6 Control of the Greenhouse White Fly 



form into bubbles which swell up very suddenly and burst, distributing 

 the dew as a fine spray. The mechanism of the bubble formation has not 

 been made out. There is at the caudal end of the vasiform orifice a small 

 trumpet-shaped organ and the tip of the lingula frequently touches the 

 mouth of this. The trumpet-shaped organ lies at the end of the furrow 

 running from the caudal air channel of the scale to the vasiform orifice. 

 No actual air channel was followed, and time did not permit of any 

 exhaustive examination of structure. A large number of scales blowing 

 bubbles in this way would form a continuous shower of a sticky spray 

 and it seems reasonable to suppose that this would be a deterrent to 

 the small parasitic hymenoptera. Bubble formation is well known in 

 another group of the Hemiptera, certain Cercopidae, the well-known 

 " f roghoppers " which form the "cuckoo spit." 



The adults exhibit a remarkable colour reaction, being strongly 

 attracted to yellow, and to green and orange in proportion to the 

 amount of yellow these colours contain. The experimental work on this 

 subject will be recounted elsewhere. 



(1) Length of life. A study of the length of Ufe of the adults, their 

 fecundity and parthenogenesis was carried out with newly emerged 

 females, alone or with single males, on small plants growing in muslin 

 covered beakers. In this way daily observations could be made without 

 disturbing the insects and these could be transferred to fresh uninfested 

 plants before their offspring attained maturity. Unfortunately Lamium 

 purpureum, a plant which thrives well under these artificial conditions, 

 was used in a number of the earlier experiments and as none of the 

 young matured these were largely wasted. 



The average fife of 16 females, including three which came by acci- 

 dental deaths, was 40 days. The longest life recorded was 104 days, on 

 Lamiuiii. The average life of 10 males was 25 days, the longest being 

 46 days, also on Lamium. 



(2) Fecundity. The average number of eggs laid was 130 per female 

 and the rate of oviposition averaged about three eggs a day. The largest 

 number laid was 534 giving an average of slightly more than five a day. 

 There appeared to be some variation in fecundity in accordance with 

 the food plant, such as Morrill and Back (2) describe for Al. citri, but the 

 experiments were insufficient for this to be certain. Oviposition began 

 on the second to fifth day after emergence in most cases. The high mor- 

 tality of the young, which occurred several times on suitable foods, was 

 due to the difficulty of keeping all the foliage healthy under conditions 

 ensuring that no invading insects could contaminate the experiments. 



