Mosquito Resistance to Bacterial Larvicidal Toxins

Abstract

Abstract:The insecticidal character of the three-domain Cry -endotoxins produced by Bacillus thuringiensis during sporulation is believed to be caused by their capability to generate lytic pores in the target larval midgut cell membranes. This review describes toxic mechanisms with emphasis on the structural basis of pore formation by two closely related dipteran-specific toxins, Cry4Aa and Cry4Ba, which are highly toxic to mosquito larvae. One proposed toxic mechanism via an "umbrella-like" structure involves membrane penetration and pore formation by the 4-5 transmembrane hairpin. The lipid-induced -conformation of 7 could possibly serve as a lipid anchor required for an efficient insertion of the pore-forming hairpin into the bilayer membrane. Though current electron crystallographic data are still inadequate to provide such critical insights into the structural details of the Cry toxin-induced pore architecture, this pivotal evidence clearly reveals that the 65-kDa active toxin in association with the lipid membrane could exist in at least two different trimeric conformations, implying the closed and open states of a functional pore.

Toxicity studies for indigenous Bacillus thuringiensis isolates from Malang city, East Java on Aedes aegypti larvae

“…Therefore, damage to the larvae can be easily observed within each section. A previous study demonstrated that the numbers of intestinal epithelial cells and peritrophic cells were increased in accordance within creasing larval toxin resistance [22] .…”

“…Some publications still use bacterial isolates from outside the mosquito habitat itself as in Wirth MC (2010), Poopathi S, (2010), and El-kersh TA (2012), whereas this research is the first study using B. thuringiensis isolates from the regions of the mosquito (East Java). The study also used Ae.…”

Bioefficacy of crude extract of Cyperus aromaticus (Family: Cyperaceae) cultured cells, against Aedes aegypti and Aedes albopictus mosquitoes

“…All tests were repeated three times on different occasions. An appropriate amount of larval food (10 mg/larva) was added to each cup after the larvae were introduced in the water containing the crude extract in the test and control cups as well. All tests were conducted in a temperature controlled laboratory with (27依2) °C and relative humidity of (80依5)%.…”

“…Larval food was provided during larval development. The number of live and dead larvae and pupae were observed and recorded every 12 h and the emerged pupae were transferred into plastic cups containing 100 mL seasoned water (10 pupae per cup) and covered with a piece of mesh cloth. Adult emergence (male and female) was observed and recorded every 12 h.…”

“…The use of insecticides is a main strategy. Chemical control of mosquito vectors is an effective way of reducing vector population, but wide-scale application of synthetic insecticides has many drawbacks such as the development of insecticide resistance among vector species, even to bioinsecticides such as Bacillus thuringiensis ( B. thuringiensis ) and Bacillus sphaericus and also to insect growth regulators such as methoprene, and adverse effect on non-target organisms and environmental contamination [8][9][10][11][12][13][14][15] . Thus the search for newer insecticides, which are environmentally friendly as well as effective without any harmful effects on non-target organisms, is important [16][17][18] .…”