Spider venom peptides Ht1a and Gg1a are toxic to honeybee parasite Varroa destructor by topical application

Global food supply strongly depends on pollination services provides by apiculturally managed honeybees. Unfortunately, environmental chemicals such as insecticides as well as many pests and diseases as well as environmental chemicals such as insecticides threaten honeybee survival, with parasitic Varroa destructor mites being a major contributor to colony losses in many regions of the Northern hemisphere. Chemical varroacidal treatments are insufficient and hampered by resistance development, urging the need for development of sustainable and environmentally friendly alternatives. Venom peptides from arthropods such as spiders or scorpions are considered excellent sources of toxins with activity against other arthropods and could therefore provide novel treatment options against parasitic varroa mites. However, only few arthropod venom peptides with acaricidal activity have been reported. We therefore performed a systematic topical screening of 50 arthropod venoms (at 10 µg/mite) against V. destructor mites, with 78% of the venoms causing 100% mortality after 24 hours. Deconvolution of two of the most potent venoms—from the Tasmanian cave spider Hickmania troglodytes and the Giant Japanese funnel-web spider Gigathele gigas —led to identification of two varroacidal venom peptides that we named Ht1a and Gg1a. Topical application of Ht1a and Gg1a reduced the survival time of V. destructor mites, without affecting honeybee survival, despite Ht1a being equally potent in inhibiting voltage-gated sodium channels from varroa and honeybee. Ht1a and Gg1a were inactive at human skeletal muscle (hNa _V 1.4), cardiac (Na _V 1.5), neuronal Na _V channel isoforms, and the human voltage-gated calcium channel Ca _V 2.2. At human α3β2/4 nicotinic acetylcholine receptors, Gg1a was inactive while Ht1a partially blocked nicotine-mediated Ca ²⁺ influx at a concentration of 10 µM. Our data suggest that Ht1a and Gg1a could be considered for development as commercial acaricides to manage varroa infestation of honeybee hives.