378 INSECTICIDES, FrN(;iCIDES, AND ^VEED KILLEES. 



146. Pyrethra. —The pyrethras, plants which Ijelong to the family 

 of CompositcP, contain an insecticidal principle. Two plants ai'e chiefly- 

 used to make pyrethra powder oi- l)ug powder ; these are Pyrethra 

 cineraria-folium, Treviv., and the Chri/santhe77iuvi coccineuvi, Willd. 

 A species originally Caucasian, Pyrethrum rosevm, contains less active 

 principles. Although cultivated in Asia, insecticidal pyrethra can 

 accommodate themselves to the South of France. Their culture might 

 produce excellent I'esults with a profitahle yield. 



Preparation of Pyrethra Powder. — -The flower, the sole organ 

 of the })lant containing the insecticidal principle, is alone ground. 

 According to certain authors the hest powder is made from unexpanded 

 flowers ; others say that the flower-hud must he perfectly closed, whilst 

 others assert that the flowers should he collected when the flower is in 

 full bloom. Pyrethra powder is made in America, Great Britain, 

 Germany. Montenegro exports into these countries 10 tons of pyrethra 

 flowers per annum. Pyrethra powder is none other than the dried 

 flower suitably and finely pulverized. It is used most often alone, 

 such as it is ; sometimes it is mixed before use with three times its 

 weight of flour, or with four times its bulk of sulphur to destroy both 

 the altise and the oidium of the vine, or again with cupric sulphosteatite 

 to destroy the altise and the mildew. 



Preparation of Pyrethra Extracts. — 1. Aqueous Extracts. — 

 6 lb. of ])yrethra powder are treated cold with 10 gallons of water. 

 Maceration lasts twenty-four hours. It is easier to make the extract by 

 aid of heat. The pyrethra powder is first made into a paste by hot 

 water, it is thinned down gradually with boiling water and cooled. 

 Before use this extract is diluted with six to eight times its volume of 

 water without losing its insecticidal properties. 



2. Soajj Extract. — Dissolve 3 lb. soft soap in 1 gallon of hot 

 water; add thereto whilst stirring with a birch-broom 1-^ lb. of 

 Dalmatian pyrethra powder and 9 gallons of cold water. Invented by 

 Dufour of Lausanne, this insecticide is one of the most perfect now 

 existing. 



3. Alcoholic Extract. — Treat 6 lb. of pyrethra powder with 10 gallons 

 of 80 per cent alcohol. Dilute before use with 5 parts of water. 



4. Alcoholic and Ammoniacal Extract. — Mohr mixes in a flask 

 100 grammes of Dalmatian pyrethra powder, 200-250 grammes of 

 alcohol, 80-100 grammes of commercial ammonia. After some days, 

 he adds 1^-2 litres of water, and heats gently for forty-eight hours. 

 [Similar proportions in the same ratio are 1 lb. pyrethra powder, 

 2-2^ lb. alcohol, O'8-l lb. commercial ammonia, and 14^-2 gallons of 

 alcohol.] The liquor is filtered and mixed as follows : — 



TABFjK IjXXXIV'. — Slioiring Composition of I'un'thra Ivscdicidcs. 



Extract ...... 



White soap 



Non-calcareous water ... 



Preference must be given to one or other of these insecticides accord- 

 ing to the resistance of the insect to be killed. 



