170 



THE AGRICULTURAL NEWS. 



May 28, 1910. 



INSECT NOTES. 



THE BLACK SCALE AND ITS PARASITE. 



With the re-establishment of the cotton industry in the 

 West Indies during the past seven or eight years, has come 

 a tremendous increase in the numbers of certain pests, which 

 previously for many years were so few as to be insignificant, 

 or were entin.-ly unknown. 



In 1903, the cotton worm made its appearance in enor- 

 mous numbers in nearly all, the cotton-growing islands; in the 

 same year the leaf-blister liiite caused much loss to cotton 

 growers in Montserrat, and it soon became known in all the 

 other islands of the Lesser Antilles, except Barbados. 



During the following year, cotton growers in Barbados 

 suffered much loss from the attacks of the black, or Hibiscus, 

 scale (Leconiiim nii/rinii), and these continued each year 

 until 1907-8. This .same scale insect has attacked cotton 

 in other islands, but it does not seem to have been at any 

 time, in any other place, such a severe pest as it was in 

 Barbados between the beginning of 1904 and the end of 

 1907. 



Black scale has been a serious pest most often when 

 old infested cotton has been allowed to remain standing 

 up to, and after, the time for planting the new crop. 

 A case in point was noted in an earlier number of the 

 Ar/rindtiira/ Xews (see Vol. V, p. 42). An account was 

 given of the loss occasioned on an estate in Barbados where 

 old cotton plants were left standing until the young ones 

 were several weeks old. There were two fields of this young 

 cotton, one of which, directly to leeward of the old field, was 

 a total loss; the other, across the wind from it, was nearly 

 in the same case. 



Many other instances have been ob.served where young 

 cotton has been infested directly from the old plants left 

 from the previous season's crop. In other cases, it has not 

 been easy to determine exactly where the infestation had its 

 origin. The black scale, however, has a long list of food 

 plants some of which might easily serve as a starting point 

 in the attack on any field. 



When the black scale first became a pest, it was noticed 

 tliat inany of the insects had the characteristic round holes in 

 the back which indicated that the parasite had emerged from 

 them. Several attempts to obtain this parasite were made, and 

 though the pupal stage was often found, no adults were 

 procured until August 1907. At this time, Officers of the 

 Department visited several estates where cotton frt)m the 

 previous season's crop was still standing. The owner of one 

 of these stated that the black scale, though present in con- 

 siderable numbers, was not a serious pest on that estate. A 

 .short .search revealed the presence of a parasite, and it was 

 found that a large proportion of the scales were parasiti;:ed. 

 Immediately after this, the parasite was found in all parts of 

 the island, and the black scale, which had been counted by 

 many planters as the worst pest of cotton, began to be 

 less serious. The parasite, which was named through the 

 kindness of Dr. L. O. Howard, by Mr. .1. C. Crawford of the 

 I '. S. Department of Agricidture, was found to be new to 

 science. Not only was it a new .species, but it represented 

 also a new genus. It is likely that this parasite {Zaloiihothrix 

 inirtim) has been the controlling influence in the spread of 

 the black scale {Leca/iium niiirum) for a long time, for the 

 scale insect has been present on certain plants and has not 

 often become such a serious pest as to attract more than 

 passing notice, until the great increase of the area planted 

 with cotton provided an abundant supply "f food and favour- 

 able conditions for its rapid development. 



On a certain estate in Barbados, the old cotton remain- 

 ing in the field in August 1907 was literally covered with 

 black scale, and weeds of .several kinds were thickly infested. 

 This old cotton was removed soon after, but the succeeding crop 

 was badly infested from these fields. The parasite was found 

 in this field about this time. In April 1908, fields on this 

 estate were examined, and it was found that, although the 

 attack of black scale had been very severe, and many plants 

 were dead, apparently as a result of this attack, the numbers 

 of the scale were much less, and a very large proportion of 

 those remaining were parasitized. 



At the pre.sent time (May 1910) there are fields of old 

 cotton on this same estate in which there are no black scales, 

 and this is true of many similar fields in other parts of the 

 island. The black scale, which only three years ago was 

 counted the worst pest of cotton in Barbados, seems to be no 

 longer a pest. 



All attempts to control this insect by spraying were 

 found to be rather expensive and unsatisfactory, but the 

 natural method of control has been successful. This consists 

 of the removal of all old cotton before planting new fields in 

 the same vicinity; the piling of all such cotton for a few days 

 to allow for the escape of the parasites then in the scales; 

 and the introduction of them into fields ' infected with 

 it. The introduction of the parasites is a very simple 

 matter and consists in collecting scale-infested twigs from 

 fields where parasites are known to be present, and tying 

 them to the branches of the cotton plants, where the 

 infestation is beginning. 



Zaiopliothrix mirum is widely distributed throughout 

 the West Indies, and by its action has probably prevented the 

 black scale from becoming a pest in those islands. The greater 

 amount of uncultivated land and the smaller proportionate 

 acreage of cotton provided conditions more natural than 

 those which existed in Barbados, and the pest never had the 

 opportunity to develop, away from its parasite, to the same 

 extent. The introduction of the parasite into fields infested with 

 black scale was carried out on several estates by Mr. .J. R. 

 Bovell, Superintendent of Agriculture, Barbados, with such 

 good results that this is now recommended as a matter 

 of general estate practice. In the same way that planters 

 apply Paris green when the cotton worm appears, so should 

 they introduce parasites when black scale does so. On every 

 estate, a sharp lookout should be kept for the first appearance 

 of black scale, just as a watch is maintained diligently for 

 the cotton worm, and twigs from sonie plant, such as cotton 

 or Hibiscus, on which black scale occurs, and is parasitized, 

 should be collected and distributed in the newly infested field. 



In addition to the parasite of the black scale, which is 

 referred to in the preceding article on this page, there are 

 other beneficial insects which are worthy of mention atthis time. 



The parasite of the white scale (C/iioiia-yis minor) has 

 been known for some time, and it exercises such good con- 

 trol that the white scale rarely becomes a serious pest on 

 cotton, though it is generally present toward the end of the 

 season. Several parasites of the cotton worm are known to 

 occur in the West Indies, and it is probably largely due to 

 the action of these beneficial insects that there have been no 

 attacks of this pest in these islands during the season 

 just past. Among these parasites may be mentioned: 

 Tric/ioi/ra/iima pretiosa, a parasite of the egg, and Chains 

 annidatiix and Sarcliophwja Irivittnta, which attack larvae 

 and pupae. The predaceous insects have also probably been 

 of great service in this matter, and among the chief of these 

 may be mentioned the species of Polistcs, including Jack 

 Spaniards, wild bees and cow bees. 



