39i 



THE AGRICULTURAL XEWS. 



December 10, 1910. 



INSECT NOTES. 



PLANT BUGS INJURIOUS TO COTTON 



BOLLS. 



At diiferent times during the past few years, cotton 

 growers in the West Indies have oliserved that a considerable 

 number of developing bolls have dropped from the plants, 

 and that others have failed to develop properly, remaining in 

 a dry and distorted condition attached to the plant, through 

 the time required for the process of ripening, and often long 

 after the crop was picked. 



The causes of the loss of bolls have been the subject of 

 investigation from time to time, on the part of the officers of 

 the Imperial Department of Agriculture, in response to 

 requests from planters, who desired to know what they were, 

 in order to be able to prevent further loss. 



In this connexion, anthracnose, boll rot and black lioU 

 have been investigated, and have been found to be responsible 

 for at least a portion of the injury. 



In a paper on Cotton Stainers (see West Indimi Bulletin, 

 Vol. VII, p. 76), the Entomologist on the Staff of the Imperial 

 Department of Agriculturestates that it is difficult to say exact- 

 ly what the nature of the injury to cotton by cotton stainers is, 

 and that the whole question of the nature and amount of the 

 injury to the cotton plant, seed and fibre, might well form the 

 subject of an extended investigation. The writer believes, 

 however, that cotton stainers injure young cotton bolls by 

 sucking the sap, and thus lessening the quantity of the yield 

 of fibre, and perhaps also aifecting its quality; that they cause 

 a certain amount of drying up of the pod; and that they check 

 the growth of the pod and of the cotton inside it. In addi- 

 tion to these injuries, the seed is often damaged to .such an 

 extent as to interfere with its power of germination, and 

 greatly to reduce the amount of oil that may be extracted 

 from it. 



The Bureau of Entomology of the United States Depart- 

 ment of Agriculture has recently issued a bulletin (No. 86) 

 entitled Plant Jjw/x Injurious to Cotton Bolls, by Dr. A. W. 

 Morrill, in which field observations and laboratory experiments 

 are shown to indicate a considerably greater injury to cotton 

 bolls from this cause than has been suspected in the past. 

 The insects referred to by the term 'plant bugs' in this bulletin 

 include several of the Hemiptera-Heteropterii, among which 

 are cotton stainers and other species of plant-feeding bugs, of 

 which near relatives are to be found in all the West Indian 

 islands. 



The West Indian insects which may be regarded as likely 

 to cause the .same kind of injury as those mentioned as plant 

 bugs in Bulletin 86 are the cotton stainers {Dysdercus spp.), 

 the green bug {Nezara viridula), the brown bug {Edessa med- 

 itahtinda), the leaf-footed bug { Lepto;/lossus phi/llopus), which 

 are more or less familiar to cotton planters in these islands. 

 There are also several others less commonly observed. 



Dr. Morrill states that it is always difficult, and some- 

 times impossible, to determine from the appearance of the 



outside of the boll, the damage done by the feeding of these 

 insects. On the inside of the carpels forming the lioll, how- 

 ever, there will be found, in the fresh, growing boll, discoloured 

 spots surrounded Ijy watery or blister-like, bright-green areas 

 contrasting distinctly with the light, dull-greenish background. 

 In many cases, particularly in bolls three-quarters grown, or 

 more, these blister-like areas increase to a diameter of 4 to 

 5 mm.; but in other cases, more especially in small, rapidly 

 growing bolls, a physiological reaction in the form of a prolif- 

 eration of tissue takes place, causing .slight swellings on the 

 smooth inner surface of the carpel. 



It should be borne in mind that the rostrum so plainly 

 visible in the i)lant bugs is not inserted into the plant tissue, 

 but that it encases the very slender setae, which form the real 

 organ for extracting the juice from plants. These setae make 

 such a minute puncture that it is practically impossible to 

 discover this on the outside, or to trace its course through the 

 carpel. On the inside, the marks or the slight swellings 

 mentioned above, will often indicate the point at which the 

 setae came through the carpel and entered the lint- and seed- 

 mass in the locule. These spots, or swellings, will often be 

 seen to have definite relation to the location of a stained spot 

 in the lint, and may generallj' be found in those bolls which 

 have failed to open properly, especially on those carpels which 

 cover locules in which the development has been entirely 

 arrested, causing shrivelled, distorted bolls. 



It is Ijelieved by Dr. Morrill that stained cotton is 

 largely produced by the puncturing of the boll by these plant 

 bugs, and he does not think that the excrement of stainers or 

 other insects has much influence in producing stained cotton. 



The injuries to the boll which result in dropping, 

 abortive or distorted development, and stained cotton, have 

 been observed repeatedly in fields where plant bugs have been 

 abundant; but in field.s and localities where these have been 

 alisent, this form of injury was not noted. The trials in 

 cages have given the same results: those plants on which 

 plant bugs were caged produced bolls which showed the 

 injuries mentioned, while those to which no plant bugs had 

 access were practically free from such injurie.s. 



A considerable portion of Dr. Morrill's observations was 

 made on a plant bug in Mexico known as the conchuela 

 [Pentatoriw ligata, Say.), and he states definitely that, so far 

 as that insect is concerned, the damage to the cotton is not 

 the result of the voiding of excrement on the lint and un- 

 opened bolls, although that is the popular belief in Mexico. 



Speaking of the staining of the lint by the stainer (Dys- 

 dercus), Dr. ilorrill mentions observations in Texas to the 

 effect that this is due to the attack by the stainers: 'on the 

 immature bolls, and on the seed at the time of opening, the 

 brownish- j'cllow colour being derived from the injured .seed 

 rather than from the excrement of the bugs.' The staining 

 of the cotton is found to be most intense next the seed, and it 

 has been noticed that sometimes cotton fibres are stained at 

 their bases, where they are attached to the seed, while toward 

 their tips, away from the seed, they are free from stain. 



The cotton stainer is counted the most serious pest of 

 cotton in Florida, and it occurs to some extent in adjoining 

 states. 



This brief account of recent observations on the plant 

 bugs and their injuries to cotton bolls should be an incentive 

 to West Indian cotton growers to note more carefully the 

 occurrence of these insects in the cotton fields, with especial 

 reference to the relative abundance of plant Imgs and bolls 

 injured in the manner indicated, for it is possible that, as 

 a result, more definite knowledge may be forthcoming, in 

 regard to the cause of Ijoll-dropping, deformed and unde- 

 veloped bolls, and stained cotton. 



