Strong mosquitocidal Bacillus thuringiensis from Mt. Everest

Upendra Thapa Shreshtha1, Kiran Babu Tiwari1, Anjana Singh2, Vishwanath Prasad Agrawal1*
(1) Research Laboratory for Agricultural Biotechnology and Biochemistry (RLABB), Universal Science College, Maitidevi, Kathmandu, Nepal;
(2) Central Department of Microbiology, Tribhuvan University, Kirtipur, Nepal

*Address for Correspondence: Prof. Dr. Vishwanath Prasad Agrawal, RLABB, Tel: +977-1-4442775, E-mail: vpa@wlink.com.np

Microbial insecticides are especially valuable as their toxicity to non-target animals and humans is extremely low compared to other commonly used chemical insecticides. They are safer for both the pesticide users and consumers of pesticide treated crops (Neppl, 2000). The soil bacterium Bacillus thuringiensis fulfills the requisites of a microbiological control agent of agricultural pests and vectors that cause massive crop destruction (Ben-Dov et al, 1999). The main target pest of B. thuringiensis insecticides includes various Lepidoptera (butterfly), Diptera (flies and mosquitoes), Coleopteran (Beatle) and some strains of nematodes (Schnepf et al, 1998). The kurstaki HD1 strain of B. thuringiensis is shown to possess wide spread insecticidal properties (Dulmage, 1970).

To study B. thuringiensis population from high altitude, soil samples were collected from Sagarmatha National Park (SNP) and Phereche of Khumbu region situated in the base camp of Mt. Everest, and processed in Research Laboratory for Agricultural Biotechnology and Biochemistry (RLABB). B. thuringiensis strains were isolated from soil samples by acetate selection method (Travers et al, 1987, Shrestha et al. 2006) and identified by standard microbiological techniques including colonial and morphological characteristics, and biochemical tests (Bergey’s Manual, 1986).

Out of 86 δ-endotoxin positive isolates (total 146), 10 randomly selected ones were used for insect bioassay. Larvae, collected from the ditches in local area of Bode, Bhaktapur, Nepal, were reared in a jar containing 100 ml of sterilized water containing 0.3 ml of 5% Brewer's Yeast and 5 ml of B. thuringiensis stationary phase culture and allowed to stand for 3 days. Although all isolates tested were effective against the larvae, isolate S6 was the most effective of all (Fig. 1).

The isolates, obtained from the soil samples above 4000m altitude where mosquitoes are not expected, may be novel. The S6 isolate showing potent insecticidal property tested against dipterans need to be studied further in larger trials so that it can have applicability to reduce the mosquitoes and different diseases caused by these vectors (Malaria, Filaria, Kalazar etc).

Fig 1: % Mortality of larvae

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