Development of an „Attract & Kill“ strategy for the control of western corn rootworm larvae
Mario Schumann
Doctoral thesis
Date of Examination:
2012-02-10
Date of issue:
2013-07-31
Advisor:
Vidal, Stefan Prof. Dr.
Referee:
Vidal, Stefan Prof. Dr.
Referee:
Schütz, Stefan Prof. Dr.
Referee:
Scheu, Stefan Prof. Dr.
Persistent Address: http://hdl.handle.net/11858/00-1735-0000-0001-BAF2-9
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Abstract
English
The western corn rootworm (WCR - Diabrotica virgifera virgifera Coleoptera: Chrysomelidae) is an important maize pest worldwide and the most damaging part of the beetle’s life cycle is the below ground feeding of the larvae on the maize roots. The larvae use CO2 to locate maize roots. This orientation cue can be incorporated into the chemical control of the larvae by attracting them to a soil insecticide (Tefluthrin) with CO2 emitting capsules, implementing an “Attract & Kill” (A&K) strategy. This mechanism is eventually aiming at enhancing insecticide activity and reducing the application rate of Tefluthrin. Due to the cryptic feeding habit WCR larvae are difficult to observe, so non destructive methodologies were developed to evaluate larval behaviour, movement and spatial distribution. Furthermore the management of the larvae with the capsules alone and in an “Attract & Kill” combination were tested under semi field and field conditions. 1. Changes in the spatial distribution of WCR larvae were studied in an observation device at a fine scale (resolution 4.5 x 5 cm) and at a semi field scale with soil stratification (resolution 16 x 13 cm) to gain knowledge on basic WCR larval spatial ecology at a plant scale: a) WCR larvae initially distribute in a major cluster close to their point of insertion and then actively disperse in the root system over time. The overall distribution in the root system remains aggregated. b) WCR larvae move to more developed root parts around the plant base and also exhibit an increased vertical movement over time. c) Differences in root phenology have a minor influence on spatial distribution changes. 2. The influence of CO2 emitting capsules on the spatial and temporal distribution of WCR larvae was investigated in an observation device. Mortality rates of WCR larvae with an A&K strategy were analysed at different application rates of Tefluthrin and compared with a conventional treatment of Tefluthrin in the root system: a) WCR larvae initially aggregate at and around the capsules but move away from the capsules over time. b) With the addition of Tefluthrin to the capsules, WCR larvae were targeted in an A&K approach. The mortality of WCR larvae significantly increased compared to a conventional treatment of Tefluthrin in the root system at lower insecticide application rates. 3. CO2 emission by the capsules and the control of the larvae with the capsules alone and in an “Attract & Kill” strategy were tested. Under semi field conditions the reduction in larval densities in the greenhouse and under field conditions the reduction in root damage was measured: a) CO2 levels around the capsules increased in the soil for up to 20 days at greenhouse and 28 days under field conditions. b) Application of the capsules between the maize rows alone reduced larval densities by up to 17 % under semi field conditions but could not reduce root damage under field conditions. c) The combination of the capsules with Tefluthrin between the maize rows reduced larval densities by up to 27% under semi field and root damage up to 30% under field conditions. The insecticide activity could not be enhanced compared to a conventional application of Tefluthrin only in the maize rows. d) The combination of the capsules with Tefluthrin in the maize rows under field conditions could increase the reduction in root damage by up to 15% at a quarter of the standard application of Tefluthrin compared to an application of Tefluthrin only.
Keywords: Western corn rootworm; larval behaviour; attract and kill; carbon dioxide
