Usurpation is a widespread strategy within solitary nesting Hymenoptera. Field (1992) listed 24 solitary wasp and 8 solitary bee species with documented usurpation strategy. Usurpation is a theft directed to an active host nest construction and nesting area. So far it has been documented among solitary bees in Megachilidae species Chalicodoma pyrenaica (Lepeletier) and Osmia tricornis Latreille (Fabre 1914), Heriades carinata Cresson (Matthews 1965), Hoplitis anthocopoides (Schenck) (Eickwort 1975), Megachile apicalis Spinola (Barthell & Thorp 1995), Megachile rotundata (Fabricius) (McCorquodale & Owen 1994), Megachile spp. (Strickler et al. 1996), Osmia lignaria Say (Tepedino & Torchio 1994), Osmia rufa (Linnaeus) (Raw 1972), and Osmia spp. (Bohart 1955), as well as Apidae species Centris bicornuta Mocsáry (Vinson & Frankie 2000), Xylocopa spp. (Watmough 1974), Xylocopa pubescens (Mordechai et al. 1978, Velthuis 1987, Velthuis & Gerling 1983, Blom van der & Velthuis 1987), and Xylocopa sulcatipes Maa (Velthuis 1987).
Osmia rufa, the species with common nest usurpation.
Nest usurpation is a theft of a host nest construction, and implies full utilization of a nest construction or a pre-existing cavity occupied by a host female, depending on species nest habit. This behaviour occurs usually in wood- and stem-bearing bees, as well as in bees living in self-made structures (Bohart 1955, Eickwort 1975, Fabre 1914, Matthews 1965, McCorquodale & Owen 1994, Raw 1972, Tepedino & Torchio 1994, Velthuis & Gerling 1983, Vinson & Frankie 2000).
Usurpation of nesting area could be understand as nest theft, but usurpers do not utilise (or only partly utilise) the stolen host construction (e.g., the entrance or the main burrow). The new owner builds a new nest construction or parallel burrows in the same place where the nest with the cells of the former owner (the host) were built. Usurpation of nesting area has been observed in some wood-nesting bees (Velthuis & Gerling 1983) and in some mason bees (Eickwort 1975, Fabre 1914).
Discarding of cell content in the usurped nest of the host can follow after the nest usurpation in some individuals. Field (1992) called this behaviour nest usurpation after host cell removal and it has been documented in Xylocopa Latreille species (Blom van der & Velthuis 1988, Mordechai et al. 1978, Velthuis 1987, Velthuis & Gerling 1983 and Watmough 1974) and Heriades Spinola (Matthews 1965). Discarding of cell content without usurpation might represent a failure of some behavioural pattern including usurpation, but not necessarily. This behaviour is not well-understood and is occasionaly observed (see Field 1992 for details).
Remnants of discarded brood cell supplies are spread over nest entrance in Xylocopa.
In some species, the usurper utilises host provisions from unfinished cells. Completed host cells are not destroyed, or only the final cell in the series is destroyed (Vinson & Frankie 2000).
Usurpation strategy is documented also in eusocial species. Within this group it is a common strategy in species where the nest is founded by a single female. Kaitala et al. (1990) developed a theoretical model of founder nesting strategies and predict evolutionarily stable strategy with a high frequency of usurpation at the end of the solitary phase. This behavioural pattern is well-studied in Bombus hyperboreus Schönherr, which usurps nests of Bombus polaris Curtis in the late solitary phase and subsequently emerging host workers then help the usurper to rear its reproductive generation (Richards 1973). It is a typical social parasitic scenario of cuckoo bumblebees (Bombus sg. Psithyrus Lepeletier) (Michener 2007), but the Bombus hyperboreus queen is normally able to rear its own brood when it does not usurp an alien nest (i.e., this behaviour is not obligate).
A competition over suitable nesting places is generally high within the genus Bombus Latreille and multiple usurpation of a single nest occurs frequently (Sakagami 1976, Paxton et al. 2001). In this case, the usurpation strategy slowly decreases towards the end of the solitary phase. This behavioural pattern has been observed in Lasioglossum malachurum (Kirby) (Zobel & Paxton 2007), even though this species is generally thought to usurp nests late in the season, according to the model of Kaitala et al. (1990). A special case of usurpation represents a situation when aggressive swarms of Africanized Apis mellifera bees usurp hives of European colonies (Schneider et al. 2004).
Potential usurpers are easily recognisable at nesting sites. They do not own a nest, yet are seen flying over the nesting site, usually from one nest entrance to the next, sometimes inspecting an entrance and entering the nest. These bees are called trap-lining bees (Packer 1986) or more frequently floaters (Wuelner 1999, Zobel & Paxton 2007). This behavioural pattern seems to be analogous to searching flight in brood parasites.
|Last Updated on Sunday, 05 February 2012 23:20|