Effect of some herbicides on the toxicity of certain molluscacides against Biomphalaria alexandrina snails.

Studies dealing with the effect of some herbicides on the molluscicidal action of certain molluscicides against B. alexandrina have been carried out. In the first part of the study the toxicity of 3 molluscicides (Copper sulphate, Niclosamide and Frescon) and 3 herbicides (Gramaxone, Preforan and Treflan) was tested individually. Results indicated that the molluscicides were more potent than the herbicides. In the second part, snails were exposed for 24 hr to one of the tested herbicides using LC0 or (Sub. lethal conc) then the toxicity of molluscicides was determined among the same snails. Data indicated that pre-exposure to herbicides caused a synergistic action with copper sulphate, while with Niclosamide and Frescon marked antagonistic effect was observed. In the third part molluscicides and herbicides were mixed in different ratios (1:2, 1:1 and 2:1) and the toxicity of the mixtures was tested. A synergistic effect was observed in the case of copper sulphate plus various herbicides especially with Treflan at 1:2 ratio. With Niclosamide and Frescon slight antagonistic effect was detected.