Psenulus

Kohl, 1897

Psenulus is a large of solitary in the Crabronidae, containing approximately 160–173 described . It represents the most species-rich genus within the Pemphredoninae. Phylogenetic analyses indicate that Psenulus is the closest living relative to bees (: Anthophila), making it significant for understanding hymenopteran evolution. Species are found worldwide but are most diverse in the Indomalayan realm.

Pronunciation

How to pronounce Psenulus: //ˈpsɛ.nʊ.lʊs//

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Habitat

nest in pre-existing cavities, including hollow stems and bamboo internodes. Psenulus fuscipennis has been documented nesting in artificial nest blocks with cavity diameters of 0.4 cm in urban environments, demonstrating adaptability to fragmented green spaces in megacities.

Distribution

Worldwide distribution with highest diversity in the Indomalayan realm (68 ). The Palearctic region contains 26 species, the Nearctic 4, and Australasia 3. The is largely absent from South America (1 species, plus ) and entirely absent from Melanesia and Polynesia. Documented in Europe, China, Crimea (Ukraine), Istanbul (Türkiye), Magnetic Island (Queensland, Australia), and Chile (adventive population of P. pallipes).

Diet

Psenulus interstitialis provisions with late-instar nymphs of Auchenorrhyncha (five documented), with fully provisioned cells containing 9–13 prey items.

Host Associations

Omalus sculpticollis - Chrysidid ; main enemy of P. fuscipennis in Crimea, attacking progeny
Melittobia acasta - Eulophid ; enemy of P. fuscipennis
Perithous septemcinctorius - Ichneumonid ; enemy of P. fuscipennis
Trichodes apiarius - /Clerid ; enemy of P. fuscipennis
Leucospis giraulti - Leucospid ; attacks late-larval or early pupal stages of P. interstitialis
Eupelmophotismus pulcher - Eupelmid ; attacks late-larval or early pupal stages of P. interstitialis
Calosota sp. - Eupelmid ; attacks late-larval or early pupal stages of P. interstitialis
Pyemotes sp. - Mite causing additional mortality in P. interstitialis
Unidentified fungus - Causes mortality in P. interstitialis

Life Cycle

Psenulus interstitialis constructs nests of up to 10 in bamboo internodes. Development from to requires approximately 30 days. The reared sex ratio is male-biased at 2:1. Multiple per year occur at lower latitudes (e.g., Queensland, Australia).

Behavior

Nesting occurs in pre-existing cavities with specific diameter requirements; P. fuscipennis exclusively used 0.4 cm entrance cavities in artificial nest blocks. Nests are multi-celled and provisioned with paralyzed prey.

Ecological Role

As of Auchenorrhyncha nymphs, Psenulus contribute to of sap-feeding insects. The serves as for diverse complexes including chrysidid, eulophid, ichneumonid, leucospid, and eupelmid , as well as mites and fungi.

Human Relevance

P. pallipes has been introduced to Chile via accidental human transportation of nests, representing a documented case of human-mediated range expansion. Some demonstrate nesting adaptability to urban environments, utilizing artificial nest blocks in fragmented city green spaces.

Similar Taxa

PsenConvergent and shared tribe Psenini; distinguished by detailed morphological characters of the propodeum and petiole
Bees (Anthophila)Psenulus is the closest living relative to bees based on phylogenetic analysis, but lacks branched body hairs and pollen-collecting structures

More Details

Phylogenetic significance

Strong phylogenetic evidence positions Psenulus as the sister group to bees, making it critical for understanding the evolutionary transition from predatory to pollen-feeding bees.

Taxonomic history

Originally described by Kohl in 1897. Recent phylogenetic studies have recovered two major clades: a Nearctic + Palearctic clade and a Neotropical clade, with the Neotropical clade showing closer relationships to Afrotropical and Oriental .