Molluscicidal activity of tobacco dust against brackishwater pond snails (Cerithidea cingulata Gmelin)

Abstract

Toxicity tests on the effect of tobacco dust against brackishwater pond snails (Cerithidea cingulata Gmelin) of various stages or size ranges were conducted under controlled laboratory conditions. The 72-h LC₅₀ for the juveniles, sub-adult and adult snails are 30, 87 and 166 kg ha⁻¹, respectively, while the 72-h LC₉₉ are 290, 522 and 712 kg ha⁻¹, respectively. The nicotine content of the tobacco dust used was 2.8%. Lethal concentration increased as the life stages or size of the snail increased. Molluscicidal activity also progressively increased with time of exposure. The nicotine content and toxicity of different types of tobacco [flue-cured (neutral), flue-cured (full-flavor), burley and batek (full-flavor)] were determined on adult snails. Lethal concentrations (LC₅₀) and (LC₉₉) decreased as nicotine content of the tobacco dust increased indicating a higher molluscicidal activity. The effective application rate is affected by the nicotine content of the tobacco dust. An equivalent nicotine concentration of ca 24 kg ha⁻¹ corresponded with the 72-h LC₉₉ under laboratory conditions. Sevenday bioassay experiments on the effect of tobacco dust on two size groups of milkfish juveniles (0.5 and 2–3 g) showed no mortalities up to the concentration lethal to the pond snails.