Ll. Lloyd 17 



under control. Apart from the fumigations the plants received the same 

 treatment. The infested plants were practically dead on August 24 and 

 the last fruit was picked from them. Their total yield was 29 lbs. 14 oz. 

 The fumigated plants were still vigorous at the last fruit picking on 

 October 8 and their total yield was 66 lbs. 8 oz. or about 4 lbs. of fruit 

 per plant. Not uncommonly tomato plants in trade nurseries are as 

 badly attacked as these and it may be stated fairly that if the plants are 

 infested early and the infestation is not checked a loss of more than half 

 the crop will be the result. 



Such a condition only obtains when the grower deals in mixed crops 

 keeping his houses occupied during the winter. The grower who only 

 grows tomatoes has his houses empty for several months and nearly 

 always commences the season free from the pest. Invasion by the insects 

 is liable to occur in May and June and it is not until the late summer that 

 fumigation becomes necessary. 



Although the cucumber was mentioned above among the favourite 

 foods of the insect, trade growers of this crop do not recognise it as a pest 

 in the Lea Valley. It is sometimes present in the houses early and late 

 in the year, but generally disappears when the weather becomes warm. 

 In the tomato houses it was observed that when the temperature of the 

 air approaches 100° F. the flies become restless and flutter up to the glass, 

 many escaping through the laps. It was found by experiments in thermo- 

 stats that they are stupified when the temperature rises to 105°. Fifty 

 flies so stupified by 40 minutes' exposure to 102-106° nearly all recovered 

 by the second day after the experiment. One out of 20 recovered after 

 5 minutes' exposure to 104-110°, It was clearly impracticable to effect 

 control of the pest in the tomato houses by so raising the temperatures 

 so no further details of the series of experiments will be given, but they 

 showed that it is the atmospheric conditions of the cucumber houses 

 which often rise above 100° that prevent the white fly from becoming a 

 serious pest there. 



8. CONTROL. 



The spread of the insect is greatly aided by the culpable negligence 

 of some nurserymen who make a business of the sale of young plants. 

 Bedding plants such as geraniums and salvias are often sold infested 

 with the pest, and even young tomato plants are sometimes sent out 

 in a similar unclean state. Probably only legislation could stop this 

 dangerous practice, but growers may be advised to ask for a guarantee 

 of cleanliness in this respect for any plants they purchase for gardens 

 around the nurseries, and especially for young tomato plants. It is 



Ann. Biol, ix 2 



