OBSERVATIONS ON INSECT PESTS IN GRENADA. 179 



The insects which are most generally associated with black blight are the Coccidae, 

 although it accompanies other insects. The presence of black bhght may nearly 

 always be taken as an indication of the presence of scale-insects or mealy bugs, or 

 both, on the trees or other plants where it is seen or on adjoining and overhanging 

 trees. That is to say, it often happens that when tall trees are infested with scale- 

 insects, other trees of lower growth, shrubs, and even the rocks and soil below may 

 be covered by black bhght, which is the result of the fungus growing on the nutritive 

 substances which have dripped down from above. 



It should be stated that it is possible for black blight to occur without the aid of 

 insects of any sort, as in the case of plants which produce a profusion of flowers secreting 

 an abundance of nectar. If this nectar drops on the leaves, black blight may develop 

 on it. The black bhght fungus also develops on extra-floral nectaries, such as those 

 formed on the principal veins at the back of a cotton leaf. 



It seems to me that it is especially unfortunate that in Grenada reference is so 

 constantly made to black bhght as a pest. If planters and others would learn to 

 refer to the insects which induce the growth of black blight and not to the com- 

 paratively harmless, though conspicuous, fungus, it would be much easier to discuss 

 the problem with them. In general, it may be said that to attempt to deal with the 

 black blight question under the comprehensive term " black blight " will in the future 

 yield no better results than in the past. It might be compared to the efforts of medical 

 men attempting to treat all the different fevers under the one head " fever." It is 

 possible to render some relief, but cures are next to impossible. 



In considering the amount of damage done by scale-insects, and generally spoken 

 of as black bhght, it must be remembered that the amount of black fungus visible 

 upon a tree or landscape is no indication of the damage done. Any estimate of this 

 must be based on the yield of fruit or other product, and on the growth and health of 

 the fcree. Scale-insects, for instance, may so seriously interfere with the natural 

 functions of the tree as to cause a falling off of the amount of fruit produced and to 

 injure it to such an extent as to cause twigs and branches to die and sometimes to 

 bring about the death of the whole tree. In considering any remedial measures for 

 the control of those insects which are accompanied by black blight, the amount of 

 the damage done must be estimated in order that calculations may be made as to the 

 expense that should be incurred for the purpose. 



One of the reasons for embarking on a campaign against black blight in Grenada 

 arises from the idea that the fungus and the scale-insects are hkely later to attack 

 cacao, when other food-plants are killed off. This supposition is not well founded. 

 In the first place the blight-infested trees are not often killed out either by the scale- 

 insects or the fungus. In the case of mangoes, which are perhaps the most universally 

 and most thoroughly scale-infested and blighted of all the Grenada trees, it would be 

 difficult, I beheve, to find any trees killed out-right by this cause. I have asked 

 several people to show me such a dead or dying tree, but I have not been shown one 

 yet. Moreover, not all mangoes are scale-attacked and blighted, and those that are 

 affected put out a full covering of new leaves each succeeding year. 



In the second place, cacao is not very susceptible to the attacks of scale-insects, 

 or any insects which induce the growth of black blight. At the present time, so far 



