Shrubs and trees as natural insect protection for grazing animals in Switzerland and the alpine region: A systematic review of in vitro, in vivo and clinical trials.

Insect infestation in grazing animals is an increasing problem due to factors such as global warming and increasing resistance to insecticides, which have a direct impact on animal health and welfare. According to reports from farmers, observations in zoopharmacognosy and the ingredients of commercial insecticides, various indigenous trees and shrubs with an insecticidal or repellent effect grow or can be planted on pastures. The aim of our systematic review (designed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement) was to identify perennial woody plants from Switzerland and the wider alpine region with a potential to affect the most common dipteran insects that are relevant for grazing animals. Based on a preselection of 399 plants, 114 publications including 403 laboratory and 10 outdoor experiments were found. Essential oils were evaluated most frequently (326 experiments), followed by extracts (118 experiments). Most frequently investigated were the aromatic herbs (Lamiales: Lamiaceae) Thymus vulgaris L., Rosmarinus officinalis Spenner, Lavandula angustifolia Miller, Salvia officinalis L., and the trees Punica granatum L. (Myrtales: Lythraceae), Laurus nobilis L. (Laurales: Lauraceae), Pinus pinea L. (Pinales: Pinaceae), Juniperus communis L. (Cupressales: Cupressaceae), Olea europaea L. (Lamiales: Oleaceae) and Alnus glutinosa (L.) Gaertner (Fagales: Betulaceae). These were studied for their effect (repellent, larvicidal, adulticidal) on mosquitoes (Diptera: Culicidae; Aedes spp., Anopheles spp., Culex spp.), and flies (Musca domestica L. (Diptera: Muscidae), and Lucilia sericata Meigen (Diptera: Calliphoridae)). The results concerning repellent or insecticidal effects provide valuable information about which trees and shrubs should be tested in future outdoor studies involving grazing animals.