Abstract
The Pselaphinae is a large subfamily of staphylinid beetles with a characteristic habitus and small body size. Detailed morphological and behavioural studies on these beetles are scarce. In this study, specimens of Bryaxis puncticollis (Denny, 1825), Bryaxis bulbifer (Reichenbach, 1816), Bythinus burrelli (Denny, 1825), Brachygluta fossulata (Reichenbach, 1816), Rybaxis longicornis (Leach, 1817), Pselaphus heisei (Herbst, 1792) and Tyrus mucronatus (Panzer, 1803), all collected in Northern Germany, have been examined with regard to their sensory organs (eyes and antennae), mouthparts and method of capturing prey. Scanning electron microscope studies revealed sex-specific differences in the numbers of ommatidia in Bryaxis puncticollis. A multitude of different sensilla on the antennae and great differences in the shape of the mouthparts were observed and peculiarities of the antennae and maxillary palps (e.g., the segment-like appendage) were examined using scanning and transmission electron microscopy. The prey-capture behaviour of these species is described in detail for the first time based on laboratory experiments using Heteromurus nitidus (Templeton, 1835) (Collembola) as prey. This behaviour seems to be tribe specific, ranging from simple seizure with the mandibles (e.g., Rybaxis longicornis, tribe Brachyglutini) to the employment of raptorial legs (Tyrus mucronatus, tribe Tyrini). The two Bryaxis species (tribe Bythinini) even employ their apparently sticky maxillary palps to capture prey. The assumption that a viscous secretion is used by these species is supported by the finding of glandular structures in the interior of their maxillary palps. Prey-capture is preceded by a complicated preparation phase in most of the species and followed by a sequence of prey-handling movements that seem to be adapted to restrain prey such as Collembola. In simple prey-choice experiments the beetles of several species preferred small prey, irrespective of their own body size. In these experiments, Bryaxis bulbifer and Brachygluta fossulata were more successful in capturing prey than Bryaxis puncticollis and Pselaphus heisei. This might be related to their different sensory equipment and different methods of capturing prey.
Highlights
The Pselaphinae is a globally distributed and very diverse subfamily of the beetle family Staphylinidae, comprising 9267 described species
Specimens of Bryaxis puncticollis (Denny, 1825), Bryaxis bulbifer (Reichenbach, 1816), Bythinus burrelli (Denny, 1825), Brachygluta fossulata (Reichenbach, 1816), Rybaxis longicornis (Leach, 1817), Pselaphus heisei (Herbst, 1792) and Tyrus mucronatus (Panzer, 1803), all collected in Northern Germany, have been examined with regard to their sensory organs, mouthparts and method of capturing prey
Bryaxis bulbifer and Brachygluta fossulata were more successful in capturing prey than Bryaxis puncticollis and Pselaphus heisei
Summary
The Pselaphinae is a globally distributed and very diverse subfamily of the beetle family Staphylinidae, comprising 9267 described species They are small predators (0.5–5.5 mm in body length) with a characteristic appearance. They possess compound eyes with only a few ommatidia. The mouthparts are prognathous, often with prominent maxillary palps and strong mandibles, indicative of a predatory life style. Saprophagy is recorded from some species of the genera Batrisodes, Claviger and Adranes, but not mycoor phytophagy (Thayer, 2005)
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