Mario Schumann

Development of a CO2-releasing coformulation based on starch, Saccharomyces cerevisiae and Beauveria bassiana attractive towards western corn rootworm larvae

BACKGROUND CO2 is known as an attractant for many soil-dwelling pests. To implement an attract-and-kill strategy for soil pest control, CO2 -emitting formulations need to be developed. The aim of the present work was to develop a slow-release bead system in order to bridge the gap between application and hatching of western corn rootworm larvae. RESULTS We compared different Ca-alginate beads containing Saccharomyces cerevisiae for their potential to release CO2 over a period of several weeks. The addition of starch improved CO2 release, resulting in significantly higher CO2 concentrations in soil for at least 4 weeks. The missing amylase activity was compensated for either by microorganisms present in the soil or by coencapsulation of Beauveria bassiana. Formulations containing S. cerevisiae, starch and B. bassiana were attractive for western corn rootworm larvae within the first 4 h following exposure; however, when considering the whole testing period, the maize root systems remained more attractive for the larvae. CONCLUSION Coencapsulation of S. cerevisiae, starch and B. bassiana is a promising approach for the development of attractive formulations for soil applications. For biological control strategies, the attractiveness needs to be increased by phagostimuli to extend contact between larvae and the entomopathogenic fungus growing out of these formulations.

The role of carbon dioxide as an orientation cue for western corn rootworm larvae within the maize root system: implications for an attract‐and‐kill approach

BACKGROUND Western corn rootworm larvae use CO2 to locate maize roots. However, the importance of CO2 as a specific orientation cue close to maize roots has not been investigated unequivocally. This study aimed at elucidating the effect of CO2 -emitting capsules in combination with a soil insecticide (Tefluthrin = attract and kill) within the root system. We hypothesized that the capsules would result in aggregation of the larvae at the soil insecticide, thus increasing its efficacy. A nondestructive observation device was used to study larval distribution and behaviour. RESULTS Spatial analysis of distance indices (SADIE) revealed aggregation of the larvae around the capsules in an attract-and-kill treatment after 4 h, which was not found with the conventional treatment without the capsules. However, larval mortality did not differ between treatments. CONCLUSION CO2 is a weak attractant for western corn rootworm larvae within the root system. Consequently, an attract-and-kill strategy based on a CO2 product will not contribute to better control compared with conventional Tefluthrin applications. Host-specific compounds, combined with a CO2 source, should be used to target more larvae, making attract and kill a feasible management option against this pest.

Dispersal and spatial distribution of western corn rootworm larvae in relation to root phenology

1 Despite the increasing economic importance of root feeding pests such as the western corn rootworm (WCR) Diabrotica virgifera virgifera, basic parameters about their below ground biology are only partly understood. The present study investigated the dispersal and distribution of WCR larvae in the maize root system during their development at two growth stages of maize (BBCH 13–14 and BBCH 17–18). 2 Dispersal of the WCR larvae increased as they developed; the larvae moved off their original place of emergence and into deeper soil layers. Overall, changes in the horizontal distribution of the larvae were more extensive than changes in the vertical distribution. 3 The spatial analysis of distance indices revealed that the larvae had an aggregative distribution throughout their development. The feeding site of larvae in the root system was determined by the stage of larval development. Initially, WCR larvae started feeding in close proximity to their emergence location and moved to more developed root tissue towards the end of their development. 4 Differences in root phenology mainly influenced the distribution of the larvae at the end of their development, when larvae exhibited increased vertical movement at a later growth stage of maize. 5 The mechanisms of these distributional changes and the implications for the management of WCR larvae are discussed, especially with regard to chemical control, because fewer larvae are expected to be targeted at a later growth stage of maize.

Soil Application of an Encapsulated CO2 Source and Its Potential for Management of Western Corn Rootworm Larvae

ABSTRACT Western corn rootworm (Diabrotica virgifera virgifera LeConte) larvae use carbon dioxide (CO2) to locate the roots of their hosts. This study investigated whether an encapsulated CO2 source (CO2-emitting capsules) is able to outcompete CO2 gradients established by corn root respiration in the soil. Furthermore, the following two management options with the capsules were tested in semifield experiments (0.5- to 1-m2 greenhouse plots): the disruption of host location and an “attract-and-kill” strategy in which larvae were lured to a soil insecticide (Tefluthrin) between the corn rows. The attract-and-kill strategy was compared with an application of Tefluthrin in the corn rows (conventional treatment) at 33 and 18% of the standard field application rate. Application of the CO2-emitting capsules 30 cm from the plant base increased CO2 levels near the application point for up to 20 d with a peak at day 10. Both the disruption of host location and an attract-and-kill strategy caused a slight but nonsignificant reduction in larval densities. The disruption of host location caused a 17% reduction in larval densities, whereas an attract-and-kill strategy with Tefluthrin added at 33 and 18% of the standard application rate caused a 24 and 27% reduction in larval densities, respectively. As presently formulated, the CO2-emitting capsules, either with or without insecticide, do not provide adequate control of western corn rootworm.

Development of an attract-and-kill co-formulation containing Saccharomyces cerevisiae and neem extract attractive towards wireworms: Development of an attract-and-kill co-formulation

BACKGROUND Wireworms (Coleoptera: Elateridae) are major insect pests of worldwide relevance. Owing to the progressive phasing-out of chemical insecticides, there is great demand for innovative control options. This study reports on the development of an attract-and-kill co-formulation based on Ca-alginate beads, which release CO2 and contain neem extract as a bioinsecticidal compound. The objectives of this study were to discover: (1) whether neem extract can be immobilized efficiently, (2) whether CO2 -releasing Saccharomyces cerevisiae and neem extract are suitable for co-encapsulation, and (3) whether co-encapsulated neem extract affects the attractiveness of CO2 -releasing beads towards wireworms. RESULTS Neem extract was co-encapsulated together with S. cerevisiae, starch and amyloglucosidase with a high encapsulation efficiency of 98.6% (based on measurement of azadirachtin A as the main active ingredient). Even at enhanced concentrations, neem extract allowed growth of S. cerevisiae, and beads containing neem extract exhibited CO2 -emission comparable with beads without neem extract. When applied to the soil, the beads established a CO2 gradient of >15 cm. The co-formulation containing neem extract showed no repellent effects and was attractive for wireworms within the first 24 h after exposure. CONCLUSION Co-encapsulation of S. cerevisiae and neem extract is a promising approach for the development of attract-and-kill formulations for the control of wireworms. This study offers new options for the application of neem extracts in soil.

Assessment of acute toxicity tests and rhizotron experiments to characterize lethal and sublethal control of soil-based pests: Acute toxicity tests and rhizotrons

BACKGROUND Characterizing lethal and sublethal control of soil-based pests with plant protection products is particularly challenging due to the complex and dynamic interplay of the system components. Here, we present two types of studies: acute toxcity experiments (homogenous exposure of individuals in soil) and rhizotron experiments (heterogeneous exposure of individuals in soil) to investigate their ability to strengthen our understanding of mechanisms driving the effectivness of the plant protection product. Experiments were conducted using larvae of the western corn rootworm Diabrotica virgifera LeConte and three pesticide active ingredients: clothianidin (neonicotinoid), chlorpyrifos (organophosphate) and tefluthrin (pyrethroid). RESULTS The order of compound concentrations needed to invoke a specific effect intensity (EC50 values) within the acute toxicity tests was chlorpyrifos > tefluthrin > clothianidin. This order changed for the rhizotron experiments because application type, fate and transport of the compounds in the soil profile, and sublethal effects on larvae also influence their effectiveness in controlling larval feeding on corn roots. CONCLUSION Beyond the pure measurement of efficacy through observing relative changes in plant injury to control plants, the tests generate mechanistic understanding for drivers of efficacy apart from acute toxicity. The experiments have the potential to enhance efficacy testing and product development, and might be useful tools for assessing resistance development in the future.

Entwicklung von Attract-and-Kill Formulierungen auf Basis von coverkapselterBäckerhefe und Neem-Extrakt

Recent studies on endophytic Kosakonia radicincitans DSM 16656T demonstrated a wide plant growth-promoting activity. The application of this Gram-negative bacterium as a biofertilizer is limited due to the lack of adequate formulation that protects the cells during drying and storage and supports plant colonization. Here we set out to elucidate the compatible solutes accumulation influence of K. radicincitans triggered by osmotic stress on its capacity as an endophyte in radish plants. We found that physiological modifications by osmotic stress treatments and accumulation of compatible solutes during cultivation, improve the capability of K. radicincitans formulated in dry beads to colonize and to promote radish growth. Thus, pre-conditioning of cells with NaCl 4% and by adding compatible solutes such as hydroxyectoine during cultivation induced a positive effect on relative gene expression response, enhancing significantly the ability to colonize plant tissue up to 10 fold. Additionally, when this osmolyte was added, either dry matter of tuber or leaves increased by 3 % and 13.59 %, respectively in comparison to beads without the bacterium. These first results indicate that a systematic approach to cultivation and formulation may increase the endophytic capacity of this bacterium.

Technical scale production of encapsulated Saccharomyces cerevisiae and Metarhizium brunneum attractive to wireworms

ABSTRACT Wireworms (Coleoptera: Elateridae) have recently become an increasing problem as agricultural insect pests due to the phasing out of effective control options. Entomopathogenic fungi such as Metarhizium brunneum have proven to be a promising microbial antagonist for wireworm control. Here, we tested whether the efficacy of M. brunneum can be increased through a combination with CO2, emitted by Saccharomyces cerevisiae, as an attractant (=attract-and-kill). We aimed at a technical scale production of a formulated biological control agent offering a practical and economically feasible application for wireworm control. Therefore, a novel technical formulation process for encapsulated S. cerevisiae (Attract beads) and M. brunneum (Kill beads) was investigated. For the bead production by jet cutting, the parameters nozzle diameter, pump speed, cutting device speed and collecting distance were evaluated. In order to dry the beads in a short time while maintaining a high cell viability, different drying temperatures during fluidised-bed drying were tested and the best results were obtained with an inlet air temperature profile between 50°C and 40°C. CO2 production of the beads in the soil was highest for co-applied Attract and Kill beads. The potential of beads to modify wireworm behaviour (Agriotes sputator) was tested in a rhizotron experiment. The Attract-and-Kill treatment (co-applied beads) significantly attracted wireworms, whereas Attract beads and Kill beads alone showed a weak, but non-significant attraction. Wireworm mortality could not be enhanced due to a low rate of mycosis from M. brunneum infection.