RESUMO
The weak ovicidal effect of the plants having molluscicidal activity is a criterion against their field application in controlling the medically important snails. Chemical molluscicides are potent against snails and their eggs. This work is a trail to use bayluscide and CuSO4 [chemical molluscicides] in sub lethal concentrations to improve the ovicidal effect of Anagallis arvensis and Calendula micrantha plants against the eggs of Biomphalaria alexandrina snails through two modes of eggs exposure. The first was the pre-exposure of snail's eggs to sub lethal concentrations of chemical molluscicides followed by plant exposure and this improve the effect of plants against the snail's eggs with a synergistic ratio ranged from 1.5 to 4.49. While the second mode of exposure is to evaluate the toxicity of mixtures of chemical molluscicides and plants against snail's eggs. It was noticed that this moda resulted in 100% mortality when eggs exposed to mixture of LC15 of C. micrantha or LC25 of A. arvensis with sublethal concentrations of the molluscicides bayluscide or copper sulphate. TLC reveals that the number of the penetrated plant compounds increased in all copper sulphate treatments and in pre-exposure of C. micrantha by bayluscide while the same number of plant compounds were penetrated in the rest of bayluscide treatments as in the cese of the plant alone. So, the increase in plant potency was through chemicals that affect the eggs' membrane to be permeable for more active ingredients [more in number or concentration or both of them] of the tested plants to become in contact with the target embryos