A review of myrmecophily in ant nest beetles (Coleoptera: Carabidae: Paussinae): linking early observations with recent findings

Abstract

Myrmecophily provides various examples of how social structures can be overcome to exploit vast and well-protected resources. Ant nest beetles (Paussinae) are particularly well suited for ecological and evolutionary considerations in the context of association with ants because life habits within the subfamily range from free-living and predatory in basal taxa to obligatory myrmecophily in derived Paussini. Adult Paussini are accepted in the ant society, although parasitising the colony by preying on ant brood. Host species mainly belong to the ant families Myrmicinae and Formicinae, but at least several paussine genera are not host-specific. Morphological adaptations, such as special glands and associated tufts of hair (trichomes), characterise Paussini as typical myrmecophiles and lead to two different strategical types of body shape: while certain Paussini rely on the protective type with less exposed extremities, other genera access ant colonies using glandular secretions and trichomes (symphile type). We compare these adaptations with other taxonomic groups of insects by joining contemporary research and early sources and discuss the possibility of an attracting or appeasing effect of the secretion. Species that are ignored by their host ants might use chemical mimicry instead. Furthermore, vibrational signals may contribute to ant-beetle communication, and chemical signals have proven to play a role in host finding. The powerful defense chemistry of paussines as "bombardier beetles" is not used in contact with host ants. We attempt to trace the evolution of myrmecophily in paussines by reviewing important aspects of the association between paussine beetles and ants, i.e. morphological and potential chemical adaptations, life cycle, host specificity, alimentation, parasitism and sound production.

The long-awaited first instar larva of Paussus favieri (Coleoptera: Carabidae: Paussini)

“…In most cases larvae have been found inside ant nests or carried about by the host ants (Luna de Carvalho, 1959, 1992Geiselhardt et al, 2007). No data on oviposition, feeding, development or behavior are available, not even for the first instar larvae of Arthropterus, hatched in captivity from eggs laid by an unidentified female (Di Giulio & Moore, 2004).…”

“…In free-living, nonmyrmecophilous larvae the terminal disk is used to trap prey through an ambush feeding strategy, after the prey are attracted to it by chemical attractants (Costa et al, 1988;Di Giulio, 1999;Di Giulio & Vigna Taglianti, 2001;Moore & Di Giulio, 2006). All described species of the monophyletic tribe Paussini are thought to be parasitic myrmecophiles as both larvae and adults (Darlington, 1950;Nagel, 1979Nagel, , 1997Di Giulio & Moore, 2004;Geiselhardt et al, 2007). Components of the terminal disk are fused in myrmecophilous Paussini larvae such that they cannot trap prey like their free-living relatives.…”

Behavior ofPaussus favieri(Coleoptera, Carabidae, Paussini): A Myrmecophilous Beetle Associated withPheidole pallidula(Hymenoptera, Formicidae)

“…All members of the ground beetle tribe Paussini (Coleoptera, Carabidae, Paussinae) are myrmecophiles and are considered to be ant parasites [8]. Like many other parasites of ants, they show striking adaptations, such as greatly modified antennae (flattened, enlarged, lenticular, globular, Psyche concave, elongate, etc.…”

“…Therefore, while they have been extensively studied from a taxonomic point of view [8], information about their interactions with hosts and their life cycle is limited and largely indirect (i.e., inferred from their structural adaptations) with few ethological observations [9]. Although several attempts have been made to rear Paussini with their host ants, this has proven to be particularly difficult, and promising results have been achieved only for a few species (5 out of the currently recognised 572 Paussini species) [8].…”

Does the decline of red wood ants after clear-cutting favour epigeic arthropods?

“…As a consequence, spatiotemporal distribution and abundance of red wood ants is of great importance for inter-specific interactions within invertebrate communities, and may affect the distribution of many other species, including myrmecophilous specialists, as well as the fitness of some vertebrates, development of the plant cover, nutrient cycles etc (Reznikova & Dorosheva, 2004;Dorosheva & Reznikova, 2006;Jäntti et al, 2007;Kilpeläinen et al, 2008;Lambrechts et al, 2008). This in turn affects community stability, the existence of forest ecosystems and co-evolution of sympatric species (Pisarski & Vepsäläi-nen, 1989;Atlegrim, 2005;Geiselhardt et al, 2007;Servigne & Detrain, 2008).…”