Pachysomoides

Strand, 1917

Species Guides

Pachysomoides is a of ichneumon wasps in the Ichneumonidae. These small specialize in attacking paper wasps (Polistes spp.) and related social wasps. Two are documented in North America: P. fulvus, which ranges broadly across the continent, and P. stupidus, found in the southeastern United States. The genus exhibits gregarious parasitoid , with multiple larvae sometimes developing on a single .

Pronunciation

How to pronounce Pachysomoides: //ˌpækɪsəˈmɔɪdiːz//

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Distribution

Two documented in North America. Pachysomoides fulvus ranges from New York to Florida, west to California and British Columbia. Pachysomoides stupidus occurs in the southeastern United States from North Carolina to Florida, Texas, and southern Illinois. A record from Brazil documents association with Mischocyttarus cerberus nests.

Host Associations

Polistes fuscatus - P. fulvus lays on larvae or pupae inside of exposed paper comb; young nests with only foundress are especially vulnerable
Polistes spp. - general association for
Mischocyttarus cerberus - first record from Brazil; females guard nests and attack approaching

Life Cycle

Females lay on larvae or pupae of paper wasps inside nest . In P. stupidus, multiple eggs (up to 31 observed) are laid on a pre-pupal ; larvae feed gregariously as external on the pupa. The host larva spins a silken cap over its cell before pupating, allowing larvae to feed undetected on the exterior of the nest. Developmental timing synchronized with host life stages. Haplodiploid genetic system: males develop from unfertilized eggs, females from fertilized eggs.

Behavior

Females approach nests to oviposit; one observation suggests oviposition into walls even when only present, with larval emerging after host hatches. Host defense include resident females guarding nests and attacking approaching parasitoids, making difficult to accomplish. Parasitoid larvae exhibit competitive behaviors over host resource allocation; males show more altruistic/less selfish resource competition than females.

Ecological Role

of social ; regulates of paper wasps and related vespids. Gregarious development on single represents significant mortality factor for host colonies.