The molluscicidal effects of Hyptis suaveolens on different stages of Bulinus globosus in the laboratory

The molluscicidal effect of the ethanolic extract of the plant Hyptis suaveolens was evaluated against different stages: eggs, juveniles and adults of the freshwater snail Bulinus globosus. Ten healthy one week old juveniles were exposed to different concentrations of the extract for 3 h, while three to four weeks old snails and the adults were exposed for 24 h. The egg masses were exposed for seven days. The mortality rates varied with concentrations and time of exposure. The LC50 values for the eggs, of one week old juveniles, three to four week old immature snails and the adult snails were 0.614, 0.196, 0.161 and 0.077 ppm, respectively. The corresponding LC90 values were 0.796, 0.353, 0.274 and 0.467 ppm, respectively. The results showed that the egg stage of B. globosus was the most resistant to the ethanolic extract of H. suaveolens.Key words: Hyptis suaveolens, Bulinus globosus, mortality rate, LC50 and LC90

Effects of varying concentrations of the crude aqueous and ethanolic extracts of Dalbergia sissoo plant parts on Biomphalaria pfeifferi egg masses.

This study evaluated, using replicated laboratory bioassays, the toxicities of the crude aqueous and ethanolic extracts of Dalbergia sissoo Roxb. 1832 (family Leguminosae) fruits, leaves, roots and stem bark against egg masses of Biomphalaria pfeifferi (Krauss, 1848), the snail intermediate host of Schistosoma mansoni (Sambon, 1907) in Nigeria. Viable 0-24 hr-old embryonated egg masses were separately exposed to five different concentrations (7.81-2000 mg/l) of extracts for 24 hrs, washed in dechlorinated tap water and incubated at room temperature for a maximum of 4 weeks. The LC50 and LC90 values of test extracts for egg masses were calculated by probit analysis. The activities of the tested extracts were concentration-dependent. However, only the ethanolic extract of the fruits demonstrated significant activity (24 hr-LC90 value < 100 mg/l: 89.29 mg/l). Mortalities of eggs were manifested at the gastrula/exogastrula and or the prehatch snail stage of development. The percentage of dead embryos at the prehatch snail stage decreased while the deaths of embryos at the gastrula/exogastrula stage increased, with increasing concentration of extract. Lethality of the ethanolic extract of D. sissoo fruits to embryonated egg masses of B. pfeifferi is an added advantage to its potential development for use as a plant molluscicide, as the overall efficacy of a molluscicide is greatly enhanced if it also shows significant toxicity towards snail eggs.Key words: Dalbergia sissoo, Biomphalaria pfeifferi, Schistosoma mansoni, Egg masse

Dockovdia cookarum infection and the prosobranch gastropod Lanistes libycus host in Omi Stream, Ago-Iwoye, south-western, Nigeria

Dockovdia cookarum infection was studied in relation to the abundance and size classes of Lanistes libycus from Omi Stream, Ago-Iwoye, Nigeria, between September 1997 and June 1998. 57.6% of the 262 L. libycus recorded were collected during periods of heavy rainfall. 17.2% (45) of the L. libycus examined had D. cookarum infection. The water mite prevalences were higher in rainy season than in dry season, and ranged between 3.0% and 44.4% monthly. L. libycus in 21-30 mm size class had the highest prevalence (73.3%). Intensity of infection was higher in rainy season than in dry season, and ranged between 1 and 6 mite(s)/snail. 2.6% of the L. libycus specimens in the 21-30 mm size class had concurrent D. cookarum and Chaetogaster limnaei infections. Key Words: Dockovdia cookarum, water mites, Lanistes libycus, freshwater molluscs, Nigeria African Jnl Biotechnology Vol.3(3) 2004: 202-20