16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
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Monitoring Agrioteslineatus and A. obscurusin organic production using pheromone traps
Sufyan, M.[1], Neuhoff, D.1& Köpke, U.1
Key words: pheromone traps, Agriotes spp., range of attractiveness
Abstract
Wireworms, particularly Agriotes lineatus and A. obscurus are becoming a problem in organic crop production causing economically severe damage on potatoes and other arable crops. Since pesticide application for direct control is not allowed in organic farming, reliable methods for quantifying wireworm infestation levels and forecasting damage are urgently needed for any control strategy. In the present work, the assessment of the range of attractiveness of pheromone traps to male A. lineatus and A. obscurus beetles was investigated in 2006 and 2007. The results indicated that the trap recovery rate of released beetles was more dependent on release distance than on time. Recovery ratesgreater than40% were only noted for short release distances (up to 10 m), while less than 10% of the beetles released at a distance of 60m returned to the traps. Recovery rates of click beetles were also negatively affected by cold and wet weather conditions. Most of the beetleswere recovered within the first 3 days.
Introduction
Wireworms, the larval stage of click beetles (Coleoptera: Elateridae), have become one of the most serious polyphagous insect threats to many agricultural crops worldwide (Parker and Howard 2001). They live in the soil for 4-5 years where they cause germination failure and injury of underground organs e.g. potato tubers. There are different species of plant damaging click beetles in Europe, butAgriotes lineatus and A. obscurus are most abundant in Germany (Furlan et al. 1999).Problems are particularly high inOrganic Farming, due to favouring crop rotations with leys and the absence of chemical control options. For these reasons, the development of alternative control strategies has become an essential task.A pheromone trapping system (Furlan et al. 2001 and Toth et al. 2003) proved to be a highly sensitive risk assessment tool to complement existingbaiting techniques (Parker 1994) and other risk assessment methods (Parker and Seeney 1997). The sex pheromone mixtures give a good indication of presence and flight peaks of the male beetlepopulations (Ester et al. 2002) and are permitted according to EU regulation 2092/91 on OF.Currently click beetle flight behaviour is monitored by using pheromone traps, but it is still unclear whether apart from monitoring, a control of soil wireworm population is possible by mating disruption. Mating disruption has been tested against some tortricid pests and was successful for controllingthe codling moth, Cydia pomonella (Moffitt and Westigard 1984) and the European grape moth, Eupoeciliaambiguella (Charmillot et al. 1987). Any potential control by mating disruption needs to consider the range of attractiveness of the pheromone. Despite the significance of pheromone traps,information onthe range of attractiveness of pheromone traps to Agriotes species is lacking. The objective of this work was to assess the effectiveness of pheromone traps to attract A. lineatus and A.obscurus on clover grass field and bare soil for forecasting wireworm damage andfor considering their use in mating disruption.
Materials and methods
The experiments were conducted at the experimental farm for organic agriculture ´Wiesengut`, University of Bonn, Germany located in River Sieg Valley/Rhineland (longitude: 7°17' east latitude: 50°48' north). The soil is acid alluvial loam andthe climate is comparatively mild with an annual average temperature of 10.2° C. The farm has been under organic management since 1987.
Experimental set up and trap types
Mark release recapture experiments were carried out in 2006 and 2007 in order to determine the average range of attractiveness of pheromone traps. Experiments were carried out on two types of soil coverage (clover grass and bare soil) in natural dispersal peaks i.e. May and June of both years.
Traps were placed at least 100 m distant to each other. Each group of 25 beetleswas released both upwind (west) and downwind (east) at distances of2, 5, 10, 15, 20 and 60m from a central YATLOR funnel trap baited with fresh lures for bothA. lineatus and A. obscurus. After the release, trap catches were recorded at 1hr, 1d,and every day up until 30d. For every assessment date the absolute (i.e. not cumulative) number of captured beetles was recorded. Data were analysed by ANOVA followed by Tukey’s test (α ≤ 0.05) using SPSS.
Source of beetles
The adults of the male click beetles, A. lineatus and A. obscurus were collected by putting pheromone traps in different highly infested fields on the farm. Field collections were made as early as possible according to species biology. All captured beetles were sexed, identified and put in aerated boxes filled with moist soil and fed with fresh gramineae leaves until experiments.
Marking of beetles
Different colours (red, green, white and blue) were used to paint the elytrae of beetles. One marking color was used for each of six distances and randomly assigned to the captured beetles. For each treatment (release distance) 25 males were marked by painting the elytrae with non washable pencils resulting in a total of 150 beetles per trial and species. One hour later, marked beetles were released in the field.
Results
Recovery rate of A. lineatus and A. obscurus
Of total of 1260 beetles released of A. lineatus in two years, 517 were recovered (Fig. 1).The moving behaviour of A. obscurus followed a similar pattern to A. lineatus and of a total of 1260 beetles released in two years, 536 beetles were recovered. High recovery rates were noted only for short release distances (up to 10 m), while less than 10% of the beetles released at 60m returned to the traps.High recovery rates were only noted for the early assessment dates (up to 3 days). Beyondthe third day, beetles were caught in small numbers, and appeared to approach the traps passively. The resultsfurther suggest that the recovery rate of released beetles (A. lineatusand A. obscurus) to the traps was more dependent on release distance than on time, while the wind direction had no effect on the recovery rate. Recovery rates of beetles appeared to be reduced by cold and wet weather conditions during both years.
Figure 1:Influence of different release distances and assessment date on the recovery rate of A. lineatus averaged over two years and four trials. Values followed by different letters are significantly different, Tukey’s test (α < 0.05).
Discussion
There were two important factors that influenced the range of attractiveness of the pheromone traps: release distance and time.Soil type and wind directionhad no effect on the recovery rate. On average,the recovery rate did not exceed 40% for either beetle species, suggesting that on average 60% of the beetles were lost,killed, or were attracted to- and chose to mate female beetles. The high recovery rates for short release distances suggested that painting the beetles was not the main reason for decreasing their recovery. However, the studied parameters were strongly affected by stress and climatic factors, particularly by rainfall. Apparently the range of attractiveness is quite low and is also influenced by the fact that beetles travelling on the soil may encounter thepheromone traps by chance.
Information on the moving behaviour of beetles is still insufficient in the literature. However, current results are supported by Vernon et al.(2001) who observed low flight activities of bothA. lineatus and A. obscurus under the field conditions in Canada. The efficacy of various alternative control methods under consideration (e.g. mass trapping, mating disruption and physical exclusion) would likely be affected by flight activity of beetles.Implications of these findings for practical control of wireworms by mating disruption are part of our ongoing research programme(Sufyan et al. 2007).
Conclusions
The presented experiments suggest that a relatively high number of traps or an extension of the trapping periods need to be considered in order to adultmonitoring. Theresults regarding the range of attractiveness show that the applied technique for male trapping issuitable for limited areas like greenhouses and small areas with high value crops sensitive to wireworms such as asparagus.Whether pheromone traps for click beetles can be used for reducing wireworm populations in the soil is still unclear. Regardless of direct control of click beetles via pheromones, the techniquecan play an important role in detecting the presence of the beetles, making prevention strategies more efficient. For organic agriculture the pheromone technique is apromising tool to cope with pest problems, which are still a major reason for yield losses in many crops.
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[1]Institute of Organic Agriculture (IOL), University of Bonn, Katzenburgweg 3, D-53115 Bonn, Germany, ,