WHAT IS BACILLUS THURINGIENSIS 1 by

Bacillus thurlngiensis (Bt) is a bacterium that belongs to the genus Bacillus. It is pathogenic to insect larvae, mainly Lepidoptera species. Several insecticidal toxins can be produced by the different strains of Bt. The most important one is the crystal (delta-endotoxin) which, alone or in conjunction with the spore, will kill the insects. Parasites and predators of Lepidoptera and beneficial insects are generally unaffected by Bt. In the U.S. commercial products of Bt are produced with the HD-1 strain and contain only the spore and crystal as their entomopathogenic ingredients. To be effective these must be ingested. Therefore timing of the application and thorough coverage of the treated foliage are important. Bt can be applied by conventional means. Highly alkaline water should not be used for mixing and excessive heat during storage should be avoided. A brief listing of Bt formulations for gypsy moth control is included. The literature contains numerous examples of microorganisms pathogenic to a variety of insect species. Known entomopathogens include some species of fungi, protozoa, microsporidia, nematodes, viruses, and bacteria. As early as 1879 a fungus, Metarrhizium anisoplia (Burges and Hussey 1 970) was applied for field control of an agricultural insect pest (Anisoplia austriaca). Since the early 1900's the Bacillus thuringiensis group of bacteria has received the most attention and for a number of years commercial formulations of Bt have been available for use in both agricultural and forest insect pest control. As the name indicates, and in common with other members of the genus Bacillus, it is a sporeforming, rod-shaped bacterium, motile by peritrichous flagella. At the time of sporulation, Bt forms a protein parasporal body termed the deltaendotoxin, commonly referred to as the crystal. When sporulation is complete, both the spore and crystal are lysed from the sporangium and released into the surrounding growth medium (Figure 1). In 1905, Ishiwata first isolated this type of microorganism from dying silkworn larvae and named it Bacillus sotto. Approximately 1 0 years later, it was found that only old sporulated cultures of the bacteria could induce disease in the silkworm. In 1911, a German entomologist named Berliner isolated a similar spore-forming bacterium from diseased Mediterranean flour moths (Anagasta (Ephestia) kuhniella) in Thuringia, hence the name Bacillus thuringiensis. This original culture was lost, but in 1927 Mattes reisolated this microorganism and it soon became the source of extensive research and early commercial development of Bt. In the mid 1 950's it was determined that the Bacillus sotto of Ishiwata and Bacillus thuringiensis of Berliner were varieties of the same species (Fast 1974). Now Bacillus thuringiensis Berliner is regarded as the type species of these bacilli collectively called the "crystalliferous bacteria". The potential for development of 6/ as a biological insecticide was demonstrated shortly after its reisolation. Indeed, in 1929 Metalnikov and Chorine (1929) reported on the control of gypsy moth with Bt. These early reports were verified in 1 960 by Cantwell and his colleagues (1961). Even before 1938 the first commercial product of Bt, Sporeine, was already available. After the second world war several U.S. firms produced Bt commercially. Until the early 1960's formulations of Bt were prepared from the Berliner strain. In the mid 1960's several other strains were investigated. The HD-1 strain became available in the late 1960's and is now used for commercial production of Bt in the United States.