AIR1-CT92-0339 Enhancement, Dispersal and Population Dynamics of Beneficial Insects in Integrated Agro- Ecosystems

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AIR Cluster X - Inputs for Non-Food Crops : Integrated Crop Protection & Biological Control

	Proposal No:	AIR2-CT-92-0339
	Date Prepared:	April 1998
	Source:	Progress Report

Enhancement, dispersal and population dynamics of Beneficial insects in integrated agroecosystems.

Objectives:
The objective of the project was to create a network among the European scientists currently working on the enhancement, dispersal and population dynamics of beneficial insects in sustainable agroecosystems. This was achieved by organising workshops and increasing contacts between the European research groups working on this complex subject. The ultimate objective was to ensure that the current research programmes, being carried out to enhance the biotic components in integrated farming systems, are as effective as possible. The environmental benefit of this project is the promotion of knowledge on how to increase biotic diversity and resilience in agroecosystems and hence to reduce the need for pesticides.

Project Work:
The objectives were achieved through a series of international workshops that discussed research progress and development of methodology for studying beneficial insects such as ground beetles, spiders, parasitoids, coccinellids and syrphids in agroecosystems. Three topics were selected:

• Estimating population densities and dispersal rates of beneficial insects in agroecosystems. [Aarhus, Denmark 1993]
• Enhancement, survival and reproduction of beneficial insects in relation to food availability and quality of the habitat. [ The Netherlands 1994]
• Analysing and modelling the population-dynamics of beneficial insects in agroecosystems. [United Kingdom 1995]

Summary:
Each workshop was attended by around 25 participants selected by the coordinators on the basis of their involvement in relevant co-operative projects in the participating countries. They included experts from a number of well established groups from Research Institutes and Universities throughout Europe. Summaries of all contributions to the workshop are available and most contributions have or will also been published by Aarhus University Press as special issues of Acta Jutlandica. These proceedings also contain special discussion papers and some reviews on selected topics. The workshops significantly increased contacts between research groups of Denmark, Great Britain, Germany, Belgium and the Netherlands. Exchange of methodologies were particularly useful with respect to habitat management (including field margins), measurement of dispersal and densities and the use of new simulation modelling techniques. Knowledge gaps have been pinpointed on larval ecology of ground beetles, mortality factors in almost all beneficials and the ecology of sinks and sources at the local and regional landscape level. Due to involvement of participants in wider agricultural research programs, the enhancement of beneficial insects has become a more apparent theme in the development of integrated, organic and other sustainable farming systems.

Introduction
The aim of integrated farming systems is to develop systems of crop production that are both economically-viable and ecologically-sustainable. A more ecological approach to farming requires systems that cope not only with regional differences but that also make optimal use of available resources and minimal use of chemicals. This generally necessitates a careful choice of crops and crop rotation, a rational use of organic and mineral fertilisers and the development of systems of integrated control of pests, diseases and weeds. To maintain and restore the multiple functions and natural balance in agricultural fields, it is important to ensure that appropriate (semi-) natural environments remain within the local agroecosystem.

Integrated pest control is based on an optimal utilisation of the natural control agents within the agroecosystem in combination with selective use of pesticides when necessary. Though the role of beneficial insects in the suppression of insect pests and factors which affect their abundance is well documented, very little is known about the population dynamics of beneficial species. Such information however is essential if in future we like to manipulate insect predators and parasites under field conditions, or at least to predict the effects that changing agricultural systems have on their populations and effectiveness.

Recent developments in ecological theory and increasing evidence from field studies indicate that the population dynamics of predators and parasites in agricultural systems should be studied not only in individual fields, but also at the farm and the landscape levels. The main reason for this is that many of the species involved are adapted to the dynamic nature of agroecosystems and, as a consequence move frequently not only between different crops and fields and but also between fields and neighbouring (semi-) natural habitats. This frequent movement of insect populations makes it extremely difficult to predict population size of any insect species within a given field.

Realising, this is a key problem in the dynamics of beneficial insects in agriculture, several research groups in Europe have started to study dispersal of predators and other useful insects in relation to scale and infrastructure of the agricultural landscape. In several European countries considerable efforts are being made to study how field margins and farming systems affect the density of beneficial insects. All of these studies all face a range of similar (methodological) problems, such as how to sample the insects adequately, how to measure dispersal and how to develop suitable models for predicting the ways insect populations change under a range of conditions.

In order to answer some of these questions, and to develop standard methods so that the results obtained throughout Europe can be compared directly between countries. There is a considerable need to set-up a network in which European science in this field can be advanced considerably by the various participants pooling their resources and information. The advantage of such a network is that much of the information for the development of adequate methods is rarely sufficient on its own to merit publication. Hence this information can only be obtained from direct dialogue between scientists. The work described in this report is a summary of results of three workshops held in 1993, 1994 and 1995 where progress in this research field was reported, methodological problems were discussed and concepts were reformulated.

Background Science and central themes:
Agroecosystems can be defined as parts of the landscape that are mainly used for the production of crops. As such the infrastructure may consist of cropped fields, managed grassland, field margins, hedges, roads, tracks and roadsides, ditches and various (semi-) natural landscape elements such as woodland. The dynamic nature of agroecosystems is most pronounced in fields that are cultivated frequently, and often ploughed annually, as part of an overall system of crop rotation. Whenever fields are cultivated, treated or disturbed anyway, local numbers of beneficial insects may change drastically and suddenly as the insects move away from unfavourable to favourable habitat patches. In addition many species complete different parts of their life cycle in different parts of the agroecosystem. Hence, the spatial arrangement of suitable habitat patches within this dynamic situation, and the scale of the various elements of the overall system, are crucial to the survival of many beneficial insects.

Whenever attempts are made to study to study population dynamics in time and space, methods have to be developed for assessing:

• The quality of the various patches within the habitat. Patch quality is strongly related to the long- and short-term management, and obviously influenced considerably by different cropping and farming systems. Quantitative methods are needed that will enable the resources available to beneficial insects to be assessed accurately. Much can be learned from factorial experiment where the enhancement and hence habitat quality was studied.
• The density of insect populations in different environments. Current sampling methods for most beneficial insects are extremely laborious, inaccurate and difficult to use in large scale mosaics of vegetation. Improvement and standardisation of methods are essential for progress of this subject.
• Movement and rates of insect dispersal. The benefits to be gained from directional traps, radar tracking, and mark-recapture techniques need to be evaluated much more rigorously and new methods should be developed.
• Models that analyse and structure data so that spatial processes can be simulated and displayed on different scales. Several techniques for analysis and modelling of spatial dynamics have been developed in the last decade. As such these models often require large data sets to show their merits, and may act as a constraint to the kind of data to be collected. To achieve more progress co-operation between theoretical biologists and agroecologists is required.

From the above, three central themes were selected to be worked out: - density, spatial heterogeneity and dispersal - survival, reproduction and enhancement - analysis of population processes and modelling of dynamics

Results and discussion.

Density, spatial heterogeneity and dispersal.
Matters of population densities and temporal and spatial distribution of individuals are very basic to all population ecological studies. Methods in this field are both practical (sampling devices, monitoring techniques) and theoretical (designing sample schemes and analysing spatial patterns). The agricultural environment as a heterogeneous and very dynamic system is causing severe methodological constraints. Three relevant topics can be distinguished:

1. estimating absolute density of beneficial predators in agroecosystems
2. estimating spatial heterogeneity within fields in relation to habitat characteristics and prey distribution.
3. estimating dispersal between fields as well as between fields and uncultivated areas.

Advances and drawbacks of different trapping methods were explicitly summarised during the meetings and guidelines were formulated to make international studies more comparable and to choose the right methodology for the scientific questions. Strong emphasis should be given to test methods which measure absolute densities against those which measure relative densities or even activity-density (like pitfalls).

Spatial heterogeneity appeared to be mostly considered as a disturbing and complicating factor in research and it is recognised that in particular at a larger scale data are scarce and also hard to obtain. Sampling in a heterogenous environment is another problem that has to be solved. By making all new and possibly old data spatially explicit, geographic information systems and ARIMA models may help to judge the importance of spatial heterogeneity.

Very different approaches are available to study dispersal by walking or flight ranging from harmonic radar tracking of individual carabid beetles in a field to monitoring a broad range of organisms by a network of dispersal-interrupting traps at the landscape scale. Dispersal appears to be not only species-specific - grouping of organisms in terms of dispersal and other ecological categories may be helpful - but also within species much variability is present (between populations, seasonal variation, and even between physiologically different individuals). There is a lack of data to feed models for dispersal (diffusion, individual based models, and landscape permeability) which are currently being developed.

Survival, reproduction and enhancement.
. Insight into the basic population parameters survival and reproduction is crucial for understanding the dynamics of beneficial insects and to create a theoretical base for understanding and applying enhancement methods. Around this themes three topics were discussed in more detail:

1. survival factors for predators and parasitoids in agroecosystems.
2. reproduction in relation to habitat quality and food availability.
3. agricultural practices which enhance numbers of beneficial arthropods.

Survival and mortality are complementary parameters that are mostly used in a simply formulated way in population studies of beneficials whereas in reality they are very complicated. Data derived from laboratory experiments cannot be easily translated to field situations but may give cues for further study under field conditions. Survival under field condition appears to be driven by multiple factors that are extremely variable in time and space. Dominant factors related to agricultural practices can be quantified and may provide handles to improve survival conditions for beneficials. Reproduction is much better studied both in laboratory and field conditions. In particular the relation with food availability is well established, though the level of food sources for polyphygous predators is difficult to assess. Indicator parameters like weight, size and hunger levels are useful to quantify habitat quality. Methods to manipulate habitat quality in terms of food level are hardly available apart from avoidance of pesticides. Field margins, unpsprayed zones, strip management and covercrops seem are promising agricultural practices to improve breeding condition for many beneficials but quantitative data are scarce. The same practices seem to be profitable for promoting higher numbers of beneficials whether by improving survival conditions or reproduction. The contribution of field margin management to overall field management is very scale dependent since effects have not been established over more than 30 meters. On a larger scale local or regional landscape structure may have a strong impact on dynamics of beneficials, especially those which have long dispersal ranges. In-field management like covercrops etc. might be effective in many cases where beneficials have low dispersal capabilities.

Analysis of population processes and modelling of dynamics.
It is felt that quantitative analysis of population processes is very much supported by modelling. For predictions and many practical purposes, statistical models are improved by monitoring data over a long range of years. This makes it possible to incorporate more factors in the predictions and make them more precise. For understanding the interaction between crops, pests, beneficials and the environment various models have proven to be a helpful tool. In this framework knowledge in many cases is gathered at one or two levels of integration (individual, population or community). The flexibility of current simulation models makes it possible to link different levels and to include the spatial aspect. Individual behaviour and physiology can be analysed in laboratory and semi-field condition and different sets of environmental constraints. Effects of the most important abiotic factors (temperature, humidity), biotic factors (like food availability) and human induced factors (pesticides and soil management) on behaviour, in particular movement, and physiology (growth, starvation and reproduction) appear to be very complex. Individual data fed into population models mainly help to guide research and to provide frameworks. Their predictive power however appear to be very short term and small scaled.

At the population level predictive models have been developed which are mainly based on plant-pest interactions and growth reducing factors like predation. Their practical application is mainly in within season prediction and supporting rules for supervised control including a judgement of the impact of beneficials. Assessment of ratio between pests and beneficials is more and more used. Spatial modelling is an increasing field of interest. Coupling GIS like systems with spatial population models is very much depending on source-sink data which are scarce and on information on dispersal and mortality rates (which are very difficult to measure). Community approaches to estimate impact of beneficials can be very useful when large research groups use the same theoretical framework and are able to quantify the impact of the major antagonistic groups. Very promising results are reached by using supply/demand models as a background for tritrophic systems. The main question whether and why complexes of beneficials are better to regulate pest population can be linked to the impact of (functional) biodiversity in agroecosystems.

Workshop Information