For spraying, microbial materials are commonly diluted with water, 

 and sometimes an ingredient such as corn sirup for a sticker is added. 

 For solid or dry applications, microbial materials are mixed with a car- 

 rier, such as clay or talc, or with an insect bait, such as cornmeal. 



Field testing of a microbial insecticide resembles field testing of a 

 chemical insecticide. Specific examples dealing with microbial control of 

 pests of forest trees and agricultural crops, are cited in later sections of 

 this report. 



Among general indications from field testing are these: 



Some microbes that do not persist or spread have to be used like 

 chemical insecticides. That is, a series of applications maybe required 

 to control a pest during crop production. Such use may give economic 

 returns if the microbial material can be obtained at a reasonable price. 



Many microbes that persist start pest-killing slowly but spread and 

 build up in numbers. Some of these can persist in the soil; some in or on 

 tissues of plants, such as trees; some only in host insects. Entomologists 

 have reported protective action of certain of these pest-killers continuing 

 for a number of years. 



Safety in Use 



Safety evidence comes from laboratory experiments with insects and 

 vertebrates and cross -infection tests. 



To start with, true insect diseases tend to be specific to insects. The 

 viruses, bacteria, and other disease agents that kill insects generally are 

 not capable of infecting other forms of life- -from plants to man- -because 

 some requirement of the microbe is not met. 



Body temperature of the host is one barrier. Some insect microbes 

 can grow only at temperatures well below those of man and warm-blooded 

 animals. Some of the sporeforming insect pathogens kill by developing 

 toxic crystals that can grow only in insects. 



Even when the laboratory specialist is satisfied that a microbe is no 

 hazard to public safety, careful tests are made to try infecting other forms 

 of life. Infection has never been reported from such tests either in plants 

 or in animal life from man to earthworms. In reverse tests, insects 

 generally have not proved susceptible to the classic diseases of man or 

 animals --further evidence that the gap barring cross -infection is wide. 



Furthermore, in natural outbreaks of insect diseases and in field 

 experiments, the true insect diseases have a long record of limiting their 

 activity to insects. 



In any case, safety can be made doubly sure by concentrating on 

 microbes that show a wide gap barring them from attacking valued life. 

 Many insect diseases are so specific that it is possible to find kinds that 

 kill a major pest yet are harmless to beneficial insects. Viruses are 

 often limited to infecting a single insect species. Even pathogens that 

 can kill a large number of species have no effect on other species. 



