Abstract
Untitled Document
Trail following behaviour of Dolichovespula saxonica, Vespula vulgaris and Vespa
crabro (Vespinae) was investigated in experiments with an artificial tunnel system.
D. saxonica that typically has free nests was found to produce trail pheromones
used for nest orientation while walking through the tunnel system as it was known
from the obligate cavity breeding species V. crabro and V. vulgaris (chapter 3).
In V. vulgaris and D. saxonica, the trail is used for nest orientation mainly
by young, inexperienced foragers. Experienced foragers orient themselves visually.
Under reduced light regime, they also orient chemically. In V. crabro, however,
the majority of foragers use the trail for orientation irrespectively of the light
regime (chapter 4). In contrast to V. crabro the terrestrial trails of D. saxonica
and V. vulgaris are not colony specific (chapter 5). These differences in trail
following behaviour between V. crabro and V. vulgaris despite their similar nest
habitats are probably due to the convergent evolution of cavity breeding in both
species. This assumption is supported by phylogenetic data obtained from other
authors.
Chemical analysis of the trail of V. vulgaris revealed that it consists exclusively
of hydrocarbons (C22-C35) that are also found on the cuticle and in the profile
of the nest odour. Most likely, the hydrocarbons are transferred by foragers passively
from their cuticles to the substrate while walking outside the nest. In this way
the nest odour is lengthened as a trail and used for nest orientation. This hypothesis
may also apply to V. crabro and could easily explain the existence of a trail
in D. saxonica (chapter 6).
Biotests with V. vulgaris demonstrate the temporal change of the nest odour. Nestmates
removed from the nest and frozen for 17 days were not accepted as colony members
and were attacked. On the contrary, nestmates only frozen for few hours were attacked
significantly less frequently.
In experiments with two V. vulgaris-nests in a twin nest box before and after
they were kept simultaneously in the same aerial space it was shown that the change
of nest odour can be induced by an exchange of volatile compounds via the aerial
surroundings the nest. 10 days after the two colonies had been placed in the same
aerial space, members of the neighbouring colony were treated with a similar low
rate of aggression as nestmates. Before the two nests were kept together the rate
of aggression was significantly higher between both colonies. Since a direct contact
of the members of both colonies was prevented, the exchange of volatile compounds
was the only possibility for the mutual adjustment of the nest odours (chapter
7).
Despite the precise ability of V. vulgaris to distinguish colony members from
alien individuals the parasitoide beetle M. paradoxus is able to stay inside the
V. vulgaris host colony without being attacked by the wasps. Whether this is achieved
by chemical mimicry was investigated in chemical analyses of the cuticular hydrocarbon
profiles of the beetle and V. vulgaris. Only 29 of the 95 cuticular compounds
of V. vulgaris could be found in M. paradoxus. Thus, the parasitoide does not
mimic the whole hydrocarbon profile of the host. However, biotest data show that
a beetle from the own nest was attacked less frequently by V. vulgaris-foragers
than a beetle from an alien colony. Among the 29 cuticular hydrocarbons of M.
paradoxus that are also found on the cuticle of V. vulgaris, there could be key
substances mimicking the colony specific quantities of the corresponding compounds
of V. vulgaris. The congruence of these key compounds may feign a colony membership
of the beetle (chapter 8).
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