Tiny silver bullets: silver nanoparticles are insecticidal in Culicoides sonorensis (Diptera: Ceratopogonidae) biting midge larvae

Authors: OSBORNE, CAMERON - Kansas State University; NORTON, AMIE - Kansas State University; WHITWORTH, R - Kansas State University; SILVER, KRISTOPHER - Kansas State University; Cohnstaedt, Lee

Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/7/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Insecticide formulations with safer environmental profiles and less impact on beneficial insects such as butterflies and bees are needed to manage medical and veterinary pests such as biting flies and mosquitoes. Silver nanoparticles have shown to kill mosquitoes, non-biting midges, and other insects. Biting midge are insect vectors of agricultural importance because they can transmit viruses. This study examines the insecticidal properties of silver particles in biting midge larvae to determine if they can be used as a treatment for larval habitats or the source populations which is where the insects hatch and become biting pests. Larval mortality was assessed daily for 7 days after exposure to concentrations of silver particles, sorghum-polymer particles, and hybrid sorghum-silver polymer particles. Both silver particles and hybrid sorghum-silver particles killed larvae, but sorghum polymer particles alone did not significantly contribute to larval mortality. The silver killed the bacteria in the water, which is the food for the biting midge larvae. But starvation did not kill the larvae, it was a toxic affect from the silver that killed the larvae. The sorghum polymer particles also did not kill the larvae. This work describes the first use of silver nanoparticles to kill biting midge larvae and shows the potential insecticide applications of these nanoparticles against this agricultural pest. The grain-polymer particles also successfully carried insecticidal AgNPs, and their utility in loading diverse compounds could be a novel toxin delivery system for biting midges and similar pests.

Technical Abstract: Insecticide formulations with safer environmental profiles and limited off-target effects are desirable to manage medical and veterinary pests. Silver nanoparticles (AgNPs) have shown to be insecticidal in mosquitos, non-biting midges, and other insects. The biting midge Culicoides sonorensis Wirth and Jones is a vector of agriculturally important pathogens in much of the U.S., and it was the goal of this study to examine the insecticidal properties of AgNPs in larvae of this species. Third instar larvae mortality was assessed daily for 7 days after exposure to concentrations of AgNPs, sorghum-polymer particles, and hybrid sorghum-silver polymer particles. Both AgNPs and hybrid sorghum-silver particles were insecticidal, but sorghum polymer particles alone did not significantly contribute to larval mortality. Concentrations of 100 mg/L AgNPs achieved greater than 50% mortality at day 7, and greater than 75% larval mortality was observed in 200 mg/L treatments within 24 h. No culturable bacteria were recovered from larval rearing media at 400 mg/L AgNPs, and bacterial growth appeared to be suppressed in a concentration-dependent manner. These data suggest C. sonorensis larval mortality is caused by AgNP toxicity and not from the reduction of bacteria (i.e., a larval food source). This work describes the first use of AgNP toxicity in the C. sonorensis and shows the potential insecticide applications of these nanoparticles against this agricultural pest. The grain-polymer particles also successfully carried insecticidal AgNPs, and their utility in loading diverse compounds could be a novel toxin delivery system for biting midges and similar pests.