37 



There is some doubt as to whether, when the rice-stalks are sub- 

 merged, the water penetrates the stalk and comes in contact with 

 the rice-borer larva. As there must be a scarcity of oxygen after a 

 sufficiently long submergence, the resistance of C. simplex to the 

 lack of this gas was tested, carbon dioxide being the medium employed 

 as it seems to have no marked poisonous effect on insects. Resistance 

 to it was found to be fairly strong when the medium was at approxi- 

 mately normal temperatures, but an increase of temperature decreases 

 the resistance. 



As the temperature of water must, therefore, have a great influence 

 on the efficacy of submergence in rice fields, the effect of high tempera- 

 ture was tested, the larvae being confined in closed vials, assumed 

 to contain sufficient air for the duration of the tests, and placed in hot 

 water of a certain temperature. The borer larvae did not die after 

 exposure to about 95° F. (35° C.) for 24 hours regardless of their age, 

 but about 108° F. (42-4° C), 27-7 per cent, of the second instar 

 larvae died in 6 hours. When the fourth and fifth instar larvae were 

 exposed to about 104° F. (40° C.) for 24 hours it was found 

 that only 4-4 per cent. died. Five minutes exposure to 122° F. 

 (50° C.) killed all the larvae of every stage. From these and other 

 results given it is apparent that a temperature higher than about 

 93°-95° F. (34°-35° C.) is injurious, though this temperature can be 

 endured for a long time. 



By preventing water from flowing into and out of a rice field in hot 

 summer the temperature of the water rises markedly above that of 

 the atmosphere. The death of the borer by flooding may therefore 

 be expected to be due to the combined action of suffocation and 

 abnormal temperature. Further experiments with vials filled with 

 hot water prior to submersion show that the temperature of the 

 water in a rice field plays a very important part. At a constant 

 temperature of about 86° F. (30° C.) 28 hours' immersion will kill 

 100 per cent. The time decreases with the rise of temperature, being 

 14 hours at 95° F. (35° C), 5 hours at 104° F. (40° C.) and 1 hour 

 at 113° F. (45° C). At temperatures over 104° F. the abnormal 

 heat of the water becomes the predominant factor, the effect of 

 suffocation being subsidiary. 



It is, therefore, probable that a satisfactory result cannot be expected 

 in rice fields with a submergence of 24 hours or less unless the maximum 

 temperature reaches 93°-95° F. (34°-35° C). In practice the author 

 is inclined to think that under favourable conditions and good manage- 

 ment about 50 per cent, of the borers can be kifled, and a better result 

 may be possible. 



Tests with a film of kerosene when submergence was in progress 

 seemed so unpromising that they were discontinued. 



Ion (O.). nysbipeHome (Thysanoptera) neiporpaflCKOM fyO. [Thysanop- 

 tera of the Petrograd District] Faunae Petropolitanae Catalogus, 

 T. ii, no. 1.— neiporpaACKUM ArpoHOWMsecKMii MHCimyT. HayMHO- 

 MccneAOBaienbCKHM OiAe/i. SHTOMo/iornHecKafl CTaH^l1fl. [Petro- 

 grad Agron. Inst., Sci.-Kes. Dcpt., Ent. Sta.'], Petrograd, Ser. C, 

 no. 1, 1921, pp. 3-16. [Received 19th November 1921.] 



This paper forms part of a series dealing with the fauna of the 

 Petrograd district. In all 37 species of Thysanoptera are dealt with, 

 18 of which are recorded for the first time from Russia. 



