BIOLOGICAL CONTROL OF INSECTS 449 



Furthermore weather factors are known to influence the adores- 

 siveness of entomogenous fungi. Most of them, especially species 

 of Sphaerostilbe, Aegerita, Aschersonia, and Beauveria, are favored 

 by wet weather or periods of high humidity coupled with high 

 temperature. If dense populations of insects occur at such times, 

 these fungi spread with great rapidity, and the insects become dis- . 

 eased in epidemic proportions. These factors may therefore be- 

 come limiting in man's efforts toward artificial control. 



Beauveria bassiana, first observed in 1835 by Bassi di Lodi as 

 pathogenic to silk-worm larvae, is among the better-known spe- 

 cies that have been used in efforts to secure control of insects. 

 Attempts extending over several seasons were made to control 

 flea beetles (Haltica) in Algeria, with the result that the adult 

 stage readily became infected, but the larvae seemed quite resistant. 

 Attempts were also made over the period 1888 to 1896 to control 

 chinch bug, Blissus leucoptenis, in Illinois by use of the related 

 Beauveria globulifera. A measure of success was obtained in these 

 trials but only when the insects were present in excessive abun- 

 dance and when hot, wet weather prevailed. 



Extensive attempts have been made in Florida to utilize naturally 

 occurring entomogenous fungi against white flies and scale insects 

 in citrus groves [Fawcett (1907, 1908), Berger (1909, 1910), Mor- 

 rill and Back (1912)]. In Florida citrus groves, several species, 

 including Aegerita ivebberi, Aschersonia aleyrodis, A. goldiana, 

 V erticilliinn cinnamomeum, Sphaerostilbe aurantiicola, and Po- 

 donectria coccicola, are of importance and have been used arti- 

 ficially. Increase of white flies and scale insects has been stimu- 

 lated there by the use of Bordeaux mixture to control citrus scab, 

 Sphacelovm fawcetti, and citrus melanose, Diaporthe citri. 



The inoculum for these entomogenous species consisted of spore 

 suspensions sprayed upon insect-infested trees or of fungus-bear- 

 ing leaves or twigs tied to such trees. In some instances the spore 

 suspensions were prepared from pure cultures and in others from 

 fungi removed from infested leaves. 



Under some conditions the results in Florida and elsewhere 

 show that the artificial introduction of fungi has very materially 

 aided in the destruction of insects [Picard (1914), Berger (1921, 

 1932), and Watson and Berger (1937)]. 



Morrill and Back (1912) concluded, however, that Aegerita 



