246 ANNUAL EEPORTS OF DEPAETMENT OF AGEICULTURE. 



INSECTS AFFECTING TROPICAL AND SUBTROPICAL FRUITS. 



Mr. C. L. Marlatt continued in immediate charge of the bureau's 

 investigations of tropical and subtropical fruit insects. 



CiTRus-FKuiT INSECTS IN CALIFORNIA. — Control of the common 

 mealybug on citrus trees has formed the major project of this in- 

 vestigation during the season of 1916-17. It has been discovered 

 that ants, especially the Argentine ant, cause an increase in the 

 severity of infestation and hinder the control of this pest. Numerous 

 experiments in orchards infested by the Argentine ant have demon- 

 strated that the common mealybug will be held in control through 

 the agency of beneficial insects where trees are kept clean of ants. 

 Fumigation with hydrocj^anic-acid gas as practiced against scale 

 insects prevalent on citrus trees has been found to be ineffective 

 against mealybugs. Spraying with water under pressure has been 

 carried on successfully. A promising new contact insecticide has 

 been developed. A Farmers Bulletin (No. 862) dealing with this 

 insect is in press. 



The work on the fumigation of citrus trees with hydrocyanic-acid 

 gas, which has been a part of this project in former years, has been 

 practically completed and the preparation of a Farmers' Bulletin to 

 serve as a manual for the conduct of fumigation work, either by indi- 

 viduals or by fumigation companies, has been nearly completed. 



Citrus-fruit insects in Florida. — The orchard demonstrations of 

 control of the citrus white fly and rust mites have been continued and 

 enlarged, and information as to methods of control lias been dis- 

 tributed by means of departmental publications and articles in the 

 local agricultural press. The methods that have been developed by 

 the bureau are coming into general adoption, and the work has met 

 with hearty appreciation on the part of State citrus growers. 



The work upon citrus insects in Florida has reached a stage when 

 it can be classed very largely as educational and demonstrational, and 

 it is planned to continue this work in future in cooperation with the 

 State extension service. 



A number of minor insect enemies of citrus have been the subject of 

 investigation during the year, and a number of new insecticides for 

 citrus pests have been tested. 



The Argentine ant in relation to citrus insects. — The investi- 

 gation of the Argentine ant in its relation to citrus insects has been 

 completed as a special project, and the information obtained will soon 

 be aA'ailable in a bulletin covering the work as a whole, and in a 

 Farmer's Bulletin summarizing the practical results. 



Insects affecting tropical and subtropical fruits and plants 

 IN greenhouses. — Eesultsof investigations on the use of hydrocyanic- 

 acid gas as a means of controlling insects in greenhouses have been 

 published as Bulletin 513 of the department. The insecticides com- 

 monly employed in the control of insects infesting greenhouse plants 

 have been investigated, and a manuscript on this subject has been 

 offered for publication. Outbreaks of the chrysanthemum and rose 

 midges and the phlox bug have received attention, and practical 

 methods of control have been worked out. Attention has been given 

 also to the control of termites in greenhouses. 



