Social parasitism in bumble bees (Hymenoptera, Apidae): observations of Psithyrus sylvestris in Bombus pratorum nests

Abstract

Summary — Females of Psithyrus sylvestris (Lep) were introduced into free foraging colonies of their host Bombus pratorum (L) and interactions of hosts and parasites during the introduction period, and their behaviour during colony development were studied. The reactions of the host bees to the introduction of social parasites in 3 observed colonies ranged from aggressive to non-aggressive behaviour. Psithyrus females cohabited with host bees for several weeks following their introduction. They did not behave aggressively towards either host queens or workers, although they showed a head-rubbing behaviour, which we interpreted as dominance behaviour, possibly related to pheromone transfer. In all the observed colonies, hosts and social parasites reproduced. Host brood was reared to adults only from eggs laid prior to the usurpation by Psithyrus, whereas Bombus eggs were destroyed thereafter. B pratorum queens emerged earlier or at the same time as drones. In contrast, P sylvestris seemed to favour protandry as a reproductive strategy, with an earlier emergence of males than females. The colony with the lowest level of aggressiveness produced the greatest number of Psithyrus reproductives.social parasitism / Psithyrus sylvestris / Bombus pratorum / dominance behaviour / aggressivity INTRODUCTION

Bumblebee inquilinism in Bombus�(Fernaldaepsithyrus) sylvestris (Hymenoptera, Apidae): behavioural and chemical analyses of host-parasite interactions

“…Avoidance was also used by B. sylvestris females during their initial introduction into the B. terrestris nest, although they responded more aggressively to attacks by these workers. Küpper and Schwammberger (1995) also found that B. sylvestris inquilines invaded nests of B. pratorum without aggression. The B. sylvestris female appeared to change her strategy when introduced into the B. terrestris colony.…”

“…However a more complete mimetism may only be possible when these inquilines nest with their natural host, B. pratorum. In this situation, B. sylvestris engaged in "head-rubbing", which consisted in moving close to a host bumblebee of B. pratorum and gently rubbing against her head or thorax (Küpper and Schwammberger, 1995). According to the authors, pheromonal communication for the establishing of dominance may be involved.…”

“…Once a female enters a host nest, the process of integration seems to depend upon the species involved. While some inquilines passively usurp host colonies (Küpper and Schwammberger, 1995), others aggressively maul their hosts to establish dominance (Van Honk et al, 1981;Fisher, 1984Fisher, , 1988. A recent study showed that nest-invading Bombus (Psithyrus) norvegicus females may use allomones to defend themselves against attacking B.…”

Host Specific Social Parasites (Psithyrus) Indicate Chemical Recognition System in Bumblebees

“…(Ps.) campestris) are nonaggressive (Hoffer 1888;Sladen 1912;Fisher 1988), whereas aggressive and non-aggressive interactions have been observed against cuckoos that produce dodecyl acetate (Sladen 1912;Van Honk et al 1981;Küpper and Schwammberger 1995). Similar compounds (e.g., decylacetate and decyl butyrate) also are found in the enlarged Dufour's glands of slave-making Formica and Polyergus ants, where they act as repellents during raids (Regnier and Wilson 1971;Graham et al 1979;D'Ettorre et al 2000;Tsuneoka and Akino 2009).…”

When does cheating pay? Worker reproductive parasitism in honeybees

“…Colonies of the bumble bee Bombus terrestris, for example, are often parasitized by the cuckoo bumble bee Bombus (Psithyrus) vestalis, which kills the host colony's queen. The B. terrestris workers then rear both the B. vestalis progeny and those of their lost mother (Kupper andSchwammberger, 1995, Erler andLattorff, 2010). Ants are also common victims of social parasitism; inquiline ants live in the nests of other species where the host workers rear the inquiline's progeny as well as their own (reviewed in Buschinger, 2009).…”