Essential oils instead of neurotoxic substance - protection from pest by the use of innovative application of pheromones
The western corn rootworm (Diabrotica virgifera virgifera), together with its relative Diabrotica barberi, represents the most threatening pest organism of corn in the USA, where it causes expenses of approximately one billion US-Dollars each year. The western corn rootworm was introduced to Europe (Yugoslavia) in 1992, where it threatens to spread over the entire continent. Due to its enormous threat to corn it has been classified as quarantine pest by the EU in the directive 77/93/EWG.
In Austria the beetle has already conquered about 80.000 ha (approximately 1% of the total territory or one third of the corn production area). Invading from the east, it has so far affected the whole state of Burgenland. On approximately one third of Austria's corn production area, there is no crop rotation, offering optimum conditions for the new pest. This means that approximately 80.000 ha now face an enormous increase in toxic pesticides.
The application of pheromones offers a sustainable form of plant protection, which is currently limited by high cost and labour intensity. Therefore, this technique is currently mainly employed with high value crops, e.g. viticulture.
Issues and Objectives
This project intended to provide fundamental data for the development of an inexpensive pheromone carrier of biological origin, which is competitive in production as well as in application. Such a carrier should enable expansion of the plant protection method called "mating disruption technique" by making it applicable for automated processing. Herewith an instrument shall be offered to substitute toxic plant protection agents with non-toxic biodegradable formulations in corn production and, subsequently, in various other crop plants.
Objective 1 is the development of new, biodegradable carriers for pheromones based on renewable resources. We built on previous research of Calantis Infochemicals GmbH regarding composition of pheromone carriers, applying them on renewable resources.
Objective 2 is the development and improvement of strategies for monitoring and fighting of Diabrotica virgifera virgifera, the western corn rootworm based on the new carrier. We wanted to investigate the possibility to apply pheromones in the control of a pest beetle, namely D. virgifera, which has so far only been realized for the biologically distinct group of moths.
Methods applied with respect to Objective 1
lnorganic and biological raw materials were tested for their suitability as pheromone carriers, comparing them with capsules of synthetic polymers. Materials tested include silica gel, cotton, filter paper, paraffin wax, paraffin oil, corn oil and oil containing seeds (grapes, sunflower, papaya and melon). Furthermore the effect of fixatives used in the perfume industry (abietic acid, main component of plant resin); glycerol tripalmitate (typical component of natural fats); corn oil; on retention of volatiles on solid and liquid carriers was studied.
Evaporation rates of ethylcaprate, a cheap and structurally close substitute for the natural pheromone of D. virgifera, were monitored at constant temperature on all materials during three weeks. Evaporation rates were determined with a laboratory precision balance.
Based on the observations with ethylcaprate, the most suitable carriers were selected and tested with the real pheromone of D. virgifera (8-methyl-2-decanol-propanoate). Additionally, the impact of three different temperatures on the evaporation rates was investigated.
Methods applied with respect to Objective 2
As a first step, a method to supply sufficient unmated adult corn rootworm beetles was developed. Environmental conditions in a controlled environment were optimized to maximize larval emergence in a short period of time. The beetles were separated manually immediately after emergence and kept isolated. The unmated adults were released into cages containing living corn plants in pots. In a first approximation, cage design was adapted to suit the necessities of the beetles and to ensure natural behaviour. Cages of dark mesh suspended from an aluminium frame turned out viable. Unmated beetles were set free in such cages, supplied with young corn plants in pots. In regular intervals females were caught and dissected to check for presence of spermatophores, sign of successful copulation.
A corn field near Deutsch Jahrndorf, Burgenland, was chosen for the tests with pheromone traps. Sticky traps and jar traps ("Steinerfallen"), equipped with a traditional or newly developed pheromone dispenser of D. virgifera, were used. Sticky traps were checked weekly or monthly for total catches, jar traps were checked monthly. All six test regimes were observed in 4-fold repetition.
Under standard conditions all tested carrier materials excluding silica gel proved superior to traditional rubber dispensers. Further more, oil-containing plant seeds performed far better under standard conditions than other materials or combinations thereof. However, with elevated temperatures the advantages of oil-rich seeds diminished. From the tests with different concentrations it can be concluded that higher pheromone levels in the substrate reduce this temperature related effect. This observation, however, needs further investigation.
The field studies were heavily affected by exceptionally hot temperatures, which reduced the advantages of the newly developed pheromone dispensers. On the other hand, in the mating disruption experiments, we achieved exceptional results. After setting up a test system that provided a regular mating success of 80% under controlled conditions, reproduction could be reduced to 20% by application of the mating disruption technique with the new pheromone dispensers. This result might be considered a turning point in the application of pheromones in plant protection, because mating disruption with biologically degradable dispensers, suitable for automated processing, has been used successfully for a beetle for the first time. The proof of concept has been achieved for a technique that is capable of reducing cost and labour intensity of the mating disruption technique, a plant protection method that substitutes hazardous insecticides with harmless natural odours.
Dr. W. Harand
Calantis Infochemicals GmbH
Mag. Eric Schneider
Project or cooperation partner
- Dr. Andreas Kahrer
AGES Österr. Agentur für Gesundheit und Ernährungssicherheit GmbH
- Univ.Prof. Dr. Franz Hadacek
Mag. Eric Schneider
Calantis Infochemicals GmbH
Linzer Straße 410, 1140 Wien