The Peritrophic Matrix (PM) structure of two grubs, Holotrichia oblita and H. parallela (Coleoptera: Melolonthidae) was observed. The effects of Helicoverpa armigera (Lepidoptera: Noctuidae) granulovirus enhancin (Ha-En) on the PMs were also measured. Compared with PMs of four lepidopteran larvae, Mythimna separata, H. armigera, Spodoptera exigua and Trichoplusia ni, the PMs of two grubs were smooth, compact and elastic but weak. Observations indicated that they might have a more elaborate structure and a greater variety of proteins. SDS-PAGE analyses revealed that Ha-En did not degrade PM proteins in the two grubs and did partially degrade PMs proteins in the four lepidopteran larvae. Western blot analyses did not reveal a positive interaction between the protein of grub PMs and IIM-specific polyclonal antiserum from T. ni (TnIIM-spa); PM proteins of the four lepidopterans interacted by staining on the nitrocellulose membrane as revealed. Taken as a group, these observations suggest that the PM structure of H. oblita and H. parallela was different from those reported for the four lepidopteran larvae.