Citrus Fruits Produce Direct Defense Responses against Oviposition by Bactrocera minax (Diptera: Tephritidae)

Plants perceive and orchestrate defense responses when
herbivorous
insects are ovipositing. Fruits, as a crucial reproductive organ in
plants, have rarely been researched on the responses to insect eggs.
Here, we found that oviposition by the specialist insect Bactrocera minax in navel oranges activated the lignin
synthesis pathway and cell division, causing mechanical pressure that
crushed the eggs. Transcriptome and metabolome analyses revealed an
enrichment of oviposition-induced genes and metabolites within the
lignin synthesis pathway, which was confirmed by histochemical staining.
Furthermore, hydrogen peroxide (H2O2) accumulation
was observed at the oviposition sites. Plant defense-related hormones
jasmonic acid (JA) and salicylic acid (SA) exhibited rapid induction
after oviposition, while indole-3-acetic acid (IAA) activation occurred
in the later stages of oviposition. Additionally, secondary metabolites
induced by prior egg deposition were found to influence larval performance.
Our studies provide molecular evidence that host fruits have evolved
defense mechanisms against insect eggs and pave the way for future
development of insect-resistant citrus varieties.