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the temperature of the damp ground at a depth of f in. being between 

 30° C. and 37° C. [86-98-6° F.] ; the surface, on which the larvae 

 rested, was much warmer, and this was the real cause of the death 

 of all the larvae and pupae within one or two days. 



Resistance to desiccation was tested with a thin layer of damp 

 earth in glass dishes. After a few hours in indoor shade at 20° C. 

 [68° F.] the earth was friable. On the following day water was 

 poured on. The first stage larvae and pupae soon came to the surface. 

 Many of the second stage larvae (all of which were alive) remained 

 stuck to the bottom and perished. Nearly all the third stage larvae 

 freed themselves and rose to the surface. In another experiment all 

 the larvae and pupae were killed b}/ 43 hours' desiccation. In a 

 further test the earth was kept moist, and all the larvae were active 

 three days later. 



To test the resistance to asphyxiation of larvae and pupae stuck 

 to the bottom, test-tubes filled with water were sealed with liquid 

 paraffin. After one hour all the first stage larvae were alive, but all 

 the others and the pupae were dead. After five hours only a few first 

 stage larvae were alive. The larvae that most easily stick to the ground 

 in desiccation (second and third stages) are those that are most easily 

 asphyxiated. 



It is concluded from these experiments that in all rice-growing 

 countries the conditions requisite for the practical application of the 

 sun's rays exist and that only the mature pupae would stand any 

 chance of yielding adults, the young pupae and all the larvae being 

 killed. This was further demonstrated in the course of some experi- 

 ments made in 1920 at the Agricultural Experiment Station at Sadova, 

 South Bulgaria. Exposure to the sun of one or two days suffices to 

 kill all the larvae. It is not necessary to dry the rice field completely. 

 The larvae are not carried out by the outflow. In a drained field 

 larvae occur in pools, such as are found in badly levelled ground. 

 In pools that dry up before water is readmitted all the larvae die. 

 In pools with a depth of 2-2| in. all are killed except the youngest, 

 and these are destroyed if the field is again drained after about a 

 fortnight. It is only in pools about 4 in. deep that the larvae can 

 survive. 



To test these conclusions an experiment was made with two neigh- 

 bouring rice field areas of 300 sq. metres each, one being used as a 

 control. Care was taken to empty the large pools in the experimental 

 area when draining. After 48 hours water was readmitted through 

 sieves preventing the entrance of new larvae. A similar portion of 

 each area was then skimmed with a sieve, when 93 larvae (or 15-16 per 

 sq. metre) were taken in the control area and not a single specimen 

 in the one treated. This work was done in July, and to ascertain 

 its value in spring and autumn it was repeated in September in rainy 

 weather. Only one quite young larva of Anopheles and three of 

 Culex were found in the treated area. 



To ensure rapid draining, groups of fields supplied from one canal 

 should be drained simultaneously. Stopping and readmitting water 

 is best done in the evening. The following plan is suggested for 

 Southern Europe : one five-day draining in April ; two four-day 

 drainings in May and two in June ; two three-day drainings in July 

 and two in August ; and two four-day drainings in September. As 

 larval development requires about a month, each individual is thus 



