Vol. XII. No. 288. 



THE AGRICULTURAL NEWS. 



lor. 



tions of the cane. A related insect nf similar habit has lieen 

 received recently from Barbuda. Thi? is Diicinatus f'ar/iatus, 

 a .smooth, shiny-black beetle ab 'Ut the size of L. tu/nitlo.<uf, 

 which is known to occur in Antigua, Ilarbuda and St. Kitts. 



The principal natural enemy ol trie common hard back 

 is one of the burrowing wasp,* of the family Scoliidae, 

 Dielis dorsalta, which occurs in Barbados, and in other 

 islands. Thi.s wasp is related to the parasite of the brown 

 bard bick (Phptalns smilhi) and that of the fiddler beetle 

 {Klis atrata), which Lave already been mentioned. 



DidU dorml'i is an insect which exhibits marked 

 colour differences in the two sexes, the dor-al surface of the 

 abdomen of the female bearing large patches of a reddish 

 colour, whilst the male shows a bright golden yellow in the 

 same positions. 



The banana root grub of liominica and St. Lucia 

 (Tomarus /jifu/jetculalus). References: Agiicnliu>al yen'S, 

 Vol. IT, p. 264; Insert Pests of the Laser Antilles 



The adult of this species is a Moderately large beetle of 

 the hard back type, measuring about 1 inch in length and 

 j;: inch in width. The grub is probably normally a scav- 

 enger in its feeding habits, but on several occasions it has 

 been the cause of serious injury to bananas, especially newly 

 planted suckers, by destroying young roots and tunnelling 

 into the soft base of the sucker. In a few instances the 

 adult beetle has been found tunnelling into the base of the 

 banana plant itself. Plantains, tannia.s, yams, and the roots 

 of young cacao plants are also attacked. 



In the ne.\t issue of the Aijricultural JVeics the subject 

 will be continued with regard to the Rhinoceros beetles and 

 other species of the sub-family Dynastidae that are known 

 to inflict damatje upon cultivated plants in the Lesser 

 Antilles. An interesting and important account will also 

 loe given concerning the natural enemies of these grubs. 



SUBSOIL WATER. 

 II. 



In Part I of this article by Mr. H. A. Tempauy, 

 B.Sc, which appeared in the last issue of the Agricul- 

 tural Ncu-s, considerations uf a general nature were 

 dealt with in regard to the e.xistence and movements 

 of underground or subsoil water: in the following 

 account will be considered some aspects of the question 

 having special reference to West Indian condition.s. 



Each island in the West Indies constitutes an entirely 

 sepirate and distinct subsoil water system in which the 

 reserve of contained moisture is continuously finding its 

 way to the sea. The majority of the islands are wholly or 

 partially volcanic in origin, and in those of smaller size, at 

 any rate, the conditions most usually met with consist of 

 a central peak or mountain range rising to a height of from 

 two to four thousand feet above sea-level, and possessing 

 numerous minor lateral spurs and escarpements .sloping down 

 more or less evenly to sea-level at the coast. The central 

 portions of these mountain ranges are usually composed of 

 compact impervious volcanic rock, whilst the mountain 

 .'.lopes and valley bottoms are generally covered to a con- 

 siderable depth with volcanic detritus and alluvium of 

 a character more or less permeable. 



Under conditions such as these, tlje rainfall is naturally 



greatest in the more mountainous centra] region, and dimin- 

 ishes as the coast is approached; the cultivated lands, on 

 the other hand, are in ni'jst cases confined to the compara- 

 tively level tracts of the coastal region, the mountainou* 

 centre being left largely in a state of nature 



In the case of certain islands, notably Trinidad, 

 Barbados, Antigua, liarbuda and St. Croix, a somewhat 

 different state is presented, volcanic formations being there 

 replaced wholly or in part by more or less permeable sedi- 

 mentary strata, the well marked central mountainous region 

 giving place, to a considerable extent, to undulating ranges 

 of hills of lower elevation. 



In all cases, however, each '"land constitutes a system 

 in which subsoil water continually drifts down to the .sea 

 from the central region, the gentral character and rate of the 

 flow being governed by local physical conditions in each case, 

 but being naturally least during dry periods. 



In general, the steeper the slopes the more rapid will 

 be the seepage How. In those islands possessing central 

 mountain chains the movement of subsoil water will show 

 very marked features. In districts such as these it is usual 

 to find an abundance of rivers and watercour.ses which owe- 

 any permanent flow that they possess during drier periods 

 to seepage of subsoil water along definite channels through- 

 out their length. In rainy weather they serve to carry off 

 the surface or storm water. 



The conditions prevailing in the central mountain region 

 will ver}' considerably afitct the character of the seepage flow 

 at lower levels. Thus, a heav}- clothing of forest on the 

 mountain sides will have a marked effect in this direction. 



The powers of forest to modify the effect of rainfall are 

 well known; a large proportion of the rain which falls in 

 forest clad region, is held up in the water-retaining surface 

 layers, whereas if the land surface had been denuded of 

 trees, this would have run off as storm water. 



The moisture held up in this way becomes subsequently 

 available for maintaining the supply of .subsoil water; and 

 when an adequate forest growth clothes the sides of the 

 central mountain region in West Indian islands, it must go 

 far to ensure a regular and even supply of subsoil water from 

 the upper to the lower levels. 



In the absence of fuch a forest clothing, a far larger 

 proportion of the rain which falls will pass off as storm water, 

 and in consequence the supply of moisture available to 

 maintain the flow of subsoil water in the dry months will be 

 greatly lessened. As a result, the lower cultivated lands may, 

 under these conditions, be subject to very con.'iderable 

 fluctuations in the level of the w-ater-table, and this may 

 adversely affect crops growing thereon. 



The effect of fluctuations of this description will tend to 

 be most marked in cases where the cultivated lands slope 

 evenly up from the sea to the bases of the mount lins and are 

 underlain by subsoils composed of volcanic detritus which 

 attain a considerable depth. Under these conditions, the 

 subsoil flow will be rapid in rainy weather, but when 

 dry weather supervenes the level of the subsoil water table 

 may drop below the reach of the growing plants. 



On the other hand, the effect will tend to be less marked 

 in the case of the broad alluvial valleys and plains rising very 

 gently from the .sea-level and enclosed by high hills, such as 

 constitute an important part of the cultivated lands of some 

 i.slands. Here the seepage flow will be slower as the height 

 above the sea is les.s, and the risk of the complete cutting off 

 of supplies of underground water during drought will be 

 minimized. This constitutes one of the reasons why bottom 

 levels are often preferred for purposes of cultivation, espe- 

 cially in dry localities. 



