Plant Sanitation. 



436 



[November, Ml. 



that the fungus was living on the nectar 

 falling upon the leaves from the flowers. 

 This idea was supported by the face 

 that there were very few scale insects 

 present on the leaves. Mr. Moore, the 

 Agricultural Superintendent in St. Lucia, 

 who first observed this suggested that 

 possibly the same thing was true in the 

 case of the mango, and if so, removal 

 of the scale insects would not have the 

 effect of removing the blight until after 

 the flowering season in the case of the 

 trees mentioned. These points, how- 

 ever, all require further investigation, 

 and at any rate, the question of the 

 prevention of black blight is somewhat 

 of a side issue. 



Comparison op Artificial and 

 Natural Methods of Controlling 

 Scale Insects. 



Before proceeding to the next division 

 of the subject, it may be advisable to 

 add that Hume in his book on Citrus 

 Fruits and their Culture, remarks that 

 the effect of attempting to combine 

 the artificial control of scale insects 

 (by means of various sprays and by 

 fumigation) with the natural coutrol 

 (by means of parasites), only results in 

 producing the bad effects of both 

 methods ; and it seems at present that 

 the natural means of control is undoubt- 

 edly the one most suited to the con- 

 ditions in the majority of the West 

 Indian Islands. The reasons for this are 

 of two kinds. In the first place, the 

 natural method of control is not so 

 expensive to institute as the artificial 

 method, involving as it does no outlay 

 on spraying pumps and materials, and 

 but comparatively little labour. Fur- 

 ther, it does not necessitate periodically 

 recurring outlays for the repetition of 

 the treatment, since once established, 

 the only cost involved, that of reintro- 

 ducing the parasites where this is neces- 

 sary by means of one of the methods 

 already described, and of replanting 

 Bengal beans (Mucuna pruriens, var.) 

 in places where their use is advisable, 

 is of very minor importance when 

 compared with the expense incurred in 

 extensive spraying operations, which 

 may have to be repeated two or three 

 times in a year. In the case of limes, 

 moreover, the value of the crop is small 

 compared with that of the more 

 specialized forms of citrus fruits, such 

 as oranges, so that it does not permit 

 expensive spraying operations to be con- 

 ducted with profit. Cost is an even more 

 important factor in the case of held fumi- 

 gation on account of the heavy outlay 

 involved in buying tents. Secondly, on 

 many estates in the West Indies, the 

 nature of the ground, its roughness and 



slope, difficulties of obtaining water, of 

 procuring sufficiently skilled labour, and 

 similar factors reuder spraying on a 

 large scale impossible from a practical 

 point of view. These same factors, more 

 especially that of* obtaining sufficiently 

 skilled labour, also prevent, to an even 

 greater extent, the use of fumigation. 



Experience in Moutserrat, where the 

 scale insects are always liable to cause 

 serious trouble, has shown that with a 

 little assistance, more especially in dry 

 seasons, the natural enemies are just 

 able to keep the insects in check. 

 Recent investigations by the Entomo- 

 logist of the Department, Mr. H, A. 

 Ballou, and by the author have shown 

 that numerous parasitic species of both 

 insects and fungi are present, and 

 possibly the control effect is due more 

 to the number of species than to the 

 number of individuals of those species. 

 Mr. Driver and his colleagues are of the 

 opinion that spraying methods are not 

 of much use ; and moreover, trees 

 examined showed clearly that where 

 sprays had been employed, the natural 

 enemies of the scales had received a 

 decided cheek. This was well illustrated 

 in one particular case. In a certain field 

 a belt of trees had been sprayed about 

 twelve months before they were ex- 

 amined, while the remainder were left 

 unsprayed. On the unsprayed portion 

 the red-headed fungus (Sphmrostilbe 

 coccophila) was abundant on the white 

 and purple scales (Chionaspis citri and 

 Mytilaspis citricola,), but on the sprayed 

 portion only a few fructifications were 

 found. This observation certainly sup- 

 ports the statement by Hume referred 

 to above. 



The following: is a short abstract of a 

 letter written by Mr. P. Foster Huggins 

 tc the St. Vincent Sentry of April 8, 1910, 

 that contains some points of interest in 

 this connection :— 



The frequent appearance of black 

 blight in St. Vincent is associated with 

 scale insects which infest either the 

 plants which exhibit the blight or over- 

 hanging trees. The author found that 

 iudividual effort to control the scales by 

 artificial means was useless, as, even 

 when the trees were cleared, they 

 rapidly became reinfested from surround- 

 ing vegetation on which the scales 

 abounded- He lost hundreds of grown 

 orange and other trees owing to the 

 prevalence of the scales, but recently 

 some of the remaining trees have shown 

 signs of improvement. This has been 

 due to the presence of a small red fungus 

 on the scales (undoubtedly Sphmrostilbe 

 coccophila), which attacked the mussel 

 scale (Mytilaspis citricola), the white 



