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Vol. 46 No. 1, 2007
Temporal Relationship between the Prey Spectrum and Population Structure of the Weevil-Hunting Wasp Cerceris arenaria (Hymenoptera: Crabronidae)
Carlo Polidori1,*, Roberto Boesi1, Carlo Pesarini2, Cristina Papadia1, Stefania Bevacqua1, Matteo Federici1, and Francesco Andrietti1
1Dipartimento
di Biologia, Sezione di Zoologia e Citologia, Universitá degli Studi di
Milano, via Celoria, 26, 20133, Milano, Italy
2Museo Civico di Storia Naturale, Corso Venezia, 55, 20121, Milano, Italy
Carlo
Polidori, Roberto Boesi, Carlo Pesarini, Cristina Papadia, Stefania
Bevacqua, Matteo Federici, and Francesco Andrietti (2007) Specialized
predators must face the problem of reductions in resources, and
variations in the prey spectrum can be expected to be reflected in
predator population traits. Cerceris arenaria
L. (Hymenoptera: Crabronidae) is a solitary wasp that hunts weevils
(Coleoptera: Curculionidae), with the individual range of prey sizes
varying according to the size of the female wasp. A nest aggregation in
Castiglione d, Adda, northern Italy was studied in 1997-1999, 2001,
2003, and 2005 in order to investigate variations in the prey spectrum
across several years, while a 2nd aggregation in Castell, Arquato was
investigated in 2001 to look for possible differences in prey selection
between the 2 populations. The captured weevils belonged to 23 species.
At both sites, the most often collected genera were Otiorhynchus Germar and Sitona
Germar, which include several pests of cultivated plants. The prey
spectrum (in terms of taxonomic identity and specimen frequency per
species) varied among the years of study in Castiglione d, Adda, with Sitona spp. being more abundant in 1997-1999 and Otiorhynchus
spp. in 2001, 2003, and 2005. According to this temporal shift in the
prey spectrum, the annual average prey size increased from 1999 to
2005. Annual average prey size in Castiglione d, Adda was always lower
than that in Castell, Arquato, where the frequency ratio of Otiorhynchus/Sitona was higher than that in Castiglione d, Adda. Prey size and the frequency ratio of Otiorhynchus/Sitona
in Castiglione d, Adda were negatively correlated to the wasp
population size, and the average wasp size increased when the frequency
of larger prey increased. We concluded that interactions between
extrinsic (prey availability) and intrinsic (wasp size distribution)
factors may strongly influence fluctuations and persistence of
specialized predatory wasp populations.
Key words: Cerceris, Prey, Curculionidae, Population ecology.
*Correspondence: E-mail:carlo.polidori@unimi.it
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