Bruchid beetles, chalcids, parasitization, niche overlap
Canada milk-vetch (Astragalus canadensis L.), North America’s most widespread species of Astragalus, is important for herbivores and granivores in natural ecosystems but suffers heavy seed losses to bruchids and curculionids. Our objectives were: (1) compile a species inventory and describe life histories of insects associated with seed production in Canada milk-vetch, and (2) determine frequencies of pod predation and primary parasitism in Canada milk-vetch. The seed predators were Acanthoscelides perforatus (Horn) and Tychius liljebladi Blatchley. Frequency of pod predation varied between two plant populations (46 and 70%) and between A. perforatus (37 %) and T. liljebladi (21 %). The primary parasitoids were two exotics [Dinarmus acutus Thomson and Eupelmus vesicularis (Retzius)] and two natives [Eurytoma tylodermatis Ashmead and an unidentified chalcid (Pteromalidae)]. Parasitism rates were 10% for T. liljebladi and 22% for A. perforatus. The seed predators had similar niches. Larvae of both species fed on the same food source (occasionally inside the same pod), and adults of both species were active on the plants concurrently. However, A. perforatus overwintered as full-grown larvae inside the pods, whereas larvae of T. liljebladi exited pods in late July and overwintered as pupae in the soil. This research identified a unique community of insects composed, in part, of two seed predators that utilized the same food source and two exotic and two native parasitoids. More research is needed to determine the stability of this insect community in response to variation in production at the first trophic level.
Proceedings of the South Dakota Academy of Science
South Dakota Academy of Science
Boe, Arvid and Johnson, Paul J., "Seed Predators of Canada Milk-Vetch and Their Parasitoids" (2008). Native Plant Focused Publications. 22.