574 



JuiLLET (A). Essais de Culture et Cultures industrielles du Pyrethre 

 de Dalmatie. — Rev. Bot. app. & d'Agn'c. colon., Paris, ii, Bull. 12, 

 31st August 1922, pp. 402-408. 

 The history of the cultivation of pyrethrum in France, and the 

 methods employed by various growers, with the advantages gained 

 by experience up to the present time, are discussed. The active 

 properties of pyrethrum flowers cannot be estimated by the weight 

 of the extract nor by the valuation of the pyrethron ; the only point 

 to be considered is the physiological dose, whether powder or the 

 insecticide products obtained from the flowers are used. An insecticide 

 with a medium degree of activity, diluted to the prescribed titration 

 and sprayed lightly over a large Pierid caterpillar, should kill it 

 within fifteen minutes, and should be equally toxic to the vine moths 

 [Clysia ambigiiella and Polychrosis hotrana]. The active properties of 

 pyrethrum flowers disappear rapidly in keeping ; they cannot be 

 considered effective after three months. The choice of an emulsifier 

 is also an important consideration. Experience with resinous black 

 soap has proved that it does not in any way alter the insecticidal 

 properties of the oleoresin of pyrethrum when used as an emulsifier, 

 and such a soap emulsion can be kept for a year without in any degree 

 losing its insecticidal value. Other emulsifiers providing stable solutions 

 are the sulphonated salts of fatty acids (such as sulphoricinates), 

 saponins, agar- agar, glycerine, etc., either alone or in Combination 

 ^see also R.A.E., A, x, 3461. The wetting properties and the surface 

 tension of the dilutions must be studied. It has been observed that 

 dilutions of 1 : 10 of the pyrethnmi soap were only slightly toxic to 

 Pierid larvae ; the toxicity increased at dilutions of 1 : 100 to 1 : 500, 

 to decrease again with further dilution to 1 : 1 ,000 and disappear entirely 

 at 1 : 2,000, corresponding to a dilution of oleoresin in the strength 

 of 1 : 200,000. These results are undoubtedly due to problems of 

 surface tension, which probably varies with the species under treatment. 



Lesne (P.). Regime et D6gats des Col6opteres xylophages du Genre 



Lyctus. — Rev. Bot. app. & d'Agric. colcn., Paris, ii, Bull. 12, 

 31st August 1922, pp. 418-420. 



A study has been made of the samples of wood in the coUecticns 

 of the Laboratory of Colonial Agronomy, Paris, with a view to dis- 

 covering the species that are attacked by xylophagous Coleoptera, 

 and to determine the kinds of wood that had harboured colonies of 

 Lyctids. The latter beetles attack dead wood, but confine themselves 

 to soft wood or the sapwocd of the harder varieties. Two species of 

 Lyctids were found to have been at work, namely, Lyctus bnmnetts, 

 Steph., of which a list of 25 food-plants is given, from Indo-China, 

 Gaboon, and the Ivory Coast, and L. africanus, Lsn., noted in four 

 species of wood from Senegal and the French Sudan. These lists show 

 that while tropical, humid countries with heavy forest vegetation are 

 favourable to L. brtmneiis, the regions in the neighbourhood of the 

 Sahara, with their relatively dry climate, are more suitable for L. 

 africanus. L. brunneus has polyphagous habits, but resinous wood is 

 not attacked by either species. Infestation is marked by the presence 

 of small circular or oval holes, surrounded by a fringe of sawdust. When 

 several generations have been at work on a piece of wood, it is reduced 

 entirely to sawdust under a very thin superficial crust, which gives 

 way under the slightest pressure. Washes of paraffin or terebenthine 

 or fumigation with sulphur or carbon tetrachloride, if carefully done. 



