250 



and in destroying them a severe winter exercises a distinctly harmful 

 influence. It is only late frosts that check insect pests, but this 

 gain is more than counterbalanced by the injury to the plants them- 

 selves. The author reviews the exceptionally severe winters of 1911, 

 1914, 1917 and 1918 and shows how, in every case, they were followed 

 by unusual outbreaks of the common insect pests. 



DEN Doop (J. E. A.). Bestrijding der Tabaksluis in Deli. [Measures 

 against the Tobacco Aphis in Deli.] — Meded. Deli Proefstation, 

 Medun, 2nd series, no, 3, 1919, pp. 1-6. [Received 10th April 

 1919.] 



In Deli, Sumatra, Myzus (Myzoides) persicae, Siilz., is chiefly found 

 at the higher altitudes. The weather also has an important effect 

 on its incidence, the main injury taking place during a prolonged 

 dry spell. Infestation occurs in circular or elliptical patches that 

 spread from the centre. The few alate individuals are chiefly respon- 

 sible for this extension, and also for the formation of new centres of 

 infestation. The Aphids avoid the sun and are found on the under 

 side of the leaves only, being therefore unable to withstand a driving 

 rain, which turns the leaves over and exposes the under-side. The 

 best method of combating M. persicae consequently consists in treating 

 the plants with a spray having the characteristics of driving rain. 

 To attain this a pressure sprayer is necessary and in order to obtain 

 a very coarse jet the resistance at the spray-nozzle must be diminished 

 by increasing the diameter of the perforations in the rose and by 

 boring them in as thin a plate as possible. A thickness of 0'2 mm. 

 [■^5 inch] was found suitable. The jet must be fan-shaped, flat, and 

 powerful. It is directed to the lowest part of the mass of foliage 

 and moved upwards, when the leaves will be turned over and washed 

 clean. A soap solution, containing soft soap 1 lb. and water (preferably 

 boiled) 2 gals., is recommended ; if water only is used some of the 

 Aphids escape. There is little danger of re-infestation by individuals 

 that fall unhurt to the ground. 



DEN Doop (J. E. A.). Aanteekeningen over de Lasioderma Bestrijding. 



[Notes on combating Lasioderma.'] — Meded. Deli Proefstation, 

 Medan, 2nd Series, no. 3, 1919, pp. 7-18. [Received 10th April 

 1919.] 



Since De Bussy published his paper on Lasioderma serricorne in 

 Sumatra [see this Review, Ser. A, v, p. 583] the position has been 

 modified in several respects, one of the most important being that 

 the chief infestation now occurs in baled tobacco and not in the sorting 

 piles. This is due to prolonged storage consequent on lack of shipping 

 facilities. The presence of L. serricorne may be ascertained without 

 opening the bales, for the beetles creep out of the bales in which their 

 development has occurred. A very careful inspection of the unopened 

 bales is therefore sufficient. If no beetles are found, it is clear that 

 no damage has been done and if only a few individuals (up to about 

 20) per day are discovered the total injury may be dismissed as 

 negligible. If the bales in and near which most of the beetles are found 

 be marked, it increases the chances of discovering the centre of 



