Polyblastus fulvilinealis

Identification to species from images alone is unusual for ichneumon wasps; this species requires expert examination. The genus Polyblastus can be recognized within Tryphoninae by specialists. Females may be observed with visible egg clusters attached to the ventral abdomen.

Associated with habitats supporting sawfly host species. Documented from riparian or semi-open areas with woody vegetation, including locations with elm (Ulmus) and other host plants for sawflies.

North America; documented from Colorado, USA. The species was described from North American material.

Adults active in early June based on observation records; likely corresponds with availability of sawfly larval hosts.

• Sawfly larvae (Hymenoptera: Symphyta) - koinobiont ectoparasitoidSpecific host species not confirmed for this species, but elm sawfly (Cimbex americana) occurs sympatrically and represents potential host. Larva feeds externally on host, which continues development until wasp emergence.

Koinobiont development: egg deposited on or near host larva; wasp larva remains attached externally to host, which continues feeding and growth; wasp pupates within host cocoon; adult emerges from host cocoon.

Females have been observed carrying multiple eggs externally beneath the abdomen, possibly resulting from unsuccessful oviposition attempts or as a mechanism to transport excess egg load. The precise adaptive significance of this behavior is unresolved. Oviposition targeting sawfly larvae.

Parasitoid regulating sawfly populations. As a koinobiont, allows temporary host survival, potentially stabilizing host-parasitoid population dynamics compared to idiobiont strategies.

• Other Polyblastus speciesMorphologically similar; require expert identification based on subtle structural characters.
• Other Tryphoninae generaShare koinobiont ectoparasitoid biology and general body form; distinguished by antennal structure, ovipositor proportions, and other technical characters.
• Idiobiont ichneumon waspsDiffer in life history: idiobionts arrest host development immediately and typically target pupal stages rather than active larvae.

• ichneumon wasp
• parasitoid
• koinobiont
• sawfly parasite
• egg-carrying behavior
• Tryphoninae
• Colorado fauna

• BugGuide
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Bug Eric: Strange Behavior Explained (Sort of)