Aleocharinae Fleming, 1821

Berx, Peter, Bosmans, Bart, Dekoninck, Wouter, Janssen, Marc, Stassen, Eugène & Crevecoeur, Luc, 2023, Faunistic survey of myrmecophilous and other ant-associated beetles and spiders in the Belgian province of Limburg (Araneae, Coleoptera, Hymenoptera: Formicidae), Belgian Journal of Entomology 141, pp. 1-61 : 30-34

Aleocharinae Fleming, 1821

With thirteen species within the genus Aleochara Gravenhorst, 1802 observed in Limburg, one would expect several of them to be found together with ants. However, it is clear that A. sparsa (2.0-5.0 mm) is the most common species with 3,710 specimens spread over 69 1 x 1 km grids (Annex), and apart from an occasional observation of A. lanuginos a (3.0- 5.5 mm), the only species of this genus frequently observed in the vicinity of ants. The use of proper sampling techniques appears to be a determining factor for the detection of this species as well. In Voeren, a total of 880 individuals were collected with pitfall traps in hollow trees, but across the whole study area, 1,404 individuals were caught with flight-interception traps (air eclectors). We emphasize that only the pitfall traps in hollow trees used in Voeren can demonstrate a connection between beetle and ant.

With 63 species, the genus Atheta Thomson, 1858 is well represented in Limburg. Many species are associated with decaying sporocarps and accordingly we collected 29% of the specimens screening decomposing mushrooms. We selected seven species that have been reported in literature in relation with ants (Annex). In Germany Frank Köhler found Atheta paracrassicornis Brundin, 1954 in a nest of L. brunneus , excavated in a hollow ash ( Fraxinus excelsior ) ( KÖHLER, 2000) but neither during the study in Tongeren nor in Voeren could we confirm these observations.

The genus Dinarda Leach, 1819 includes only species that coexist with ants. Erich Wasmann (1889, 1894), who may be regarded as the pioneer in the study of the life cycle of Dinarda , closely observed these beetles in artificial nests and concluded that the Dinarda species are indifferently tolerated by the host ants. He distinguished four species: D. dentata Gravenhorst, 1806 , D. märkelii Kiesenwetter, 1843 , D. hagensi Wasmann, 1889 , and D. pygmaea Wasmann, 1894 . In the classification, he not only paid attention to the morphological differences, but also considered the different host ants with which they were found. From his observations the following combinations have been noted:

D. märkelii associated with F. rufa , F. polyctena and F. pratensis

D. dentata associated with F. sanguinea

D. hagensi associated with F. exsecta

D. pygmaea associated with F. fusca

It is noteworthy that the first three Dinarda’ s which are coloured red to dark brown are found with Formica species which show a similar colour pattern, while D. pygmaea is more uniformly dark gray, just like the host ant F. fusca . This conclusion may be premature, as D. pygmaea was also found with F. rufibarbis ( HÖLLDOBLER, 2019) . On the other hand, the other species were until now not found with F. fusca .

In 74 grids of 1 x 1 km, we recorded 490 specimens of Drusilla canaliculata (4.0- 4.8 mm) (Annex). This staphylinid beetle is ubiquitous present in nests of several genera of ants, Formica , Lasius , Leptothorax , Myrmica , Ponera and Tetramorium ( DONISTHORPE, 1915) . Many species of ants associated with this beetle build a ground nest, which may explain why 97% of the individuals collected were caught with pitfall traps in the field and only a single specimen with a light trap. Whether D. canaliculata develops in ants’ nests is not very clear, but larvae were also found in nests in addition to the adult beetles ( DONISTHORPE, 1927). It is certain that the beetle predates the ants, but it has also been observed that beetles are brought to the ant nests by the ants themselves.

Haploglossa gentilis (3.0-4.0 mm) and to a lesser extent Haploglossa marginalis (3.0- 3.5 mm), was observed in several nest boxes of the common kestrel ( Falco tinnunculus Linnaeus, 1758 ) ( STRUYVE, 2006). Data obtained here can link these rove beetles to the colonies of the treedwelling ant species L. fuliginosus . An observation in the southeast of Limburg shows that Haploglossa gentilis can be present in a large concentration in or near the nest of L. fuliginosus . From a hollow oak tree ( Quercus robur L.), about 10 litres of pulverized wood was collected above a nest, from which 264 beetles were taken.

The rove beetle Lomechusa emarginata (3.5-4.5 mm) ( Fig. 26D ) uses the hospitality of two different species of ants during its development. From autumn to spring, as an adult beetle, it seeks shelter in a colony of Myrmicine ants while in early summer it searches for a red wood ant nest to lay eggs that will develop in this environment into a new generation of adult beetles. However, the beetles were not only found in red wood ant nests but were also observed with F. fusca . Donisthorpe (1927) repeatedly reported the presence of F. fusca as a host. He recorded several observations of this ant species in the months of April and May and found larvae in the months of June and July. In the same months, the beetles were also found in the nests of F. rufa and in April he observed workers of F. fusca carrying ten beetles into their nest during an hour and a half. During the winter months he noticed beetles in the nests of Myrmica scabrinodis , M. ruginodis , M. rubra and M. sulcinodis . It is suspected that the adult beetles stay near the Myrmicine ants during the winter months because of the presence of brood on which they can feed. In the lab, Donisthorpe (1927) found that when the beetles moved from the nest of a Myrmica sp. to that of a Formica sp. , they remained in seclusion for twenty-four hours before entering the new nest. Apparently, the beetle first wants to get rid of a hostile Myrmica smell before confronting the new host. ( DONISTHORPE, 1927)

On May 24, 2007, we found a specimen of L. emarginata in Zutendaal (Lieteberg) in the nest of M. ruginodis built in a shady place under the moss. In this nest only eggs and larvae, but no nymphs of the host ant were present. Sietske and Sieger Verbeeck (two grandchildren of the first author) found a worker of F. fusca with this rove beetle between its jaws on 15 April 2009 at Hasselt Kiewit, which only confirms Donisthorpe’s observations.

The genus Pella Stephens, 1835 contains 30 species distributed in the Palaearctic region ( MARUYAMA, 2006) and six of these species have been observed in the province of Limburg: P. funesta (Gravenhorst, 1806) ( Fig. 26E ), P. humeralis (Gravenhorst, 1802) , P. cognata (MÄrkel, 1842), P. limbata (Paykull, 1789) , P. lugens (Gravenhorst, 1802) and P. laticollis (MÄrkel, 1845). The Pella beetles, included in this study are all associated with the dendrobiont ant L. fuliginosus as the main host. P. humeralis is also noticed with F. rufa and F. pratensis and in a few observations P. lugens is recorded in a nest of L. brunneus .

From observations both in the lab and in the field, Hölldobler et al., (1981) gives us a description of the life cycle of Pella funesta and notes that this rove beetle deposits eggs, larvae and pupae on the garbage dumps of the ant, a nesting chamber where the attention of the ants is probably less vigilant. Foraging around the nest usually takes place at night. During the day these beetles take shelter. Most observers assume that they feed exclusively on dead ants and their waste, but nocturnal observations indicate that they are also present on the foraging trails of L. fuliginosus and that they attack, kill and eat living ants. In their feeding behaviour, the beetles are obviously opportunistic. As long as corpses are available, they will opt for the easy meal but during periods of scarcity they will switch more quickly to predatory behaviour by attacking ants. Accurate observation and biochemical research have revealed that in aggressive contact by the ants, the beetles can repel the attacks both by adapted behaviour, such as feigning death, and by releasing chemical compounds from abdominal glands. In the typical characteristics of these rove beetles, Hölldobler supposes preadaptations in the evolution towards a higher degree of myrmecophily ( HÖLLDOBLER et al., 1981). A more recent study of three species of the genus Pella , P. cognata , P. funesta and P. laticollis reveals few specific differences both in behaviour and in chemical interaction between these beetles and ants with emphasis on the different reactions of L. fuliginosus in response to the dispersion of glandular secretions ( STOEFFLER et al., 2011). The presence of the six species from the genus Pella in the locations where L. fuliginosus is observed, is clearly demonstrated in our long-term research. In the forest complex, Jagersborg, situated in Maaseik, the presence of a colony of L. fuliginosus was confirmed by the observation of a nest in a hollow birch. Sampling of invertebrates around this tree was performed from mid-April until mid-July by means of pitfalls and a window trap. Pella cognata , P. humeralis , P. limbata and P. lugens were captured in the same period and in the same vicinity. The presence of different species in the same neighbourhood is probably not uncommon. In another deciduous forest, Kolmontbos in Tongeren, we found three different rove beetles: P. funesta , P. lugens and P. laticollis by sieving the nesting material of L. fuliginosus from a hollow oak.

Two rove beetles closely related to Pella were also added to the list: Zyras collaris (Paykull, 1800) (4.0-5.0 mm), with thirteen specimens and Z. haworthi (Stephens, 1832) (5.5-7.0 mm) with three specimens (Annex). In a recent study only one for each of the two species was captured in Baden-WÜrttemberg ( Germany) and due to the observation of only 18 ( Z. collaris ) and ten ( Z. haworthi ) individuals between 1950 and 2000, the authors label them as ‘two rare myrmecophilous species’. Their research was carried out on the chemicals from the tergal glands of this rove beetles with a remarkable conclusion. Analysis of the secretions (Oi -pinene, β -pinene, myrcene and limonene) of these glands and the reaction when confronted with the presence of L. fuliginosus indicates that this is a unique composition. The researchers found no flight response or aggressive reaction in the ants when confronted with this secretion. The ants, on the contrary, showed a behaviour that they also exhibit when interacting with aphids. Since the identified terpenes are known to be present in some aphids as well as in their honeydew, it is assumed that these Zyras beetles mimic this composition in the pursuit of peaceful contact with the ants ( STOEFFLER et al., 2013). From literature we know that Z. collaris is associated with ants but not exclusively, while Z. haworthi is associated with Lasius and Formica species ( HASTIR & HAUBRUGE, 2002).

Figures

Fig.26. A, Aloconota gregaria (Erichson, 1839) (range 2.7-3.8mm). B, Euryusa optabilis Heer, 1839 (2.7 mm; range 2.5-3.0mm). C, Leptusa pulchella (Mannerheim, 1830) (3.2 mm; range 2.7-3.2mm). D, Lomechusa emarginata (Paykull, 1789) (4.5mm; range 3.5-4.5 mm). E, Pella funesta (Gravenhorst, 1806) (5.2 mm; range 5.0-5.5 mm). © U. Schmidt.