282 



THE AGRICULTURAL NEWS. 



Skptembee 7, 1918. 



INSECT NOTES. 



INSECT PESTS IN ST. LUCIA, 1917-18- 



The annual report on the working of the Agricultural 

 Department, St. Lucia, for the year 1917-18, which is 

 reviewed on p. "285 of this issue, contains a section on Insect 

 Pests and Fungus Diseases. The portion dealing with insect 

 pests, which is reviewed herewith, consists of a report by 

 Dr. J. C. Hutson, acting Entomologist, Imperial Department 

 of Agriculture, on the Black Weevil Borer of Banana, with 

 notes on other insects; and notes by the Agricultural Super- 

 intendent on a few miscellaneous insects. 



Dr. Hutson visited Sr. Lucia in July 1917 for the 

 purpose of invesuj.'niing ihe habits of the black weevil borer 

 of hiMAwa. (Cos»:i>p<)/ift's soniidiis). Bananas and plantain.s 

 are not grown in St. Lucia as definite crops, but they are to 

 be foucd in small clumps or patche.s all over the island, and 

 these plants are used as wind belts and temporary shade 

 in young cultivations of cacao. Dr. Hutson's investigations 

 were mostly carried on in connexion with scattered clumps 

 of bananas and plantains in the plots of peasant proprietors 

 on the slopes of the Morne, above Castries. 



Several different varieties of banana are grown in St. 

 Lucia, such as the plantain, the Makabou (the bluggoe of 

 Grenada), the Gros Michel, and the fig banana. 



The black weevil was found wherever these different 

 varieties were examined, and it is probable that the black 

 weevil borer occurs wherever the banana is grown in St. 

 Lucia. This insect was found to attack all the varieties of 

 banana mentioned above, but it seems to prefer the plantain, 

 with the result that the plantain is going out of cultivation 

 and the Makabou taking its place. 



The borer was not found in young banana clumps which 

 had been recently planted. All the material for investigation 

 was obtained froui ilje older stools, many of which were in an 

 abandoned and neglected condition, and in stools which had 

 been planted within two or three years and had not suffered 

 very much from the attacks of the borer. An interesting 

 description is given of a typical neglected and overgrown 

 stool of plantains, infested with weevil. A clomp of this 

 type is made up of a number of shoots of different ages all 

 crowded together very closely just as they originally grew, no 

 attempt having been made to prune out any suckers, except 

 such as had been taken for planting new land. The original 

 paren; bulb, or at any rate the oldest bulb in the stool, was 

 genernily found to be in a more or less decaying condition, 

 and riiidled through and through by the tunnels of the black 

 weevil grubs. This stump, however, was still fairly firm and 

 had not broken up at all. In do instance were any weevil 

 grubs found in any old stumps of this description. 



Next in point of age there might be .some two or three 

 daughter stems which had already borne, and had been cut 

 down leaving, in some case?, a stump 2 or ■'> feet high. 

 Sometimes these stumps had fallen over, while those that 

 remained standing could easily be pushed over. The under- 

 ground bulbs were usually pretty well riddled with tunnels 

 and discoloured but in no way disintegrated. Occa.sionally a 

 few larger grubs anil pupae were still to be found in the tun- 

 nels. Then, next in succession there might be some two or three 

 stems in the car y fruiting stage, ranging from stems from 

 which the flowering shoot had not yet emerged to those which 

 were bearing a small bunch of ftuit. These plants were still, 

 as a rule, in a fairly vigorous condition, and cou'd very seldom 

 be pushed over. The bulbs when dug up and examined were 

 usually found to be attacked by the grubs of the black 



weevil in all stages of development, and .sometimes pupae or 

 newly issued weevils were to be seen in their cells. 



Of the young suckers of ditferent sizes which may be 

 seen pushing up all over the clumps, the larger ones are 

 sometimes slightly attacked on ihe side nearest the parent 

 bulb but a cross section through the sucker at the point of 

 attack showed that the grubs had only barely cut into the 

 outer surface of the sucker, ai d then probably turned back 

 into the parent bulb again. 



These young suckers were examined for the tunnels of 

 newly hatched larvae,but instances of these could net be found, 

 so that it seems likely that the weevils are not attracted to 

 young suckers under St. Lucia conditions. Several newly 

 planted suckers were examined for grubs of the weevil 

 but in no instance were any grubs found in such plants. 

 It would appear from the foregoing that there is a period 

 during the life of the banana plant when it is most attractive 

 to the egg-laying weevil. This period appears to be, ia 

 St. Lucia, the time when the flower and fruit are being 

 developed. 



The weevil begins to lay its eggs in the plant about the 

 time that the flowering shoot is in the process of developing 

 with the bulb as a reservoir of food for the future bunch, or 

 even at somt time previous to the formation of the shoot, 

 and that it continues to breed in the bulb till the tissue has 

 begun to deteriorate. The process of deterioration is prob- 

 ably hastened by disea.se, and by the attacks of the grubs 

 themselves. 



During this period of infestation the weevil appears tn 

 pass through several generations, the bulb being more and 

 more riddled by each successive generation. 



In the maiter of control, the need of good cultivation 

 is strongly emphasized. It should be the aim of every 

 banana jirower to keep his plants in as healthy a condition 

 as possible all the time, so that the bunches may be fully 

 developed before the attacks of weevil grubs can reduce the 

 food supply stored up in the bulb and thus indirectly imoair 

 the size of the bunch of fruit. 



The disposal of the stem and the infested bulb after the 

 bunches of fruit have been cut is a problem not easy of s^lu- 

 tion. It has been recommended for Jamaica that these be 

 cut in thin pieces and spread out on the ground. Such pieces 

 should serve as traps to attract the adult weevils, and these 

 should be collected from time to time. If the old banana 

 material is cut in small enough pieces, it is not likely that 

 the grubs would be able to develop in them; but this is a 

 point on which definite information does not seem to exist. 



The introduction of the predaceous Histerid beetle from 

 .lava to ])rey upon the weevil is suggested as likely to be 

 a useful measure. 



< )ther insects attacking the banana in St. Lucia 

 are the large Dynastid beetle (Tomarus Intuhercnlatits) 

 which attacks the newly planted bulbs of iilantain and the 

 Makabou banana, and also attacks youn>! tannias and 

 dasheens; and the striped weevil borer {Metamasius scriaus) 

 which is well known as the weevil borer of sugar cane. 



Limes were found to be attacked in St. Lucia by the 

 adults of Diapnpcs ixhbrniatiis, var. piinctatiis. Diapripes 

 ahlinviattis is known in Barbados as the root borer of sugar- 

 cane. The adults and egg mas.ses were found on the leaves 

 of the lime trees, but no ob.servations were made ■)n the 

 attacks of the grubs on the roots of these trees. 



The purple scale (Lep'dosuphcs beikii), the snow scale 

 (Chioiunpii n'/ri), and the green scale (Coirus Ti/r/i/h) were 

 common on trees that were at all neglected or suffering from 

 insufficient drainage. The white-headed and red-headed fungi 

 were abundant on the ptirple .scale and the black fungus 



