Reviewing the role of microbial volatile organic compounds as potential oviposition elicitors for the horn fly, Haematobia irritans(Diptera: Muscidae).

Haematobia irritans (L.) (Diptera: Muscidae), commonly known as the horn fly, is one of the most economically significant ectoparasites of cattle worldwide, causing substantial losses in meat, milk, and hide production. Its management has historically relied on broad-spectrum insecticides, whose overuse has driven the emergence of resistant populations and raised environmental concerns, emphasizing the urgent need to alternative, ecofriendly control strategies. A key yet underexplored aspect of horn fly biology is behind one of its characteristic behaviors, oviposition behavior: gravid females deposit eggs almost exclusively in very fresh cattle dung, a preference that diminishes rapidly with time post-defecation. Although volatile organic compounds (VOCs) from dung are known to mediate this behavior, the biological origin of these chemical cues remains poorly characterized. This review proposes that microbial volatile organic compounds (mVOCs) produced by the cattle dung microbiota-particularly anaerobic bacteria derived from the bovine rumen-are major elicitors of horn fly oviposition behavior, constituting a transkingdom chemical signaling system. By systematically cross-referencing VOCs reported in fresh cattle dung with compounds known to elicit electrophysiological and behavioral responses in H. irritans, we identified four key semiochemicals of probable microbial origin: phenol, p-cresol, indole, and α-pinene, produced by bacterial families including Enterobacteriaceae, Clostridiaceae, Paenibacillaceae, and Lactobacillaceae. The temporal decline in dung attractiveness is proposed to reflect the succession of the microbial community from anaerobic to aerobic dominance, with a concomitant shift in the mVOC profile. This hypothesis is further supported by the observation that the early developmental stages of H. irritans harbor an anaerobe-dominated microbiota. This framework may provide opportunities for the development of environmentally friendly blends for horn fly management.