chemical insecticides, cultural practices, and quarantines, to varied 

 biological controls that include parasites, predators, and lethal diseases 

 of pests. 



Advantages of the Microbial Method 



Merits of microbial control of insects are mainly these: 



• A high kill of some serious pests can be achieved. 



• Some microbial insecticides can be processed quickly for mass pro- 

 duction, and some without elaborate equipment- -a point of special interest 

 in countries where chemical industry is not advanced. 



• In some cases, a microbial insecticide applied once will persist and 

 protect an agricultural locality for years. It may even spread its beneficial 

 effect beyond the area treated. 



• Usually a microbial insecticide and a chemical insecticide can be 

 mixed and applied at the same time without interference, if combining 

 them would give an advantage. 



• Microbes that cause insect diseases tend to be so different from 

 those attacking other forms of life that a selected kind need pose no 

 hazard to man, livestock, wildlife, or plants. They offer a solution to some 

 situations in which chemicals leave objectionable residues. 



HOW THE METHOD EVOLVED 



Early History 



Though the fact that insects have diseases has been known for 2,000 

 years, killing pests with diseases could not be tried until the nineteenth 

 century, when discoveries about disease organisms paved the way. As 

 early as 1834, an Italian, Bassi, proved with silkworm experiments that 

 a microbe could cause an infectious disease. By 1873, Le Conte in the 

 United States first stated the proposition that insect diseases were worth 

 careful study for pest control. 



For a long time, efforts --in many countries - -to introduce agents of 

 insect diseases into pest-ridden localities met with frustration. Some- 

 times, a success was achieved but could not be repeated. The main reason 

 for failures was a lack of exact knowledge about the relationships of a 

 microbe to its insect host (an insect of a kind providing the microbe's 

 requirements). 



Clear-Cut Successes 



From the 1930's on, dependable results began to come through research 

 programs that provided every kind of working knowledge that researchers 

 could think of. Three examples that are cited often are the bacterial control 

 of the Japanese beetle; virus control of the European spruce sawfly; and 

 the use of a virus and a bacterium, either one satisfactory, for killing the 

 alfalfa caterpillar. 



