Fig 1.
Design of the laboratory formicarium for housing myrmecophile beetles and host ant colonies.
The interconnected nest chambers are set in gypsum plaster and covered by a glass plate. The internal nest opens into an arena where food for the ants is provided and where beetles are placed for adoption experiments.
Fig 2.
Scanning electron microscopic images of the abdomen of mymecophilous staphylinid beetles.
Above: Lomechusoides strumosus; Below: Lomechusa pubicollis. AG indicates the lobes of the paratergites with the dense endowment with trichome hairs. This area is richly endowed with exocrine gland which are called “adoption glands”.
Fig 3.
Adoption gland complex: Longitudinal section through the abdominal paratergal lobes of Lomechusoides strumosus.
The picture above shows two lobes with trichome setae and glandular cells (GC). Below: The second major cluster of gland cells near the bases of the tergal lobes; the glandular ducts (GD) open through the cuticle near a tracheal tract. These glands are most likely part of the adoption gland complex.
Fig 4.
Adoption gland complex: Longitudinal section through the abdominal paratergal lobes of Lomechusa pubicollis.
(a) A lobe with trichomes and many glandular cells (GC), the ducts (GD) of which open through cuticle channels between the trichome setae. (b) Some areas of the lobes which have no trichomes, have glandular epithelia (GE) the cells of which open through cuticle channels (CuC). (c) The second cluster of gland cells on the bases of the trichome lobes the ducts of which open through the cuticle near a major tracheal tract.
Fig 5.
Transversal section through the lateral edge of the abdominal tergites adjacent to a paratergal trichome lobe of Lomechusoides strumosus.
Although in this part of the adoption gland complex trichome setae are sparse or absent, large glandular cells (GC) with many internal vacuoles open through ducts and cuticle channels (CuC).
Fig 6.
Longitudinal sections through the abdominal tip of Lomechusoides strumosus.
(a) Overview of the abdominal tip. Part of the post-pleural gland (PplG) is visible. (b) Close-up of tergites VIII and IX, showing the well-developed glandular epithelium (GE) in both segments. (c) Close-up view of tergite IX showing the cylindrical glandular cells in glandular epithelium (GE). (d) Glandular cells (GC) with ducts at the edges of tergite VIII.
Fig 7.
Post-pleural gland in Lomechusoides strumosus.
(above) Glandular cells (GC) and ducts that open in densely packed pores (GDO) in the pleural intersegmental membrane. (below) Large glandular cells (GC) with duct cells (DC).
Fig 8.
Post-pleural gland and other glandular structures in the abdominal tip of Lomechusa pubicollis.
(a) Post-pleural gland with glandular cells (GC) and duct cells (GD) opening through the pleural intersegmental membrane between the abdominal segment VIII and IX. (b, c). large glandular cells (GC) in the posterior part of the abdomen with large intra-cellular reservoirs (GR).
Fig 9.
Scanning electron microscopic images of the abdomen of Lomechusoides strumosus.
PLG: opening of the post-pleural gland. DTG: opening of the defense tergal gland.
Fig 10.
Longitudinal section through the defense tergal gland of Lomechusoides strumosus.
(top) The complex gland structure consists of the glandular cells (GC) with duct cells (D) that open through the cuticle of the 7th abdominal tergite into a reservoir (R). Part of the reservoir membrane is a glandular epithelium (GE). (bottom) Close-up of the glandular epithelium (GE) showing the large cylindrical glandular cells.
Fig 11.
Schematic illustration of the major exocrine glands in the abdomen of Lomechusoides strumosus.
The green area of abdominal segments II to V is the adoption gland complex (AG). Between abdominal segments VI and VII is the defense tergal gland or repellent gland, the reservoir (Re) of which opens between these two segments. The repellent secretion is a mixture of the secretions of the glandular epithelium (RGE) and the glandular cells (RGC). PlG indicates the location of the post-pleural gland. HG: hindgut; R: rectum. The blue area indicates the appeasement gland complex.
Fig 12.
Longitudinal sections through the head of Lomechusoides strumosus.
(a) Overview of part of the head. Br: brain; M: muscle; GC: glandular cells near the base of the mandibles. (b) Close-up of these gland cells that open through the cuticle channels (CuC). (c) Longitudinal section through the mouth parts. Lbr: labrum; M: mandible, with an epithelium consisting of sensory and glandular cells (GC/SC) in the posterior. Ga: galea. (d) Glandular cells (GC) in the labium (Lab).
Fig 13.
Glandular epithelium (GE) in antennal segments of Lomechusoides strumosus.
Fig 14.
Scanning electron microscopic images of the cuticle glandular pores of Lomechusoides strumosus.
(a) Labrum with densely spaced pore plates (GPpl). (b) Close-up of cuticle of the 8th abdominal tergite. Many of the pore plates and pores (GP) are less than 10 μm apart. (c) Close-up of a glandular pore plate. Its diameter is less than 2 μm.
Fig 15.
Scanning electron microscopic images of the side view of Lomechusoides strumosus (a) and Lomechusa pubicollis (b). Close-up of the femur (Fe) of L. strumosus (c); the trichome setae are clearly visible. (d) Close-up of the femur of L. pubicollis. Trichome setae are absent.
Fig 16.
Trichome glands in the femur of Lomechusoides strumosus.
(above) Scanning electron microscopic image of the ventral side of the femur. Box indicates the location of the histological preparation shown in bottom panel. (below) Glandular cells (GC) inside the femur.
Fig 17.
Longitudinal sections through the leg of Lomechusoides strumosus.
(a) and (c) Longitudinal sections through the femur showing the densely packed glandular cells (GC) with the cuticle channels (CuC). (b) and (d) Longitudinal sections through tibia proximate to the femur, showing the dense layer of gland cells with ducts through the cuticle.
Fig 18.
Longitudinal section through part of the alimentary tract of Lomechusoides strumosus.
(above) Crop (Cr) and proventriculus (PrV). The crop is lined with layers of longitudinal and transversal muscles, and in the lumen the sclerotized spines are visible. (below) The transition from crop via proventriculus to midgut (MG). The midgut is endowed with many diverticula (DiV) along its entire length.
Fig 19.
Sections through the hindgut of Lomechusoides strumosus.
(a) Longitudinal section through the hindgut (HG) and rectum (R). (b) and (c) Transversal sections showing the large gland cell nuclei (GCNu) in the hindgut epithelial cells (HGE). (M) Muscle tissue surrounding hindgut layer. (d) Transversal section of hindgut showing the microvilli structure (MiVi) of the hindgut cells.
Fig 20.
Adoption process in Lomechusoides strumosus.
At first encounter the ants often lick the distal part of the beetle’s extended femur (above) or the proximate part of the beetle’s tibia (below).
Fig 21.
Adoption process in Lomechusoides strumosus.
The abdominal tip is the most frequently encountered body part of the beetles which the prospective host ants inspect and lick. During this process the beetle attempts to touch the ant with its antennal tip (b, c, d). Finally, the beetle unrolls its abdomen (e, f) while the ants continue to lick the abdominal tip.
Fig 22.
(above) Often the beetle exudes an opaque, white droplet from its abdominal top, which is taken up by the ant. Presumably it originates from the hindgut/rectum. (below) Occasionally a whitish, clear secretion appears at the lateral sides of the abdomen where the post-pleural gland opens. This secretion is also licked by the ants.
Fig 23.
Parts of the beetle body contacted prior to adoption.
We recorded the number of times ants contacted various body regions of newly introduced beetles (n = 10). The beetle’s abdominal tip and legs received the highest and second highest proportion of contact, respectively (bars are means with standard error).
Fig 24.
Adoption process in Lomechusoides strumosus.
After aggressive behavior of the ants has waned due to the appeasement behavior (a), the beetle allows the ant to access the adoption glands (the trichome area at the margins of the first abdominal segments; b, c, d).
Fig 25.
Adoption process in Lomechusoides strumosus.
In the last phase of the adoption process the ant grasps the beetle on the trichome hairs and lifts it up. The beetle assumes a pupal position and is carried into the nest.
Fig 26.
Ants preferentially shared food with familiar beetles.
Beetles fed with labeled honey water were placed with familiar or unfamiliar beetles. Beetles from both groups successfully obtained food from their host ants, but familiar beetles obtained significantly more food than unfamiliar beetles (bars are means with standard errors).
Fig 27.
Beetles did not share food directly with ants, over time.
Over 48-hrs, beetles that fed on labeled food emitted significantly higher impulse counts than the ants they were housed with (LMM, P < 0.00001). Beetles lost a small proportion of their signal, while ants obtained a significant (but low-level) signal between the first final sampling periods (LMM, P < 0.0026), possibly from consuming beetle feces or excretions. Each trial (n = 4) is represented by a different color. Beetle impulse counts are represented by open circles, and associated ants with closed circles.
Fig 28.
Trophallaxis between Lomechusoides strumosus and host ant Formica sanguinea.
Often the ant approaches the beetle and licks its head (a). The beetle seeks contact with the ant’s labium (b, c). This usually leads to regurgitation of food by the ant. During the trophallactic act shown in (d), the ant’s mandibles are closed, but the labium is extended. This somewhat resembles the feeding behavior which ants exhibit during larval feeding.
Fig 29.
Trophallaxis interactions in Lomechusoides strumosus.
The host ant Formica sanguinea regurgitates food to the beetle (above). The ant’s mandibles are opened, the labium is extended. This resembles the feeding behavior among adult ants. (below) Occasionally two beetles have mouth to mouth contact, however we could not find evidence that they exchange food.
Fig 30.
Scanning electron microscopic images of the mouth parts of Lomechusoides strumosus.
(left) Close-up of ventral view of galea (Ga) and lacinia (La) of the maxillae. (right) Dorsal view maxillary palps (MP), galea (Ga), and mandibles (Ma).
Fig 31.
Scanning electron microscopic images of the mandibles of three aleocharine beetle species.
Lomechusoides strumosus (a) and Lomechusa pubicollis (b) both have a large protheca (PT) in contrast to Pella sp. (c) where the protheca is much smaller.
Fig 32.
Scanning electron microscopic images of the head and antennae of male Lomechusoides strumosus.
(a,b,c,d,) Different views and magnifications of the typical hair tufts (AT) the beetle males display on their third and fourth antennal segments.
Fig 33.
Mating in Lomechusoides strumosus.
Fig 34.
Spermatheca of Lomechusoides strumosus.
(left) The sclerotized spermatheca (SpT) and spermathecal gland (SpTG). (right) Close-up of the spermatheca gland (SpTG) showing the densely packed duct cells (SpTGD).