362 



Tids bug also lives on red root and pig weed, and these weeds should 

 not be permitted near celery beds. Onion thrips (Thrips fabaci) 

 caused a loss of over 50 per cent, of the crop. Sodium nitrate, 50- 

 100 lb. to the acre, was beneficial in some cases. Black-leaf 40 and 

 kerosene emulsion were apphed too late for satisfactory results, 

 though the former (at 1-500 with 3 lb. soap) sprayed with a fine 

 nozzle held close to the plant gave good results elsewhere. This 

 spraying should be repeated a second time, to destroy insects hatching 

 from eggs abeady laid. 



Corrosive sublimate gave promising results in preliminary experi- 

 ments in the control of radish and onion maggots [Phorbia brassicae 

 and Hylemyia antiqua]. 



Gibson (A.). Some recent work on the Control of the Cabbage Root 

 Maggot. — loth Ann. Rept. Ontario Veg. Growers' Assoc, 1919 ; 

 Toronto, 1920, pp. 67-70. 



Experiments to test the efficacy of applications of corrosive sub- 

 limate in controlhng the cabbage root maggot [Phorbia brassicae] are 

 described. Solutions of various strengths were used, but the weakest, 

 1 oz. in 10 gals, water, applied three times proved as effective as stronger 

 solutions and more frequent appHcations. The first application was 

 made four, the next ten, and the third twenty days after the plants 

 were put out in the field. Of the plants thus treated those destroyed 

 by maggots ranged from nil to four per cent., while in untreated 

 plots the damaged plants varied between 52 and 80 per cent. The 

 cost of the treatment, including labour and material, was about half 

 as much again as that of the usual procedure with tarred felt paper 

 disks. Corrosive subhmate had no harmful influence on the plants 

 or on soil organisms ; under field conditions the growth of the plants 

 seemed to be stimulated. 



McDonnell (C. C), Roark (R. C.) & Keenan (G. L.). Insect 

 Powder. — U.S. Dept. Agric., Washington, D. C, Bull. no. 824, 

 3rd June 1920, 100 pp., 4 plates. 



Experiments undertaken to discover the active principle of 

 pyrethrum powder made from the flowers of Chrysantliemum cinerariae- 

 folium showed that all the common organic solvents completely 

 remove the insecticidal principle. It is not removed by steam 

 distillation, either in neutral, acid, or alkaline solution. It is insoluble 

 in water and dilute acids, but dilute potassium hydroxide solution 

 removes nearly all the active principle, which contains no nitrogen 

 and is not an alkaloid. A considerable amount of resin is present in 

 pyrethrum, but this is inert when tested upon cockroaches. Alcohohc 

 potash saponification completely destroys the insecticidal activity 

 of the petroleum-ether extract, the ester being spht up into acids and 

 resinous materials. The results of the work indicate that the insectici- 

 dal activity of pyrethrum is due to a mixtm'e of acids and esters which 

 first benumb and subsequently kiU the insects brought into contact 

 with it. While it is generally considered to be harmless to the higher 

 animals, a number of cases where it has produced symptoms of a 

 more or less serious nature are recorded. 



