Pleolophus basizonus
(Gravenhorst, 1829)
Pleolophus basizonus is a European ichneumonid introduced to North America between 1939 and 1949 as a agent targeting in forest . The has established successfully in Ontario, Quebec, and Michigan, dispersing primarily by at rates sufficient to explain observed field spread of 4–9 km per year. Females exhibit sophisticated -dependent including discrimination against parasitized , mutual interference in -laying, and escape responses to density mediated by trail odor recognition. The species responds positively to host density and has become integrated into native parasitoid attacking jack pine sawflies.
Pronunciation
How to pronounce Pleolophus basizonus: //pliːəˈloʊfəs ˌbeɪziːˈzoʊnəs//
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Habitat
Jack pine (Pinus banksiana) stands; forest supporting
Distribution
Native to Europe (Denmark, Norway, Sweden); introduced and established in North America: Ontario and Quebec (Canada), Michigan (USA). Documented spread includes 81 km in Ontario, 109–161 km in Quebec, and 172 km in Michigan. Present throughout western Saint-Maurice River watershed in Quebec by 1965–1968.
Host Associations
- Neodiprion swainei Middleton - primary most abundant in Quebec; pest of jack pine
- Tenthredinidae - infesting forest trees; general group
Behavior
Females do not fly unless disturbed; occurs primarily by with mean ground speed of 20.9 cm per minute in observation trays. Possible short and water transport while within cocoon have been suggested but water dispersal is not confirmed in Quebec. Females discriminate against parasitized hosts within narrow limits (0.4–1.4 per cocoon), show mutual interference in egg-laying at high :host ratios, and exhibit density-dependent escape reactions to parasitoid density. These result from recognition of repellent trail odors deposited by searching females. Response to high parasitoid densities leads to dispersal and occupation of additional, less favorable .
Ecological Role
of , particularly Neodiprion swainei; agent introduced to supplement natural mortality factors. is proportional to , indicating positive . Constitutes important addition to parasitoid complex in North American jack pine . Density-dependent individual collectively produce apparent density-independent response to host availability.
Human Relevance
Introduced intentionally to Canada (1939–1949) for of pests in forestry; established now contribute to natural suppression of Neodiprion swainei and related sawfly in jack pine stands.