Innovative organic aphid control in the protected cultivation of peppers and berries (BIOTRACT) (BIOTRACT)

Aphids represent one of the most significant threats in various outdoor and protected cultivations, resulting in significant economic losses. Biological control using natural enemies such as predatory insects and parasitoid wasps is a crucial tool in managing these pest insects, but it still does not proceed optimally. The overarching objective of this project is to enhance the biological control of aphids in economically important fruit and vegetable crops by applying microbial attractants and repellents to improve existing monitoring techniques and develop a new, innovative control technique. Previous research based on laboratory experiments by the applicants has demonstrated that insects can be effectively attracted or repelled by odors of microbial origin. Specifically, the following sub-objectives are aimed at: (i) optimization of existing monitoring systems, (ii) development and application of suitable sugar blends to support natural enemies through an insect-attracting feeding device, and (iii) development and application of an attract & kill control strategy for hyperparasitoids. An inventory of hyperparasitoids in Flanders was conducted as the basis for the work plan. The research focused particularly on the protected cultivation of peppers and small fruits in Flanders.

Results

WP0: Inventory of hyperparasitoid communities in protected cultivation of pepper and raspberry

The objective of this work package was to inventory the hyperparasitoid community in the protected cultivation of pepper and raspberry in Flanders. This inventory took place at five pepper and five raspberry farms, which were sampled monthly for one year (from March to October). The found individuals were identified to genus level based on morphological characteristics and counted. A subset of these individuals was further identified to species level via DNA analysis. It was found that hyperparasitoids are present early in the growing season and remain present throughout the entire season in pepper and raspberry cultivation. Furthermore, it was observed that hyperparasitoids of the genus Dendrocerus constitute the main part of the hyperparasitoid community in both pepper and raspberry. As such, Dendrocerus hyperparasitoids represent an important target for improving biological aphid control using parasitoids. In the execution of our further experiments, significant emphasis was therefore placed on Dendrocerus. Additionally, it was concluded from this work package that banker plants can be used to monitor the hyperparasitoid community. The results of this work package have been published in a scientific journal (van Neerbos et al., 2024), as well as in Proeftuinnieuws (Clymans et al., 2023).

WP1: Screening and identifying microbial attractants and repellents

The objective of this work package was to screen a set of bacteria for attraction or repulsion of selected target insects, i.e., the aphids Amphorophora idaei and Myzus persicae var. nicotianae, the aphid parasitoids Aphidius colemani, A. ervi, and A. matricariae, and the hyperparasitoids Asaphes suspensus and Dendrocerus aphidum. A pre-screening of 7 bacteria (5 Bacillus strains, 1 Curtobacterium strain, and 1 Staphylococcus strain) that were promising in previous research led to a selection of three strains that were further evaluated in this WP. The different bacteria were evaluated using choice experiments with a 2-arm (Y-shaped) olfactometer, where insects were given the choice between a scent of the bacteria (fermentation medium) and a control scent (non-inoculated medium). It was concluded that the behavior of the insects strongly depended on the tested bacterial strain, ranging from attraction to repulsion. Furthermore, it was concluded that the response of the insects varied between and within the different trophic levels. After chemical analysis of the emitted odors, the relative amount of each component in each odor blend was correlated with the observed behavior of the 7 target insects in the Y-tube. It was found that benzaldehyde and styrene were significantly attractive to A. colemani, and that linalool and acetic acid were significantly attractive to D. aphidum. Based on this, synthetic VOC blends were composed, and it was found that a blend of 1 µg styrene and 10 ng benzaldehyde attracted A. colemani more strongly in the olfactometer than the individual components, while D. aphidum was significantly repelled by this blend. A reverse trend was observed for a blend of linalool and acetic acid, as well as for both components individually. In summary, it was concluded that we succeeded in developing a synthetic VOC blend (styrene/benzaldehyde) that can attract desired parasitoids and repel unwanted hyperparasitoids under laboratory conditions, and a second blend (linalool/acetic acid) that can attract hyperparasitoids and repel Aphidius parasitoids. The results of this work package have been published in a scientific journal (van Neerbos et al., 2023a), as well as in an industry magazine (van Neerbos et al., 2021).

WP2: Utilization of microbial attractants and repellents

The objective of this work package was to apply the developed VOC blends to develop innovative tools to improve the biological control of aphids. Specifically, in a first experiment, a suitable dispenser and dose of the styrene-benzaldehyde blend were identified for attracting Aphidius parasitoid wasps under practical conditions. Subsequently, attempts were made to optimize existing monitoring techniques based on the developed blends, and a management strategy (attract & kill) for hyperparasitic wasps was evaluated based on the identified VOC components. Finally, a feeding device was developed to provide beneficial Aphidius parasitoids with sugars to meet their energy needs. In the future, this device could be further improved with attractive odors to enhance its effectiveness (easier localization by the parasitoids).

It was found that a dose of 10 mg styrene and 100 µg benzaldehyde could attract Aphidius parasitoid wasps up to a distance of 5 meters. The results of this experiment have been published in a scientific journal (van Neerbos et al., 2023b), as well as in an industry magazine (Mertens et al., 2022). Subsequently, it was tested whether this blend could also improve the monitoring of Aphidius parasitoids. For this purpose, a large number of Aphidius parasitoids were released in a greenhouse, and the blend was placed near transparent adhesive plates to monitor the parasitoids. Unfortunately, this experiment resulted in a very low recapture of the parasitoids. Although the precise reasons for this low recapture are not yet known, it may have been due to the presence of Aphidius predators or aphid colonies influencing the behavior of the parasitoids. Finally, the effectiveness of linalool as an attractant in an "attract & kill" strategy for hyperparasitoids was tested. For this, multiple doses of linalool were tested in combination with transparent adhesive plates. The results of this experiment suggest that while linalool shows potential as a basis for an attract & kill strategy for hyperparasitoids, the substance is also attractive to beneficial insects, which is undesirable. Furthermore, survival experiments were conducted at laboratory and greenhouse levels to develop a sugar blend that improves the survival of parasitoids but not hyperparasitoids. From the experiments, it was found that a blend of glucose and melibiose significantly improves the survival of Aphidius, while this was not the case for Dendrocerus. Additionally, a feeding device was developed to provide the sugars, and the survival of the parasitoids was significantly improved compared to a control treatment.

WP3: Evaluation of developed strategies for improved aphid control

In this work package, the developed strategies were evaluated under (semi-)practical conditions for improved biological control of aphids. In a first experiment, it was investigated whether application of the styrene-benzaldehyde blend in Omnilure odor dispensers could increase the biological control efficiency of Aphidius. In a second experiment, it was tested whether supplemental feeding of the parasitoids could increase biological control efficiency. For the first experiment, the styrene-benzaldehyde blend was placed near plants with aphid colonies, both in a pepper and a raspberry greenhouse. In the pepper greenhouse, A. colemani was used, and in the raspberry greenhouse, A. ervi was used. After 48 hours, the number of parasitized aphids was counted. It was found that when the styrene-benzaldehyde blend was offered near plants with aphid colonies, 1.5-1.8 times more aphids were parasitized. In the second experiment, it was found that the use of the commercial sugar blend Attracker® did not improve the parasitization efficiency of Aphidius compared to a control treatment. This was unexpected, as we had found in WP2 that offering sugars can extend the lifespan of Aphidius parasitoids. Other interfering sugar sources may have been present during the experiment (nectar, honeydew), rendering supplemental feeding ineffective. In future research, we will investigate whether the application of the styrene and benzaldehyde blend can still be optimized and whether it remains effective when not offered near aphid colonies. Additionally, we will further explore whether we can identify an additional component that can be added to linalool to make the attraction of hyperparasitoids more selective.

WP4: Dissemination of project results

In this work package, specific tasks and the necessary time investment were provided to disseminate, demonstrate, and implement the acquired project knowledge in the sector. This was done through user group meetings, with an average attendance of 15-20 people. Satisfaction surveys indicate that the user group was very satisfied with the project (4.5/5) and the achieved results (4/5). During the project, 3 articles were published in scientific peer-reviewed journals. Additionally, the results were disseminated through various publications in industry magazines. The results were further disseminated through study days and conferences. Finally, the project results were communicated at a closing study day organized in December 2023. The program was widely distributed (see, for example, https://www.groentennieuws.nl/article/9574458/slotevent-over-bladluisbeheersing-in-paprika-en-houtig-kleinfruit/). In total, 50 people participated in this study day, which concluded with a small networking event.

Publications in peer-reviewed scientific journals

van Neerbos, F. A. C., Dewitte, P., Wäckers, F. L., Wenseleers, T., Jacquemyn, H. & Lievens, B. (2023). Bacterial volatiles elicit differential olfactory responses in insect species from the same and different trophic levels. Insect Science, 30: 1464-1480. https://doi.org/10.1111/1744-7917.13176

van Neerbos, F. A. C., Mertens, R., Wäckers, F. L., Bosmans, L., Jacquemyn, H. & Lievens, B. (2023). Distance-dependent attraction of the generalist aphid parasitoid Aphidius colemani towards synthetic volatile organic compounds under greenhouse conditions. Entomologia experimentalis et applicata 171: 846-856. https://doi.org/10.1111/eea.13340

van Neerbos, F. A. C., Alhmedi, A., Van Herck, L., Van Erkel, E., De Vis, R. M. J., Clymans, R., Beliën, T., Jacquemyn, H. & Lievens, B. (2024). Seasonal changes in aphid hyperparasitoid occurrence in sweet pepper and raspberry in Belgium. BioControl. https://doi.org/10.1007/s10526-024-10248-3

Publications in sector journals

Proeftuinnieuws

Lievens, B., Jacquemyn, H., Bosmans, L., Beliën, T. & Wittemans, L. (2019). Nieuw project gaat de strijd aan met bladluizen in paprika en kleinfruit. Proeftuinnieuws 14.

van Neerbos, F. A. C., Jacquemyn, H., Lievens, B., Alhmedi, A., Beliën, T., Van Herck, L., Wittemans, L., Mertens, R. & Bosmans, L. (2020). Microbiële geurstoffen bieden perspectief bij biologische plaagbestrijding. Proeftuinnieuws 19: 20-21. https://www.proeftuinnieuws.be/rubrieken/thema/microbiele-geurstoffen-bieden-perspectief-bij-biologische- plaagbestrijding

van Neerbos, F. A. C., Goelen, T., Jacquemyn, H., Lievens, B., Mertens, R., Bosmans, L., Alhmedi, A., Beliën, T., Van Herck, L. & Wittemans, L. (2021). Sluipwespen in paprikagewas houden met synthetische lokstoffen. Proeftuinnieuws 9: 30-31. https://www.proeftuinnieuws.be/rubrieken/thema/sluipwespen-in-paprikagewas-houden-met-synthetische-lokstoffen

Mertens, R., Bosmans, L., van Neerbos, F. A. C., Jacquemyn, H., Lievens, B., Alhmedi, A., Beliën, T., Van Herck, L., Wittemans, L. & De Vis, R. (2022). Synthetische lokstoffen trekken sluipwespen aan over 5 m afstand. Proeftuinnieuws 6: 20-21. https://www.proeftuinnieuws.be/rubrieken/thema/synthetische-lokstoffen-trekken-sluipwespen-aan-over-5-m-afstand

Clymans, R., Van Erkel, E., Van Herck, L., De Vis, R., Alhmedi, A., Beliën, T., van Neerbos, F. A. C., Jacquemyn, H. & Lievens, B. (2023). Verschillende soorten hypersluipwespen wisselen elkaar af in paprika. Proeftuinnieuws 19: 20-21. https://www.proeftuinnieuws.be/rubrieken/thema/soorten-hypersluipwespen-in-paprikaserre-in-kaart-gebracht

NOBL

Lievens, B., van Neerbos, F.A.C., Jacquemyn, H., Beliën, T., Alhmedi, A, Wittemans, L., Bosmans, L. & Mertens, R. (2020) BIOTRACT – Innovatieve biologische bladluisbestrijding in de beschermde teelt van paprika en kleinfruit. NOBL 2020: 66-67.

FRUIT

Alhmedi, A. & Beliën, T.  & De Vis, F. (2022) IPM in kleinfruit: goed starten, monitoren en bijsturen. Fruit 5: 6-7. https://vakbladfruit.be/2022/03/16/ipm-in-kleinfruit-goed-starten-monitoren-en-bijsturen/

Alhmedi, A. & Beliën, T. (2022). Waarom moet je mieren in de boomgaard beheren? Fruit 6: 8-9. https://vakbladfruit.be/2022/03/30/waarom-moet-je-mieren-in-de-boomgaard-beheren/

Alhmedi, A. & Beliën, T. (2022). (Natuurlijke vijanden). De vijand van mijn vijand is mijn vriend. Fruit 9: 5-7. https://vakbladfruit.be/2022/05/11/de-vijand-van-mijn-vijand-is-mijn-vriend/

Alhmedi, A. & Beliën, T. (2022). Hyperparasitoïden, een grote uitdaging voor de biologische bestrijding tegen bladluizen. Fruit 20

Alhmedi, A. & Beliën, T. (2023). Ongewenste sluipwespen in je fruitteelt. Fruit 5

Alhmedi, A. & Beliën, T. (2023). Belang van temperatuur voor effectiviteit van sluipwespen. Fruit 11. https://vakbladfruit.be/2023/06/07/belang-van-temperatuur-voor-effectiviteit-van-sluipwespen/

Alhmedi, A. & Beliën, T. (2023). Bladluizenbestrijding in de herfst. Fruit 19-20

Other

Alhmedi, A. (2020). De grote frambozenluis Amphorophora idaei. Publicatie voor website & leden PCFruit

Schouten, L. (2021). Lokstoffen helpen bij biologische bestrijding van bladluis – Nieuweoogst.nl L. Bosmans. https://www.nieuweoogst.nl/nieuws/2021/08/30/lokstoffen-helpen-bij-biologische-bestrijding-van-bladluis

Visser, P. (2023). Luisbeheersing in paprika en kleinfruit is complex. GFactueel.nl