362 



THE AGRICULTURAL NEWS. 



November 12, 1910. 





INSECT NOTES. 



SCALE INSECTS AND BLACK BLIGHT 



IN GRENADA. 



A paper on this subject, by Mr. G. (I. Auchinleck, B.Sc, 

 Superintendent of Agriculture, Grenada, was l>rought up for 

 discussion at a meeting of the Agricultural and Commercial 

 Society in that island, in September last. This is of consider- 

 able interest, as it summarizes much of the latest work that 

 has been done in Grenada, in this connexion, so that the fol- 

 lowing abstract of it is presented here. 



Consideration was given, first, to the way in which the 

 fungi obtain their food, and it was shown that this is depend- 

 ent upon whether they happen to be parasites or saprophytes; 

 in the former case they obtain nutriment directly from living 

 plants or animals: in the latter, they feed on dead matter. 

 The important point is that black blight {CajDiodium sp.) 

 belongs to the latter class of fungi. The cells of which it is 

 composed are able to absorb sugary liquids through their 

 ■walls and to use them in growing, and producing new cells. 

 In the special instance, the sugary liquid employed is obtain- 

 ed from animals. The question for consideration, then, has 

 to do with the way in which this material is provided. If 

 this matter is explained, valualile indications are obtained as 

 to the way in which lilack blight may be controlled. 



The sugary liquid is made up of the excretions of scale 

 in.sects and mealybugs. It is therefore to these animals that 

 attention must be given, when means are being devised for 

 combating the pest. Thirteen varieties of such insects have 

 been found in Grenada, so far, by Mr. Auchinleck, who 

 exhibited specimens of the most common kinds, as follows: 

 the mango scale, on mangos, honeysuckle, guavas, cashews 

 and imported [Jants; the line scale, on mangos and Strych- 

 nos; the star .scale, on the mango and oleander: Barber's 

 mealy Inig, on cacao; the black scale, on the 'almond', pigeon 

 peas and the star apple; and the red scale, on tamar- 

 inds. It was pointed out that the last scale pre.sents 

 a curious characteristic in that it is one of the few 

 that are commonly fonnd on the upper surface of leaves; the 

 circumstance is due to the fact that the leaflets of the tamarind 

 close together at night, and thus cause the upper surfaces to 

 be more adequately protected from dews than the lower ones. 



All the insects mentioned belong to the order of the 

 bugs, or Hemiptera (see Agricullnrnl Keies, Vol. YII, \>. 138). 

 These possess mouth parts suited for sucking, and the females 

 are often wingless, and thus cannot travel far. Some of them 

 are able to give out a sweet liquid in fairly large quantities, 

 and it is on this that the black blight lives as a saprophyte. 

 Among animals that make use of this liquid as food are ants, 

 ■which do not destroy the insects which produce it, as is .some- 

 times supposed, but seek the secretion for their own uses. 



These matters lead to the consideration of the methods 

 that may be employed for controlling black blight. They 

 may be divided into(l) artificial methods and (2) natura 



methods. Among the former are included the lopping of 

 infested trees; the entire removal of the leaves by plucking; 

 the treatment of trees with white lime: spraying with whale 

 oil soap, kerosene and various oily compounds; the fumigation 

 of trees: and the dusting of the plants with dry contact 

 poisons, such as sulphur or Paris green. These are not pre- 

 sented as lieing necessarily of a practical nature; they are 

 suggestive, and are forming the subject of experiments in 

 Grenada. The following table gives particulars of actual 

 trials that have been made: — 



Treatment. Xo of trees. Cost per tree. 



Removing loaves 1 6rf. 



Spraying with kerosene ... 6rf. 



Fumigating (shrulis) 4 9rf. 



Dusting with sulphur (four times) 2 \s. 



„ „ Paris green 4 2s. 



Spraying with whale oil (large trees) ... 10s. 



It should be stated that experiments in lopping and liming 

 were made with trees, when it was found, in some cases, that 

 the cost of treatment was entirely covered by the returns from 

 the sale of the cordwood obtained, even after the cost of the 

 lime- wash used had been deducted. 



An enumeration is made of the chief objections to the 

 artificial treatment of plants for black blight. They are: the 

 cost of materials and of labour: the unsightly appearance of 

 lopped trees; the loss of fruit resulting from heavy pruning; 

 and the destruction of beneficial insects, together with the 

 harmful ones. These objections have caused attention to be 

 turned to natural methods of control, and much work is lieing 

 done in this direction, particularly on the part of the Imperial 

 Department of Agriculture, especially as regards the study of 

 the natural parasites of scale insects. As a result of this 

 work, four fungi which destroy scale insects have been recog- 

 nized in the West Indies (see Af/ricidtiiral Kews, Vol. VIII, 

 pp. 299 and 411), and studies of the life-history of lady-birds 

 and minute insects, which are the enemies of scale insects, have 

 lieen made. As far as Grenada is concerned, two insect para- 

 sites of the scales have been found, namelj' lady-birds de.stroy- 

 ing the orange mussel scale, and a minute insect which is para- 

 sitic on the black scale: while of fungi, the red-headed fungus 

 {S^ykaerostinie coccophila) and the shield scale fungus have 

 been found. 



As the present article is more particularly concerned with 

 the insect enemies of the scale insects that are followed by 

 black blight, special attention will be given to these. The 

 lady-birds are predaceous; this means that they actually devour 

 the scale insect; and each kind of lady-bird generally feeds on 

 one kind of scale insect, only. That these useful insects do not 

 effect more in the reduction of the numbers of scales in Grenada 

 is proliably because they are themselves destroyed to a large 

 extent by their natural enemies, i'he insects that are parasitic 

 on scale insects are so minute as to be hardly visible to the 

 naked eye. It is the larvae of these that destroy the scale 

 insects, for their eggs are laid in the bodies of the 

 latter, and the larvae when hatched proceed to feed on the 

 scales. It has been recommended by Mr. H. A. Ballon, M.Sc, 

 Entomologist to the Department, that use of these flies may 

 be made by enclosing branches of trees, having infected scales 

 on them, with muslin bags, and then employing the tiies thus 

 collected to infest other scales. 



Mr. Auchinleck's interesting paper concludes with 

 descri])tions of the two fungi that have lieen found to occur 

 in Grenada, which are parasitic on the scale insect. In 

 connexion with these, reference may be made to the article 

 in the Aijriciilliiral Xi"':-! quoted above. 



