X 



66 



Experiments with trioxymethylene and Paris green— -the larvae 

 being allowed to feed for three seconds or less — showed that of ten 

 larvae feeding on the former none were dead sixteen hours after, 

 while four out of nine feeding on the latter died within three hours, 

 and a fifth in less than five. In another series trioxymethylene, lead 

 arsenate and Paris green were compared, the dosage of the first two 

 poisons varying from four to fifteen seconds and that of the latter 

 from two to ten seconds. All larvae fed on trioxymethylene died 

 in less than an hour, those fed on Paris green died within less than 

 two hours, while of the lead arsenate series practically all survived 

 until the next day or later. These experiments showed that though 

 Paris green did not always cause a more rapid death than trioxy- 

 methylene, the proportion surviving after a very small dose was 

 less in the case of Paris green than the other poisons ; this is of con- 

 siderable importance, as it is not always possible to give larger doses 

 when treating a stream or pond. Various laboratory accidents showed 

 the extreme sensitiveness of the larvae to minute quantities of Paris 

 green. It is possible that certain digestive fluids of the larvae act as 

 solvents for Paris green, as this substance freed from the water- 

 soluble portion by long treatment with water was still poisonous. 

 Lead arsenate and arsenic trioxide were much inferior to Paris green, 

 and powered arsenopyrite seemed wholly inert. 



Field experiments are described, and the breeding places success- 

 fully treated included impounded water with larvae protected b}?- 

 floating wood, cold water in a ditch immediately below a spring, the 

 larvae being protected by thick watercress, ponds covered with grass 

 or Myriophyllum, cow tracks in a wet pasture, and an old ditch with 

 water covered with duckweed and partly protected by overhanging 

 weeds. In small pools a few pinches of the diluted Paris green sufficed 

 to destroy the larvae. The species of Anopheline /larvae do not 

 differ in their resistance to this poison. 



A dilution of about 1 part of the poison to 100 parts of inert dust 

 is a satisfactory mixture. Diluents are fine sand, rotten wood dust, 

 and road dust, the latter mixed with some fine clay being the most 

 effective. The quantit}^ of Paris green to be used depends on the 

 character of the breeding place, and about 10 c.c. to 1,000 sq. feet 

 is recommended. Throwing the dust into the air by hand is the best 

 means of distribution. 



The best results are obtained on sunny days. The frequency of 

 treatment depends on the temperature of the water. The cost of the 

 poison and the danger of poisoning the operator or the water are 

 discussed. As regards the latter, only a minute quantity of Paris 

 green is dusted over a very large surface, and of that only a small 

 fraction is water-soluble. The poison had no effect on top minnows 

 or any other aquatic animal, however dehcate, other than the surface- 

 feeding Anopheline larvae. The chief disadvantages of the use of 

 arsenic dust is that its use is limited to such larvae, the eggs and pupae 

 of all mosquitos and the larvae of Culicines being apparently unaffected. 



Fletcher (T. B.). Report of the Imperial Entomologist. — Set. Repts. 

 Agric. Res. Inst., Pitsa, 1920-21, Calcutta, 1921, pp. 41-59, 

 1 table, 6 plates. [Received 18th January 1922.] 



A larva of Haematopota javana, Wied., was found underground 

 near the roots of indigo. Pupation occurred after ten days, and the 

 adult emerged five days later. 



