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Illinois Natural History Survey Bulletin 



Vol. 27, Art. 2 



spectacular as sponsors and interested ob- 

 servers had hoped. These projects have 

 been greatly underestimated by the pub- 

 lic; control of insects by their diseases has 

 a value that should not be ignored. 



If nothing more, these studies demon- 

 strate the important role that insect dis- 

 eases play in the natural control of many 

 important pest species. They also shed 

 light on the epizootiology of these dis- 

 eases, which may prove to have even fur- 

 ther value. Unfortunately, in practically 

 all cases these projects were initiated on 

 the premise that an epidemic would be 

 initiated that could and would completely 

 eliminate the pest species in a matter of 

 days or weeks. When extermination of 

 the ofifending pest was not immediately 

 forthcoming, public sentiment turned 

 from hope to disgust and ridicule, and re- 

 searchers were forced to abandon their 

 studies for lack of financial support. It is 

 doubtful whether there is a single case in 

 which an honest appraisal of the long- 

 range or even the immediate value of dis- 

 ease inoculation or dissemination, or a 

 combination of both, has been made. In 

 recent years we have belatedly come to 

 realize that insect pathogens have not 

 been adequately explored nor their poten- 

 tial value determined. We and others are 

 renewing our efforts in this basic field of 

 research. 



The performance of a protozoan dis- 

 ease of the European corn borer, a disease 

 which, like the parasites of the hessian fly, 

 apparently accompanied the host when it 

 migrated to North America, seems worthy 

 of mention. In Illinois the disease was 

 first observed in the north central part of 

 the state in 1945, 6 or 7 years after the 

 borer made its first appearance in Kanka- 

 kee County. The disease was artificially 

 introduced into all sections of the state by 

 colonizing disease-infected borers in many 

 widely scattered counties. It is now prev- 

 alent in all parts of the state and has for 

 several years been an important, if not 

 the most important, factor in holding 

 corn borer populations to relatively low 

 levels, where they can be successfully con- 

 trolled by other means at a greatly re- 

 duced cost. 



In a co-operative effort, the Illinois 

 Natural History Survey, United States 

 Department of Agriculture, and Illinois 



Conservation Department introduced a 

 virus disease obtained from Canada to 

 combat a serious outbreak of a pine saw- 

 fly, Neodiprion sertifer, that in 1952 was 

 raging out of control in the Henderson 

 State Forest. The virus took hold in a 

 spectacular fashion, and sawflies died by 

 the thousands. Whether the virus can be 

 given full credit or not remains to be de- 

 termined. In any case, the sawfly has not 

 been reported as doing serious damage in 

 that area since 1953. 



The value of parasites imported from 

 abroad to help control accidentally intro- 

 duced species has also been underesti- 

 mated. Here, as in an effort to control 

 an insect pest by disease, the public seems 

 to expect the immediate annihilation of 

 the pest species or it regards the effort as 

 a complete failure. To demonstrate that 

 a species need not be annihilated to be 

 prevented from causing appreciable dam- 

 age, let us look at the record. The hes- 

 sian fly and the wheat midge were both 

 introduced in colonial days as immigrants 

 from Europe. Fortunately, several of 

 their European parasites came along with 

 them in the same lots of straw, but, as 

 usually happens, each pest reproduced 

 and spread faster than its parasites. In 

 due time the parasites overtook their hosts, 

 and, for over a century, they have been 

 important factors in preventing these 

 pests from eliminating wheat production 

 from the list of agricultural enterprises 

 in Illinois. 



When the oriental fruit moth appeared 

 in Illinois in 1927, the Illinois Natural 

 History Survey, in co-operation with the 

 United States Department of Agriculture, 

 obtained, for release in Illinois, oriental 

 fruit moth parasites (principally Macro- 

 ceutrus ancyVworus) reared in New Jer- 

 sey. These were colonized at several 

 points in the infested southern Illinois 

 counties. At first the results of the ex- 

 periment did not appear promising, but 

 consistent recoveries were made in 1934, 

 and eight surveys made since then have 

 shown that parasitism by this species 

 ranged from 17.3 to 53.2 per cent and 

 averaged 36.5 per cent. While the para- 

 site has not eliminated its host, it has held 

 the population to a level where peaches 

 can be adequately protected with a mini- 

 mum use of insecticides. The average 



