Development of a simulation model for the population dynamics of the onion fly Delia antiqua in Germany*

Delia antiqua is a serious pest of many species of the genus Allium, including onions and chives. Over a period of two years (1997/1999), we have developed a model to simulate the population dynamics of D. antiqua based on an extended Leslie model. The model structure as well as the developmental functions for the different life stages of D. antiqua are presented. Using daily mean air and soil temperatures, the model calculates the population matrix for developmental stages of D. antiqua including eggs, larvae, pupae and adults. The simulation can be used to optimize the timing of control measurements against a specific life stage of D. antiqua. Flight activity can be simulated using wind speed as additional information. Simulated flight activity and the observed flight activity of D. antiqua monitored with water pan traps in three different regions of Germany in 1998 are presented and discussed. The model, which was programmed as part of the SWAT 3.5 package of programs to simulate the population dynamics of root‐fly pests in horticultural crops, will also be available via other expert systems such as PASO.     

Exceeding the threshold value for Trioza apicalis Förster 1848 in carrot fields did not cause damage as revealed during monitoring in Germany from 2017–2020

Journal of Plant Diseases and Protection - The carrot psyllid Trioza apicalis Förster 1848 is a carrot pest in Europe that can cause serious damages in case of massive occurrence. Damages up...     

Routine On-farm Soil Tillage Helps Control Asparagus Fly (Plioreocepta Poeciloptera)

Asparagus fly (Plioreocepta poeciloptera (Schrank, 1776)) is a serious pest in German asparagus (Asparagus officinalis L.) production. To evaluate the effects of different routine on-farm soil tillage measures on the number of flies emerging the following spring, asparagus fields in Lower Saxony, Germany, were investigated. Soil samples were taken before and after tillage in autumn 2017 and autumn 2018. Investigations were also conducted in both years on the effect that the soil depth at which asparagus fly pupae were buried had on the emergence of adult flies.

This study revealed that the number of emerging flies was not reduced by mulching, but was significantly reduced by subsequent tillage and/or tillage and dam formation. The emergence rate of adult flies was significantly reduced the deeper the pupae had been buried the previous autumn. The effects also depended on the year. The highest mean emergence rate observed was 68% and 45% for pupae buried at a depth of 10?cm and 20?cm, respectively. In conclusion, the key mechanism causing a decrease in asparagus fly population the following spring through routine on-farm tillage could be the burial of pupae when forming dams. Routine on-farm soil tillage can be regarded as a physical measure for controlling asparagus fly and is therefore an essential tool in the integrated pest management of asparagus production.

     

Einsatz der Pheromonverwirrungstechnik zur Regulierung der Rosskastanien-Miniermotte Cameraria ohridella Deschka u. Dimić (Lep.: Gracillariidae)

The horse chestnut leafminer is an introduced invasive pest that every year causes extensive damage to the leaves of the white flowering horse chestnut tree. An environmentally friendly method to control insect pests involves the use of sex pheromones for mating disruption. A large quantity of artificial pheromone is released into the insect plant system confusing males to the extend that they are unable to locate receptive females. In order to test the potential efficacy of the mating disruption technique on the horse chestnut leafminer we set up semi-field trials with closed experimental units and varying leafminer densities. We counted the number of leaf mines on pheromone treated horse chestnut trees and compared them with an untreated control. Mating disruption lead to a significant reduction in damage by more than 90% in the first and second generation of the leafminer, irrespective of the initial leafminer density. Although these results are very encouraging, high population densities of the horse chestnut leafminer in nature and the patchy distribution of horse chestnut trees in the cities will challenge the efficacy of mating disruption in the field. Further experiments are planned with open experimental units and typical horse chestnut trees in various parks and gardens.     

Stakeholder participation in the distribution of freshwater in the Netherlands

It is widely recognized that integrated approaches are required to manage our limited water resources in an effective and sustainable manner. In the Netherlands, this is mostly realized by organizing integrated spatial development processes. This paper presents a discussion in which the distribution of freshwater is integrated with spatial development in the southwestern Delta in the Netherlands. This discussion is characterized by uncertainty in knowledge and stakeholders with diverging perceptions. By actively involving these stakeholders in a process of problem structuring, it was possible to reach an agreement on the preferred direction for solutions. Problem-structuring involves that stakeholders actively participate in formulating the problem and its solutions. It is characterized by interaction between stakeholders and the integration of expert knowledge and stakeholder knowledge. Based on these practical experiences, we conclude that putting integrated water management into practice benefits from a problem-structuring approach. This enhances learning processes and contributes to the development of an agreed upon and valid knowledge base. As the context of such processes is highly dynamic, there is a need for transparent and adaptive process management.     

Testing mating disruption of the horse chestnut leafminer <Emphasis Type="Italic">Cameraria ohridella</Emphasis> (Lepidoptera: Gracillariidae) in field tents

Since the beginning of the invasion of the horse chestnut leafminer, Cameraria ohridella Deschka and Dimic 1986 (Lepidoptera: Gracillariidae), into Europe over 20 years ago the damage to white flowering horse chestnut trees, Aesculus hippocastanum L (Sapindales: Hippocastanaceae) has remained extensive. This study evaluates the possible use of pheromone mating disruption as a control option against the horse chestnut leafminer. The heterogeneous distribution of ornamental trees in parks and gardens requires a different approach to evaluate pest control than in homogeneous crop fields, orchards or plantations where mating disruption is usually applied. For this reason we set up field experiments with host trees of the same age and size in field tents with a defined number of leafminers in two different densities. In the first experiment the effective quantity of newly developed C. ohridella pheromone dispensers was tested by recapturing males using traps baited with virgin females. Ninety-five percent less males were captured if three or more dispensers were positioned at a 4 m radius around the outside of an experimental tent. This set up was then used in the second experiment where male and female leafminers were released into field tents in order to assess the effect of pheromone on the reduction of leaf mining damage. Surprisingly, the pheromone dispensers were found to have no effect on the number of leaf mines at either low or high leafminer densities. Mating sites of the horse chestnut leafminer, multiple matings and distribution of pheromone dispenser are discussed as possible factors influencing the outcome in this study.     

Biodegradation: The Reason for the Inefficiency of Small Organic Acids in Chelant-Assisted Phytoextraction

Natural low molecular weight organic acids (NLMWOA) have been shown to be useful in enhancing phytoextraction without a high leaching probability. Nevertheless, their efficiency has in many cases been unsatisfactory. The objective of this study was to investigate the reason for the inefficiency of three NLMWOAs (citric acid, oxalic acid and tartaric acid) in enhancing phytoextraction. In several experiments attention was directed not only to the biodegradation of the NLMWOAs, but also to the microorganisms involved, and their influence on the bioavailability of Cu. During a time period of 96 h the biodegradation of the NLMWOAs increased the natural pH-value of the soil by approximately 1 unit and decreased the bioavailability of Cu from 175 mg kg^?1 to approximately 140 mg kg^?1. As microorganisms were detected with polymerase chain reaction sequencing and with the aid of high performance liquid chromatography measurements, it can be deduced that the fungi, Cordyceps sp., Paecilomyces sp. and the bacteria Burkholderia sp. can degrade all three used NLMOWA. A successive application of the three NLMWOAs to increase the efficiency is therefore not feasible, because with each NLMWOA application the number of microorganisms which can degrade the NLMWOAs increases and thus the degradation is accelerated. These results combined with result from previous studies show that the NLMWOAs are unsuitable in enhancing phytoextraction of heavy metals from the soil.