Control of insects by bacteria

Abstract

SUMMARYAll bacteria in microbial insecticides are species ofBacillusand form spores since they have to survive in the environment and on the shelf. They can be formulated as wettable powders, suspensions and dusts for application with conventional pest control machinery. All are safe to man and virtually all non-target organisms. Development costs are relatively low, but host specificity greatly restricts markets, the largest beingca. 2000 tons per annum in the West forB. thuringiensis. All act only after ingestion, a disadvantage because there is no contact action and usually only larvae are attacked. Three main groups have special features that determine their commercial success.TheB. popilliaegroup is produced onlyin vivowhich limits production by three small firms. The Japanese beetle has been controlled in grassland in the warm parts of the USA by single applications of spores in heaps, spaced 2 m each way. The bacterium spreads slowly to untreated areas, is very persistent and kills only by infection.TheB. thuringiensisgroup kills larvae of Lepidoptera, mosquitoes and blackflies, mainly by gut poisoning with a protein crystal toxin. It rapidly paralyses mouthparts and gut, stopping crop damage. It is readily produced by deep liquid fermentation, but does not persist and needs repeated application during the pest season. Products containing no beta exotoxin can be applied at unlimited dosage to food crops up to harvest. Only one application is needed for stored grain. After 20 years' use of strains against Lepidoptera, a different strain is now used commercially against mosquitoes and blackflies (only 5 years after its discovery), although improvements in formulation for aquatic application are needed. A recent new product based on the beta exotoxin is used in Finland only against flies in pig houses because it has some vertebrate toxicity.TheB. sphaericusgroup is similar toB. thuringiensis, except that its proteinaceous toxin is different, is situated in the spore wall in strain 1593, and attacks only mosquitoes. Now at the pilot production stage, its commercial future depends on whether it is more potent thanB. thuringiensisagainst certain species and whether it can recycle to give effective extended mosquito control in some environments.Intensive selection from natural isolates has improved potency 100 to 600 fold. This selective effort must be maintained and improved by genetic manipulation, which can be used to develop greater potential, particularly since DNA coding for the crystal toxin is carried on plasmids. This also gives speculative hope that the toxin may be incorporated into natural aquatic bacteria for mosquito control and into plants for protection against lepidopterous larvae. A great advantage is that these bacteria do not harm beneficial fauna to cause pest resurgence. At present, the main use lies in integrated pest control systems, although bacteria are not likely to supplant chemical insecticides on a large scale in the near future.

An Insight into Sweet Potato Weevils Management: A Review

“…Among the most commonly used bacteria in pest management, industrially produced Bacillus popilliae falls into Group 1, which has long-term economic control on pests. On the other hand, industrially produced Bacillus thuringiensis falls into Group 2, which has practical but transient control of pests, and lastly Bacillus sphaericus falls into Group 3, which has mixed characteristics of Groups 1 and 2 [76].…”

BIOLOGICAL AND MOLECULAR STUDIES ON THE TOXIC EFFECT OF VEGETATIVE INSECTICIDAL PROTEIN (VIPs) OF Bacillus thuringiensis EGYPTIAN ISOLATES AGAINST WHITEFLIES

“…Due to its well-known insecticidal activity, many Bt-based commercial formulations are available on the market (Burges, 1982).…”

Insecticide

“…Bacterial insecticides represent the largest and widest used group and reviewed by Burges (1982) and Lysenko(1985). All of those used are sporeformers, since the spores can be readily stored in dried form and applied by conventional means as wettable powders or dusts.…”

“…It has the advantage that once spores are introduced into the environment the bacterial population is sustained by reinfection of the insect hosts, but the disadvantage that spore production requires expensive in-vivo production using insect pupae and is now of declining importance. It is highly specific, does not infect vertebrates, and despite production of a crystal toxin is nontoxic to mammals by repeated oral administration (Burges, 1982).…”