106 



THE AGRICULTURAL NEWS. 



Makch 29, 1913. 



INSECT NOTES 



ROOT BORERS AND OTHER GRUBS 

 IN WEST INDIAN SOILS. 



The insects which attack crops underground are at the 

 jjresent time being recognized as of consideral'le importance, 

 and interest in these insects, especially in the larvae of 

 certain beetles, is being manifested in many parts of the world. 



It is the purpose of this series of articles to present 

 a review of the situation with regard to those beetle larvae 

 which are known in the West Indies to attack the under- 

 ground portions of the sugar-cane and other crop plants, with 

 observations on related species of which the adults are 

 known, whilst the habits of the larvae are unknown. 



The insects to be dealt with belong to the natural order 

 Coleoptera, and are placed in the two important groups, the 

 Khynchophora which includes the weevils, bill-bugs, and 

 ■snout beetles (in the West Indies certain of these are known 

 to many persons as lady-birds) and the Lamellicornia or 

 Scarabeidae, among which are included the ordinary hard- 

 ijacks. May beetles and many others. 



Information with regard to several of these insects has 

 heen presented from time to time in the publications of the 

 Imperial l)epartment of Agriculture and in other literature. 

 Reference to the more important of these will be found in 

 connexion with the account of each in the pre.sent article. 



EHVKCH0PHOE.\. 



The root borer of the sugar-cane {Diaprepes alhre- 

 riatus, L.). References: Agricultural i\>('s, Vols. X, p. 218, 

 XII, p. 58 — this latter is a review of a report on insect 

 pests in Barbados and refers to previou.s accounts and 

 gives a description of the occurrence of this pest and its egg- 

 laying habits in Barbados during 1909- 10, with figures of 

 adult and larva; Weit Indian Bvlletin. \'ol. IV, p 37, 

 contains an account by the Rev. N. B. Watson, FES., of 

 the life-history, with a figure of the larva; Ins'-rf Pests of 

 the Less'-r Antilles, p. 66, give.s a general account of the 

 pest, with figures of adult, larva, eggs, and nature of injury 

 to canes. 



Diaprepes aldreriatu.i occurs in Barbados, St. Lucia and 

 Dominica. It is only in Barbados, hcwever, that it is 

 recognized as a serious pest, where, in one section of the 

 island, it has for several years been the cause of sutticient 

 injury to ripening canes to bring about a very considerable 

 loss in the yield of sugar. 



Ill June 1900 and 1901, the root borer was rejiorted to be 

 attacking canes, and in the latter of these years it was discov- 

 ered by Mr. Maxwell-Lefroy, then Entomologist on the staff of 

 the Imperial Department of Agriculture, feeding on the roots 

 (■f the Ba.ha.inA gTsxsa {Cynodon dactylon). About this time 

 (1901-2) Mr. AVatson worked out the life-history of the 

 Diaprepes a/iOrevial us, beginning, in the first instance, with 

 grubs found feeding on the roots of sweet potato; the results 

 of this study were published in the Weft ludi'iu BuUetin, in 

 1903 (reference given above). At this time, however, the 

 insect was not considered a pest, and was thought to be of 

 interest only on account of occasional occurrences in connex- 

 ion with sugar-cane and sweet potatoes 



In 1903, a weevil grub believed to be the larva of 

 Oiapi'ej/es ahbreriatxts was recorded as causing injury to the 

 root of a cacao tree in St. Lucii. This apiiears to be the 

 only reported occurrence of this insect causing injury to crops 

 outside Barbados. Several references are made to the 

 <K-curience of Dia/nepes in Barbados in the next few years. 

 ' In 1909, the serious nature of attacks of this insect appear to 



have been realized for the first time, and from then to the 

 present season sugar-cane growing in a limited area in the 

 south-western portion of the island has suffered from repeated 

 attacks. '" 



During 1912, lime plants in pots at the Office of the 

 Imperial Department of Agriculture were killed as the result 

 of the feeding of root borer grubs on the cortex or outer 

 portion of the root, the injury being similar to that observed 

 in the case of the cacao tree in .St. Lucia, already mentioned 

 The grubs were probably in the mould with which the pots 

 were filled, and the lime roots were eaten in the absence of 

 other food. 



According to the re|)orts of the Barbados Local depart- 

 ment of Agriculture (1909-10, 1910-11 and 1911-12) 

 Diaprepes abl/reviatus has been f^und attacking canes ia 

 nearly all parts of the island, but the district already men- 

 tioned is the only locality where the attack has caused serious 

 loss. From the latest of these reports it a[)pears that, since 

 February 1912, the root borer has been the subject of 

 a systematic enquiry involving weekly field work. 



No parasite of this insecc has yet been found, and no 

 insecticide application has given any definite results. 



The suggested means of control are (a) rotation of 

 crop', (b) digging out of infested stools immediately after 

 reaping the canes, (c) collecting the adult beetles by hand. 

 In considering these measures the following points are to be- 

 taktn into account, (a) In planning a rotation of crops it 

 must be remembered that the root borer attacks sweet 

 potato, Indian and (Ittinea corn, and these would not be 

 suitable as crops for this purpose. The following, which are 

 not at all or only slightly attacked, might be found useful in 

 this connexion; cotton, cassava, eddoes, woolly pyrol anct 

 pigeon peas, (b) The results of the attacks of the root 

 borer are first noticed in nearly full-grown canes as these 

 begin to ripen, and a.-; this occurs at the beginning of the dry 

 season, the effect of root injury becomes apparent with the 

 increased demand on the root system for moisture. Canes 

 suffering from such an attack need to be reaped at once ia 

 order to avoid total loss of juice. At this time the majority 

 of the root borer grubs are in the base of the stools or in the 

 immediately adjoining soil. If the stools are allowed to 

 remain in the ground until they begin to dry, the grubs will 

 be found to have left them, in search of more suitable food 

 or for the purpose of burrowing deep into the soil, where 

 they lie dormant, awaiting more favourable conditions for 

 feeding, (c) The collecting of the adults gives promise of 

 being decidedly the most satisfactory method of controlling 

 this pest. From April to June, these weevils emerge, and 

 at that time can be collected from their hiding places 

 in the sheathing ba.ses of the leaves of cane and corn 

 plants or among the leaves of pigeon peas and other vege- 

 tation growing near the infested cane. On one estate 

 over 9,600 beetles weri collected in one week. To be really 

 effective this work of collecting ought to be most thoroughly 

 carried out on all estates in the infested area in order to 

 ensure satisfactory progress. 



The eggs of the root borer are laid in small clusters on 

 the leaves of the cane near the tips, where these have been 

 split by the action of the wind, two portions of the leaf being 

 stuck together by means of an adhesive substance deposited 

 by the egg-laying female beetle, in such a manner as to con- 

 ceal and protert the eggs. The newly hatched larvae drop to ■ 

 the ground and enter the soil. 



The injury to sugarcane caused by root borers is of 

 two kinds. The young borer grubs feed on the fibrous roots, 

 acting reallj at this time as root trimmers, whilst later, when 

 they have become more fully grown, they penetrate into the 



