STUDY OF EFFECT OF SEPEDON SENEX W. (SCIOMYZIDAE) LARVAE ON SNAIL VECTORS OF MEDICALLY IMPORTANT TREMATODES

OOKAEW PRAKOBVITAYAKIT BEAVER

ABSTRACT: Laboratory experiments were carried out to determine the potential value of Sepedon senex 'W: in the control fresh-water snail populations. Prey selection by Sepedon senex w: larvae, their consumption capacity, survival, and their ability to kill snail prey were determined. The effects of prey and predatOr densities on the rate of predation were investigated, and the searching, killing and consumption efficiencies of Sepedon senex 'W: larvae were determined. Observations of the vertical distribution of certain fresh-water snails in aquaria and preliminary studies on mass rearing of Sepedon senex w: were carried out.

Killjng selection and efficiency of the larvae depended on the relative sizes of snails and larvae. The daily consumption of the larvae depended on their stage of development and increased with prey density but decreased with increasing larval density. When searching for prey, the rate of movement of larvae increased with decreasing distance between predator and prey (P < 0.05). Searching efficiency increased with prey density and increasing age of the larvae. The later instar larvae detected snails from longer distances and sooner than the younger ones. Younger larvae spent much more time handling snail prey than older larvae. Handling. time increased slightly with prey density.

Most of the non - operculate snails studied were distributed at a depth of 0-1 cm, which is within reach of Sepedon senex W. larvae.

Protein food for adults increased larval consumption, conversion efficiency, growth rate, and shortened the developmental period at every stage. Larvae fed with live snails had higher conversion efficiency, and higher growth rates than those fed with freshly crushed snails. The conversion efficiency of the larvae increased with age. There was a tendency for the female population to increase when adult S. senex were fed with protein-rich food.

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Department of Biology, Chiang Mai University, Chiang Mai 50002, Thailand.

Received 12 June 1989