645 



Dutch Indies, tlie wild food-plant of this species is Ipomoea 

 anuatica. Phaseolus mungo is also attacked and often stripped bare. 

 When driven by hunger, the caterpillars migrate in large bodies to 

 the neighbouring teak bush, in which the bulk of them perish. The 

 damage done to Lpoinoea batatas depends very largely on the date of 

 appearance of the pest ; if the young plants are healthy and growing 

 well the damage is not so great, as this plant has a remarkable power 

 of recovery from injury. The destruction in a plantation of Phaseolus 

 munrjo is much more serious and often complete. Tobacco, following 

 a crop of Ipomoea, is not attacked, nor is Hevea or coffee. Though 

 the damage may be serious in some cases, this insect is also useful, 

 as it greatly assists the colonisation of Trichogramma. 



A caterpillar feeding on a variety of cowpea (Vigna cafjang) made 

 its appearance in the middle of November and did a good deal of 

 damage, and may also prove to be a pest of tobacco. It has not been 

 identified, but is tiiought to be a species of Mods {Remigia). A large 

 number of the larvae are attacked by fungus diseases and the eggs 

 are parasitised by Trichogramma. On some plantations of Phaseolus 

 mungo, the caterpillars of a species of Phytometra occurred ; they 

 resembled those of a species known to feed on tobacco. They fed 

 readily on tobacco when there was no other food, but preferred 

 Phaseolus and its varieties ; they were heavily parasitised. 



DE BussY (L. P.) & DiETZ (P. A.). Verbranding door Schweinfurter 



Groen. [Scorching with Paris Green.] — Meded. v. h. Deli Proefst. 

 Medan, ix, pt. 1, June 1915, pp. 15-25. 



During the years 1907-14, more than five times as much Paris 

 green as lead arsenate was used in the Dutch East Indies, despite the 

 fact that the latter does not scorch tobacco. Not only is Paris green 

 used in preference to lead arsenate, but unsuitable materials are used 

 for diluting it, before dusting the tobacco plants. Damaged, and 

 therefore acid, meal which is often used, will itself scorch the leaves, 

 while ashes, being alkaline, do even greater damage when rain falls 

 after the dusting ; coarse sand causes serious mechanical injury to 

 the tender surfaces of the tobacco leaf. The irregular composition of 

 the Paris green is, however, mainly responsible for the damage. 

 Properly made, the average composition of Paris green should be 

 58 per cent. AS2O3, 31 per cent. CuO, and IC per cent, acetic acid. 

 The method of preparation is largely to blame for the defects, as many 

 samples contain free soluble As^^O.-j and this in itself is largely the cause 

 of the scorching which results. Details are given of a number of 

 experiments which support this contention and analyses of samples. 

 Planters are stro)igly advised to submit this insecticide for analysis. 

 They should never buy Paris green which contains more than 0*4 per 

 cent, of arsenious acid, soluble as such in water, nor use more than 

 1 per cent, of the green as a dusting powder or one-tenth per cent, if 

 dissolved in water or Bordeaux mixture. If the percentage of soluble 

 acid is at all high, careful trials must be made with weaker dusting 

 mixtures, from .[ to ^ per cent., and the greatest care taken to secure 

 a thorough and uniform niLxture of the green with the diluent. 

 Plants should only be dusted when the leaves are quite dry. 



