In this proof-of-concept study, an agricultural biocide (imidacloprid) was effectively loaded into the mesoporous silica nanoparticles (MSNs) with different pore sizes, morphologies and mesoporous structures for termite control. This resulted in nanoparticles with a large surface area, tunable pore diameter and small particle size, which are ideal carriers for adsorption and controlled release of imidacloprid. The effect of pore size, surface area and mesoporous structure on uptake and release of imidacloprid was systematically studied. It was found that the adsorption amount and release profile of imidacloprid were dependent on the type of mesoporous structure and surface area of particles. Specifically, MCM-48 type mesoporous silica nanoparticles with a three dimensional (3D) open network structure and high surface area displayed the highest adsorption capacity compared to other types of silica nanoparticles. Release of imidacloprid from these nanoparticles was found to be controlled over 48 hours. Finally, in vivo laboratory testing on termite control proved the efficacy of these nanoparticles as delivery carriers for biopesticides. We believe that the present study will contribute to the design of more effective controlled and targeted delivery for other biomolecules.

A pesticide delivery system made of biocompatible components and having sustained release properties is highly desirable for agricultural applications. In this study, we report a new biocompatible oil-core silica-shell nanocapsule for sustained release of fipronil insecticide. Silica nanocapsules were prepared by a recently reported emulsion and biomimetic dual-templating approach under benign conditions and without using any toxic chemicals. The loading of fipronil was achieved by direct dissolution in the oil core prior to biomimetic growth of a layer of silica shell surrounding the core, with encapsulation efficiency as high as 73%. Sustained release of fipronil in vitro was tunable through control of the silica-shell thickness (i.e., 8-44 nm). In vivo laboratory tests showed that the insecticidal effect of the fipronil-encapsulated silica nanocapsules against economically important subterranean termites could be controlled by tuning the shell thickness. These studies demonstrated the effectiveness and tunability of an environmentally friendly sustained release system for insecticide, which has great potential for broader agricultural applications with minimal environmental risks.

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Scots pine (Pinus sylvestris L.) sapwood was treated with quat-silicone micro-emulsion (\40 nm), amino-silicone macro-emulsion (110 nm), alkyl-modified silicone macro-emulsion (740 nm) and solutions of inorganic water glass. Three treatment concentrations of 5, 15 and 30% (w/w) were used for the impregnation of the test specimens. Termite resistance was assessed following a 16-week field trial conducted in northern Queensland, Australia. Two different field sites were chosen for exposure to feeding by Coptotermes acinaciformis (Froggatt) and Mastotermes darwiniensis (Froggatt). Following exposure, the test and feeder specimens were inspected and assessed for termite damage using a visual rating system (from 10 sound to 0 completely destroyed) and individual mass losses. The specimens treated with quat-and amino-silicone emulsions resisted damage by both termite species, even at less than 15% weight percent gains (WPGs). Alkyl-modified silicone macroemulsion and water glass treatment induced somewhat less resistance to termite damage, but imparted protection at higher WPGs.

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