BUREAU OF ENTOMOLOGY. 311 



station continued through the growing season of 1921 and confirmed 

 earlier conchisions of the superiority of a distilhite cresylic acid soap 

 emulsion spray. Further progress was made in the investigation of 

 liquid hydrocyanic-acid gas. 



In the southern San Joaquin Valley, in cooperation with the en- 

 tomologist of the California Fruit Growers' Exchange, experiments 

 were made to determine the comparative merits of dusting and spray- 

 ing for the citrus thrips. The dusting method was found to be de- 

 cidedly inferior to spraying. 



CiTRus-FKuiT INSECTS IN FLORIDA. — At the Oi'lando, Fla., station 

 work on the rust mite has been continued throughout the year. This 

 project has proven to be a most intricate one, as it has been very dif- 

 ficult to determine the host plants of the mite or satisfactorily to 

 study its life history. Methods for rearing the rust mite, however, 

 have now been developed and new facts relating to its life history 

 discovered which bear directly on methods of control. Several 

 forms of sulphur have again been tested against the mite, and the 

 merits of sulphur dusts in comparison with liquid sulphur sprays 

 determined. Continued progress has been made in the use of Bor- 

 deaux-oil emulsion spray for the simultaneous control of citrus dis- 

 eases and insects, as mentioned in the last report, the work being 

 carried out in cooperation with the Bureau of Plant Industry of this 

 department. Experiments are in progress to develop an adhesive 

 for sulphur, so that if possible it will remain on citrus foliage a 

 much longer period than at present. 



Investigations of insect-killing fungi. — Studies of insect-killing 

 fungi in Florida, especially in relation to their value in the control 

 of citrus insects, were made. Further information has been obtained 

 concerning the fungus diseases of the citrus mealybug. This knowl- 

 edge will be of distinct advantage to growers, and it is hoped will 

 save them material expense by eliminating the very unsatisfactory 

 remedial measures employed in the past. While the fungus has not 

 as yet been cultivated on artificial media, it can be disseminated by 

 means of distributing infested insects. The mealybug can be reared 

 in quantity on potato sprouts, infected with the disease, and readily 

 distributed to citrus growlers. As stated in the last report, fungus 

 parasites of the rust mite have been discovered and further knowledge 

 concerning them secured. It is believed that one of these fungi can 

 be grown artificially and thus be utilized at times when it will do 

 most good. The fungus will supplement the use of sulphur sprays, 

 especially in earl}' spring, when for any reason these treatments can 

 not be given. Further experiments in the use of fungus parasites 

 of the white fly and purple scale have showm that by spraying with 

 a spore solution, largely during the crawling stages, a mortality of 

 fibout 85 per cent can be obtained if the host plant is in some way 

 protected from rains after treatment. The discovery of the desir- 

 able stage of the insects at which to make the application of the spore 

 mixture points out the need of a medium which will serve to stick 

 the spores to the leaves and insects in spite of rains. 



Insects affecting mango, guava, and other subtropical fruits. — 

 Investigations of these insects have been continued, with headquar- 

 ters at Miami, Fla. Biological studies of the avocado white fly, 

 Tnaleurodea foridensls^ have been completed. Various parasites 

 have been found which attack the species, some of which have been 



25684— A GR 1923 21 



