Development of sol–gel formulations for slow release of pheromones

Abstract

A new type of dispenser for slow-release of sex pheromones and other semiochemicals was developed based on sol-gel polymers that can be useful for monitoring, mass trapping, and mating disruption in integrated pest management (IPM). Sol-gel matrices exhibit glass characteristics and allow control of the degree of crosslinking during the polymerization process in order to provide an optimal release rate for a particular pheromone. The advantages of sol-gel (silica) matrixes include keeping the added molecules chemically stable and enabling the sol-gel material to be applied in any desired thickness and pheromone quantity, and thereby readily modify release rates. In addition, sol-gels are primarily silica and water that are common in the environment and therefore safe for field dispensing. We developed a method for the entrapment of pheromones in sol-gel matrices that allowed release at an almost constant rate over many days in the field. For example, 2.5 mg (E)-5-decenyl acetate pheromone of peach twig borer, Anarsia lineatella, entrapped in various sol-gel formulations released 14-45 lg/day for up to 28 days. The codling moth (Cydia pomonella) pheromone in sol-gels was used in field tests to capture more codling moth males than unbaited control traps. We describe how the method may be modified to entrap other types of pheromones by making sol-gels with different pore sizes.

Slow Release of Plant Volatiles Using Sol-Gel Dispensers

“…Silica aerogels are unique porous materials that often contain Ͻ10% silicon dioxide and Ͼ90% air. The pore size of a sol-gel dispenser affects the release rate of the volatiles within (Zada et al 2009). Alkyl trimethoxysilane controls cross-linking of the polymer, and therefore pore size (Zada et al 2009).…”

“…Based on the synthetic method of Zada et al (2009), we screened sol-gels for their suitability as volatile dispensers, and then studied the release characteristics of different volatiles from the selected sol-gel. The structural stability of the selected sol-gel and the half-lives (t 1/2 ) of the volatiles in dispensers were examined.…”

“…The residual amounts of the plant volatiles in the sol-gels were determined at 0, 3, 6, 12, 17, 24, 26, and 28 d using a modiÞcation of an established extraction method (Zada et al 2009). In this method, the sol-gel disperser was dissolved in 1 ml of methanol and shaken for 2 h in an ultrasonic bath cooled with ice.…”

“…However, silicone rubber does not degrade readily in the environment. Zada et al (2009) developed alternative slow-release dispensers for sex pheromones us-ing silica-based sol-gel polymers. The advantages of sol-gel matrices over silicone rubber septa include increased chemical stability of the added compounds, the ability to be applied with any desired thickness or volatile concentration, and regulation of the compound release rate by controlling the degree of crosslinking during the polymerization process (Zada et al 2009).…”

“…Therefore, solgel dispensers speciÞcally for slow release of plant volatiles should be developed. In the current study, based on the method of Zada et al (2009), an optimal sol-gel formulation for release of tea (Camellia sinensis (L.) O. Kuntze) volatile compounds was developed with four comonomers, including tetramethyl orthosilicate (TMOS), methyltrimethoxysilane (MTMOS), ethyltrimethoxysilane (ETMOS), and propyltrimethoxy orthosilicate (PTMOS). The effects of increasing the volatile volume and of changing the volatile type in the sol-gel dispensers were investigated.…”