308 



THE AGKICULTUKAL NEWS 



October 6, 1917. 



OBSERVATIONS ON THE COTTON 

 STAINER IN ST. VINCENT. 



In tlie late.st number of the West Indian Bulletin 

 (Vol. XVI, No. 3) is to be found a paper by Mr. W. X. 

 Sands, Agricultural Superintendent, St. Vincent, giving an 

 account of the observations recently carried out by him in 

 connexion with the life-history, habits, food-plants, and 

 control of the cotton stainer in that island. The following 

 summary will show that Mr. Sands has made some observa- 

 tions of considerable interest and value, and that under 

 his direction an enerj etic camj;aian has been carried out 

 against the wild food-plants of this pest. 



The association of the cotton stainer ( Dysdercus delauneyi, 

 Leth.) with certain destructive internal boll diseases which 

 have caused large losses of seed-cotton within recent years 

 in St. Vincent, has made it imperative to carry out some 

 control measures against this pest, and it was thought 

 advisable to work out the liie-history of the species. 



A short description of this insect is given, and it is 

 stated that this species occurs throughout the coastal district 

 of St. Vincent, and is found in other West Indian islands, 

 its range e.xtending from Montserrat to Grenada. 



The life-history was worked out in the laboratory in 

 breeding cages consisting of hurricane lamp chimneys inverted 

 in lids of butter tins. River sand to a depth of 2 inches 

 was placed in the bottom of each chimney, food was supplied 

 as needed, and the top kept covered with gauze. Records 

 ■were made daily between 7 a.m. and 10 p.m. from December 

 1916 to April 15, 1917. 



Experiments were made in the cages to tind out where 

 the eggs are laid by supplying the insects with (a) seed-cotton, 

 (b) old cracked cotton bolls, (c) freshly opened bolls, (d) un- 

 opened cotton bolls, but no eggs were laid anywhere but in the 

 sand at the bottom of the chimneys. The eggs were found to 

 be laid in pits, and covered with sand by the female. The 

 operation of egg-laying was witnessed several times in the 

 laboratory, and the results gave a clue to the place and 

 manner of oviposition in the field. It was found that eggs 

 are deposited in masses in the ground, and covered over, but 

 the act of oviposition was not observed in the field, since it no 

 doubt takes place at night, and no observations on this point 

 ■were made after 7 p.m. Frequent search for eggs on all 

 parts of the cotton plant, silk-cotton, and John Bull trees 

 over a considerable period has been without result. 



The eggs are smooth, ovoid, and creamy white with 

 a pearly lustre. Tliey are slightly sticky when first laid, 

 but .separate freely when dry. They change in colour before 

 hatching, at first becoming tinged with yellow, and by the 

 seventh day they are deep orange. Eggs kept dry in 

 glass tube.s hatch in seven days; those laid in moist, sandy 

 soil take .seven and a half to nine days to hatch. The eggs 

 appear to be nearly always fertile. 



After hatching, the stainer bug moults five times before 

 reaching adult stage in from twenty-seven to thirty days. 

 The sexes mate within three or four days after maturing, and 

 eggs are laid for a new generation in about six to eight days 

 later. Tables are given showing that the complete life-cycle 

 occupies from forty-seven to forty-nine days. 



Before a moult the insects collect together in masses 

 sometimes on any plant that provides .shelter, and this habit 

 partly accounts for the erroneous ideas about the feeding 

 habits of the stainers. 



Observations sh'^'W that dark greenish-yellow excrement 

 was not voided until maturity was reached. In other stages 

 the excrement was colourless or slightly tinged only. This 

 is an important point, as showing that the younger stages, or 



nymphs, cannot damage seed-cotton by staining, even if 

 present in large numbers. 



Another point of considerable interest is that young 

 nymphs are apparently unable to feed on unopened fruits of 

 silk-cotton, John Bull, or cultivated cotton, and experiments 

 made in the laboratory in this connexion tend to show that 

 in the immature stages the insect cannot pierce and feed 

 through the carpels. Farther experiments are to be made 

 on this point before any definite conclusions can be drawn. 



The egg-laying habits of the female are described in 

 detail, showing how she digs a small pit, places her eggs and 

 covers them over so as to make them as inconspicuous as 

 pos.sible. Therefore they are difficult to find in the field. 



Up to the present the cotton stainer has not been found 

 to breed on any other species of food-plants but those belong- 

 ing to the Malvaceae, and the related Sterculiaceae. A list 

 of food plants is given, the most important being ihe silk- 

 cotton (Eriodendron anp-acluosum), the 'John Bull' or niahoe 

 (Thespesia populnea), and the 'Mahoe cochon' or 'Stave wood' 

 (Sterculia carihaea). In certain districts in February, March 

 and April when food is scarce and the weather is dry, cotton 

 stainers may be observed feeding on the flowers of the 

 following plants: guava, cacao, banana, plantain, Cycas 

 ctrcindlis, Euphorbia canariensis, and galba, and the secre- 

 tions of scale insects. They have not been observed to 

 breed on such plants. Observations in the field show that 

 periodical flights of cotton .stainers in considerable numbers 

 take place from one food-plant to another. 



In St. Vincent it is required by law that all cotton 

 plants, wild and cultivated, be pulled up and burnt by 

 April 30 in each year. Most of the cultivated plants are 

 destroyed by the end of February, at the completion of the 

 crop. Planting of the new crop begins in .May with the rains, 

 so that there is an interval during which the stainers must 

 have food other than cotton to carry them over from one 

 .season to another. 



Investigations made throughout the island showed that 

 the chief nurse trees are the silk-cotton and the John Bull. 

 An account of these trees in relation to the cotton stainer 

 was given by Mr. Sands in the Agricultural X'ews, Vol. XV, 

 Xos. 369, 370, and 373 (1916) under the title 'Native food- 

 plants and feeding habits of the cotton stainer in St. Vincent.' 



The case against the silk-cotton tree may be summed 

 up as follows: 'It is a tree which provides, when it fruits, 

 a large amount of food for the cotton stainer, and so 

 enables the insect to feed and breed extensively, and tide 

 over a season when it is so important that its numbers 

 should be reduced to a minimum for the protection of the 

 annual cotton crop, planted in May, June, and July: therefore 

 it should be destroyed.' 



An ( )rdinance was pas.sed to provide for the destruction 

 of these native food-plants, and the eradication was carried 

 out betweeen August 1916 and April 1917 by the Agricul- 

 tural Department, at Government expense. During the 

 period 1,542 silk-cotton trees, 11,570 John Bull trees, and 

 several thou,sand seedlings were destroyed at a total cost of 

 £300. A copy of the Ordinance is included in the paper. 



Further suggestions made by Mr. Sands for controlling 

 the cotton stainer are' — 



(a) A close season for cotton from February to May, 



(b) The trapping of the pest by means of cotton seed, 

 .seed-cotton, ir cottonseed meal .just before the cotton starts 

 to flower. 



(c) The collection of cotton stainers in the field. 



In regard to (a) it is thought that if a close season for 

 Sea Island cotton from February to May is instituted, cotton 

 planted in the latter month would not flower before July, 



