Constitutive upregulation of tyrosine metabolism is associated with pyriproxyfen resistance in eggs of the Asian corn borer, Ostrinia furnacalis.

The juvenile hormone analogue (JHA) pyriproxyfen is widely used for controlling public health and agricultural pests, primarily through its effects on metamorphosis and reproduction. However, its activity against lepidopteran pests and the mechanisms of resistance, particularly in the egg stage, remain poorly understood. This study investigated the ovicidal activity of pyriproxyfen against the Asian corn borer, Ostrinia furnacalis, characterized the potential for resistance development, and elucidated the underlying molecular mechanisms. Pyriproxyfen exhibited potent, age-dependent ovicidal activity, with an LC50 of 0.769 mg/L against newly laid eggs. While adult exposure did not affect longevity or fecundity, it significantly reduced egg hatch rates, demonstrating a strong transgenerational effect. Continuous laboratory selection for 17 generations produced a strain with >200-fold resistance, which showed significant cross-resistance to another JHA, fenoxycarb, but not to neurotoxic insecticides. Synergism bioassays implicated enhanced metabolic detoxification by P450 monooxygenases, carboxylesterases, and glutathione S-transferases in the resistant strain. Comparative transcriptomics revealed that resistance was associated with the constitutive upregulation of genes in the tyrosine metabolism pathway, including 3,4-dihydroxyphenylacetaldehyde synthase (DHPAAS), tyrosine aminotransferase (TAT), and prophenoloxidase-activating enzyme (PPAE), as well as several cytochrome P450 genes. This was biochemically validated by significantly elevated phenoloxidase (PO) activity in resistant eggs during late embryogenesis. Crucially, pyriproxyfen exposure suppressed the expression of these same tyrosine metabolism genes in susceptible eggs, suggesting that resistant eggs overcome this suppression through a pre-adaptive enhancement of cuticle melanization capacity. This study provides the first evidence of high-level pyriproxyfen resistance in lepidopteran eggs and uncovers a novel resistance-associated mechanism involving the constitutive activation of the tyrosine metabolism pathway. These findings have significant implications for resistance management and highlight the insect egg as a dynamic battleground for insecticide action and adaptation.