Grain polymer microparticles with toxic silver nanoparticle cargo are lethal to Culicoides sonorensis biting midge larvae

Micro- and nanoparticles have numerous applications in pharmacology, energy production, and agriculture, and can be designed to carry diverse nanomaterials as cargo. We recently found that a grain-polymer microparticle could carry toxic silver nanoparticles (AgNPs) and were lethal when ingested by mosquito larvae. Here, we examine if a similar method could kill larvae of the agriculturally important biting midge pest, Culicoides sonorensis. Third instar C. sonorensis larvae were exposed to sorghum polymer microparticles (SPPs), AgNPs, and AgNP-bound SPPs (AgSPPs) at varying concentrations, and larval mortality was assessed over 7 days. Greater than 90% larval mortality was achieved with AgNP concentrations of 200 and 400 mg/L by day 7, and AgSPPs caused only slightly less mortality to larvae. Additionally, greater than 50% larval mortality was observed at both 200 and 400 mg/L concentrations at 24 h post exposure. The SPP treatment alone did not significantly contribute to larval mortality at any concentration tested (25-400 mg/L), and larvae survived in water-only controls at greater than 90% for the duration of the study. These findings show that AgNPs are insecticidal to C. sonorensis larvae, albeit at much higher concentrations than those observed in mosquitos (1-100 mg/L). Our novel SPP was well-tolerated by larvae and successfully transported lethal concentrations of AgNPs to larvae. Silver nanoparticle insecticides, and SPPs as novel toxin delivery systems, could be a new approach to control Culicoides and similar agriculturally important pest insects.