58 THE REPORT OF THE No. 36 



''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. 



"3. The infections secured by artificial means of introducing fungi, while 

 successful in introducing fungi, have thus far proved of little or no avail in 

 increasing their efficacy after they have once become generally established in a 

 grove. 



"4. Experiments by the authors, and by citrus growers in co-operation with 

 the authors, involving the treatment of thousands- of trees with suitable 'checks' 

 or 'controls' have shown that when fungus (red or yellow Aschersonia) even in 

 small quantities is present in a grove, there is no certainty that from three to 

 six applications of fungus spores in water solution will result in an increased 

 abundance of the infection on the treated blocks of trees by the end of the season. 

 In some of the most important and carefully planned and executed experiments, 

 the fungus has increased more rapidly in sections of the groves which were not 

 sprayed with spore solutions than in the experimental blocks." 



The. brown-tail caterpillar is attacked by the fungus Entomophthora aulicae, 

 and an attempt was made by Speare and 'Colley in 1912 to use it in the control 

 of the pest. They state that considerable success has attended their efforts, not 

 that the fungus is a "cure-all" but it is a powerful check. Under proper conditions 

 of introduction from sixty-three to one hundred per cent, of the caterpillars can 

 be destroyed. 



Reference has already been made to the "wilt disease" of the gipsy-moth 

 caterpillars as a factor in the control of these pests in New England. It made 

 its appearance about 1900, and is now distributed over the territory infested with 

 the gypsy moth, according to Glaser. It is an infectious disease but epidemics oc- 

 cur only in localities infested heavily with the gypsy moth. Infected caterpillars 

 became flaccid, and later their tissues disintegrate completely, due to the fermenta- 

 tive and toxic nature of the virus. The brown liquid of a dead caterpillar shows 

 under the high power of the microscope large numbers of polyhedral bodies of 

 various sizes, but the exact nature of the casual organism has not been determined. 

 The virus is filterable with difficulty. 



The success of wilt infection experiments is absolutely dependent upon atten- 

 tion to seemingly insignificanti details, but this much is known, that infection 

 takes place through the mouth by means of the food. 



It is possible that further studies of the disease will evolve some practical 

 method of using the virus for the destruction of larger numbers of the cater- 

 pillars. Already, however, it has been ascertained that climatic conditions appear 

 to bear an important relation to wilt in the field, and that temperature has an 

 Important relation to the period of incubation of wilt. 



4. The Relation of Insects to Inorganic Nature. 



This relation has also been investigated by many workers, for it has long 

 been known that insects are influenced profoundly by climatic conditions. The 



