Increased Nest Density of the Digger Wasp Bembix rostrata as a Response to Parasites and Predators (Hymenoptera: Sphecidae)

Abstract

Wasp Bembix rostrata as a Response to Parasites and Predators (Hymenoptera: Sphecidae).-Entomol. Gener. 12 (1): 07 1-075; Stuttgart 1986.-[ Article]. Solitary wasps are affected by a wide variety of organisms acting as parasites or predators. Observations in a nesting aggregation of the digger wasp Bembix rostra ta Linnaeus 1758 revealed the fly Me topia le ucocephala Rossi 1790 to be important as a nest parasite. The frequency of these parasitic flies correlated significantly with increased density of B. rostrata nests. Calculated per nest , however, the relative incidence of such animals was declining as nest density increased. The same tendency was noted for ants visiting the nesting area. These findings may support the hypothesis of gregarious nesting as a "selfish herd" mechanism against parasites and predators. Key w 0 r d s: Gregarious nesting-selfish herd-nest density-Me topia leucocephala-Bembix rostra ta. The digger wasp Bembix rostrata Linnaeus 1758 provides a good example of gregarious nesting. This wasp prefers sandy habitats, exposed to the sun, and in Europe occurs as far N' as Denmark and S' Sweden. It is one of the largest Hymenoptera in this area, with a length of 13-25 mm [Lornholdt 1975]. Living in dense and numerous aggregations,

Anthropogenic induced changes in nesting densities of the dune-specialised digger wasp Bembix rostrata (Hymenoptera: Sphecidae)

“…As shown by Schöne & Tengö (1981), Larsson (1986) and Peeters et al (2004), B. rostrata requires habitat with considerable bare sand for gregarious nesting. In dunes, these conditions occur naturally by sand displacement caused by strong winds .…”

“…Possibly, trampling also affects larval survival directly during winter and spring, periods with lower additional disturbance. In general, nesting densities with additional anthropogenic disturbance are extremely low (Larsson, 1986), perhaps below lower critical population sizes and populations are possibly only maintained by rescue-effects from neighbouring populations with nondisturbed conditions. Furthermore, even if populations persist under trampling disturbances, smaller nesting aggregations are more strongly affected by parasites (Metopia leucocephala, Sarcophagidae, Diptera) and predators (see Larsson, 1986).…”

“…In general, nesting densities with additional anthropogenic disturbance are extremely low (Larsson, 1986), perhaps below lower critical population sizes and populations are possibly only maintained by rescue-effects from neighbouring populations with nondisturbed conditions. Furthermore, even if populations persist under trampling disturbances, smaller nesting aggregations are more strongly affected by parasites (Metopia leucocephala, Sarcophagidae, Diptera) and predators (see Larsson, 1986). Therefore, it can be concluded that population sizes are declining rather due to the deterioration of nest site quality by changes in the structure of the soil surface (Gess & Gess, 1993), than by the decrease in availability of resources (Kearns & Inouye, 1997;Potts et al, 2003;Steffan-Dewenter & Leschke, 2003).…”

“…Bembix rostrata is a specialised, gregariously nesting digger wasp found in sandy regions of Europe (Larsson, 1986), the wasp nesting in sand dunes with low vegetation cover (Klein 1996;Peeters et al, 2004). It is the largest European species of digger wasps and is threatened in many countries (Zegers, 2001;Van der Meer, 2002;Provoost & Bonte, 2004).…”

A nesting aggregation of the solitary bee <i>Megachile atrata</i> (Hymenoptera: Megachilidae) in the Philippines

“…The most commonly cited biotic factor is parasite pressure. As an example, Larsson (1986) inferred this as a key factor in the solitary soil-nesting wasp Bembix rostrata (Linnaeus), suggesting not collective active defense but a selfish-herd effect. The introduced fire ant Solenopsis geminata (Fabricius) is abundant in the study area and could certainly pose a threat to brood and provisions, although it is doubtable that aggregated nesting can provide any protection against these much smaller insects.…”