A study under semi-field conditions on the efficacy of insecticides against Meligethes aeneus F. – Methodical approach and analysis

Abstract: Oilseed rape (Brassica napus L.) is one of the most important oilseed crops in the world. One of the major pests is the pollen beetle (Meligethes aeneus F.) (Nitidulidae). Under certain conditions the beetle can cause yield losses of up to 100%. One contributing factor is the decreased sensitivity to pyrethroid insecticides which has been reported from several European countries. There are two methods for insecticide susceptibility tests: insecticides can be tested in field trials or in the laboratory using the ‘glass vial testing method’. The presented approach is a semi-field method coming with precise statements of the reactions of the beetles to insecticides under realistic field conditions. The method is implemented to study the efficacy of insecticides with different mode of actions. Pollen beetle populations were collected from untreated fields in Saxony-Anhalt, Germany. Six insecticides with different mode of actions were sprayed in the field. Treated plants were cut and brought into the greenhouse on nine sampling occasions. Each plant was placed into a perforated plastic bag with 10 beetles. The vitality of the beetles was observed after two and five days following inoculation. To describe the efficacy of insecticides the beetles were divided into three categories (alive, damaged and dead). These observations were interpreted as a realization of classified ordered categorical random variables. For the analysis we used a threshold model (generalized linear model). The dependence of the observations due to repeated observations on the same plant was accounted for by a random plant effect. The comparison of the different insecticides and their significance test was made by using the marginal expectation values. For the computational implementation, we used the procedure NL MIXED (SAS 9.3).