Sepedon macropus (Diptera: Sciomyzidae) Introduced into Hawaii as a Control for the Liver Fluke Snail, Lymnaea ollula1

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Abstract
Liver fluke, Fasciola gigantica Cobbold, is the most important parasitic disease of beef and dairy cattle in the State of Hawaii and has been in the Islands since 1892. The intermediate host of this parasite is the fresh water snail, Lymnaea (Fossaria) ollula Gould. Another aquatic snail, Pseudosuccinea columella Say has proven to be a vector of liver fluke under laboratory conditions. Both snails are found in streams, taro paddies and swamp habitats. Because of the importance of this problem, Sepedon macropus Walker was introduced in an attempt to control these aquatic snails. Under Hawaiian climatic conditions, the life cycle of this predator is approximately 22 to 24 days. The egg stage is 3 days, larval stage 11 to 12 days and pupal stage 7 to 8 days. Two methods were employed in rearing the larvae and these consisted of the use of petri dishes and redwood troughs. The former was employed initially to increase the breeding stock, while the latter was applied later in order to obtain mass production. Nutrition studies indicated that greater fecundity and longevity were obtained by a diet of crushed snails, water and honey, made available to the breeding stock. The males outlived the females; the average life span of the male was 100 days, that of the female was 69 days. The ratio of egg production as indicated in these studies was 184 eggs obtained in which the normal diet was honey and water as against 14,824 eggs, when crushed snails were added. Releases of S. macropus have been made on the five major islands of the State, and to date recoveries of the fly have been reported only from Oahu and Kauai. In areas where establishment of the fly has occurred, usually half an hour of trapping will result in the capture of 50 to 100 flies, indicating the adaptability of this sciomyzid species to Hawaiian conditions. Judging by the encouraging progress taking place, it appears that this introduced predator may become an important contribution in the control of Fasciola gigantica in the State of Hawaii.

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