The diversity of pattern recognition receptors (PRRs) involved with insect defense against pathogens

•PRRs constitute a fundamental and core part of the insect immune system.•Insects take efforts to expand the repertoire of PRRs which is called ‘diversity’ in this review.•The diversity of PRRs includes genetic variability, isoform diversity, and ‘part-time’ PRRs.•PRRs with opsonin function and regulation of signaling pathways also show the diversity of PRRs.