74 



THE AGRICULTURAL NEWfc. 



Makch 10, 1917 



INSECT NOTES. 



THE SCARABEE AND OTHER PESTS 

 OF THE SWEET POTATO. 



In view of the present food situation, special efforts are 

 being made to plant various crops Laving a distinct food 

 value. Among these will be the sweet potato, which is one 

 of the commonest articles of food in these islands. It is 

 advisable at the present time, therefore, to bring to the 

 attention of planters and peasant proprietors some of the 

 more important insects which are liable to attack this crop, 

 and to suggest measures for iheir control. 



Such insect pests as the scarabee or Jacobs, (Eitsce^iex 

 [t'ryptorhynchus] hatatae), the sweet potato moth {Protoparce 

 i-inyulata, ¥.), red spider (Tetranyehus telarius), etc , are well 

 known to all growers of sweet potatoes and their importance 

 is fully realized, often only after the damage has been done. 



In these islands the sweet jiotato Is attacked by various 

 pests, most of which get their food from the leaves of this 

 plant and can therefore be controlled by the use of stomach 

 poisons or contact insecticidis- 



The scarabee, on the oiher hand, cannot be controlled in 

 the ordinary way by poisoiis, since it spends most of its life 

 underground, inside the potato tubers or in the plant stem. 

 It must, therefore, be checked by some other means, and 

 the most practical method known at present seems to 

 be that cf starving it out by systematically depriving 

 it of its food-plant. It. is known that the scarabee 

 generally becomes a pest where sweet potatoes are grown 

 for two years or more in the same fields, but that its ravages 

 can be reduced by a judicious rotation of crops. Rotation of 

 crops alone, however, is not stringent enough, and the food 

 blockade to be effective, must be drawn still tighter. This 

 can be done by planting potato >lips known to be free from 

 scarabee in land where no potatoes have grown for some time, 

 and by keeping this up season after sea.son accompanied at 

 all times by clean cultivation. 



In the first place, choose a plot of land where there have 

 been no potatoes for several seasons, and plant it with 

 'pickings' or small pieces of roots taken from fields known 

 to be free from the scarabee. These roots should first be 

 carefully examined for any signs of the beetle, and all roots 

 showing the slightest traces of infestation .--hould be destroyed. 



This lan.1 can be used as a nursery plot, and as soon as 

 the plants are large enough, take cuttings and plant them in 

 uninfested land. In those islands where the E.xperiment 

 Station does not make a practice of growing and distributing 

 sweet potato cuttings, the establishment of a nursery and the 

 growing of plants for distribution are usually done by 

 e.state managers, who thus can insure the peasant proprietors 

 getting a supply of clean plants. It then remains for the 

 peasant growers themselves to see to it that these clean 

 cuttings are set out in land where the scarabee has not been 

 present for several years, and as far removed as possible from 

 infestation by this insect. 



The nursery plot referred to above should not be kept 

 up for more than si.x to eight months, as after that time there 

 is a possibility of the plants becoming infested with scarabee. 

 At the end of this period the lann used for the nursery can 

 be forked over, and, if free from scarabee, can be used again 

 for the same purpose. All land badly infested with scarabee 

 can be planted in other crops, but care should be taken to clean 

 the land as thoroughly as possible after gathering in the potato 

 crop. All infested material, .such as roots, vines, etc., should 

 be buried with lime. 



The following may be given as an e.xample of the 

 practical value of using clean plants in the control of the 

 scarabee or Jacobs. - ' 



It has for some years been the practice at the Experiment 

 Station in Antigua to grow different varieties I'f sweet 

 potatoes. In this way the best varieties have been obtained, 

 and the.se have been gradually distributed to growers 

 throughout theisland. who have e.xtensively availed themselves 

 of these oiiportunities of obtaining good cuttings. In the 

 course of this work an area free from the scarabee has been 

 has been effected, though perhaps this was not one of the 

 gradually obtained, and the control of this pest at the St ition 

 original objects of the experiments. Within the last few 

 years there has been a noticeable decrease of Jacobs in Antigua, 

 and there is no doubt that the distribution of clean plants 

 throughoutthe island, and the subsequent care in growing them 

 have largely contributed to this decrea.se. This does not 

 mean, however, that this pest is permanently controlled in 

 Antigua, but that it has been reduced to the position where it 

 can be kept in check in the future by a continuous employment 

 of the same good methods. We have every reason to believe 

 that these methods will be carried on with this further object 

 in view, now that its importance has been realized. 



The control of the scarabee or Jacobs has often been 

 mentioned in the publications of the Imperial Department, 

 but it has been given again at the .same length in order 

 to emphasize its importance at the present time and 

 encourage growers to more persistent efforts to get rid of this 

 pest. 



While the scarabee is by far the most injurious pe.st of 

 sweet potatoes, there are others which attack this crop from 

 time to time, as is shown by the annual seports from the 

 different islands. 



Severe attacks of the caterpillar of the sweet potato moth 

 (I'rotoparce cingulaUi, F. ) sometimes result in the complete 

 stripping of the vines over large areas; but fortunately, these 

 attacks are comparatively rare, since this pest is usually 

 controlled by its natural enemies, chiefly parasites This 

 and other caterpillars, such as those of St/iepta hdritalU, Wlk., 

 attacking the leaves, can be killed by the use of arsenical 

 poisons, such as Paris green, or arsenate of lead. The latter 

 is preferable, as it is less likely to damage the leaves. 



Several species of thrips sometimes occur on the under- 

 side of the leaves, ])erhaps the commonest being Eutluips 

 insularis, Franklin. The red spider mite {I'etrani/c/ius telarius) 

 is also found on the underside of the leaves, and, as is also the 

 case with thrips, is more abundant in dry weather, and 

 especially in dry districts. Both thrips and 'red spider' can 

 be controlled by dusting on a mixture of sulphur and lime, 

 care being taken to reach these pests on the underside of the 

 leaves. 



Flea- beetles sometimes cause slight damage to the 

 leaves of sweet potatoes, and grubs of the sugar-cane root 

 borer and of the hard back occasionally attack the roots. 



The sweet potato weevil (Cyhu formicarius) is 

 a pest in Jamaica, llritish Guiana, Cuba, the Bahamas, 

 and the Southern United States, but .so far is not known 

 to occur in the Lesser Antilles. Its damage to the 

 sweet potato is somewhat similar to that of the scarabee, 

 and the remedies given for the scarabee can be applied to the 

 weevil. 



Mention may be made here of the slug ( Veronicella 

 occidentalis) which attacks many plants, including the sweet 

 potato, when these are first .set out, and sometimes does 

 considerable damage. It is known in Dominica as the 'palute' 

 and is called the 'leather jacket' in St. Lucia. At present 

 the chief method of control seems to be collecting the slugs 

 by skewering them un sharp-pointed stakes or iron rods. 

 Some estates have tried the keeping of ducks to control this 

 pest, wdth good results. 



J.C.H. 



