WORKING KNOWLEDGE FROM LABORATORY AND FIELD 



Research on any microbial insecticide is detailed and complex. Here 

 is a little information to indicate the kind of questions dealt with, and 

 procedures and findings of the laboratory and field studies. 



What Pathogens to Try Out 



The field of search for microbial material is wide, since pathogens 

 that infect insects number thousands. Many can be ruled out at the start 

 because they cause only mild infections or are otherwise clearly unsuit- 

 able. Microbes worth testing have been found among bacteria, viruses, 

 fungi, and nematodes. A bacteria-carrying nematode, known as DD-136, 

 has shown that it can infect and kill many insect pests by introducing its 

 bacterial load; and, in tests so far, this nematode has not been found 

 harmful to plants, warm-blooded animals, or man. Recognized sources 

 include also the protozoa and rickettsia, although on these little testing 

 has been done. 



How a Pathogen Works 



Preliminary work includes taking note of symptoms that are often 

 distinctive and useful in judging the killing rate of a disease. Signs of 

 infected insects may be inability to feed, stunted growth, discoloration, 

 paralysis. Disease-killed insects may hang in profusion on trees or other 

 plants, or lie in masses on the ground, with characteristic appearance. 



The laboratory specialist examines individual insects in stages of 

 infection, to learn where, how, and at what speed an infection develops 

 in an insect host. Organs, such as the digestive tract, are isolated for 

 damage appraisal. Body tissues are microscopically examined. Usually, 

 microbial infections kill by growing in the insect and breaking up tissue 

 or by introducing substances toxic for the insect. Facts about the disease 

 pattern are basic guides to dosages, timing, and other management of a 

 prospective microbial insecticide. 



What is the Infection Route 



In insect life, two infection routes are most common. Many fungi 

 produce spores that find their way onto a prospective host. These spores 

 send out strong threadlike substances that can push through an egg shell, 

 grub cuticle, or even the exo-skeleton that adult insects wear like armor. 

 Nematodes also can pierce the body wall. Most of the bacteria, viruses, 

 and protozoa cannot invade this way, and they are usually taken in with 

 the insect's food. Establishing the main route is a guide to application. 

 Some microbial materials can start a strong pest-killing attack only if 

 applied to soil; others only if applied on plants. 



How Timing, Temperature, and Moisture Influence Results 



Temperatures at which insect pathogens can work differ greatly. Each 

 pathogen and each insect has a range of temperatures that it can stand. 

 Temperature testing determines the tolerances to heat and cold for a 

 pathogen and insect host. Within these limits, the range at which infection 



