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NOTES ON A COLOUR TROPISM OF ASTEROCHITON {ALEURODES) 

 VAPORARORIUM, WESTWOOD. 



By Ll. Lloyd, D.Sc. (Leeds). 



During 1919-20 an investigation into the habits of Asterochiton {Aleurodcs) 

 vaporariorwn. Westw., was being carried out at the Lea Valley Experimental Station, 

 Cheshunt, with a view to controlling its attacks on tomatoes under glass. The 

 station exists for the study of scientific problems connected with the glasshouse 

 industry, and as the staff is small, the work is necessarily confined to strictly economic 

 lines. Points that appear in the course of the investigations cannot be followed to 

 their ultimate conclusion in these earlier years of the station's existence if they seem 

 to be of theoretical rather than of practical importance. The following notes 

 relate to such a problem, which it has been decided to record, though in a very 

 unfinished state. 



A habit of this whitefly of settling upon clothing led to a short study of its colour 

 reactions. All the experiments were carried out in a heated greenhouse in December 

 and January. A wooden cage was used, 18 in. by 18 in. by 24 in. high, with the 

 bottom six inches forming a wooden well, and above this four sides and a roof of 

 mushn. An exactly similar wooden framework without the muslin was also 

 emplo}-ed, its sides and roof being open to the greenhouse. 



Experiments with Transmitted Light. 



Various weak solutions in water of substances conveniently to hand were made 

 up. Clear white glass corked tubes one inch in diameter and three in length were 

 filled with the solutions to a depth of one and a half inches, and the outsides of the 

 tubes to the same depth were thinly smeared with a clear adhesive composed of resin 

 and castor oil. The tubes were then hung by strings around the four sides of the 

 frame so that they were equidistant from each other and about fifteen inches from 

 the centre of the well. Cut infested foliage was placed in the floor of the well. During 

 the tests the positions of the tubes were interchanged, the least attractive to the 

 position of the most attractive, and so on, or the whole frame was revolved through' 

 90°. The insects were removed by means of a needle and counted at intervals of 

 from one hour to two days. 



Experiment 5. 



December 3rd ; bright sun ; exposure, seven hours of daylight. Twelve weak 

 solutions were made up at random to give a wide range of colours ; 452 flies were 

 trapped, and their distribution is shown in diagram 1 by the continuous line. The 

 following solutions were attractive in order of merit : light yellowish-green (picric 

 acid+jodgriin), fluorescent (weak eosin), greenish -yellow (picric acid), orange 

 (orange G.). The following gave negative results : water, bright red (fuchsin), blood 

 red (Congo red), blue-green (methyl green), pale blue (methylene blue), indigo 

 (nachtblau) and violet (gentian). 



Experiment 6. 



December 5th-6th ; dull ; exposure 16 hours' daylight. Solutions as above, 

 with three others added ; 266 flies were trapped, ancl their distribution is shown 

 in diagram 1 by the broken fine. The same solutions as in the last experiment, 

 together with purple (potassium permanganate) , proved negative. The eosin solution 

 was only moderately attractive, and a strong solution of potassium bichromate rather 



