Plant Sanitation. 



[November, 1911. 



definite conclusions. They may, how- 

 ever, be useful as suggesting lines of 

 work for future investigation. The 

 matter is one of some importance locally, 

 as fructifications are often wanted for 

 purposes of spreading the fungus, and, 

 as has been noted, they cannot always 

 be found. When this is due to the 

 greater vegetative activity of the 

 fungus, it might be spread with equal 

 effect by using branches of trees on 

 which fructifications of the fungus had 

 formerly been observed, but f r oni which 

 they had subsequently disappeared. 

 The mycelium of the fungus would then 

 be present. But when the absence of the 

 fructification is due to the disappear- 

 ance of the fungus owing to want of 

 food, such material would be nearly use- 

 less for infection purposes. In this case 

 the scale insects themselves would prob- 

 ably ba far from numerous, and those 

 present would be mainly dead, unless 

 the tree had been reinfected with insects 

 while the fungus had not had time to 

 obtain a hold. 



Effects of Climate. 



The general climatic factors which 

 may have an influence on the effective- 

 ness of these fungi are three, namely, 

 Temperature, Wind and Moisture, 



Temperature. — The four species of 

 fungi known in the West Indies all 

 belong naturally to the tropical or sub- 

 tropical regions, and consequently can- 

 not be expected to flourish in colder 

 parts of the world. This expectation 

 has been fully borne out in the case of 

 the red-headed fungus (SplveroHtilbe 

 coccophila). Several attempts have been 

 made to introduce it into the more 

 northern of the United States and into 

 Canada, but it has never been suffi- 

 ciently vigorous under the colder condi- 

 tions to be of any economic importance 

 in controlling insect pests. 



Wind. — Parasitic fungi are never so 

 effective in windy situations as in 

 sheltered ones. In fact, they are rarely 

 found in places where they are exposed 

 to any severe winds, This is probably 

 mainly due to the drying effects of the 

 wind. The shield scale fungus (Cephalo- 

 sporium lecanii) has been found by Mrs. 

 Patterson in St. Vincent attacking the 

 mango shield scale (Lecanium mangi- 

 ferce), which was growing on a tree in a 

 very windy place, but the fungus was 

 not of luxuriant growth and did not 

 appear to be nearly as effective as it is 

 in calmer places. 



Moisture-— This is the most important 

 factor influencing the growth of these 

 fungi— a fact which is clearly illustrated 

 by the relative effectiveness of the 



fungi in the different islands. The 

 parasites are very plentiful in Dominica, 

 where the rainfall varies on some 

 estates from 100 to 150 inches in a year, 

 and in St. Lucia, where there is almost 

 as heavy a rainfall, at any rate in some 

 districts. As already stated, since the 

 year 1903, there has not been a single 

 outbreak of scale insects of any really 

 serious dimensions in Dominica. Dr. 

 E. W. Berger remarks that under 

 natural conditions, fungi were able to 

 control the attacks of white fly once 

 every three years. It would seem, how- 

 ever, that in Dominica the scale insects 

 are kept in check much more effectively 

 than this. On the other hand, in Anti- 

 gua and Barbados, and possibly even 

 St. Vincent, they are not nearly as 

 effective. In the former case this is 

 probably owing to drought; in the 

 latter, the causes would appear to be 

 more complicated, as the island is not 

 excessively deficientin rainfall. In fact, 

 at one time citrus trees could be grown 

 there with success, though now, more 

 especially since the eruption in 1902, 

 they are persistently destroyed by the 

 attacks of scale insects. The actual 

 reasons for this require further investi- 

 gation, as at least three species of para- 

 sitic fungi are known to be present on 

 scale insects in the island. 



A good instauce of the effect of 

 drought is furnished by the outbreak 

 of scale insects in Montserrat and 

 Dominica already referred to, which took 

 place in 1903. It was found that while 

 both the white and purple scales (Chio- 

 naspis citri and Mytilaspis citricola) 

 were present in both islands, the greater 

 part of the damage in Montserrat was 

 due to the white scale (Chionaspis citri), 

 while in Dominica, which even in a dry 

 season is damper, the purple scale 

 ( My tilaspis citricola) was more serious. 

 It has since been found that under nor- 

 mal conditions the black fungus (Myri- 

 angium Dura^i) acts as an efficient 

 check on the white scale in both islands, 

 while observations show that in Mont- 

 serrat this scale never becomes serious 

 unless the tree is suffering from drought. 

 This would appear to indicate that, in 

 1903. the drought in Montserrat was so 

 severe as to check the black fungus 

 and thus enable the white scale to 

 become numerous. In Dominica the 

 drought was not so severe as completely 

 to check this fungus, though the more 

 delicate red and white-headed fungus 

 parasites of the purple scale (Sphceros- 

 tilbe coccophila and Ophionectria cocci- 

 cola) were rendered ineffective. These 

 observations would appear, then, to 

 bring out two points. Firstly, the effect 



