1921 ENTOMOLOGICAL SOCIETY. 57 



An interesting relation is the double-host relation of many aphids. Nearly 

 every year adds to the number of aphids that have this relation, and future 

 studies will perhaps furnish an explanation of tins interesting movement in early 

 and late summer to the host plants. The relation is of interest to the economic 

 worker as it suggests additional means of control. 



Another inter-relation somewhat closely related to the foregoing is that 

 of useless plants and insects. 'One instance will suffice. The hawthorns act 

 as hosts for many insects that are injurious to the apple. It is clear that this 

 relationship demands more careful study by economic entomologists. 



With regard to the utilization of fungous and protozoan diseases 1 in insect 

 control, it may be said that many experiments have been conducted within the 

 last thirty }^ears with the object of controlling injurious insects through the 

 artificial production of epidemics of fungous diseases. As in the case of parasitism, 

 unexpected difficulties have appeared under field conditions. It was soon discover- 

 ed 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 con- 

 ditions 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 

 spore emulsions of Botrytis oassiana 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. Tuheuf also obtained like results with Cordyceps 

 militaris. 



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

 connection with the artificial use of Sporotriclium gldbuliferum 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 

 accomplishes results upon bugs confined in cramped quarters and without food, 

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

 an entirely different situation is presented." 



In 1912, Morrill and Black experimented with the artificial use of the white 

 fly fungi, Aegerita weoberi, Aschersonia aleyrodis and A. flavocinta. They sum- 

 marized their conclusions in these words : 



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

 century, called attention to the importance of white muscardine (Isaria Densa Link.) 

 as a check on many insects. Metchnikoff, and Krassilstscik cultivated tlhe green mus- 

 cardine (MetarMzium anisopliae Sorokin) flor the control of AnisopTia and the beet 

 weevil (Cleonus punctiventris). 



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

 Cordyceps melolonthae Tail., Isaria densa, and Botrytis tenella Sacc. 



