Process-based modeling of the control of beet armyworm, Spodoptera exigua, with baculoviruses in greenhouse chrysanthemum

This thesis describes the development of a process-based simulation model for the population dynamics of beet armyworm, Spodoptera exigua , and baculoviruses in greenhouse chrysanthemum. The model (BACSIM) has been validated for two baculoviruses with clear differences in biological characteristics, Autographa californica multicapsid nucleopolyhedro-virus (AcMNPV) and Spodoptera exigua MNPV (SeMNPV). The validated model has been used to generate scenario studies, which are used for the evaluation of the potential of baculoviruses as biological control agents.The first requirement for the construction of BACSIM is quantitative understanding of the processes that determine the chrysanthemum- S. exigua -baculovirus system, such as insect behavior and population dynamics, the baculovirus infection cycle and virus transmission routes. These processes have been studied and described in chapters 2 to 5.S. exigua parameters : The developmental rate and background mortality of populations of S. exigua larvae have been quantified on chrysanthemum in a greenhouse situation (chapter 4). In addition, the preference of feeding sites and leaf visit rate of S. exigua larvae have been studied on chrysanthemum plants under controlled conditions (chapter 4).Baculovirus parameters : The infectivity and speed of action of AcMNPV and SeMNPV has been determined for various stages of S. exigua larvae that were reared on artificial diet (chapter 2). To study the effect of the host plant on the baculovirus infection cycle the infectivity and speed of action of SeMNPV has also been determined for S. exigua larvae reared on chrysanthemum (chapter 4). S. exigua larvae reared on chrysanthemum appeared to be more susceptible to SeMNPV than larvae reared on artificial diet. The polyhedron inactivation rate of AcMNPV and SeMNPV on greenhouse chrysanthemum has been quantified in chapter 3 and 7, respectively. Wild-type AcMNPV and SeMNPV have marked differences in infectivity and speed of action, but the relative inactivation rates of AcMNPV and SeMNPV polyhedra were not significantly different. The deletion of the egt , pp34 or p10 genes from AcMNPV had no or only a marginal impact on the infectivity, speed of action or inactivation rate of this virus (chapter 2). In other virus-host combinations such deletions had a major effect on these parameters. As the AcMNPV recombinants behaved biologically in a similar way as wild-type AcMNPV, wild-type AcMNPV and SeMNPV were chosen as viruses for the model system.Baculovirus transmission : Horizontal transmission of SeMNPV in S. exigua populations with varying densities of primarily SeMNPV-infected larvae has been studied in chrysanthemum under greenhouse conditions (chapter 5). The distribution of polyhedra released from SeMNPV-killed larvae over chrysanthemum plants has been quantified in detail under controlled conditions (chapter 4). The vertical transmission rate of SeMNPV in S. exigua populations has been determined by the quantification of the percentage of first instar larvae originating from egg batches produced by sublethally infected moths that contracted SeMNPV (chapter 5).The process-based simulation model BACSIM is based on a detailed quantitative description of the behavior and population dynamics of insects, plant growth characteristics, spray deposition, the baculovirus infection cycle and transmission routes (chapter 7). These data were obtained from experiments mentioned above, or were retrieved from literature. The evaluation of the biological control of insect pests with BACSIM offers the possibility to include many treatments and situations, to simulate baculoviruses with extreme biological properties and to include many covariables that may modify the efficacy of baculoviruses in practice, such as crop age and temperature. In addition, this simulation approach allows optimization procedures that can assess optimal virus properties and spraying regimes under varying conditions.The BACSIM model has been validated with independent data of ten greenhouse trials in which the efficacy of AcMNPV and SeMNPV against synchronized populations of S. exigua larvae in chrysanthemum was assessed. Dose- and time-mortality relationships of different virus concentrations and S. exigua target stages were determined and crop injury assessed as the total leaf area consumed (chapter 6). The validation of the simulation model BACSIM with the independent data of AcMNPV and SeMNPV applications in greenhouse chrysanthemum was in general satisfying. Mortality levels of AcMNPV and SeMNPV infected larvae were generally predicted within a 25% error margin compared to the observed values. None of the deviations were higher than 40%. All values of simulated foliage consumption, caused by S. exigua populations treated with AcMNPV or SeMNPV applications, fell within the 95% confidence intervals of measurements. However, simulated time-mortality relationships gave generally lower survival times than was measured in experiments. A hypothesis that may explain this discrepancy is the functioning of the underside of chrysanthemum leaves as a refuge area where S. exigua larvae are exposed much less to polyhedra (chapter 8).Scenario studies with BACSIM were carried out to evaluate the effectiveness of different spraying regimes, dosages, UV protection agents and speed of action of viruses in different pest situations (chapter 9). The recommended dosages of SeMNPV applications based on simulations with BACSIM corresponded well with recommended SeMNPV dosages determined for cultivation practice. An early timing of virus applications, soon after egg batch deposition, appeared to be essential for effective control. UV-protection agents may contribute only marginally to effective biological control in the glasshouse. The decay rates of SeMNPV and AcMNPV already ensure a period of exposure to active virus that is long enough for caterpillars to acquire a lethal dose under practical conditions. The effect of genetic improvement towards shortening the survival time of infected larvae depends on the situation in which such a virus is used. When used in a situation with constant immigration of pest insects, a greater reduction of feeding injury is achieved with a faster killing virus than with a wild-type virus. When, however, immigration of pest insects occurs by way of sudden influxes, resulting in synchronous insect populations in the crop, it appears that early timing of virus applications is more critical to reduce crop injury than using a fast-killing virus. In such a situation, good monitoring followed by virus application is indispensable, and may even alleviate the need for a fast killing virus.Besides the use of BACSIM as a tool to assist in the determination of effective spraying regimes of (genetically modified) baculoviruses or formulations under varying conditions, the model can also be used as a tool to gain insight in the insect-baculovirus-crop system. For example, BACSIM may be used to address fundamental ecological questions or used to evaluate the relative importance of viral characteristics for crop protection purposes. In addition, BACSIM may contribute to the assessment of risks associated with the use of genetically modified baculoviruses by the generation of quantitative information of the population dynamics of recombinant baculoviruses in crops. Finally, the methodology described in this thesis may form a basic concept for process-based modeling of more complex systems, such as the control of bollworm with baculoviruses in cotton.</p

Plaagregulatie door groenblauwe dooradering

Landschapselementen vormen de groenblauwe dooradering van het landschap. Hoewel ze geen productiefunctie hebben, kunnen ze toch een positieve bijdrage leveren aan de landbouw. Veel natuurlijke vijanden, die plagen in landbouwgewassen kunnen reguleren, zijn namelijk afhankelijk van deze groenblauwe dooradering. De aanwezigheid van voldoende en de juiste soort groenblauwe dooradering kan dan ook tot een verhoogde plaagonderdrukking leiden en bijdragen aan een duurzame landbouw met een minimaal gebruik van bestrijdingsmiddelen

Plaagonderdrukkende landschappen op de computer

Uit empirisch onderzoek wordt steeds duidelijker dat de inrichting van het agrarisch landschap de onderdrukking van plaagorganismen in de landbouw kan beïnvloeden. In dit artikel wordt geïllustreerd hoe simulatiemethoden van ruimtelijke dynamische interacties tussen natuurlijke vijanden en plaagorganismen op landschapsschaal gebruikt kunnen worden om meer inzicht te krijgen in de werking van biologische bestrijding in een landschapscontext. Dergelijke modellen kunnen goed helpen bij het zoeken naar een landschapsinrichting die biologische bestrijding maximaal ten goede kom

Agroforestry systems can mitigate the impacts of climate change on coffee production: A spatially explicit assessment in Brazil

Climate change may impose severe challenges to farmers to maintain agricultural production levels in the future. In this study we analysed the effect of projected changes in climate on the area suitable for coffee production in 2050, and the potential of agroforestry systems to mitigate these effects in a major coffee production region in southeast Brazil. We conducted a spatially explicit analysis with the bioclimatic model MaxEnt to explore the area that is suitable for coffee production in 2050 when coffee is grown in unshaded plantations and in agroforestry systems. The projected climate in 2050 was assessed using 19 global circulation models, and we accounted for the altered microclimate in agroforestry systems by adjusting the maximum and minimum air temperature. The climate models indicated that the annual mean air temperature is expected to increase 1.7 °C ± 0.3 in the study region, which will lead to almost 60 % reduction in the area suitable for coffee production in unshaded plantations by 2050. However, the adoption of agroforestry systems with 50 % shade cover can reduce the mean temperatures and maintain 75 % of the area suitable for coffee production in 2050, especially between 600 and 800 m altitude. Our study indicates that major shifts in areas suitable for coffee production may take place within three decades, potentially leading to land conflicts for coffee production and nature conservation. Incentives that contribute to the development of coffee agroforestry systems at appropriate locations may be essential to safeguard coffee production in the southeast of Brazil.</p

Opportunities and limitations for functional agrobiodiversity in the European context

To counteract the negative effects of intensive agriculture there is increasing interest in approaches that reconcile agricultural production with the conservation and sustainable use of biodiversity and associated ecosystem services. Integration of functional agrobiodiversity (FAB) in agricultural systems holds promise to meet these challenging objectives, but requires the generation, transfer and implementation of tailor-made knowledge, and policy development. Currently various initiatives are undertaken across Europe to develop and assess the potential of biodiversity-based management practices by farmers, industry, researchers and governmental and non-governmental organizations. In this paper we show that the Convention on Biological Diversity and planned reforms in EU policy offer scope to further implement FAB concepts via legislation for biodiversity conservation, pesticide use, water quality, environmental protection and conservation of genetic resources. At the same time we observe that there are still impediments to the adoption of FAB approaches, including (i) translation of general knowledge to tailored, ready-to-use management practices, (ii) limited information on the effectiveness of FAB measures in terms of crop yield and quality, profitability, and reduction of agrochemical inputs, (iii) lack of appropriate financial accounting systems that allow fair accounting of the private investments and public benefits, and (iv) the implementation of FAB measures at the right spatial scales, which requires coordination among the various actors in a region. Current and new legislation may provide incentives to address these limitations and contribute to the further development and integration of FAB concepts in agricultural systems in Europe

Transmission dynamics of the multicapsid nucleopolyhedrovirus SeMNPV in Spodoptera exigua populations in greenhouse chrysanthemum

The multicapsid nucleopolyhedrovirus, SeMNPV, is naturally maintained in Spodoptera exigua populations by vertical transmission from females to eggs and by horizontal transmission from cadavers of caterpillars to other caterpillars. Laboratory and greenhouse experiments were conducted to quantify transmission rates and provide baseline data to assess the potential of this virus to maintain itself naturally in pest populations after application in biocontrol programs. As to vertical transmission, 18% of the first instar larvae originating from egg batches produced by infected moths contracted SeMNPV, while 34% of the egg batches gave rise to one or more infected first instar larvae. As only few large egg batches were virus-free, 70% of all uninfescted larvae hatched in egg batches that contained one or more infected larvae. Substantial horizontal transmisson was observed under greenhouse conditions. Presence of 0, 1 or 10 infected first instar larvae in a batch of 100 first instar larvae resulted in survival to the fifth instar of 41, 30 and 20%, respectively. However, the effect on crop injury was marginal. The observed high transmission rates favour the maintenance of SeMNPV in S. exigua populations in greenhouses