Glyphosate and Melanization

Melanin 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.

黑色素（melanin）是一种广泛分布于所有生物界的黑褐色色素，具备多种生物学功能，涵盖紫外线防护、体温调节、氧化产物清除、节肢动物免疫以及微生物毒力调控。鉴于黑色素在生物圈中具备广泛功能，尤其是在昆虫免疫防御中的关键作用，解析环境条件如何影响黑化反应（melanization）具有重要科学意义。草甘膦（glyphosate）是目前全球应用最广泛的除草剂，可抑制黑色素生成。本研究阐明了草甘膦抑制黑化反应的分子机制，并证实了该除草剂对昆虫的多效性影响：草甘膦可作为抗氧化剂，破坏黑化反应中的氧化还原平衡；该除草剂可降低蜡螟幼虫感染后的存活率，提升疟疾传播媒介蚊虫的寄生虫载量，并改变成年蚊子的肠道微生物组组成。上述研究结果表明，草甘膦在环境中的累积可通过以下途径加剧所谓的“昆虫末日”（insect apocalypse）现象——该现象以物种数量持续下降为核心特征——即通过抑制黑化反应、损伤昆虫免疫功能以及扰动微生物组组成，使昆虫对病原微生物的易感性显著升高，进而推动该现象的发生。