Effects of formic acid on Amblyomma americanum (L.) (Ixodida: Ixodidae)

Authors: Showler, Allan; BAILEE, DORSEY - Schreiner University; CAESAR, RYAN - Schreiner University

Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/3/2020
Publication Date: 2/26/2020
Citation: Showler, A., Bailee, D.N., Caesar, R.M. 2020. Effects of formic acid on Amblyomma americanum (Ixodida: Ixodidae). Journal of Medical Entomology. https://doi.org/10.1093/jme/tjaa037.
DOI: https://doi.org/10.1093/jme/tjaa037

Interpretive Summary: Ixodids, or hard ticks, are blood feeding parasites that transmit many disease agents of humans, livestock, and wildlife. As resistance to conventional synthetic acaricides becomes more problematic, natural products are being investigated as alternative control tactics. Formic acid, produced by ants, is commercially available for fumigating pestiferous varroa mites in honeybee hives, and it has reported to repel ixodids. Lone star tick larvae and nymphs were used as a model ixodid to investigate deterrent, repellent and lethal effects of formic acid. Although formic acid failed to deter or repel the ticks, it was highly toxic as a fumigant to larvae. Contact by crawling on wet, moist and dry treated surfaces under ventilated conditions caused substantial mortality to larvae within 30 – 120 min, and temporary immersion killed most larvae by 24 h after removal from 5% formic acid. Substantial nymphal mortality occurred after relatively short exposure to a treated surface. Formic acid volatiles were more lethal to lone star tick immatures than direct contact with the external integument.

Technical Abstract: Ixodids are blood feeding ectoparasitic vectors of many disease agents that infect humans, livestock, and wild animals. As ixodid resistance to conventional synthetic acaricides becomes increasingly problematic, natural products are receiving greater attention as possible alternative control tactics. Formic acid, produced by ants, is a commercially available product for fumigating varroa mites, Varroa destructor Anderson & Trueman, infesting honeybee, Apis mellifera L., hives, and it has been reported to repel ixodids. Lone star tick, Amblyomma americanum (L.) (Ixodida: Ixodidae), larvae and nymphs were used as a model ixodid to investigate deterrent, repellent and lethal effects of formic acid as a fumigant and contact toxin. Although formic acid failed to deter or repel A. americanum, it was highly toxic as a fumigant to larvae at a 1% concentration even when exposure was limited to 5 min. Contact by crawling on wet, moist and dry treated substrates under ventilated conditions causes >90% mortality to larvae in 5% formic acid concentration treatments within 30 – 120 min, and temporary immersion killed approximately 60% of the larvae by 24 h after they were removed from the 5% formic acid treatment solution. Substantial nymphal mortality occurred after 1 – 1.5 h following exposure to substrate treated with the 10% concentration and immersion killed approximately 45% of the nymphs. It appears that formic acid volatiles are more lethal to A. americanum immatures than direct contact with the external integument.