Biology of Acarophagous Scydmaeninae

Abstract

Some Scydmaeninae are strict specialists that feed exclusively on heavily sclerotized oribatid or uropodine mites. The chapter reviews the available literature on the feeding habits of Euconnus , Stenichnus , Scydmaenus , and Cephennium beetles and presents previously unpublished observations on Neuraphes and Microscydmus species. Species with unspecialized mouthparts attack the mite’s gnathosoma, removing movable parts to gain access to soft tissues. They also often remove genital or anal plates to feed through the resulting openings. In Euconnus that are specialized to feed on ptyctimous (i.e., capable of encapsulating) oribatids, a sticky droplet of digestive juice exuded onto the predator’s mouthparts is used to capture mites. The prey is then lifted and covered with noxious digestive juice, which weakens or kills the encapsulated mite . Once the muscles responsible for maintaining the encapsulation are relaxed, the prey’s prodorsum opens, and Euconnus beetles use their mandibles to crush the mite’s ventral plates and gain access to the flesh. In Scydmaenus that are specialized to feed on non-ptyctimous Oribatida and Uropodina, the mandibles play a major role both in capturing prey and in breaching the mite’s defenses. The prey’s legs are often cut off if they are long or spiny, which facilitates the subsequent attack on the gnathosoma. Cephenniini are the “hole scrapers”: they have paired labial suckers on the prementum, which are used to immobilize their prey. Once the mite adheres to the suckers, the predator’s mandibles slowly grind a small hole in the prey’s cuticle. Digestive juices are then injected; through the same puncture, liquefied tissues are ingested. The entire feeding process can take many hours. Some species show preferences toward particular mite taxa and may play a significant role in the oribatid or uropodine mite population dynamics.