Glyphosate Inhibits Melanization and Increases Insect Susceptibility to Infection

SUMMARYMelanin is a black-brown pigment found throughout all kingdoms of life playing diverse roles including: UV protection, thermoregulation, oxidant scavenging, arthropod immunity, and microbial virulence. Given melanin’s broad functions in the biosphere, particularly in insect immune defenses, it is important to understand how environmental conditions affect melanization. Glyphosate, the most widely used herbicide, inhibits melanin production. Here we elucidate the mechanism underlying glyphosate’s inhibition of melanization demonstrate the herbicide’s multifactorial effects on insects. Glyphosate acts as an antioxidant and disrupts the oxidation-reduction balance of melanization. The drug reduced wax moth larvae survival after infection, increased parasite burden in malaria-transmitting mosquitoes, and altered midgut microbiome composition in adult mosquitoes. These findings suggest that glyphosate’s environmental accumulation could contribute to the so called insect apocalypse, characterized by species declines, by rendering them more susceptible to microbial pathogens due to melanization inhibition, immune impairment, and perturbations in microbiota composition.