Electrospun fibers for Pest Control

Pest management is not restricted to agricultural land as it also applies to homes and build-up areas. A network of fibers from electrospinning instead of powder or aerosols provides several advantages for controlling and keeping out pests. The fibrous network may be used as a physical barrier to keep out the pests or it may be loaded with active chemicals. The amount of chemicals needed may be reduced as the fiber matrix protects the loaded chemicals from the environment while slowly releasing them for pest management.

Agriculture

A method of controlling insect pests is to use pheromones to lead them to traps. Electrospun nanofiber with its large surface area is able to effectively release the pheromones for this purpose. Bansal (2010) showed that it is possible to electrospin nanofibers incorporated with pheromone for plant protection against Lobesia botrana (grape vine moth). However, this study used a complex emulsion mixture containing 1 wt% oligolactide /pheromone/Brij S20 dispersion/16 wt% polyhexyleneadipate-block-methoxypolyethyleneglycol dispersion/polyethylene oxide for electrospinning. Bisotto-de-Oliveira et al (2014) incorporated Trimedlure (synthetic attractant) into electrospun nanofibers for controlling medfly population. Ethylcelluose, polyethylene glycol (PEG- PCL), polyvinyl acetate- vinyl pyrrolidone and polycaprolactone were each blended with Trimedlure using organic solvents and electrospun to form nanofibers. Up to 10% w/v of the active ingredient was added. Their studies on the field showed that the chemically treated membrane is effective in attracting the flies.

Given that different polymers may be electrospun to give fibers, selection of the polymers for encapsulation of pheromones need to be tested to find the best combination in attracting the targeted pests. Parameters such as post-spinning pheromone loading factor and pheromone release rate needs to be considered. As shown by Bisotto-de-Oliveira et al (2015) in their encapsulation of synthetic sex pheromone of Grapholita molesta, the amount of pheromones in electrospun fibers were different in polyvinyl acetate/polyvinyl pyrrolidone (PVAc/PVP), polycaprolactone (PCL) with THF and PCL with DCM. Such difference in load retention may be due to the lost of pheromone to the surrounding during electrospinning.

Electrospinning may also be used for encapsulating pesticides and it may be useful in keeping airborne pests from landing on the plants. The mesh of fibers from electrospinning can be easily sprayed and this forms a fibrous network across neighbouring plants. This functions as a physical and chemical barrier against potential pests. Zhao et al (2013) has successfully prepared avermectin (AVM)-loaded cellulose acetate nanofibers from electrospinning. The release of AVM from the nanofibers occurred in two stages with a fast initial release followed by a continuous slow release.

Household

Electrospun fibers may be used to control pests that are found at home. It has been suggested that the nonwoven electrospun nanofibers may be used to trap bed bugs. This is based on the hypothesis that the bed bug legs would get entangled and be trapped. There are very little if any scientific publications on using electrospun nanofibers as bed bug trap but there is a startup that is commercialising such a device in 2013. There is a report of a study on electrospun nanofibers as bed bug trap by Leibowitz et al (2013). Using electrospun polystyrene nonwoven nanofiber mesh, they reported capture of six bed bugs in it over five days. The capturing mechanism is based on immobilization where the bed bugs legs get entangled in the fibers.

In many countries, mosquitoes are vectors for dangerous diseases including malaria, dengue fever and Zika virus. Clothing offering protection against mosquitoes is important for any person venturing into known mosquito infested area or high risk region. In a demonstration of the potential use of electrospun fibers for protection against mosquitoes, Teli et al (2017) encapsulated citronella into electrospun polyvinyl alcohol (PVA)/starch nanofibers. The resultant fabric was tested to be effective in reducing mosquito bites. Ciera et al (2019) examined the effectiveness of electrospun polyvinyl alcohol (PVA) nanofibers loaded with mosquito repellent, permethrin, chilli and catnip oil respectively. Tests using A. gambiae s.s. mosquitoes showed that all the repellents significantly reduce the number of mosquito landings compared to the control (PVA nanofibers without repellent) with chili and catnip oil in PVA nanofibers showing mosquito landing reduction of 51% and permethrin with 89% reduction. This shows the effectiveness of electrospun mosquito repellent loaded nanofibers in repelling mosquitoes. More tests are needed to determine the duration of repelling efficacy and stability of the compound in storage.

A fine mesh of electrospun nanofibers are known to exhibit high transparency [Liu et al 2015]. While this has been tested for use as an air filter, the same fine mesh may also form a physical barrier against insects and other pests. With pore size typically in the region of a few microns, this would exclude most insects while maintaining high visibility across it.