Polyblastus fulvilinealis
Hall, 1919
Polyblastus fulvilinealis is a small ichneumon in the Tryphoninae. It is a koinobiont ectoparasitoid of larvae, meaning the continues development until the wasp larva completes its growth. Females have been observed carrying multiple externally beneath the , a whose precise function remains unclear. The occurs in North America and has been documented in Colorado.
Pronunciation
How to pronounce Polyblastus fulvilinealis: //ˌpɒlɪˈblæstəs ˌfʊlvɪlaɪˈniːəlɪs//
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Identification
Identification to from images alone is unusual for ichneumon wasps; this species requires expert examination. The Polyblastus can be recognized within Tryphoninae by . Females may be observed with visible clusters attached to the .
Habitat
Associated with supporting . Documented from riparian or semi-open areas with woody vegetation, including locations with elm (Ulmus) and other host plants for sawflies.
Distribution
North America; documented from Colorado, USA. The was described from North American material.
Seasonality
active in early June based on observation records; likely corresponds with availability of larval .
Host Associations
- Sawfly larvae (Hymenoptera: Symphyta) - koinobiont ectoparasitoidSpecific 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 .
Life Cycle
Koinobiont development: deposited on or near larva; larva remains attached externally to host, which continues feeding and growth; wasp pupates within host cocoon; emerges from host cocoon.
Behavior
Females have been observed carrying multiple externally beneath the , possibly resulting from unsuccessful oviposition attempts or as a mechanism to transport excess egg load. The precise adaptive significance of this is unresolved. Oviposition targeting larvae.
Ecological Role
regulating . As a koinobiont, allows temporary survival, potentially stabilizing host-parasitoid compared to idiobiont strategies.
Similar Taxa
- Other Polyblastus speciesMorphologically similar; require expert identification based on subtle structural characters.
- Other Tryphoninae generaShare koinobiont ectoparasitoid and general body form; distinguished by antennal structure, ovipositor proportions, and other technical characters.
- Idiobiont ichneumon waspsDiffer in : idiobionts arrest development immediately and typically target pupal stages rather than active larvae.
More Details
Egg-carrying behavior
The observation of a female carrying multiple external prompted inquiry among hymenopteran . One hypothesis suggests eggs remain on the ovipositor after unsuccessful oviposition attempts, though why multiple eggs accumulate is unexplained. Koinobiont ichneumons typically carry larger egg loads with smaller individual eggs compared to idiobionts, which may predispose them to external egg transport.
Research significance
This contributed to a 2011 study on loads and life-history trade-offs in Ctenoplematinae (Cummins et al., Annals of the Entomological Society of America), demonstrating phylogenetic constraints on reproductive strategies in ichneumon wasps.