IMPACT OF EIGHT BACTERIAL ISOLATES OF Bacillus thuringiensis AGAINST THE TWO LAND SNAILS, Monacha cantiana AND Eobania vermiculata (GASTROPODA: Helicidae).

Under laboratory conditions, eight native bacterial isolates of Bacillus thuringiensis, were tested for their molluscicidal activity against the two land snails, Monacha  cantiana (Montagu) and Eobania vermiculata (Muller) at a constant concentration (7x10­­­­­⁶ cfu/ ml) using three methods of application. Results revealed that all tested isolates applied via food or soil had no adverse effect on the tested land snails and resulted no mortality in M. cantiana  and E. vermiculata as well.  However, results clearly indicate the molluscicidal properties of the tested isolates and identify Bt-k64  ,Bt- B33 as well as Bt- W123  as potentially effective against M. cantiana and  E. vermiculata when bacterial isolates were introduced to snails via food and soil simultaneously (concomitant treatment). For eight bacterial isolates, the percentage mortality ranged from 33% to 86.6% for the clover land snail, M. cantiana , while in the brown land snail, E. vermiculata the percentage mortality ranged from 6.6% to 53%. after four weeks of treatment
B. thuringiensis  designated as Bt- K64 was the most effective one against the two land snails, M. cantiana and E. vermiculata with percentage mortality 86.6% and 53.0% , respectively whereas, B. thurinigensis  designated as Bt- B123 was the least toxic isolate  with mortality 33% and 6.6% respectively. M. cantiana was more sensitive to the tested isolates than Eobania vermiculatum.
Moreover, the molluscicidal activity of the three isolates of the bacterium, B. thurinigensis designated as  Bt-W123 ,  Bt-B33  and Bt-K64  at  three concentrations (1x10­­­­­⁶ , 1x10⁷ and 1x10⁸ cfu/ ml) against M. cantina under laboratory condition at 15ºC±3 and 60 ±5% RH. was undertaken.  Isolate Bt –B33 and isolate Bt –W123 showed higher toxicity  to the target snail than isolate Bt –K64 with mortality increasing with an increase in the concentrations of isolates as well as the period of exposure. At the highest concentration ( 1x10⁸) the bacterial isolate Bt –B33 was the most toxic which killed 53% of the land snail M. cantiana after two weeks from treatment and 73.3% and 86.4% after three and four weeks of experiment