Eicosanoids represent a category of oxygenated C20 polyunsaturated fatty acids that play a crucial role in regulating various physiological functions in insects. These compounds are synthesized from phospholipids through the enzymatic activity of phospholipaseA2 (PLA2). In this study, we investigated four PLA2 genes encoded in the western flower thrips, Frankliniella occidentalis, with a focus on understanding their specific functions through a variety of experimental approaches. Among the four PLA2s identified, Fo-PLA2A and Fo-PLA2B fall under the category of Ca2+-independent cellular PLA2 (iPLA2), while Fo-PLA2C and Fo-PLA2D are classified a secretory PLA2 (sPLA2). Enzyme activity assays showed that all developmental stages of the thrips exhibited significant activity against both types of PLA2 substrates (arachidonic acid (AA) and non-AA), albeit with variations in enzyme kinetics across different developmental stages. Further examination revealed that all four PLA2 genes were expressed in every developmental stage. Fo-PLA2B and Fo-PLA2C displayed higher expression levels in larvae, while Fo-PLA2A and Fo-PLA2D were predominantly expressed in female and male adults, respectively. These findings support the hypothesis that PLA2s likely serve specific functions during distinct developmental stages. Our results indicated that PLA2s play pivotal roles in mediating various physiological processes such as immunity, development, and reproduction. So, the differential expression of certain PLA2s in various stages suggests that each PLA2 may have a specific role during different stages. Additionally we conducted flouorescens in situ hybridization (FISH) analysis to localize PLA2 transcripts in different tissues, shedding light on their specific functions within these tissues. In summary, the four identified PLA2s are associated with distinct catalytic activities and exhibit differential expressions across developmental stages and tissues, collectively contributing to various physiological processes.

Phospholipase A2 (PLA2) catalyzes the committed step for eicosanoid biosynthesis. Two cellular PLA2 genes (iPLA2 and cPLA2) have been identified in Spodoptera exigua. PLA2 activity varied among developmental stages and different tissues. There was a positive correlation between PLA2 activities and their expression levels. Interestingly, there was significant inhibition by sPLA2 inhibitor, suggesting a presence of sPLA2 in S. exigua. An entomopathogenic bacterium, Xenorhabdus hominickii, infection suppressed expression of PLA2 genes and its extract inhibited enzyme activities. Oxindole of a bacterial metabolite of X. hominikii inhibited PLA2 activity and expression.