Environmentally friendly alternatives safe to non-target organisms for the control of insects vectoring phytopathogens are in the focus of agricultural research worldwide. In Europe, many fruit trees of the family Rosaceae are seriously affected by phytoplasmas of the apple proliferation group. Phytoplasmas are specialized bacteria that are obligate parasites of plant phloem tissue and transmitting insects (vectors). Psyllids of the genus Cacopsylla, small phloem feeding insects, play the crucial role in transmission of fruit phytoplasma diseases from plant to plant, which causes yearly crop losses of half a billion Euro in Europe. To overcome the spreading of these diseases, especially their transition from infected to healthy plants, the solution is to adopt and promote the concept of Integrated Pest Management (IPM). According to a definition of the FAO, IPM regards the consideration of all available pest control techniques and subsequent integration of appropriate measures that discourage the development of pest populations and keep chemical pesticides and other interventions to levels that are economically justified and reduce or minimize risks to human health and the environment.
The phytoplasma vectoring insects use chemical cues for orientation and host identification. It is well known that secondary plant metabolites can affect insect behavior. Floral biodiversity is a vast source of biologically active ingredients for use in crop protection. Interspecific active compounds, so-called allelochemicals, are metabolites, which are either plant volatile organic compounds (VOCs) or essential oils distilled from plant extracts, and they may affect growth, reproduction or behavior of target species. They can modify structure and dynamics of populations or communities of either plants, animals or microorganisms.
In fact, the use of plant-based products has attained a lot of significance. Typical applications are the use of attractive VOCs as lures in traps, repellent compounds for scaring off pest insects, or the combination of attractive and repellent compounds in push-and-pull strategies. However, several factors appear to limit the successful use of allelochemicals. The major obstacle in field conditions is their high volatility, which reduces efficacy over longer periods. For that reason, the most important consideration is improving the longevity of those substances that are effective but volatile. Therefore, efficient dispenser matrices that ensure controlled release rates of allelochemicals, suitable for the use in the field, need to be developed in order to enable a sustainable management of such insects.
Nanotechnology is an expanding and highly versatile technology. Indeed, it has arisen as a robust scientific and commercial engine providing global economic benefits. With expanding knowledge of nanomaterial manufacturing techniques, many research groups focus on the preparation of novel nanomaterials for various applications. Included in the various techniques already reported, electrospinning became apparent due to its ability to produce nanostructures with unique properties such as a high surface area and inter/intrafibrous porosity. In this respect, particularly appropriate for agricultural applications are nanoparticles derived from biopolymers with low impact on human health and the environment. Some studies showed that the encapsulation in nanofibers increased the thermal stability and limited the volatility of VOCs, compared to unformulated volatiles, which were already lost after 1 day of storage under the same conditions. Thus, nanotechnology offers great promises for delivery systems as an innovative tool.
The development of nanoformulations will enable the use of VOCs for so-called push-and-pull systems to prevent the migration and proliferation of psyllids in orchards, resulting in a strong reduction of new infections by phytoplasmas. The push-and-pull strategies consist of a behavioral manipulation of an insect vector by the integration of two different stimuli. A repellent makes the protected resource unattractive or unsuitable to the vector (push stimulus), while luring it toward an attractive source or attractant (pull stimulus), e.g. located in a sticky trap. By conducting fundamental research on multitrophic interactions between plants, phytoplasmas and insect vectors, the isolation and identification of attractive and repellent infochemicals paved the way for applying this very innovative control strategy in pest control. In our study, we investigate the use of nanofibers to deliver both attractive compounds (Pull) and insect repellents (Push). While the field of insect repellents is moving forward, there are no systems for dispensing repellent substances in crop protection available on the market.
My innovating idea is to increase VOCs longevity through encapsulation in nanofibers made of biodegradable polymers. I will formulate this way both attractive and repellent VOCs for the development of multi strategy devices, which on one hand will repel psyllids from the orchards and on the other will attract them to traps.
- Investigating VOCs for attracting and repelling vector insects: Volatiles will be sampled from plants using an appropriate headspace device. Samples will be analysed using an automated thermal desorber connected to a GC-MS (gas chromatograph coupled with mass spectrometer). The volatile compounds will be identified by comparing the characteristic ion fragmentation pattern (mass spectrum) with data from mass spectra libraries (NIST 08 Mass Spectral Library, National Institute of Standards and Technology, Wiley; JKI-OW Library) and by comparing retention times of standard compounds. The behaviour modifying activities of single compounds and blends of several compounds will be investigated in behavioural tests.
- Selection of biopolymers as suitable dispensers for VOCs under laboratory conditions: Several polymers will be tested individually for their suitability for production of nanofibers through electrospinning technique (Cellulose acetate, poly (ethylene carbonate) (PEC), polyethylene oxide (PEO), poly (lactic acid) (PLA), Polycaprolactone (PCL), polyethylene glycol (PEG). By using a very innovative combination of a microchamber (Markes, Germany) combined with a thermal desorber coupled with a GC-FID system (PerkinElmer) the levels and proportions of volatile organic compounds (VOCs) emitted by nanofibers will be measured under controlled conditions (temperature, airflow, humidity).
- Field tests: The push-and-pull strategies will be evaluated in the experimental area at Julius Kühn-Institut, Dossenheim, Germany. I will conduct field experiments with formulated allelochemicals in nano-dispensers as described above. I will use psyllids as target organisms and test the effect of both repellent and attractive compounds in a push-and-pull strategy.
The expected result of this research is to explore the beneficial use of this innovative technology as control tool, in order to help to diminish the application of chemical pesticides in fruit cultivation and production in Germany and Europe. The methods and control tools developed in this project should be explored on other continents for the control of e.g. the vectors of the pear decline disease in North America, Africa and Asia, and the Asian citrus psyllid (Dyaphorina citri), the vector of the Citrus greening disease Huanglongbing (HLB) in Brazil, North America and many other Citrus growing countries. Furthermore, with this study we can increase knowledge of eco-friendly techniques for pest management that can improve agricultural production by reducing the use of insecticides. Moreover, extending the use of these techniques for attracting insect’s natural enemies enhancing biological control (nanofibers could also be used for that purpose in green houses), and even controlling urban plagues in the future.
Bruna Czarnobai De Jorge, Brazil/Germany