— 19 — 



The utilization of fungous and protozoan diseases in insect c<Mitrol.(*) 



Many experiments have been conducted within the last thirty years with the 

 object of controlling injurious insects through the artificial production of epi- 

 demics of fungous diseases. As in the case of parasitism unexpected difficulties 

 have appeared under field conditions. It was soon discovered that "fungi are very 

 dependent upon external conditions, and in many cases the apparent absence of a 

 particular fungus in a locality is usually an index of conditions unfavorable for 

 its development and an artificial introduction will be useless" (Glaser). 



Out of the large number of experiments that have been carried out, I shall 

 briefly refer to a few of the most outstanding ones. Franz Tangl in 1892 used 

 s]>ore emulsions of Botrytis bassiana against the caterpillars of the nun moth of 

 Central Europe. While the experiments were eminently successful in the labor- 

 atory where all the infected caterpillars died of "muscardine", those carried on 

 outdoors gave negative results. Tubeuf also obtained like results with Cordyceps 

 militaris. 



Many of us perhaps are familiar with the work of Snow and Forbes in con- 

 nection with the artificial use of Sporotrichum globulifcriim against chinch bugs. 

 Later Billings and Glenn also carried on experiments with the same fungus. Their 

 results are summarized as follows : — 



1. — "In fields where the natural presence of the fungus is plainly evident, its 

 effect on the bugs cannot be accelerated to any appreciable degree by the 

 artificial introduction of spores. . 

 2. — "In fields where the fungus is not in evidence spores introduced artificially 



have no measurable effect. 

 3. — "Apparent absence of the fungus among chinch bugs in a field is evidence of 



unfavorable conditions rather than lack of fungous spores. 

 4. — "Laboratory experiments can be made to prove that artificial infection ac- 

 complishes results upon bugs confined in craniped quarters and without food, 

 but in the field, where fresh and usually drier air prevails and food is abun- 

 dant, an entirely different situation is presented." 



In 1912 Morrill and Back experimented with the artificial use of the white 

 fly fungi, Acgerita webbcri, Aschcrsonia aleyrodis and A. flarocinia. They sum- 

 marized their conclusions in these words : 



1. — "The fungus parasites thrive only under suitable weather conditions during 

 a period of about three months each year ; generally speaking the summer 

 months in the case of the two Aschersonias and the fall months in the case 

 of the brown fungus. 

 2.— "Under natural conditions, without artificial assistance in spreading, the fungi 

 have ordinarily, in favored localities, controlled the white fly to the extent of 

 about one-third of a complete remedy through a series of years. 



(*) — European botanists, such as DeBary and Tulasne, about the middle of the last 



century called attention to the importance of white muscardine {Isaria detisa Link.) as a 



check on many insects. Metchnikoff, and Krassilstscik cultivated the green muscardine 



( Metarhiziuni anisopliae S>oro\i\T[) for the control oi Aiiisoplia and the beet weevil ( C/conus 



pundiventris^ . 



Efforts have also been made to check the white grub in Europe by means of Cordy- 

 ecps inelolo7ithae Tul., Isaria densa, and Botrytis tenella Sacc. 



