Comparing ortho- and para-anisaldehyde effects on horn fly and house fly egg hatching, larval development through adulthood, and adult mobility, mortality, and repellency

Authors: Showler, Allan; Atkinson, Jessica

Submitted to: Biopesticides International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/23/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Para- and ortho-anisaldehyde isomers were assessed for their effects on horn fly and house fly egg hatching, larval development to pupae, adult emergence, direct contact and fumigation on adults, and adult repellency. p-Anisaldehyde was more toxic than o-anisaldehyde to horn fly eggs. Both isomers were more potent against horn fly eggs than against house fly eggs. Increasing p-anisaldehyde concentration increased inhibition of horn fly egg hatching. o-Anisaldehyde was the more inhibitory isomer against larval development to pupae of each fly species, indicating a distinct isomer effect, but a lesser species effect. Development of pupae to adults was less affected by the isomers than pupal development to adults. Direct contact with p-anialdehyde caused greater immobilization of horn flies but high concentrations of each isomer were strongly immobilizing or lethal. Fumigation using p-anisaldehyde induced limited immobilization; a 2.5% concentration caused substantial mortality of the fly species by 1 h of exposure. o-Anisaldehyde as a fumigant was not as lethal to horn flies as it was to house flies. p-Anisaldehyde was more repellent against house flies than to horn flies at a >0.375% source concentration, and o-anisaldehyde repelled both species. Applications of the isomers for control of horn flies and house flies will depend upon the route of exposure, concentration, target species and life stage, and practicality.

Technical Abstract: Para- and ortho-anisaldehyde isomers were assessed for their effects on horn fly, Haematobia irritans irritans (L.), and house fly, Musca domestica L., egg hatching, larval development to pupae, adult emergence, direct contact and fumigation on adults, and adult repellency. p-Anisaldehyde was more toxic than o-anisaldehyde to horn fly eggs. Both isomers were more potent against horn fly eggs than against house fly eggs. Increasing p-anisaldehyde concentration increased inhibition of horn fly egg hatching. o-Anisaldehyde was the more inhibitory isomer against larval development to pupae of each fly species, indicating a distinct isomer effect, but a lesser species effect. Development of pupae to adults was less affected by the isomers than pupal development to adults. Direct contact with p-anialdehyde caused greater immobilization of horn flies but high concentrations of each isomer were strongly immobilizing or lethal. Fumigation using p-anisaldehyde induced limited immobilization; a 2.5% concentration caused substantial mortality of the fly species by 1 h of exposure. o-Anisaldehyde as a fumigant was not as lethal to horn flies as it was to house flies. p-Anisaldehyde was more repellent against house flies than to horn flies at a 0.375% source concentration, and o-anisaldehyde repelled both species. Applications of the isomers for control of horn flies and house flies will depend upon the route of exposure, concentration, target species and life stage, and practicality.