of 10 km. Consequently, the results support the hypothesis that initial aphid population sizes and epidemics may be predicted in fields within a 10 km radius. For farmers, this may imply that they can rely their decision of whether to spray against aphids on observations made by other nearby farmers or by the consultancy service.

Dronninger af humlebier søger forladte, velisolerede musereder for at stifte familie. Her kan de ikke alene holde varmen, men også hæve temperaturen med op til 15 grader.

In this paper we examine the hypothesis that diapause induction in the polyvoltine pod midge Dasyneura brassicae Winn. (Diptera: Cecidomyiidae) is controlled by cumulative global solar radiation during the larval stage. The correlation between field observations of relative diapause for 3 years and four environmental factors (daylength, temperature, cumulative daylight time, and cumulative global solar radiation) was investigated. The cumulative global solar radiation during the larval stage clearly showed the strongest correlation with the observed relative diapause. It was estimated that larvae which cumulated less than 71.1 kWh m-2 entered diapause. Compared to former theories on diapause induction in insects, this hypothesis explains how temperature and light can function together and, furthermore, it removes the requirement for biological clock involvement in diapause induction in insects.

Nontimber forest products are a source of income for women in rural African communities. However, these products are frequently damaged by insect pests. The present study investigates the diversity and damage rates of insect pests that attack Carapa procera seeds and Lophira lanceolata fruits. The experiment was set up in western Burkina Faso and, for C. carapa, consisted of pests collected from seeds that had fallen to the ground and from stockpiled seeds. For L. lanceolata, pests were collected from fruits on the trees, and on the ground. The collected samples were sent to the laboratory to estimate the proportion of damaged seeds/fruits and rear the insects. The results showed that Ephestia spp., Tribolium castaneum, Oryzeaphilus spp., and Tenebroides mauritanicus were the pests of Carapa procera seeds and Lophira lanceolatafruits. Ephestia spp. was recorded as the main pest of both C. procera and L. lanceolata, whereas T. castaneum was only detected from seeds of L. lanceolata. For C. procera, the stocks were the most infested (29 %) by Ephestia spp. The infestation rate of fruits of L. lanceolata by Ephestia spp. on trees (31.42 ± 3.75 %) was less than the rate of fruits by T. castaneum on the ground (44.00 ± 3.5 %). The different body sizes of Ephestia spp. may indicate the occurrence of two putative species, one from C. procera and another one from L. lanceolata. This work provides important information that could contribute to the setting up of a local-scale sustainable management framework for oil tree pests in Burkina Faso and surrounding countries.

We present a simulation study of the role of birds and egg pod predators in the population dynamics of the Senegalese grasshopper. The model was an energetics-driven ecosystem model that included a natural Sahelian grass, millet, grasshoppers, the egg pod predators bombyliidae and Tenebrionidae, and 24 species of birds that prey on grasshopper nymphs and adults. The model simulated the rain-dependent dynamics and migration along a five-location south–north transect in Niger and Senegal, and the main outputs were the grasshopper pressure on the transect, measured as accumulated transect grasshopper days, and the density of eggs ready to emerge the following rainy season. The model was calibrated using observations from transects in Niger (2003, 2004) and Senegal (2004). When input data from Niger 2003 and 2004 were applied, simulated reductions in grasshopper pressure during the rainy season from egg pod predators and birds, respectively, were within a range of 18–25%, but taken together the overall reduc...

Preference studies of many different collembolan species have categorised collembolans being selective in their food choice. To clarify whether collembolan food selectivity is related to fitness parameters, three species, Folsomia fimetaria, Protaphorura armata and Heteromurus nitidus, were fed three fungal species, Alternaria infectoria, Mucor hiemalis and Penicillium hordei, representing fungi of high, medium and low preference. The fungal diets were grown on soil and collembolan growth, survival and fecundity were measured. The fungus A. infectoria supported growth, survival and reproduction best in all three species of collembolans, while the fungus P. hordei was of low food quality. M. hiemalis was of medium quality and F. fimetaria was the only collembolan reproducing on M. hiemalis. F. fimetaria favoured reproduction over growth when confined to M. hiemalis. When P. armata was fed M. hiemalis it reached a size where reproduction normally starts, but no young were produced. This suggests that M. hiemalis lacks nutrients necessary for reproduction. H. nitidus did not perform well on any of the fungi offered, which were generally of low food quality for this species. In this study, where the fungal growth substrate is soil, there is a clear relationship between collembolan fitness and their food choice in contrast to some other studies where substrates optimised for fungal growth had been used. We show that specific fungal species are important for resource allocation to growth or reproduction and closely connected with food choice. Further, we argue that natural fungal growth substrates, such as soil, should be used in experiments of this kind.

Oecophylla longinoda is a species of eusocial colony living ants that prey upon other insects to feed their larva. Many of these insects are considered pests. An ecosystem model of the interactions between an O. longinoda colony and its potential prey is under construction by the team behind this article, and it is unknown which functional response equations are useful for eusocial insect colonies. We investigated the search rate of O. longinoda using artificial feeding experiments in a Tanzanian cashew (Anacardium occidentale L.) orchard to determine the search efficiency of the ants, and to assess which functional response equation can be used for eusocial insects. Artificial feeding experiments consisted of providing each of ten colonies 50 pieces of sardine (175 mg dry weight in average) in cashew trees at time 0 and counting the remaining food items at four intervals of 45 minutes during a seven day period. The equations of Gutierrez-Baumgärtner, Lotka-Volterra, and Nicholson-Bailey were assessed and the Nicholson-Bailey equation was found to be most suitable. The Gutierrez-Baumgärtner equation is useful if the demand for storage can be assessed. A large variation in search rates was found between the observed colonies and this problem is discussed in relation to Oecophylla sp. efficacy as a biological control agent.

The aim of this study was to assess, whether organic dairy farming has increased the biological diversity of field boundary vegetation when compared to conventional dairy farming, and if increasing organic farming duration affected diversity. The diversity of plant species in field boundaries was found to be higher under organic than under conventional farming. Analysis of community patterns revealed that ruderal species and species with affinity to nutrient rich conditions were most common in conventional field borders, whereas stress-tolerant species were more abundant around organic farming. These differences occurred only 3-4 years after conversion to organic farming.

Short-range predator-prey interactions among small soil-dwelling arthropods are poorly understood. In this study, we measured the behavioural interactions between the predacious mite Hypoaspis aculeifer Canestrini (Gamasida: Laelapidae) and its collembolan prey Folsomia fimetaria L. (Collembola: Isotomidae) and the influence of sex, size, starvation, and poisoning with the organo-phosphate dimethoate. Pairs of mite and springtail were placed in 18-mm diameter test arenas with a plaster of Paris substrate and their behaviour were measured by a computerized vision system, which automatically detected the locomotory activity of the two animals, their encounters, and the precise time of capture and killing. Data suggest that neither the mite nor the springtail possesses near-field sensory detection of the opponent. A Cox regression model showed that mite sex, size ratio between the predator and prey, average mite velocity, and encounter rate had a significant influence on the mite-capture efficiency (springtail survival). Female H. aculeifer demonstrated higher capture efficiency than males by catching and killing their prey after fewer encounters. Surprisingly, starvation had only a moderate effect on the mite locomotory behaviour and no influence on the capture efficiency as such. Also, springtail survival was independent of its moulting stage. Sublethal poisoning with dimethoate, on the other hand, dramatically increased the mite's capture rate, probably by impeding the evasive response of the springtail.

A new and simplified method for extraction of ergosterol (ergosta-5,7,22-trien-3beta-ol) from fungi in soil and litter was developed using pre-soaking extraction and paraffin oil for recovery. Recoveries of ergosterol were in the range of 94-100% depending on the solvent to oil ratio. Extraction efficiencies equal to heat-assisted extraction treatments were obtained with pre-soaking extraction. Ergosterol was detected with thin-layer chromatography (TLC) using fluorodensitometry with a quantification limit of 8 ng. Using visual evaluation of images of TLC plates photographed in UV-light the quantification limit was 16 ng.

Oedaleus senegalensis is a serious pest of millet in the Sahel, but the correlation to crop loss remains largely unknown. Therefore, the correlation between densities of O. senegalensis, defoliation level and millet yields was investigated in Niger in 2008, and a simple model to foresee the yield based on these parameters was developed. The yield was significantly correlated to both the density of O. senegalensis and the defoliation level on 17 September. The best model toforesee millet yield involved grasshopper density and cumulated rainfall and may be regarded a tentative method in O. senegalensis control.

Summary The spring and summer abundance of soil living mites and Collembola was investigated in organically grown field plots which had been covered with either the nitrogen catch crops winter rye, hairy vetch, fodder radish and a control (stubble). The catch crops were incorporated in the soil shortly before sowing of spring barley with under sown clover grass. Microarthropods were extracted from 10 cm deep soil samples and were taken in May, June and August. The densities of both microarthropods were extremely high with up to 120,000 Collembola m−2 and 90,000 mites m−2. The highest densities of Collembola were found in the plots with fodder radish as a catch crop, and the most abundant species were Tullbergia sp., Isotoma notabilis and Folsomia fimetaria. The mite fauna consisted mainly of Mesostigmatic and Prostigmatic mites and was more abundant in the catch crop plots than in the control plots in early June. The input of organic matter from the catch crops is supposed to be part of the reason for the high microarthropod densities, but the barley with undersown clover grass may also play a role.

Egg production by the cereal spider Erigone atra was used as a fitness parameter for evaluating the food quality of two species of Collembola: Folsomia fimetaria and Isotoma anglicana. Drosophila melanogaster was used as reference prey. We tested the hypothesis that due to differences in food quality, the two Collembola species would affect the reproduction of the spider differently. The quality ranking of the prey types turned out as: I. anglicana > D. melanogaster > F. fimetaria. With F. fimetaria alone, spiders were unable to maintain reproduction. E. atra was more efficient in utilising I. anglicana and D. melanogaster. Thus, daily consumption rates of I. anglicana were lower in spite of higher egg laying rates by E. atra. A mixed diet of F. fimetaria and D. melanogaster resulted in a lower reproductive output than a pure diet of D. melanogaster, indicating a toxic element in F. fimetaria. In the mixed diet F. fimetaria had a negative influence on the consumption capacity of the spider towards D. melanogaster, while D. melanogaster had a positive influence on the consumption capacity towards F. fimetaria. It is concluded that a high abundance of I. anglicana may support a high reproductive output of E. atra, while the presence, of F. fimetaria in fields may reduce the spider's reproductive output.

The relationship between crop architecture and spray interception was investigated in spring barley at two developmental stages. Height and outer surface area were determined for stems, leaves and ears, when present. To trace the droplet interception by the crop a Nuorescent dye was used. To avoid diffi- culties in measuring spray deposition on plant surfaces, the non-intercepted pesticide at di†erent heights in the air between the plants was determined from the deposit on glass strips placed horizontally at di†erent crop strata. A regres- sion model was used to relate the glass strip measurements to the plant surface measurements. Analysis of the crop architecture indicated that the position and size of the leaves, the stem thickness and stem surface could all be described as a function of the height of the Nag leaf. Analysis of deposition measurements showed that stems, leaves and ears all contributed signi-cantly to spray interception, which correlated in a log-linear way with plant surface. The plant surfaces of stems, leaves and ears showed no signi-cant di†erences in the fractions of droplets that were captured per unit of surface area, which fraction was indicated as the "k valueI. This showed that the droplet interception in spring barley could, in prin- ciple, be modelled using a single coefficient. As a one-parameter model would restrict interpretability and comparability of the present results with other studies, the approach with separate k values was nevertheless preferred when analysing the deposition pattern in the crop and on the soil. The prospects of using crop height as the main model parameter for crop architecture in future predictions of pesticide deposition in cereals are discussed. 1998 SCI ( Pestic. Sci., 53, 252E262 (1998)

Weaver ants (Oecophylla spp.) are managed in plantations to control insect pests and are sometimes harvested as a protein-rich food source. In both cases, the amount of insect prey caught by the ants is imperative for returns, as more prey leads to more effective biocontrol and to a higher production of ants. Malaise-like traps placed in trees may catch flying insects without catching ants, as ants may use pheromone trails to navigate in and out of the traps. Thus, ants may increase their prey intake if they are able to extract insects caught in traps. In a mango plantation in Tanzania, we estimated the amount of insects caught by simple traps (cost per trap = 3.9 USD), and whether Oecophylla longinoda was able to collect insects from them. On average, a trap caught 110 insects per month without catching any weaver ants. The number of insects found in traps with ant access was 25% lower than in control traps (ants excluded), showing that ants were able to gather prey from the traps. Ant activity in traps increased over time, showing that prey extraction efficiency may increase as ants customize to the traps. The prey removed from traps by ants constituted 5% of the number of prey items collected by O. longinoda under natural conditions (without traps), potentially increasing to 14% if ants learn to extract all insects. Thus, prey intake may be increased with 5–14% per 3.9 USD invested in traps. These numbers increased to 38 and 78%, respectively, when light was used to attract insects during night time. Combining ant predation with insect trapping is a new approach potentially building increased returns to ant biocontrol and to ant entomophagy.

Mismanagement of soil fertility is one of the major challenges for farmers in the Sahelian zone of Niger. This study, conducted in 2012 and 2013 in western part of Niger, aimed at examining the effects of combined Zai and Mulching techniques on soil fertility and millet productivity. The experimental design was a randomized Fischer block with four treatments (Zai, mulching, Zai + mulching and Control) and four replicates. In the Zai treatment, 200 g cattle manure was added per Zai hole (2.8 t/ha) and millet straw (2.0 t/ha) was spread in the mulching treatment. The control treatment did not receive cattle manure or millet straw. The measurements concerned grain and straw yield of millet (Pennisetum glaucum (L.) R. Br.) as well as physico-chemical soil characteristics. The results show that the Zai + mulching treatment improved soil fertility parameters and grain yield significantly. The content of available phosphorus and clay in the soil was doubled after two years. The soil organic carbon content had increased from 0.45 to 2.1 g kg-1. The cation exchange capacity and pH had increased by one compared to the control. The content of total nitrogen (0.1 to 0.2 g kg-1) and total potassium (8.6 to 57.8 mg kg-1) did not vary significantly between treatments. An increase of 250 kg ha-1 grain of millet compared to the control was obtained. Concerning the straw yield, the highest values were obtained by Zai treatment in both years (855±216 kg ha-1 in 2012 and 843±313 kg ha-1 in 2013) and Zai + mulching in 2013 (888±251 kg ha-1). The combination Zai + mulching improved the soil fertility and millet productivity and can be used to restore degraded soils.

The interaction between the pod gall midge (Dasyneura brassicae Winn.) and its most important parasitoid (Platygaster oebalus Walk.) in rape fields was investigated by aid of a computer model. The model is driven by temperature and the population dynamics is modelled by a distributed delay procedure. A relatively large program procedure was used to describe the functional response. Simulation of the population dynamics over 10 years demonstrated that the parasitoid gets the highest population if it exploits the host egg masses lightly, i.e., aggregated response would reduce the population size. The model was used to investigate how vulnerable the populations of both host and parasitoid are to insecticide applications, and was able to explain a change in emergence pattern of P. oebalus which seems to have occurred in Danish rape fields.

The population development of the pod gall midge ( Dasyneura brassicae Winn.) in winter rape and spring rape ( Brassica napus L.) is described by a computer model. The model is temperature driven and the population dynamics is described by a distributed delay procedure. Simulation by the model was found to be a useful tool to gain more information from a life-table investigation than can be obtained by traditional life-table analysis. Further the model was able to quantify the consequence of a density-dependent process in the life cycle. The output from the model was very sensitive to changes in egg-larval mortality. The strong sensitivity was largely due to an inversely density-dependent mortality later in the life cycle. This was the pre-cocoon mortality, that most likely is caused by natural enemies.

The developmental time of the juvenile stages of the pod gall midge (Dasyneura brassicae Winn.) was investigated in the laboratory at constant temperatures. The results were used to estimate the developmental zero (6.7°C for egg-larval stage, 8.1°C for development in the soil) and the thermal requirements (134°DD for egg-larval stage, 141°DD for the development in the soil). The results were generally found to be consistent with developmental data in the literature. Using the parameters from the development in the soil, the degree day model was found only to produce good predictions of the time of emergence in spring 1988. The model was unable to describe the effect of the very dry spring 1989. Zusammenfassung Uber die Entwicklungsdauer der Kohlschotengallmucke Dasyneura brassicae Winn. (Dipt., Cecidomyiidae) Die Entwicklungsdauer des Ei-Larvenstadiums und die Dauer des „Kokonstadiums” im Boden wurden im Laboratorium bei 5 konstanten Temperaturen untersucht. Die Beobachtungen wurden zur Schatzung der Parameter des Grad-Tag-Modelles verwendet. Der Entwicklungsnullpunkt lag bei 6,7 °C, und die Entwicklung dauerte 134°DD fur Ei und Larve. Fur die Entwicklung im Boden betrug der Entwicklungsnullpunkt 8.1 °C und die Dauer 141 °DD. Die Parameter wurden zusammen mit Bodentemperaturen von 1988–1989 in das Grad-Tag-Modell eingesetzt. Die Resultate wurden mit Beobachtungen uber den Flug der Kohlschotengallmucke verglichen. Eine Ubereinstimmung wurde nur fur 1988 gefunden. Das Wetter im Winter und Fruhjahr 1989 war anormal mit relativ hohen Temperaturen und geringen Niederschlagen. Unter diesen Bedingungen versagte das Grad-Tag-Modell.

Tillage operations and field traffic may cause soil compaction and alter the pore characteristics in soil. These practices often lead to a reduction in habitable pore space for the soil mesofauna. In the present study the abundance of some euedaphic species of Collembola was investigated under a range of soil bulk densities normally found in agricultural soils. The study was performed using containers with defaunated soil that was compressed to six levels of bulk density in the range 1.02–1.56 g cm−3. One of the following species was added to a separate series: Mesaphorura macrochaeta, Protaphorura armata, and Folsomia fimetaria. The number of individuals and the concentration of ergosterol (used to estimate fungal biomass) were measured after each experiment and related to bulk density and pore size distribution. A series of experiments in which straw was added to the soil in order to increase microbial life was also included. Only F. fimetaria was used in the straw amended series. In the soil experiments without straw amendments, the numbers of M. macrochaeta and P. armata, were significantly reduced when bulk densities increased from 1.37 to 1.47 g cm−3. F. fimetaria did not exhibit any significant response to compaction. The ergosterol concentration was independent of bulk density. When straw was added, the abundance of F. fimetaria declined significantly with increasing bulk density from 1.21 g cm−3. The decline in collembolan numbers was probably due to the decline in coarse pores (>120 μm) because the ergosterol concentration was independent of bulk density. These results show that soil structure and decline in habitable pore space are the key parameters in the abundance of euedaphic Collembola in soil.

Summary 1. The Collembola is one of the important prey groups for generalist arthropod predators in agro-ecosystems. Differences in the quality of available species may play a significant role in the build-up of a community of natural enemies. The value of some common epigeic and hemi-edaphic Collembola as prey for adults and larvae of the carabid beetle Bembidion lampros was assessed in laboratory experiments. 2. Consumption capacity, egg production and the efficiency of converting prey into eggs were used as quality criteria for beetle adults, kept on diets of the collembolans Isotoma anglicana, Isotoma notabilis, Isotomurus prasinus, Folsomia fimetaria and Lepidocyrtus cyaneus, with fruit flies Drosophila melanogaster used as a high quality comparison prey. Survival, developmental time and teneral adult weight were used as quality criteria for beetle larvae on diets of Isotoma anglicana, Isotoma notabilis, F. fimetaria, D. melanogaster and a starvation treatment. 3. Collembola were offered to adults in dead and live treatments to assess the cost of prey capture and handling in relation to prey quality. 4. Bembidion lampros ate more dead than live Collembola. Egg production declined over time on all collembolan diets, indicating a lower quality of all species compared with D. melanogaster, but there was considerable variation between species. The highest food conversion efficiency occurred on F. fimetaria, L. cyaneus and D. melanogaster, while Isotoma notabilis could not be utilized by B. lampros for egg production. 5. Larvae completed development with low mortality on Isotoma anglicana and F. fimetaria, although there were differences in developmental time. The two Collembola seemed to be of relatively higher quality for larvae than for adults. Significantly higher teneral weight occurred on a diet of D. melanogaster compared with the Collembola. 6. The effect of Collembola quality on the beetle fecundity and larval developmental time suggests that agricultural management for natural enemies, should aim to benefit the species composition of the prey population.

Direct topical impact of an insecticide spray on a population of a non-target leaf-eating beetle, Gastrophysa polygoni, was studied, and the relative importance of phenology, instar susceptibility and instar specific exposure was evaluated. Two insecticides, cypermethrin and dimethoate, were investigated. In the laboratory, topical toxicity to eggs, second-instar larvae and adults was recorded in dose-response experiments. The spatial distribution of larvae and eggs were measured in the field. Deposition of insecticide onto eggs, second-instar larvae and adult specimens was measured at different positions within the crop canopy by use of a dye tracer technique. A temperature-driven population model was constructed to simulate population development of all life stages in the field. The model was based on laboratory measures of growth and development at various temperatures. Mortality due to direct insecticide exposure was calculated as a function of population demography, spatial distribution of individuals, spatial deposition of the insecticide, and stage-specific susceptibility. Cypermethrin had the greatest impact, reducing population size by 19-32%. The life stages most sensitive to cypermethrin were the larval instars. As the population developed from eggs to larvae and imagines, the impact of one spraying first increased and then decreased according to the proportion of larvae in the population. Dimethoate had less effect on the population, i.e. 1.9-7.6% reduction. Dimethoate was most toxic to the egg stage, and consequently the effect on the population decreased as the proportion of eggs decreased due to hatching. The direct effect of insecticide spraying was significantly affected by all three factors investigated, i.e. phenology, life stage susceptibility and stage-specific exposure. The latter factor is composed of both spray flux at various spatial positions in the canopy and the ability of different life stages to retain spray droplets.

One of the great challenges in ecotoxicology is to extrapolate results from exposure-effect experiments in the laboratory to a prediction or understanding of exposure-effect relationships at ecosystem level. A range of tests has been developed or is under development (Kula et al., 1995) for the assessment of exposure - effect relationships in terrestrial systems. Most of these are single-species tests and the interpretation of the results are problematic because they do not include the interactions, which take place in a community consisting of a large number of interacting species under natural climatic conditions

Vegetation data including plant cover, biomass, species richness, and vegetation height was sampled on a copper-contaminated field with total copper contents varying from 50 to almost 3,000 mg/kg soil. The field was covered by early succession grassland dominated by Agrostis stolonifera. Plant cover, biomass, species richness, and vegetation height generally decreased with increasing copper content, although the highest biomass was reached at intermediate copper concentrations. Multivariate statistical analyses showed that plant community composition was significantly correlated with soil copper concentration and that community composition at soil copper concentrations above 200 mg/kg differed significantly from community composition at lower copper levels. Comparison of single-species (Black Bindweed, Fallopia convolvulus) performance at the field site and in laboratory tests involving field soil and spiked soil indicates that the laboratory tests conventionally applied for risk assessment purposes do not overestimate copper effects. Interaction between copper and other stressors operating only in the field probably balance the higher bioavailability in spiked soil.

Desertification and land degradation affect the livelihood of a large number of people in the drier areas of the world, but there is no generally accepted scale, on which the degree of degradation can be measured. However, scientists are working on finding indicators of degradation, although it can be difficult to identify to what these indicators might be related.In this paper, we have investigated a number of soil-physicochemical parameters in relation to a degradation scale of land uses. The results show that high sand content and C/N values may be used as indicators of degradation, and high contents/values of carbon, organic matter, nitrogen, available K+, CEC, SBE may be used as indicators of no or weak degradation. CEC showed the steepest gradient in relation to land use and may be the most useful soil physicochemical degradation indicator.The investigated land uses had different densities of trees, which was the reason for suggesting the vegetative biomass relative to a virgin forest situation as a scale of degradation. Desertification and land degradation affect the livelihood of a large number of people in the drier areas of the world, but there is no generally accepted scale, on which the degree of degradation can be measured. However, scientists are working on finding indicators of degradation, although it can be difficult to identify to what these indicators might be related.In this paper, we have investigated a number of soil-physicochemical parameters in relation to a degradation scale of land uses. The results show that high sand content and C/N values may be used as indicators of degradation, and high contents/values of carbon, organic matter, nitrogen, available K+, CEC, SBE may be used as indicators of no or weak degradation. CEC showed the steepest gradient in relation to land use and may be the most useful soil physicochemical degradation indicator.The investigated land uses had different densities of trees, which was the reason for suggesting the vegetative biomass relative to a virgin forest situation as a scale of degradation.

Simulation models must be clear in their concepts and design to be useful tools for ecological research. To facilitate clear and efficient model development, we present a modelling framework (OOMP) based on the concepts of the metabolic pool model and on object-oriented programming techniques. Modellers can use OOMP: (1) to increase productivity through the safe reuse of existing code; (2) to produce clear and more understandable code; (3) to prolong the life-span of their model through easier code maintenance; and (4) to enhance scientific communication through the use of a common conceptual and technical framework. We first explain the concepts of the metabolic pool approach and summarise the terminology of object-oriented design (OOD) and then show how OOMP reflects both. Finally, we discuss the advantages of OOD over earlier programming methods and compare our modelling framework with others. OOMP offers a selection of generic modelling components that the modeller can refine and combine to build a desired model. Modellers can make use of OOMP (1) as a technical platform for model development or (2) as a source of OOD principles that can benefit any modelling project.

In agricultural soil, a suite of anthropogenic events shape the ecosystem processes and populations. However, the impact from anthropogenic sources on the soil environment is almost exclusively assessed for chemicals, although other factors like crop and tillage practices have an important impact as well. Thus, the farming system as a whole should be evaluated and ranked according to its environmental benefits and impacts. Our starting point is a data set describing agricultural events and soil biological parameters. Using machine learning methods for inducing regression and model trees, we produce empirical models able to predict the soil quality from agricultural measures in terms of quantities describing the soil microarthropod community. We are also interested in discovering additional higher level knowledge. In particular, we have identified the most important factors influencing the population densities of springtails and mites and their biodiversity. We also identify to which agricultural actions different microarthropods react distinctly. To obtain this higher level knowledge, we employ multi-objective regression trees. ispartof: Ecological modelling vol:191 issue:1 pages:131-143 ispartof: location:SLOVENIA, Bled status: published