And Formica Polyctena Först. (Hymenoptera: Formicidae)
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© Entomologica Fennica. 15 March 2007 Behavioural and socially parasitic relations between Polyergus rufescens (Latr.) and Formica polyctena Först. (Hymenoptera: Formicidae) Wojciech Czechowski Czechowski, W. 2007: Behavioural and socially parasitic relations between Polyergus rufescens (Latr.)and Formica polyctena Först. (Hymenoptera: Formi- cidae). Entomol. Fennica 18: 5464. Polyergus rufescens (Latr.), an obligate slave-maker, and Formica polyctena Först., an aggressive, territorial wood ant species, rarely co-occur in the field, and there are almost no data on their mutual relations under natural conditions. These interactions were studied in the Bia³owie¿a Forest (NE Poland), based on two P. rufescens colonies (with Formica fusca L. slaves)nesting within the territories of F. polyctena. The wood ants routinely searched the immediate vicinity of P. rufescens nests, whereas P. rufescens ants raided F. fusca colonies very close to F. polyctena nests or their columns passed right next to them, they eventually crossed wood ants foraging and removal routes, and even directly attacked F. polyctena colonies and robbed their brood. Interspecific relations in these partic- ular situations are described and discussed in the contexts of supposed chemical camouflage/mimicry of P. rufescens and interspecific competition hierarchy in ants. W. Czechowski, Museum and Institute of Zoology PAS, Laboratory of Social and Myrmecophilous Insects, Wilcza St 64, PL-00-679 Warszawa, Poland; E-mail: [email protected] Received 19 May 2006, accepted 11 December 2006 1. Introduction reviews see Czechowski 1996, 2003b)and be - havioural ecology (e.g. Punttila et al. 1996, Cze- Formica sanguinea Latr., the European blood- chowski 2000, Czechowski & Vepsäläinen 2001, red ant, and Polyergus rufescens (Latr.), the Eu- Czechowski & Markó 2006). P. rufescens is a ropean Amazon ant, are Palaearctic, facultative rare oligotope of dry grasslands, and therefore it and obligate respectively, slave-making social has little chance of encounters with wood ants in parasites of Serviformica For. ant species. F. the field. No wonder that reports on relations be- sanguinea, a common polytope of dry habitats tween P. rufescens and wood ants under natural (including forests), frequently co-occurs with conditions are scarce. Thus Forel (1900)de - wood ants (Formica s. str.)and, unavoidably, of - scribed a queenright (polygynous)colony of F. ten comes into direct contact with them; it is even pratensis Retz. (otherwise a polytope of dry habi- able to use wood ants as (atypical)slave species. tats)mixed with P. rufescens and F. (Servi- There is abundant literature regarding these inter- formica) fusca L. workers. As for behavioural actions, both with regard to social parasitism (for data, Dobrzañski & Dobrzañska (1978)and ENTOMOL. FENNICA Vol. 18 Relations between P. rufescens & F. polyctena 55 Dobrzañska & Dobrzañski (1989)mentioned a P. wood ant F. polyctena. PR-I inhabited a ne- rufescens colony that was gradually destroyed as glected coniferous-deciduous forest plantation, a result of heavy losses when its raids crossed a nesting in a part of it which was not intensively route of nearby F. rufa L. More recently, Cze- searched by wood ants coming from a vast multi- chowski (2006)reported that a F. polyctena nest polydomous system consisting mainly of Först. route was a factor indirectly promoting small, often unstable stump-side nests; its raids, supposed emancipation of F. fusca slaves from however, entered the intensively searched part of colonies of P. rufescens. Mabelis (2000)noticed the habitat (see Czechowski & Markó 2006 and that P. rufescens (with F. fusca slaves)did not re - Fig. 1 in Czechowski 2007). PR-II lay in a dry act aggressively towards F. rufa workers in the light spruce-pine forest, within the area inten- vicinity of its own nest, and concluded that the sively searched by F. polyctena, at a point where latter might also be enslaved. Deconinck et al. wood ants routes forked, 7.5 m away from the (2001)subsequently announced that conclusion nearest fairly big F. polyctena nest FP-I (Æ»60 as a fact, most probably too rashly. Then, as so far cm), a member of a well established polydomous there has been no reliable confirmation of P. colony comprising a few nests. Contacts between rufescens using Formica s. str. workers as atypi- the two species were observed in the following cal slaves. However, on the analogy of F. sangui- situations: (1)everyday encounters of P. rufes- nea, another slave-maker, this possibility can not cens (and its F. fusca nestmates)with F. polyc- be ruled out. tena in the vicinity of the Amazons nests, (2) The aim of this paper is to present the results crossings of F. polyctena nest-areas or its forag- of field observations of spontaneous relations be- ing routes by P. rufescens raiding columns, and tween the Amazon ant P. rufescens and F. po- (3)direct raiding of P. rufescens on F. polyctena lyctena, a common wood ant species. These rela- colonies. tions included mutual behavioural responses of the heterospecific individuals (and especially their groups)encountering in various situations, 3. Results as well as socially parasitic relationship between the slave-maker and F. polyctena as a possible 3.1. Relations in the vicinity atypical host species. of the P. rufescens nests P. rufescens nest PR-I lay in the zone only 2. Study area, material and methods sparsely searched by wood ants. However, in 2002, that nest was investigated by the nearest The investigations were conducted in the (10.2 m) F. polyctena colony, which nested in a Bia³owie¿a Forest (NE Poland)near the village of shady, overgrown place and was evidently look- Topi³o from 2001 to 2003 from mid-July till mid- ing for a new nesting place (establishing small August, i.e. within the period of P. rufescens raid- short-lived trial nests here and there). Usually in ing activity. Two big colonies of P. rufescens, the afternoons, single F. polyctena scouts came PR-I (found in 2001), nesting inside a rotten right up to nest PR-I, thoroughly searched the stump and in the soil at it, and PR-II (found in area and returned straight to their nest. During the 2002), nesting in a low earth bank, were observed reconnaissance they avoided contact with occa- practically every day within the study periods sionally encountered Amazon workers and their when the weather seemed to be good enough for numerous F. fusca slaves; the former paid no at- Amazons raids. Their raiding columns were esti- tention to these scouts and the latter sometimes matedtocompriseupto2,000workers.Thecal- harmlessly chased the intruders over a few centi- culations (very rough estimates)were based on metres (compare to the event described in subsec- the number of individuals crossing an imaginary tion 3.3). line in a unit of time, and the time it took the entire The mean dynamic density (± standard devia- tight column to cross that line. tion)of dispersed wood ant workers around the Both colonies nested within territories of the other P. rufescens nest, PR-II, measured at noon 56 Czechowski ENTOMOL. FENNICA Vol. 18 ca. 1 m away from the main nest holes, was 15.5 ± Markó 2006). The raided nest itself was situated 5.2 inds. × 0.25 m2 ×5min1 (n = 6). Besides their 4.5 m away from one of those two nests. That frequent encounters with enslaved F. fusca, Amazons raid did not provoke any response which were a matter of course in those circum- from nearby colonies of F. polyctena or even visi- stances, there were not even the slightest conflicts ble interest on the part of wood ant workers which between them and no aggressive behaviour to- were densely searching the area. Later both out- wards single Amazon ants was recorded. During bound and inbound raiding columns of PR-I were mass raiding activities of P. rufescens (recruit- seen many times to pass very close to nests of F. ment circling around the nest, marching out and polyctena (even less than 0.5 m from mound return of raiding columns), dispersed F. edges), again with no or hardly any response of polyctena usually simply moved aside without the wood ants. Once a group of about 20 F. po- protest. Aggressive responses of some F. polyc- lyctena workers coming down the mound at- tena towards P. rufescens were rare. Such aggres- tempted to attack an inbound column of P. ru- sive wood ant individuals were generally driven fescens but their attack was prevented within sec- away or sometimes even immediately killed. The onds by a few Amazon ants from the column only violent conflict noticed close to nest PR-II which launched a counter-strike without letting happened in 2002, when a pre-raid circle of ex- go of the pupae in their mandibles. tremely excited Amazon workers, so-called ac- Foraging routes of F. polyctena within the tivists according to Dobrzañskas and Dobrzañ- raiding distance of colony PR-I were not very dis- skis (1960)terminology, moved too close to the tinct. P. rufescens columns would cross them main F. polyctena FP-I foraging route that ran 1 without the slightest difficulty and frightened mfromtheP. rufescens nest entrances. That sec- wood ant foragers would then scatter towards the tion of the route was 1.5 m wide and the mean dy- sides or wait on grass blades for the column to namic density (± SD)of wood ants within it was pass. as high as 766 ± 42 inds. × 0.25 m2 ×5min1 (n = Raids of colony PR-I on F. fusca co-nesting 5). Only this route, and only in this (initial) sec- with F. polyctena in one stump (a plesiobiosis fre- tion, was impassable for P. rufescens, both single quently observed in this habitat; see Czechowski scouts and raiding columns (see below), and nor- 2002)took place three times during one season mally the Amazons did not try to move in that di- (2002).