138 



THE AGRICULTURAL NEWS. 



April 26, 1913. 



INSECT NOTES 



ROOT BORERS AND OTHER GRUBS 



IN WEST INDIAN SOILS. 



In the last issue of the Agricultural Xews it was stated 

 that the continuation of the above notes in the I'resent 

 number would concern the family of beetles conimonlj* known 

 ■as hard backs. The subject is now continued as follows: — 



SCARABAEFDAE. 



The insects which are groui-ed t'geiher in this large 

 family are numerous and widely distributed. They are 

 ■divided, according to the habit of feeding, iii'u two groups: 

 the leaf chafer.s, .Melolonthidae; and the scavengers, Dynas- 

 tidae. At the present time only the leaf chafers would be 

 •taken into consideration but for the fact that certain of the 

 scavengers have at times functioned as pests of more or less 

 severity. This raises the question as to how far the feeding 

 "habits of so-called scavenger beetles are constant, and 

 -whether these insects may not all be able to subsist on 

 .living plant tissue when by reason of their unusual numbers, 

 or a lack of the preferred food, they are driven to it 



MELOLONTHIDAE. 



The brown hard back in Barbados {Phytaluf siiii/hi). 

 3leferences: Agricultural News, IX, p. 186, {Cydoctph- 

 <da); Report on Phytalm smithi, Arrow, in Mauritius, by 

 D. d'Emmerez de Cbarmoy, Mauriliu.=, 1912; Annual lieports 

 ^f the Local Department of Agriculture, Bdrbados. 



This insect is known to occur in Barbados and Mauritius. 



Of all the insects under consideration in the present 

 series of articles none has gained such world wide notoriety 

 as I'liytalus smithi. The enormous increase of this insect 

 ■within four years from the lime it was first known to exist 

 in Mauritius, to such an extent that it seemed to threaten 

 the e.xtinction of the sugar indu.stry of that island, amply 

 illustrates the danger attending the transportation of an 

 insect of this kind from its native environment into 

 a locality where its natural enemies do not exist. No other 

 insect of this series has formed the subject of such complete 

 scientific investigation as Pht/talus smii/ii, the results of 

 which are recorded in the report by de ( harmo}', referred 

 to above. 



Phytalus smithi exists in Barbados, being found in the 

 soil of cane field.^, gardens, and of plant tubs. The adult 

 insect is slightly longer and narrower than the ordinary 

 hard back, and the legs are more slender. 



In 1906 specimens of the adult beetle were forwarded 

 to the Imperial I)epartment of Agriculture with the infor- 

 mation that they had been found among the leaves of sugar- 

 cane plants on which they had apparently been feeding. 



In May J 910, the beetle occurred in considerable 

 •numbers in two localities near P.ric'getown, Barbados, where 

 from .500 to 600 were captured during one night on rcses 

 and other garden plants. (See Agricnlliiral Xews, Vol. IX, 

 p. 180, wliere this insect is referred to as C i/docephala sp.) 

 At this time the larvae of the beetle were not known, being 

 «onfused with those of the common hard back {LIgyrns 

 iumiilosus), which will be described later. 



In Watson"s paper on the root borer of the sugar-cane 

 ■^see reference under root borer above), and in one by H. A. 

 iallou, entitled Review of Insect Pests Infesting the Sugar- 

 •cane ( HV>' Indian Bulletin, Vol. VI, p. .37). grubs of the 

 liard back (/,. tumulosiis) are mentioned, in both of which 

 the reference probably failed to distinguish between that 

 -«pecies and Phytalus smithi. 



At the present time the brown hard back is known to 

 occur in some numbers in the same sugar cane fields where 

 Diajirnpes <ihl:rei ialus (loc cit.) is a serious pest. Phytalus, 

 however, is not considered to cau.se any appreciable injur}' ia 

 the.se fields. This condition is due largely, perhaps entirely, 

 to the fact that the grubs of Phytalus are extensively para- 

 sitiz.erl, and by that means ett'ectually held in che^k. The 

 paia.-itic insect is a small black wasp, Tiphi'i parallela, 

 iSmiiJi, of the hymenopterous famdy Scoliidae. 



It is probible that very little would be known of this 

 brown hard back and its parasite in Barbados even at tha 

 pre.seoc lime, but for the fact that the grubs of this insect 

 occur in the same fields with the root borer. The root borer 

 has been the subject of regu'ar investigation extending over 

 a considerable period, and during this study obrervationa 

 on Phytalus have been made incidentally. 



The extreme abundance of Phytalus in Mauritius may 

 be indicated by merely staling the numbers of the beetles 

 that were captured by hand collection and destroyed. The 

 total catch for the season, August 1911 to April 1912 inclu- 

 sive, was over 20 millions, whilst the largest catch for any one 

 day (or night) was nearly 3 millions. The weight of these 26 

 millions of beetles is stated to have been about 20 long tons. 



The method adopted for control, which gives promise of 

 greatest etHciency, is that of collecting by hand. The canes 

 in the case of badly infested fields are removed and the 

 ground is cleared of trash. At the time when the adults are 

 emerging, small leafy branches of trees are stuck into the 

 soil, and on these the newly emerged beetles congregate. 

 •The collections are made at night by labourers, who carry 

 small lights and collect the insects in suitable vessels. 



Phytalus :<7iutki is a root trimmer rather than a root 

 borer. The larvae feed on small roots and are often to be 

 found in greatest numbers in the middle of the banks, rather 

 than in the cane holes. 



At the present time Phytalus smithi appears to be known 

 only in Barbados and Mauritius. (I rowing sugar-cane plants 

 in soil have been imported into Mauritius from Barbados, 

 and it may be that this insect pest was introduced in the soil 

 with the canes. Since there is sufficient likelihood of this 

 hanpening, canes ought not to be transported in this manner 

 from one countrj- to another. 



The small brown hard back in St Kilts {Lachnosterna 

 patrudis). Reference: AyricuUuial Kewa, XI, p. 29S. 



This insect is known to occur in St. Kitts and Domiuica. 

 It was found in .St. Kilts by the Entomologist on the Staflf 

 of the Imperial Department of Agriculture during a visit to 

 that island, in 1912. Although it occurred in great numbers 

 in the soil of the cane fields in one locality, and in smaller 

 numbers in others, and perhaps to a limited extent in all the 

 canegrowing sections of the island, none of the planters 

 seemed to recognize it when specimens were .shown to them, 

 or even to know of its previous existence. As an explanation 

 of this condition it may be stated that probably the adults 

 are not at all attracted to light, and that the larvae when 

 seen in the soil arc mistaken for small larvae of the ordinary 

 hard back, Li'/yrus tiimuloxus, as was the case for many years 

 in I'.arbados with Phytalus smithi and its larva. The adult 

 of Lachnosterna patmelis has, so far, only been found in 

 tlie soil in cane fields and other cultivated lands, and if 

 observed in such situations might also be considered by 

 planters as very small, immature specimens of the commDn 

 hard back. 



The larv.ae of L. patmelis are probably root trimmers in 

 their feeding, i.e. they feed on small fibrous roots of sugar- 

 cane and other plants growing in the soil inhabited by them. 



