Mesoleius tenthredinis

Distinguished from other ichneumonids by its specific association with larch sawfly hosts; morphological identification requires examination of wing venation, ovipositor structure, and body proportions typical of the genus Mesoleius. Detailed embryological studies show reduced periplasm, proliferation of middle plate cells after overgrowth by lateral plates, and incorporation of deutoplasmic granules in serosal cells—traits that differentiate it from related ichneumonids such as Pimpla turionellae, Banchus femoralis, and Diadegma vestigialis.

Larch forests; specifically associated with Larix (larch) trees where its host, the larch sawfly, occurs.

Native to Europe; introduced and established in southern Manitoba and Saskatchewan, Canada. Present in British Columbia where it remains effective. Records also indicate presence in the conterminous 48 United States.

• Pristiphora erichsonii - primary hostLarch sawfly; eggs deposited into host larvae where embryonic development occurs
• Lugaeonematus erichsoni - primary hostSynonym or related larch sawfly species; historical biological control target

Embryonic development occurs entirely within host larvae, requiring approximately 120 hours at 23°C and 72% relative humidity in susceptible host populations. Development proceeds through syncytial cleavage, blastoderm formation, and differentiation of germ layers with formation of serosa and amnion from blastoderm margin. Normal incubation period is 7 to 10 days. Encapsulated embryos can remain viable for up to seven months though development is arrested. No information available on larval, pupal, or adult stages outside host context.

Endoparasitoid biology; females oviposit eggs directly into host larvae. Encapsulated embryos can hatch after removal from host and placement in Ringer's solution, indicating prolonged viability under arrested conditions.

Parasitoid regulating populations of larch sawfly in forest ecosystems; introduced biological control agent with variable effectiveness depending on host immune response.

Introduced intentionally for biological control of larch sawfly, an economically important forest pest. Effectiveness varies geographically due to evolved host immunity in some populations. Presence of a putative baculovirus in ovarian tissues may have implications for biological control program sustainability.

• Pimpla turionellaeSimilar embryonic development indicating shared primitive endoparasitoid characteristics; differs in periplasm reduction, middle plate cell proliferation timing, and serosal deutoplasm incorporation
• Banchus femoralisOther monembryonic ichneumonid with distinct embryogenesis; M. tenthredinis shows greater similarity to Pimpla than to this species
• Diadegma vestigialisOther monembryonic ichneumonid with distinct embryogenesis; M. tenthredinis shows greater similarity to Pimpla than to this species

• parasitoid
• biological control
• ichneumonid
• larch sawfly
• endoparasitoid
• encapsulation
• host immunity
• baculovirus
• forest pest management
• introduced species
• embryology

• BugGuide
• GBIF taxonomy match
• NCBI Taxonomy
• Catalogue of Life
• EMBRYOGENESIS OF MESOLEIUS TENTHREDINIS MORL. (HYMENOPTERA: ICHNEUMONIDAE)
• A putative baculovirus in the ichneumonid parasitoid, Mesoleius tenthredinis
• THE INTRODUCTION AND ESTABLISHMENT OF THE LARCH SAWFLY PARASITE, MESOLEIUS TENTHREDINIS MORLEY, INTO SOUTHERN MANITOBA (HYMEN.)
• THE CAPSULE AND ITS RELATION TO THE EMBRYOGENESIS OF THE ICHNEUMONID PARASITOID MESOLEIUS TENTHREDINIS MORL. IN THE LARCH SAWFLY, PRISTIPHORA ERICHSONII (HTG.) (HYMENOPTERA:TENTHREDINIDAE)
• THE NATURAL IMMUNITY OF THE LARCH SAWFLY (PRISTIPHORA ERICHSONII (HTG.)) TO THE INTRODUCED PARASITE MESOLEIUS TENTHREDINIS MORLEY, IN MANITOBA AND SASKATCHEWAN