31G 



THE AGRICULTURAL NEWS. 



October 23, 1915. 



INSECT NOTES. 



INSECT PESTS OF LIMA BEANS IN 



ST. VINCENT. 



The following notes by .Mr. S. < '. Harland, B.N<-. 

 Assistant Agricultural Superintendent, have been 

 forwarded b\ the Superintendent to this Office for 

 publication. The observations contained in the notes 

 ;n imporl wit. in view of the suggested i xtension ofthe 

 area under Lima beans in St. Vincent and other 

 colonies. Ii would appear that the Cryptorhynchus 

 borer referred to may be found to be troublesome; but 

 the remaining pests d seem to be very serious: — 



During the past foui months a special study has been 

 made, at the St. Vincent Experiment Station, of the insect 

 pesta of Lima beans. It was considered of the utmost 

 importance that before a large area was planted in this crop, 

 1 a knowledge as possible should be obtained of the 

 insects with which planters may have to contend. It was 

 thought advisable to devote some attention to the insect pests 

 of allied indigenous s[>ecies, since amongst these might 

 possibly be found the wild fond plant of some dangerous pot 

 of Lima beans. It will he seen that some success has 

 attended this line of work. 



A large number of insects are capable of attacking Lima 

 beans, but the following appear to be the most important: — 



(1) An undetermined Cryptorhynchus borer. 



(■_') The bean leaf roller (Eudamus proteus, I..). 



(.'!) An undetermined leaf blotch-miner. 



(i) The Lima bean caterpillar. 



'I'm: ( 'H\ PTOKm NCH1 - BORER. 



The writer's attention was Hist called to this borer in 

 May 1915, at the Experiment Station. It was noticed 

 during the examination of some poll I. na beans th.it 

 man} plants possessed leaves of an unhealthy yellow 

 colour, as if attacked by wilt. Further examination 

 disclosed the fact that the base of the stem and man} 

 of the nodes were abnormally swollen, that the stem 

 tunnelled, and that small white grubs were present 

 either in the nodes themselves or in the connecting 

 tun 8< ! weevils, very similar to the cassava weevil, 



but smaller, were at the same time observed near the base of 



atem. The larvi btained from the plants produced 



adults identical in appearance with these. 



Ii: 1 \ loi ■ REFERENCES. A -lent note on the borer 



appears in the Agricultural Sews, Vol. \|V, No. 344, 

 p. 218). Previous to this, the only reference to it which has 

 hitherto appeared in the agricultural literature of the West 

 Indie- i> to be found in the Annual Report of the Departm- 

 ent of Agriculture of St. Vincent for 1910, (). 2_'. It is 

 there mentioned as a pest of Jerusalem pea (P/taseolus 

 trmervi$)b) Mr. W. II. Patterson, tic then Resident Waster 

 at tin- Agricultural School, inthe following terms : "When 

 the plants should have flowered, the leaves and stems turned 



yellow, having the appearance of suffering fr Irought, 



though ample moisture was present. This was due to 

 the attack ot an undetermined weevil, the larvae of which 



bore into and tunnel the stems." Tie- writer goes on 



to say that the attack was so serious that no seeds were 



obtained from [-acre, and that efforts to find other! I 



plant- were w ithout success. 



LIFE-HISTORY. A complete life history of the Weevil 



has no; been workedout, but certain information has come to 

 light which may prove helpful in combating it, should 

 ision arise. The duration of the larval and pupal periods 

 ram ot be more than two or three weeks, since adults have 

 been reared from plants less than five weeks old, and the 

 pupil period bas been determined with certainty to last 

 from five to -even t],i\ < only. 



habits of larvae. At the beginning of the attack 

 one or two larvae are found in the lowest node, which, as 

 a result of irritation, becomes greatly enlarged. At this 

 ige, the whole larval period is passed in the node and it 

 is only later that the stem becomes tunnelled. The eggs are 

 laid in the node, just under the epidermis. If the plants 

 are attacked when young they are either completely killed, 

 or fail to make further growth. Older plants seem to adapt 

 themselves somewhat to the presence of the weevil and do 

 not sutt'er so much. The base of the stem may become 

 enormously swollen. A single plant of Kounceval pea 

 (Yigna unguiculata) was 5 inches in circumference at this 

 portion, which was completely riddled with borings and 

 contained twentj two specimens of the weevil in all stages 

 of development. 



THE pupal period. When fully grown, the larva is 

 about 6"5 mm. long by 3"5 mm. broad. It pupates in situ, 

 forming a rough pupa-ease ofthe dead fibres of the stem. 

 When the adult emerges aftjr live or six days, it proceed- 

 bite its way out. 



HABITS OF ADULTS. The adults, as well as the larvae, 

 feed on the host plant, eating the young shoots and stem. 

 Several weevils were introduced into an insectary where 

 a young seedling was growing. They simulated death for 

 a short time, but soon made for the stem. Some remained 

 there at the base near the ground : others buried themselves 

 near by. At the end of the second day it was observed that 

 part of the stem had been eaten just below the cotyledons, 

 and that sap was oozing from it in many places. Subsequently 

 it was established that the Wei wis feed only during the night, 

 being quiescent in the day. The seedling did not recover 

 from the damage inflicted on it by the weevils. 



The adult weevil probably lives for a considerable time: 

 some were kept alive in captivity for more than a month. 



HOST PLANTS. The following cultivated plants are 

 attacked more or less severely: Lima bean {Phaseolus limn 

 tus), cowpea (Yigna var.), and Rounceval pea, 



Jerusalem pea (Phaseolus ti'inervis), haricot or French bean 

 (Phaseolus vulgaris). 



As the pest seemed to confine itself to the genera 



Phaseolus and Yigna, careful search was made of the wild 

 specie- of these genera found in St. Vincent. It was dis- 

 covered that the common leguminous weed, Phaseolus 

 semierectus, and the less common Vigna luteola are almost, 

 invariably attacked by the borer, which, however, does not 

 appear to check their growth to any extent. 



Other species ot these . irded from St, Vincent 



an- a- follows: P. adenanthus, V. sinensis, I". vexillata. 



These have not lieen examined. 



distribution. The Cryptorhynchus borer is found in 



all puis of St. Vincent, and in Bequia; it does not appear to 

 be present iii Union [sland, although Phaii tins semieri 

 is exceedingly abundant, 



control Should tin- cultivation ot Lima beans be 

 taken up in St. Vincent, the best means of control would 

 appear to !"• in the uprooting and destruction of all plants ot 

 Phaseolus semieri tus and Vigna Intuitu adjacent to the fields. 

 In view of the habit of the weevil of remaining at or near 

 the base of the stem, hand collecting might possibly meet 



