Dendrosoter protuberans (Hymenoptera: Braconidae), an Introduced Larval Parasite of Scolylus multistriatus1

Abstract

Dendrosoter protuberans (Nees) is easily reared in the laboratory, oviposits through bark onto larvae of the smaller European elm bark beetle, Scolytus multistriatus (Marsham) (Coleoptera: Scolytidae), can overwinter in the central United States, and reproduces itself under field conditions. Oviposition is more effective in parts of dead elms where the host bark beetle larvae are not beneath a thick layer of bark. The field development time for D. protuberans at Delaware, Ohio, ranged from 28to 52 days compared with that of its host S. multistriatus , which ranged from 51 to 62 days. Under standard laboratory rearing conditions of 29.4°C and 40% relative humidity, D. protuberans completes its life cycle in about 20 days, whereas S. multistriatus takes about 35 days. Overwintering D. protuberans emerged 29 March 1967 at Delaware, Ohio. In the overwintering plots in Ohio and Missouri, 23% of the available hosts were parasitized. The parasitism rate in the free-flight plots ranged from 23 to 37% in Missouri and from 23 to 31% in Ohio. Three indigenous parasites, Spathius canadensis (Ashmead), Cheiropachus colon (L.). and Entedon leucogramma (Ratzeburg), are commonly found in elm wood naturally infested by S. multistriatus. S. canadensis , and C. colon , like D. protuberans , oviposit through the bark onto beetle larvae, and thick bark limits their efficiency, whereas E. leucoyramma enters the female beetle gallery and oviposits in the eggs of S. multistriatus .