The first morphological description of the immature stages of Thiasophila Kraatz, 1856 (Coleoptera; Staphylinidae) inhabiting ant colonies of the Formica rufa group

Abstract

This article for the first time presents the morphology of the egg, three larval instars, pupal cocoon, prepupa and pupa of myrmecophilous rove beetle Thiasophila angulata (Erichson, 1837) along with illustrations of structural features and chaetotaxy. Morphological comparisons are made between larval instars, and between the mature larva of T. angulata and other known larvae of Aleocharinae belonging to the tribes Athetini, Hoplandriini, Liparocephalini, Lomechusinii and Oxypodini. Pupae of T. angulata and two other species of Aleocharinae: Pella laticollis (Märkell, 1844) and Haploglossa picipennis (Gyllenhal, 1827) are compared. The mature larvae of T. angulata were observed to vary morphologically depending on the ant host species (Formica polyctena, F. rufa or F. truncorum). Host-related variation was observed in median larval body length, head and pronotum width and structure of the antennae.

First description of the larva of Dinaraea Thomson, 1858, with comments on chaetotaxy, pupa, and life history based on two saproxylic species from Europe (Staphylinidae, Aleocharinae, Athetini)

“…Apart from the clearly smaller body size (see Table 1), features exclusive to L1 include: (1) the absence of some setae on the dorsal surface of the head and thorax, and on the dorsal and ventral surfaces of the abdomen, (2) the presence of short subapical setae on the urogomphi, (3) egg bursters on some thoracic and abdominal tergites, (4) a darker terminal antennal segment than in L2–3, and (5) markedly longer urogomphi and their apical setae than in later stages. These morphological differences between the younger and older larval instars in Dinaraea are of a similar nature to those in other tribes of Aleocharinae (Table 2) (Ashe and Watrous 1984, Ashe 1986, Zagaja et al 2014, Staniec et al 2016). They enable one to easily distinguish L1 from the older larval stages without recourse to metric analysis.…”

“…Measurements of the head and pronotum of the two Dinaraea species indicate that their larval development involves three stages (Table 1): this is typical of most known aleocharines (White 1977, Ashe and Watrous 1984, Ashe 1985, Ashe 1986, Zagaja et al 2014, Staniec et al 2016). Only in the case of Pella species ( P. laticollis ) (Lomechusini), inhabiting ants’ nests, were just two larval stages found; this is due to the faster rate of development of these rove-beetles (Hölldobler et al 1981, Staniec et al 2009).…”

“…The combination of characteristics that enable mature larvae of Dinaraea to be distinguished from known larvae of other genera within the subfamily Aleocharinae are as follows (Paulian 1941, Pototskaya 1967, Topp 1975, Ashe 1981, 1985, Ashe and Watrous 1984, Ahn 1997, Jeon and Ahn 2009, Staniec et al 2009, 2010, 2016, Zagaja et al 2014, the present study): (1) body narrow, elongate, dorso-ventrally flattened, sides almost parallel; (2) pronotum slightly wider than (at most 1.1 as wide as) head; (3) antennal article I longer than wide; (4) sensory appendage (Sa) of antennal article II acorn-shaped, longer than antennal article III; (5) length ratio of antennal articles I and II – 1:1.6; (6) central region of anterior margin of labrum protruding and crenate; (7) mandibles with one large and two-five small subapical teeth; (8) mala at least slightly widened at adoral margin; (9) adoral margin of mala with eight large and approx. 15 small teeth; (10) length ratio of article I and III of maxillary palp – 1:1.5; (11) ligula finger-like, 2.5 × as long as wide; (12) hypopharynx with approx.…”

“…A combination of 17 diagnostic features (see “Generic diagnosis…”) have been proposed for the mature larva of Dinaraea , described above, which enable it to be distinguished from other known older larval stages of Aleocharinae (Paulian 1941, Pototskaya 1967, Topp 1975, Ashe 1981, Ashe and Watrous 1984, Ashe 1985, Ahn 1997, Jeon and Ahn 2009, Staniec et al 2009, 2010, 2016, Zagaja et al 2014). In this respect the genus Dalotia (Da) Casey, (Athetini) most closely resembles the genus Dinaraea (Di) (Ashe and Watrous 1984), and the small differences relate solely to: (i) body habitus – moderately dorso-ventrally flattened in Di or cylindrical in Da ; (ii) shape of antennal article I longer than wide in Di or wider than long in Da ; (iii) structure of anterior margin of labrum central region protruding and crenate in Di or wholly rounded and smooth in Da ; (iv) seta Da1 on pronotum absent in Di or present in Da ; (v) setae D3 and P5 on abdominal sternite I absent and present respectively in Di , or present and absent in Da .…”

Body size in the ant-associated isopod Platyarthrus hoffmannseggii is host-dependent

“…Therefore, we argue that the isopods found in both host types form no distinct races. Some studies relied on very subtle morphological variation to split the taxonomic status of a myrmecophile in different lines each specializing on related ants (Zerche, 2009;Zagaja, Staniec, & Pietrykowska-Tudruj, 2014). However, in the case of unspecialized myrmecophiles, which poorly interact with their host, easily switch between related hosts and do not match the nestmate recognition cues (Parmentier, 2016), divergent selection is expected to be low.…”