Vol. XVI. No. 384. 



THE AGRICULTURAL NEWS. 



11 



themselves to the underside of the leaves after the manner 

 of scale insects. They are yellowi.sh at first, but become 

 dark-brown in later stages; the tlor-sal surface or back is 

 covered with spines. The pupa case is broadly elliptical 

 and dense black with the upper surface arched and armed 

 with many long spines. The adults as seen at rest on the 

 underside of leaves, present a slaty-blue to blue-black appear- 

 ance, with their rather large front wings arched over the 

 hinder part of the body and almost completely hiding its 

 brightreddish orange colour. The front wings have whitish 

 markings which under a good lens are seen to be semi- • 

 transparent areas, while the smaller hind wings are uniformly 

 dark. This aleyrodid is commonly known in Cuba as the 

 niasca prietci, which may be translated 'black fly'. The 

 Spanish name, however, is nearly always used and has been 

 officially adopted. 



CONTROL ME.VSURES. 



The control measures against the spiny white tly con- 

 sisted in spraying the trees with an oil and soap emulsion, 

 and were supervised by the entomologist and an assistant 

 during the first few weeks. To begin with, the following 

 formula was u,sed: whale oil soap, 2 lb.; heany paraffin oil, 

 2 gallons: water, 1 gallon. These materials were mixed in 

 the usual way to form an emulsion. One gallon of this 

 concentrated solution was used with each .50-gallon barrel 

 pump. A somewhat larger quantity of soap was used at 

 first to take up any free oil that might tend to snrch the 

 leaves. The amount of soap was gradually lessened 

 after the foliage showed no .signs of 'burning'. The 

 main part of the grove consists of medium-sized trees 

 planted in well-spaced rows, which permitted the use of 

 barrel sprayers. These were used at first mounted on 

 low iron wheels supplied with them, but the heavy nature of 

 the soil after rutins soon made this method impracticable; the 

 barrels were, therefore, dismounted and used in larger wheel 

 carts with gond results. The remaining portion of the 

 grove is planted as a nursery of small trees, which were 

 sprayed by means of knapsack pumps. 



When the control vrork was begun by the entomologist 

 a large portion of the grove presented a blackened appearance, 

 due to the fact that the upper surface of the leaves was 

 covered with the sooty mould which often accompanies 

 a severe white fly infestation, while the underside was 

 thickly encrusted with the black immature stages of the 

 insect. The leaves were in a wilting condition as a result 

 of the continual drain on their vitality. During the early 

 days of the spraying the winged adults were numerous 

 enough to form distinct clouds as they rose to escape the 

 spraying machine. 



The writer, as Assistant Kntoniologist from the E.vperi- 

 ment Station, took on the woik when the second spraying 

 was nearly completed, and the general improvement on the 

 above conditions was very marked. The trees were resuming 

 their normal healthy and vigorous appearance, and were 

 putting forth an abundance of new shoots. It was on these 

 younger leaves that most of the adults that had survived or 

 had recently emerged were to be found, and numbers of eggs 

 had been freshly laid. With the aid of a good lens it was 

 seen that the larval and pupal stages had suffered heavily, 

 and that a large percentage of the eggs had shrivelled up 

 before hatching. However, the numbers of all stages that 

 still survived were large enougii to necessitate a third spray- 

 ing, which followed immediately on the .second. This third 

 spraying killed numbers of the adult white flies just at the 

 time of emergence from their pupa cases when ihey are in 

 a helpless state and unable to escape by a quick flight. The 

 immature stages, particularly the freshly laid eggs, seemed to 



have been fairly well destroyed by the spray. Still better 

 results would have been obtained had it not been for the 

 exceptionally wet season, which not only delayed the trans- 

 portation of fre.sh supplies from time to time, but eventually 

 caused a temporary suspension of the .spraying operations 

 themselves. The writer during most of his stay in the 

 Onantanaino di.strict was engaged in field inspection work, 

 and could only take note of the spraying work in the 

 intervals between trips. The control work, howevet, could 

 fortunately be left in the hands of two competent assistants, 

 who carried the operations through in spite of many diflicul- 

 ties. Xot the least of these was the fact that the scene 

 of operations was some -300 miles from the base of supplies 



OBSERVATIONS CONNECTED WITH THE INSPECTION WORK. 



The main obj' ct of the inspection work was to determine 

 as far as possible ihe limits of the spiny white fly within the 

 Guantanaino valley in order- that proper measures might be 

 adopted for restricting it within the determined area. 



The valley, about 200 square miles in extent, falls natur- 

 ally into two distinct regions: a broad rather flat eastern 

 district, which is devoted almost entirely to sugar-cane, and 

 a narrow and more mountainous portion where coffee, cacao, 

 bananas, etc. are grown, often in mixed groves. With the 

 exception of the Finca Montesano, where the control work 

 against the spiny white fly is in progress, and one or two 

 smaller fincas also attacked by this insect, there are no 

 continuous areas where citrus is grown commercially. 



Plants of the citrus genus, however, mostly oranges and 

 grape-fruit, are to be found throughout the valley, being 

 fairly thick in the towns and villages, but only very sparsely 

 scattered in the sugar-cane district and among the mixed 

 groves mentioned above. 



The inspection of the main portion of the valley, which 

 was done by the writer and an assistant mostly on horseback, 

 showed that practically all the citrus trees within a well 

 ilefined area of the valley and foothills were more or less 

 infested with the spiny white fly, while other plants such as 

 mango, guava, etc., were occasionally attacked. 



It will be seen that the spiny white fly must be carefully 

 watched for in the tropical Americas, including the West 

 Indies, and especially in the citrus-growing regions. Its 

 great rapidity of dispersion under favourable conditions makes 

 it a potential pest, which, given a fair start, is capable of 

 inflicting considerable damage in a comparatively short time. 



J.C.H. 



TONS CANE PER TON SUGAR. 



A modern sugar factory is capable of recovering some 

 .S7' to S9° per cent, of the .sucrose in the cane in the form 

 of commercial (96°) sugar. The manner in which the work 

 of the factory is influenced by the saccharine richness of the 

 cane is shown in the following table, which is ba.sed on the 

 a.ssumption th*t the factory turns out 87 l'>. of 9()" sugar for 

 every 100 ib. of sugar in the cane: — 



Per cent, sucrose .Sugar (96°) Tons cane 



in cane. from 100 cane. per ton sugar. 



10 8-70 11 'oO 



11 9.57 10-45 



12 10-45 9-58 

 1 .3 1131 8-85 



14 12-18 8-21 



15 1305 7-66 



16 ■ 13-92 7-19 



