Temporal transition of nesting activities in the digger wasp Bembecinus tridens (Hymenoptera, Crabronidae).

A nest aggregation of Bembecinus tridens (Hymenoptera: Crabronidae) was investigated through observations of marked individual females in Northern Italy, in order to quantify frequencies, duration, and sequence of the nesting activities. Wasp females dug unicellular (in one case multicellular) nests preferably on oblique surfaces. Nest digging occurred mainly in the morning, while definitive nest closing was performed only in the afternoon, and nests were frequented by the owners for 3.52 days on average. One to eight nests were dug by single females in rapid succession in the area observed, revealing a rapid dispersion towards other sites. Provisioning and non-provisioning (control) flights were positively correlated and occurred mainly in the late morning. A number of orientation flights followed most exits from the nests but was higher at the end of nest digging. Nest closing lasted more at the end of provisioning and at the end of digging. Provisioning began more frequently one day after nest digging (and oviposition), less frequently two days after, and the number of prey per day was negatively correlated with the number of provisioning days. Data are consistent with a situation of primitive progressive provisioning, and match that of other species of the same genus

Temporal transition of nesting activities in the digger wasp, Bembecinus tridens (Hymenoptera: Crabronidae)

A nest aggregation of Bembecinus tridens (Hymenoptera: Crabronidae) was investigated through observations of marked individual females in Northern Italy, in order to quantify frequencies, duration, and sequence of the nesting activities. Wasp females dug unicellular (in one case multicellular) nests preferably on oblique surfaces. Nest digging occurred mainly in the morning, while definitive nest closing was performed only in the afternoon, and nests were frequented by the owners for 3.52 days on average. One to eight nests were dug by single females in rapid succession in the area observed, revealing a rapid dispersion towards other sites. Provisioning and non-provisioning (control) flights were positively correlated and occurred mainly in the late morning. A number of orientation flights followed most exits from the nests but was higher at the end of nest digging. Nest closing lasted more at the end of provisioning and at the end of digging. Provisioning began more frequently one day after nest digging (and oviposition), less frequently two days after, and the number of prey per day was negatively correlated with the number of provisioning days. Data are consistent with a situation of primitive progressive provisioning, and match that of other species of the same genus

Mud-Ball construction by sceliphron Mud-Dauber wasps (Hymenoptera: Sphecidae): A comparative ethological study

Mud-ball construction by Sceliphron mud-dauber wasps (Hymenoptera: Sphecidae): a comparative ethological study. Zoological Studies 51(7): 937-945. Mud-dauber wasps of the genus Sceliphron build aerial nests using mud collected at humid-soil sources and carried to the nest in the form of spherical mud-balls. We recorded and analyzed a series of video-sequences of 5 (3 native and 2 alien) species of Sceliphron in Italy, in order to compare their mud-ball-building behavior. Four phases were recognized: I) patrolling the ground in search of a suitable place for mud-ball building; II) removing leafs, twigs, or small stones from the chosen area; III) forming the mud-balls; and IV) flying off with the mud-balls. The duration of all these phases were similar among species, with the only exception being phase IV, which was shorter in S. curvatum. In all species, mud was shaped into a ball by the combined action of the legs and mandibles, but important differences also emerged in some details of this behavior. In particular, S. curvatum maintained the longitudinal axis of its body parallel to the ground as it worked the mud, and its antennae rapidly tapped the ball. On the contrary, in the other 4 species, the mud was pulled under the mentum and retained laterally by the 1st pair of legs, while the body axis was maintained almost vertical, and the antennae were not involved in mud shaping. Because S. curvatum belongs to a different subgenus compared to the other 4 species, we suggest that mud-ball-building behavior may potentially represent a useful taxonomic and perhaps phylogenetic character.Thanks are extended to the farmers which kindly permitted us to carry out the study on their proprieties. F. Rigato kindly helped determine the species of wasps observed in the study. The present work was supported by a 3-yr Fondo per gli Investimenti della Ricerca di Base grant, RBAU019H94-001 (2001), and by a postdoctoral contract to CP (Program JAE-Doc “Junta para la Ampliación de Estudios” funded by the Spanish Research Council (CSIC) and the FSE).Peer Reviewe

Weight, volume and unbalancing: loading constraints of mud dauber wasps carrying mud balls

Load-carrying capacities of flying animals have important effects on their reproductive success, because it is expected that better performing individuals will benefit during activities such as foraging and nest building. Individually marking Sceliphron mud dauber wasp females and collecting their mud balls at three field sites, we investigated whether wasps maximize mud ball lifting and we evaluated whether the characteristics of soil affect wasp\u2013mud ball size relationships. Sceliphron destillatorium, larger than Sceliphron spirifex, collected on average heavier and larger mud balls, and individual female body mass was positively correlated with the mass and volume of carried mud balls. Rarely mud balls reached a weight close to the theoretical maximum. On the other hand, the volume of mud balls roughly coincided on average with the theoretical maximum. A simple theoretical model showed that loss of balance during loaded flights is in part responsible for the failure to maximize the mass lifted, reducing the load-carrying capacity with a per cent value that is independent of the wasp\u2019s size. Soil characteristics also seem to affect the lifting dynamics of wasps: similar-size females carried significantly lighter mud balls in denser-soil sites. Our results showed that the volume is the strongest factor limiting mud ball carrying. The effect of such limitations, moreover, may change depending on the physical properties of the material used for nest construction

Occupational pensions and interfirm job mobility in the European Union Evidence from the ECHP survey

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