PGE2 mediation of egg development in Western flower thrip, Frankliniella occidentalis.

ABSTRACT

Eicosanoids mediate various insect physiological processes, including reproduction. Especially, the eicosanoid prostaglandin E2  (PGE2 ) is known to mediate oocyte development in some insects. The explosive reproductive potential of the Western flower thrips, Frankliniella occidentalis, damages various agricultural crops. However, little is known about the underlying physiological processes of egg development in this pest. This study found that treatment with aspirin (ASP) (a specific cyclooxygenase (COX) inhibitor) used to inhibit PGE2 biosynthesis during ovarian development significantly suppressed the reproduction of female F. occidentalis. However, the addition of PGE2 to ASP-treated females significantly rescued the suppressed reproduction. PGE2 was detected in growing ovarian follicles in an immunofluorescence assay. The hypothetical biosynthetic machinery of PGE2 was predicted from the F. occidentalis genome and included phospholipase A2  (PLA2 ), COX-like peroxidase (POX), and PGE2 synthase (PGES). Three specific PLA2 s were highly expressed in female adults during active oogenesis. Specific POX and PGES genes also showed high expression during active oogenesis. The adverse effect of ASP treatment on oogenesis was observed in follicle formation in the germarium where the follicle numbers in an ovariole were decreased, which resulted in hypotrophied ovaries. This impairment was rescued by the addition of PGE2 . ASP treatment also significantly inhibited chorion formation and suppressed gene expression associated with choriogenesis, which included chorion protein, mucin, and yellow while it did not inhibit vitellogenin gene expression. However, the addition of PGE2 induced the expression of the target genes suppressed by ASP treatment and rescued chorion formation. These results suggest that PGE2 mediated ovarian development by affecting follicle formation and choriogenesis in F. occidentalis.