Larvicidal activity of Bacillus thuringiensis ssp. israelensis against the dengue mosquito, Aedes aegypti (L.) and its effect on the behavior and survival of water bug Diplonychus rusticus F.
2016
Javier, P.A. | Albaytar, A.B.
The larvicidal activity of Bacillus thuringiensis subsp. israelensis (Bti) against the different larval instars of dengue mosquito, Aedes aegypti (L.) was determined in the laboratory. Cadavers of infected A. aegypti larvae was also fed to healthy A. aegypti larvae and mortality was determined at 24 and 48 hrs after feeding. Likewise, the effect on the behavior and survival of water bug, Diplonychus rusticus F. (predator of wrigglers), was determined when exposed to Bti-infected larvae. Bti at recommended rate caused 100% mortality among all instars of A. aegypti larvae. Feeding healthy larvae with Bti-infected mosquito cadavers also caused 98% larval mortality in 24 hrs. Incorporation of Bti in bamboo leaf infusion as oviposition attractant provided -0.19 oviposition activity index (OAI) compared to -0.12 OAI in water with Bti, which suggests that Bti has very little effect on the oviposition activity of gravid female A. aegypti. Numerically, there was higher mean number of eggs laid in Bti-treated leaf infusion than in Bti-treated water. On the other hand, Bti is non-toxic to D. rusticus nymphs exposed to Bti water and when fed with Bti-infected larvae. However, in the laboratory, the release of first, second and third nymphal instar water bugs in Bti-treated water prevented them from diving through the water due to surface tension which caused body desiccation and ultimately, death of the water bugs. This was not observed in the fourth and fifth instar water bug nymphs. Results suggests that the granulated form of Bti is highly effective against the larvae of A.aegypti in container and could be compatible with water bugs in the 'attract-and-kill strategy' for reducing dengue mosquito population in the field.
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