Mechanism of locust egg susceptibility to diafenthiuron: micropyle permeation and serosal cuticle disruption lead to embryonic lethality.

Chemical pesticides constitute a core cornerstone of modern agricultural pest control practices. Contemporary management paradigms remain narrowly focused on post-embryonic pest stages, creating critical knowledge gaps in ovicidal intervention strategies that are pivotal for effective source-specific pest population suppression. Locusta migratoria is one of the key pests that pose a serious threat to agricultural production. However, current control measures for this pest are mainly focused on the nymph or adult stages. As a widely deployed thiourea insecticide, diafenthiuron exhibits excellent control efficacy against a variety of polyphagous agricultural pests. Here we systematically investigated the lethal effects of diafenthiuron on L. migratoria eggs and its ovicidal mechanism. Ultrastructural analysis based on transmission electron microscopy and concentration-gradient immersion bioassays targeted at locust eggs clearly demonstrated that the micropyle serves as the primary entry portal for diafenthiuron penetration into the egg interior. Crucially, the compound disrupts the formation of the serosal cuticle, a key chitinous barrier essential for normal insect embryogenesis and egg development. Treated eggs exhibited a statistically significant reductions in cuticle thickness and notable structural disorganization relative to untreated control groups, ultimately inducing distinct concentration-dependent embryonic lethality in target pests. These key findings reveal a previously unrecognized defensive function of the serosal cuticle in blocking xenobiotic infiltration and advance our comprehensive understanding of insect egg protective systems. The dual mechanism of micropyle accessibility and serosal cuticle resistance establishes a practical framework for stage-specific agricultural pest control and provides valuable insights for rationally optimizing ovicidal pesticide development.