I. Occurrence, nest construction and sexuals [ ] II. Inquilines in the nests of social wasps




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W Biegel (1953)

[ On the biology and ecology of social wasps ]


Sitzber. physik.-medizin. soz. zu Erlangen 76: 115-153

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I. Occurrence, nest construction and sexuals

[...]
II. Inquilines in the nests of social wasps

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In the course of my studies it was shown that in relation to inquilines two ecological nest types are important among the nests of social wasps. They are:-

1. ground-based nests

2. free-hanging nests

These two types are sharply distinct in the composition of their associated fauna. To the free-hanging type of nest belong all those nests that are above ground in trees, dense bushes, on buildings, or in addition half in the ground and in closed spaces. Thus nest type shows a very poor varety and abundance of associated fauna. It is characterised by a relatively low humidity and - in germanica and vulgaris nests of this type - bad heat insulation. To this type belong: all the Dolichovespula nests that I found; almost all nests of Vespa crabro (except Nest 7), and some of the nests of the vulgaris-germanica group and the nests of Vespula rufa.

Earth nests encompasses all nests built wholly in the ground. It is characterised by great diversity of the types and abundances of the associated fauna. The nest type is characterised by the relatively high humidity in the inner nest and the good heat insulation. [...]
The free-hanging nest type

[...] As occasional inquilines of the honeycomb are Volucella pellucens, inanis and zonaria......

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Ground-based nests

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Volucella larvae

The larvae of the species named below live on the honeycomb of ground nests, more rarely in those of free-hanging nests. During all the autumn in all the wasp nests that I studied, I found the larvae of Volucella in variable numbers (up to 260). The adults of inanis and pellucens eclose in May, while those of zonaria in July. All species have one generation. Oviposition follows at the latest in July and August (the larvae I found came from the earliest nest collections at the end of August and beginning of September - mostly shortly before the last moult. Females lay their eggs on the inner side of the nest envelope on the upper edge of the honeycomb mass. I was unfortunately unable to establish how the early larval instars feed, after they let themselves fall into the honeycomb, since the nests as already mentioned were later collected. Probably however the young larvae live as sapro- or coprophages, and only later (perhaps after the first moult) transfer to a predatory mode. The later larvae stages parasitize the nest. On honeycomb that has been taken out on commonly sees the Volucella larvae creeping from cell to cell. Capped cells were never sucked out. Living wasp larvae serve as food, but never the pupae, although Volucella larvae will also take wasp pupae in rearing dishes. The opinion expressed by many authors (Erne 1876 and others) that Volucella larvae feed on dead larvae and pupae in my view does not correspond to the facts. Volucella larvae are rather more typical syllesten [technical term in myrmecophily] and at least the older larvae are never saprophaous or coprophagous.



Volucella larvae pupate about mid-Oct to mid-Nov. To pupate the larvae go into the soil at the base of the nest cavoty. Sometimes when a nest is in a different place., one finds the puparium in the corresponding substrate, eg between the wickerwork of a case. Overwintering therefore also takes place in these places.

Sack (1931) thought that inanis occurred in hornet nests.All the Vespa crabro nests that I found were completely free of Volucella larvae. However, I did find inanis in some nests of Vespula vulgaris. Also Volucella zonaria occurred in some vulgaris nests. However, the main bulk of the larvae I found were V.pellucens, which were not only in vulgaris but also in germanica nests. The number of nests collected and studied allowed me I think to conclude that the hitherto supposed specialisation of the Volucella species rests on a flase assumption. Rather there are the following connections between the speceis of the genus Volucella and social wasps:



Whilst V.pellucens does indeed occur just as much in vulgaris as in germanica nests, the two other Volucella speceis are specialised to vulgaris. The nests of Vespa crabro and Dolichovespula are completely free of Volucella larvae.

V.pellucens occurred in 14 nests of germanica (a total of 823 larvae) and in 19 nests of vulgaris (1341 larvae). V.inanis was found in 8 (191 larvae) and V.zonaria in 6 (126 larvae) vulgaris nests.
[...]

Significance of inquilines for the nests of social wasps

The inquilines of wasps, particularly the syllestens and parasites, naturally play a large role in the life of wasp nests. The earlier entering forms, such as Volucella species, penetrate into the nest at a point when it is in full bloom. There are factors here that we cannot yet prove. To these belong also in my view the mimicry of Volucella species.In this connection however it should be stressed that for example Eristalis tenax which also has a similar mimetic colour pattern, forms some of the main prey of wasps. [...]


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