31 1 



THE AGRICULTURAL NEWS. 



September 25, 1915. 



INSECT NOTES. 



NOTES ON AN INTERNAL DISEASE OF 



COTTON SEED. 



Eft W . Lawrence Balls, k. \. (Cantab.). 



As a supplement to the articles on The Internal 

 Disease of Cotton Bolls in Nos. 344 and 345 of this Journal, 

 it may be of use to its nailers to know of some similar 

 unpublished observations made incidentally by the writer in 

 Egypt, in connexion with pure strain seed supply, during 

 which the diseased condition of some seed was traced quite 

 definitely to a Cotton Stainer Bug (Oxycaiemis hyalipennis). 



The circumstances were such that it was easy to fix the 

 responsibility. They wen- as follows: the Giza Cotton 

 Station is on a site which has always abounded with the 



bugs; there were hundreds of stored samples of seed from 

 1905 I" 1912, all marked with the date of picking, and the 

 exacl site in which they were grown. In the season of 

 1912 pickings were made oti every day of the season 

 (September-November), and picking was continued from 

 mid August until January: moreover, some of those pickings 

 made (lining the winter consisted of cotton which had been 

 allowed tfurposelyto hang on the plants since it first ripened. 

 Lastly, every main group of cotton was represented. Statis 

 tied data were available as to the life-history of almost every 

 plant ami plot concerned, and all microscopical examination 

 \\;i- conducted on the spot by the writer, with the usual 

 refinements of technique. 



It will suffice to state the main results, and the obvious 

 conclusions. The percentage of seed which failed to germin- 

 ate- was proportional to the duration of the time during 

 which the seed-cotton had been hanging on the plant, at 

 any one season of the year. For equal times of exposure 

 the severity of the damage was proportional to the abundance 

 of Stainer Bugs. The proportion of damaged seed in extreme 

 i ases rose to 98 percent. Examination of seed which had failed 

 to germinate snowed a In-own discoloration of the embryo 

 root in the earliest stag- this discoloration subsequently 

 extending, though never involving the whole embryo; the 

 localization of the disease to this part of I In- embryo corres- 

 ponded with the fact that the bugs accumulate for feeding 

 round the point of the seed where the lint is most scanty, 

 and are but seldom found feeding on other parts ot the 

 seed-coat. 



Since it seemed at first uriliki ly that the puncture made 

 by the bug should in itself cause the death of the embryo, 

 (or rather, of its root, which comes to the same thing in 

 practice), damaged seed was examined in various ways for 

 fungi and bacteria which might have been introduced 

 through tin- punctures. The anthxacnese fungus was sus- 

 pected, since it is very common in Egypt, though not 

 a serious pest, but it was finally found that neither this 

 fungus, nor any other, nor even bacteria, were habitually 



present in the damaged embryos. The brown portions 



consisted of cells in various degrees of nnhealthiness on the 



margin, with (had and disintegrated cells near the centre, 

 only the cell walls being normal. The parts of the embryo 

 which were normal in appearance consisted of normal 

 live cells. 



Further tests made by exposing healthy seed to the bugs 

 for a week or two showed clearly that the saliva of the bug, 

 like that of most other bugs, was in some way poisonous, and 

 that for sometime after the proboscis of the bug had been 

 withdrawn it continued I" destroy the cells with which it 

 same in contact. So far as the writer is aware, no - 



statement of the poisonous nature of this cotton stainer bug's 

 saliva has yet been made. Circumstances prevented the 

 writer from completing the investigation by ascertaining the 

 nature of the poison. 



Summing up, it was evident in the ease of the seed, and 

 is probable in tic- case of the boll as a whole, that the damage 

 done by stainer bugs is less due to the nutriment they 

 remove than to the poisons which they leave behind. 

 Secondarily, fungi and bacteria may gain a foothold and cause 

 complications through the punctures which the bugs make. 

 Lastly, on the same plant seeds ami bolls may be diseased in 

 all these ways, and also by specific parasites such as 

 anthracnose. 



WHAT CACAO THRIPS SIGNIFY IN 

 GRENADA. 



A species oi this insect [Heliaihript rubroeinclus, < riard.) 

 has been known to occur in Grenada sill • 1 S '.'S. It his from 

 time to time been the subject f correspondence between this 

 Department and the Government of Grenada, and it has been 

 considered a pest of cacao by planters and others. 



At the present time thrips probably occurs in all parts of 

 Grenada, ami perhaps in everj cacao field. It was, however, 

 only in certain fields and often in small anas in those fields 

 that planters considered that damage resulted from attack 1>\ 

 thrips. The remarkable thing about the • i urrence of thrips 

 is that attacks occur year after year on the same area-, on 

 the same trees even, sometimes spreading a little: but a thrips 

 area one year is liable or certain to be a thrips area every 

 year. 



Cacao thrips in Grenada has been the subject of observa 

 tion by the Entomologist of the Imperial Department from 

 1900 to the present time. 



It appears that a sufficient amount of information is 

 now available to enable a general statement to be made as 

 to the economic status of cacao thrips. 



Lefroy stated in paragraph 5 of tint report of his visit 

 to Grenada, dated October .">. 11)00, that the discoloration of 

 the pods which results from thrips attacks, makes it difficult 

 to tell when they are ripe, and that this increases the cost "I 

 gathering, since tic- pods have to be tapped or scratched in 

 order that the pickers may be able fi > -ee the real colour of t he 

 pod. Otherwise this insect does not appear in any way 

 very injurious or troublesome, and none but a very simple 

 remedy would be worth adopting. 



Liter Lefroy summarized the situation in the following 

 words: 'Thrips may be regarded as a possible enemy to 

 cacao rather than as an actual pest. There does not appear 

 to be any serious cause for alarm at the present time and the 

 chance of the cacao suffering materially from the attacks of 

 this insect is, in my opinion, remote.' ( lies/ Indian Bulletin 

 Vol. 11, p. 185.) 



These opinions appear to be applicable at the present time, 



the experience of cacao planters .luring the past fourth en years 

 having served to confirm the early belief as to the nature of 

 the attacks. 



At the same time, however, it must lie stated that the 

 cacao growers still refer to the injury done by thrips, and 



they reCOgnizi their estates certain fields, or patches in 



fields, where thrips attacks occur year after year, ami they 

 also want to know what remedies to employ to check the 

 thrips. 



Formerly tin- impression prevailed that the cacao thrips 



was always most abundant dining dr\ weather, and that 

 wet weather Was favourable to the plants and unfavourable 

 to this insect. This idea is based "ii observations, corres- 



