362 



THE AGRICULTURAL NEWS. 



November 16, 1918. 



INSECT NOTES. 



REPORT* ON CACAO THRIPS (HELIO- 

 THRIPS RUBROCINCTUS) IN 

 GRENADA IN 1917. 



This report contains an account by Mr. F. W. L'rich of 

 a visit in 1917 to Grenada which was made at the request 

 of the Government of that island. 



The title cf the report is 'Thrip?, Black Ants, and other 

 Insect Pests of Cacao in Grenada, and a note on Coco-nut 

 Disease. IJeport presented to the Government of Grenada by 

 F. W. l'rich, Entomologist, Board of Agriculture, Trinidad.' 



Mr. I'rich's occurrad during the period August 18 

 to September 25, 1917. It appears to have resulted from 

 a somewhat more extensive occurrence than usual of thrips 

 ( Helii'thrips rubrocinctus) during the latter part of the year 

 1916 which caused members of the Agricultural and Com- 

 mercial Society to view the situation with alarm. The 

 attention of ihe Government was directed to this serious 

 menace to the staple industry of the island, and in a reso- 

 lution dated November 29, 1916, the hope was expressed 

 that Mr. Urich's services might be obtained for a few weeks 

 at as early a date as possible 



During his visit Mr. Urich inspected cacao in most 

 parts of the island, and gave spraying demonstrations in 

 several districts. 



As far as the information regarding thrips is concerned, 

 the report contains nothing new. Mr. Uritb found that thrips 

 probably occurs on every cacao estate, but that its serious 

 attacks appear to be confined to the .southern and western 

 parts of the island. 



With regard to the .status of thrips in (irenada, Mr. 

 Urich found himself at variance with the frequently expressed 

 opinion of the officers of the Imperial 1 )epartment of Agricul- 

 ture. He states that 'the position of thrips is that of a first clas.s 

 primary pest of cocao, which demands serious and united 

 attention on the part of all cacao planters, especially those in 

 the western and southern parts of.jhe island. While good 

 cultural methods will help to keep down the numbers of 

 thrips, this is not enough and regular spraying must be 

 resorted to. It is the only sure "way of keeping it in bounds 

 and preventing it affecting the cacao crop.'.' 



I 'rider the heading 'Uecommendatioiis', the following 

 statements occur: 'if thrips are to be kept under in the island a 

 univer.sal campaign i.s necessary, and every {danter and peasant 

 proprietor should endeavour tn spray his cacao trees for thrips 

 at the right time. . . If .'•rpraying is not taken up universally, 

 then the Government may coii.sider the advisability of intro. 

 dneingasuch measures as it sees fit to make the control of 

 thrips by spraying compulsory for all. Stress is put on 

 spraying, as it is the writer's opinion that although thrips can 

 be controlled to a certain extent by cultural mothod.s, it is 

 absolutely necessary that it be sprayed also.' 



In 1900 Mr. Maxwell- Lefroy, the l"ntoniologist(in the Stall 

 of the Imperial Department >A Agriculture, considered thrips 

 a possible enemy to cacao rather than an actual jiest. He 

 recommer. led spraying as an emergency measure, and advo- 

 cated good cultural methods for keeping the health and 

 vigour iif tlje cacao trees at the highest level, and the thrips 

 at the lowes^. For the past seventeen years this has been the 

 steadfast policy of the Imperial Dspartraent of Agriculture, 

 as is shown by all the publi-^hed accounts of cacao thrips, 

 and all references to this inject in connexion with its occa- 

 sional outbreaks. 



In 1915 the writer of this review went further, and 

 stated that outbreaks of thrips indicate that something is 

 wrong with the attacked trees, and that thrips, in Grenada 

 at least, ought to be considered a useful insect, because its 

 presence is a certain indication that the trees are suffering 

 from some untoward condition. (Vide Aqricultural ."\rrcf 

 Vol. .\IV, p. .-514.) 



The factors which may affect cacao trees, anJ are observed 

 to result in enormous increase of thiips. are root disease, 

 unfavourable soil conditions, including shallow, infertile soil, 

 lack of drainage or impropar drainage, lack of organic matter 

 in soil, lack of proper shade for plants and soil, exposure to 

 wind, or any other cultural or environmental condition which 

 affects the health of the tree. 



Cultural treatment of cacao plantations for the 

 control of thrips is fundniiental, and may reasonably be 

 expected to reduce the numbers of this insect to such a point 

 that spraying will only be necessary under exceptional 

 circuuLstances, and at widely separated times. As an insect, 

 thrips is pre.sent on nearly every cacao tree in Grenada at 

 almost all times, and it also occurs on several other trees: 

 but it is only at certain times in certain districts, or even on 

 certain trees, that outbreaks occur, and the same trees and 

 the same localities are the sites nf their development year 

 after year. 



Once the outbreak has fairly started, however, the 

 insect, favoured by the condition of the trees in the thrips 

 'patches' or 'areas' where it ni.ay be said to be endemic, 

 breeds to numbers beyond the capacity of these trees to " 

 support, and they may e.xtend to the surrounding trees, and 

 the more general occurrences or epidemics take place. 



There are in Grenada nuny areas in which thrips 

 appear never to have occurred to such an e.\tent as to 

 cause appreciable loss of crop or apparent injury to the tree.', 

 although it appears that these trees at most times carry 

 a few thrips, and are in some cases in close .juxtaposition 

 to areas which have been severely attacked. 



In the report tinder consideration it is stated that 'the 

 pest is not widespread yet, but as it may become so it is 

 necessary that it .should be controlled before it gets o'.U of 

 hand.' 



In 1900 thrips jccurred in all parts of the island, even a.s 

 in 1917, and although during that period of seventeen years 

 no continued, systematic spraying for the control of thrips has 

 been practised f ir any length of time, Mr. Urich states that 

 the pest is not 'widespread yet.' During the same period the 

 exports of cacao hive ri.sen from .');3,000 bags in 1900 to 

 77,000 bags in 1917. The crops for tbe jears 1916 and 1917 

 were the largest in the history of the cacao industry in 

 Grenada. 



The following figures show the amounts of cacao 

 exported from ( henada in each year from 1900 to 1917: — 

 Year. Xo. of bags. Year. No. of bags, 



The cacao industry lias made this progress over a long 

 period of years without any remedial measures being applied 

 other than the improvement of cultivation, which has natur- 

 ally resulted from extended experience and increased know- 



