Pygostolus

Members of Pygostolus can be distinguished from other Blacinae by features of the genus-level diagnosis, though specific diagnostic characters require specialist examination. The genus is placed in Blacinae based on morphological characteristics typical of that subfamily. Species-level identification relies on examination of morphological details described in taxonomic revisions.

Associated with agricultural and natural habitats supporting host weevils of the genus Sitona, particularly leguminous crops including sweetclover (Melilotus officinalis). Field studies have been conducted in cage environments in North Dakota, USA and Sweden.

Recorded from Denmark, Norway, and Sweden; introduced to North America (specifically North Dakota, USA) for biological control studies. Native distribution appears to be Palearctic, though precise range boundaries are not well documented.

Two discrete generations per year observed in Swedish populations of P. falcatus, developing in early and mid-summer within overwintered weevils. Overwintering occurs as first-instar larva in weevils that became adult the previous summer.

• Sitona lineatus - endoparasitoidhost of P. falcatus, Swedish origin
• Sitona hispidulus - endoparasitoidhost of P. falcatus, Swedish origin
• Sitona humeralis - endoparasitoidhost of P. falcatus, Swedish origin
• Sitona cylindricollis - endoparasitoidsweetclover weevil, target for biological control; host of P. falcatus in North America

Egg deposited in host haemocoele; egg increases dramatically in volume (up to 335 times original size). Trophamnion cells dissociate and grow with larva. Supernumerary larvae eliminated after eclosion, resulting in solitary development. Five larval instars described. Development temperature-dependent: 58 days at 15°C, 28 days at 20°C, 22 days at 25°C, 21 days at 30°C. Final-instar larva emerges from host 15–16 days after egg deposition at 74°F (approximately 23°C). Overwinters as first-instar larva in weevils that became adult the previous summer. First-instar larval diapause common, arrested at 10°C.

Oviposition occurs in both light and complete darkness. No preference among Sitona species evident for oviposition. Oviposition prevents host reproduction in weevils developing in summer and eliminates reproduction in overwintered weevils. Host dies within hours of parasite larva emergence. Adult longevity temperature-dependent: 29, 22, 12, and 6 days at 15, 20, 25, and 30°C respectively when provisions available. Adult survival extended by access to honey, water, sweetclover, and hosts.

Parasitoid of Sitona weevil populations in leguminous crop systems. Potential biological control agent, though effectiveness limited by low parasitism of new weevil generation and diapause of first-instar larvae. Maximum parasitism rate of 73.3% observed for mid-summer generation of P. falcatus in Sweden. Poor phenological synchrony with host population reduces biological control value.

Investigated as biological control agent for sweetclover weevil (Sitona cylindricollis), an agricultural pest of sweetclover crops. Imported to North America and studied in field cages for potential release. Value as control agent limited by biological constraints including diapause and phenological asynchrony.

• Other Blacinae generaSimilar subfamily placement requires careful morphological examination for generic distinction; Pygostolus distinguished by genus-specific morphological characters

• parasitoid
• parthenogenetic
• thelytoky
• biological control
• weevil parasite
• Braconidae
• Blacinae
• Sitona

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Pygostolus falcatus(Nees) (Hymenoptera, Braconidae), a parasite ofSitonaspecies (Coleoptera, Curculionidae).
• Development, Survival and Phenology of the Sweetclover Weevil Parasitoid, <i>Pygostolus Falcatus</i> (Hymenoptera: Braconidae)