244 GERALD C. DUDGEON — A PROPOSED METHOD OF CONTROLLING 



organised annual campaign was instituted to carry out a mechanical method of 

 destruction with the assistance of a law. This law compelled cultivators to 

 destroy egg-masses and larvae as soon as they appeared, under penalty of fine 

 or imprisonment. 



The cost to the Government for these annual campaigns has varied from 

 £E. 10,000 to £E. 20,000, but this amount represents but a small proportion 

 of the cost to the people themselves. Many other means of destruction have 

 been recommended from time to time, but all have proved more costly, too 

 dangerous to life, or less efficacious than the Government method. 



Among the many important matters which required immediate attention 

 when the Agricultural Department of Egypt was organised by myself in 1910, 

 none was more urgent than the control of agricultural pests. The examination 

 of all that had been done in the past shewed that artificial means alone had 

 been relied on for destructive agents, and that no experiments had been con- 

 ducted to ascertain whether the insect pests were themselves susceptible to 

 any disease. It was obvious that if it were found that they were susceptible, 

 and that such a disease could be easily transmitted and rapidly spread among 

 them, a very great economy could be effected, compared with the cumbrous 

 and very expensive mechanical means which had been hitherto employed. 



To this end, in collaboration with Dr. Lewis Gough, Entomologist to the 

 Agricultural Department, bodies carrying diseases known to attack lepidopterous 

 insects, especially silkworms, in different parts of the world, were introduced 

 and the larvae of Prodenia litara were infected from them. 



Muscardine and other fungoid diseases were found unsuitable owing to the 

 dryness of the climate. Pebrine and flacherie were tried, but the results with 

 these as well as with all others were negatived by the superinfection of a 

 protozoan disease known as " grasserie " (Miser osporidium polycdricum, Bolle) 

 which had been procured in dead bodies of silkworms from Austria. This 

 disease was of such extreme virulence that it pervaded the whole experimental 

 area, destroying all the larvae of Prodenia which were being kept for other 

 purposes. 



One month after this disease had devastated the experimental laboratory it 

 was found difficult to procure Prodenia larvae, from any part of the country, 

 which were not infected by the disease. The attack of cotton worm in this year 

 (1912) was very severe and reached its height by the end of the first week in 

 July, after which it rapidly subsided and by the beginning of August it was 

 almost impossible to obtain any larvae for experimental purposes which had not 

 contracted the disease. There is little doubt that the outbreak in the country 

 was spontaneous and not connected with the introduction which had been made 

 in our laboratories. The spontaneity and virulence of the attack was so remark- 

 able that I was induced to re-examine the imperfect details which had been 

 collected with regard to the cotton worm visitations in previous years. As a 

 result I found that an almost identical condition existed in 1895, which year was 

 followed by two others in which the pest was almost negligible. 



The next step was to insure the continuity of the disease. In the spring of 

 the present year, 30,000 silkworms were infected by spraying their food with 

 water in which the macerated remains of one diseased cotton worm had been 



