OBSERVATIONS ON INSECT PESTS IN GRENADA. 181 



It must be remembered, however, that in those districts where the parasitic fungi 

 do not thrive naturally, it will be necessary to make the introduction year after year, 

 and in addition, to improve the conditions by providing shelter belts, where these 

 are needed. 



A feature in the control of scale-insects by natural enemies which should not be lost 

 sight of is this : — Such control never results in complete eradication of the host, and 

 so long as there is a sufficient number of scale-insects present to provide host material 

 for parasites, there will be a sufficient number to provide for the continuation of 

 scale-insects for the growth of black blight. 



More judgment should be used in the matter of lopping scale-infested and blighted 

 trees. I saw one very striking instance of indiscriminate lopping. A tree standing 

 by the road-side had just been lopped and the lopped branches still lay upon the ground. 

 The leaves were completely covered with black blight on their upper surfaces, and 

 with the mango shield-scale on the under sides. The scale-insects were thoroughly 

 infested by the shield-scale fungus, every scale having apparently been killed by it. 

 A few yards away another mango tree had been lopped a few months before, and 

 when seen had put out a vigorous growth of shoots and young leaves, which were 

 severely infested with the mango shield -scale. Had the first-mentioned tree been 

 left untrimmed, the fungus would soon have spread to the other and checked the 

 scales, and in the case of its own new growth it would have been protected for some 

 time by the great abundance of fungus on the old leaves ; bub the removal of all this 

 fungus-bearing material left the new growth exposed to insect attack without check. 

 If it is a reasonable practice to pin in or tie in a few leaves bearing the fungus as a 

 means of introducing it, how much more effective it must be to have a whole tree full 

 left standing near by. The lopping of scale-infested trees in which there are no 

 fungoid or other natural enemies would be beneficial treatment, but the lopping of 

 trees without regard to the presence of the parasites of the scales and merely because 

 they are covered with black blight is likely to do more harm than good. 



The insect parasites of scale-insects are of several kinds. Probably the most useful 

 and the most abundant of these are the hymenopterous parasites, which live inside 

 the scale-insect. When they become adult they escape from the scale through a little 

 hole in the back, and such holes are an indication of their presence and beneficial 

 action. 



The great need in Grenada is for the planter and small grower alike to reaUse the 

 part played by scale-insects, to recognise their fungus parasites, and to know how to 

 look for signs of the insect parasites. This would seem to be a good line of work for 

 the Agricultural Department to carry on and it is certain that with better loiowledge 

 of these things the attitude toward black blight will be very much changed. 



<C177) G 



