Effects of Two Formulations Based on Bacillus thuringiensis subsp. israelensis on Aedes aegypti Mosquito Larvae under Laboratory Conditions

Abstract

Toxicity and persistence of two formulations based on Bacillus thuringiensis subsp. israelensis applied to Aedes aegypti mosquito larvae were tested under laborabory conditions. The formulations were: a) water dispersible granules (product VectoBac WDG), and b) aqueous suspension (product VectoBac 12AS). The effects of both products on mosquito larvae were tested immediately after their dilution in pure water (zero time) and in 1-, 2-, 8- and 13-day old solutions. The two products were also tested in mixtures of water and clay at a rate of 0.5 g clay/150 ml water immediately after product dilution, and in one-day old solutions containing 0.1 and 0.05 g of clay in the same amount of water. The product VectoBac WDG was persistant and highly effective against Ae. aegypti larvae in pure water after the longest experimental period of 13 days, and significantly more effective than VectoBac 12AS at equal rates of application. The effectiveness of VectoBac 12AS weakened significantly after 8 and 13 days of treatment, compared to the effects at zero time and in 1- and 2-day old solutions. High clay content in water significantly reduced the larvicidal effectiveness of both products, indicating its possible compromising role during product application in practice.

U laboratorijskim uslovima ispitivana je toksičnost i trajnost delovanja na larve komarca Aedes aegypti dve formulacije na bazi Bacillus thuringiensis subsp. israelensis: a) vododisperzibilne granule (preparat VectoBac WDG) i b) tečna suspenzija (preparat VectoBac 12AS). Utvrđivani su efekti oba preparata na larve u čistoj vodi neposredno posle njihovog rastvaranja (nulto vreme), a potom u rastvorima starim 1, 2, 8 i 13 dana. Takođe, testirani su efekti preparata u vodi sa glinom u količini 0,5 g na 150 ml vode, neposredno posle pravljenja rastvora, i efekti preparata u istoj zapremini vode sa količinama gline od 0,1 i 0,05 g, u rastvorima starim jedan dan. Konstatovano je da je preparat VectoBac WDG perzistentan i visoko efektivan u delovanju na larve Ae. aegypti u čistoj vodi tokom 13 dana posle primene (koliko je trajao eksperiment) i u istim dozama značajno je efektivniji nego VectoBac 12AS. Efektivnost preparata VectoBac 12AS značajno slabi osam i 13 dana nakon primene u poređenju sa efektima ispoljenim u nulto vreme i jedan i dva dana kasnije. Kod oba preparata larvicidnu aktivnost značajno smanjuje visok sadržaj gline u vodi, što ukazuje na njenu moguću ulogu u kompromitovanju praktične primene ovih preparata.