154 



THE AGRICULTURAL NEWS. 



May 9, 1914. 



INSECT NOTES. 



CONTROL OF THE ONION THRIPS IN 

 THE UNITED STATES. 



The onion thrips, which is a serious pest of oniou3 iti 

 the United States, has been the subject of extensive investi- 

 gations in different parts of the country. The Experiment 

 Station Hecoid, for October 1913, gives a summary of a paper 

 on this subject by Mr. F. H. Chittenden, which appeared in 

 the Yearhooh- of the United States Department of Agriculture, 

 191-2, pp. 319-34. 



In view of the recent developments of an important 

 onion industry in Antigua, information as to the control of 

 the pests is likely to be of interest to planters in that island, 

 and it may be of value in other localities, since onions 

 throughout the West Indies are liable to thrips attack. 



The summary mentioned is reproduced herewith. 



Of the insect enemies of the onion, the onion thrips 

 (Thrips tahaci) is the most important. It causes injury to 

 the onion crop practically throughout the country, pro- 

 ducing a condition somewhat generally known as 'white 

 blast', 'white blight' and 'silver top'. It is also the cause of 

 'scullions' or 'thick neck', terms used for the undeveloped and 

 unmarketable bulbs. This thrips is now found in practically 

 all cultivated fields in the United States, as well as in many 

 uncultivated areas, .so that there is always danger of infesta- 

 tion to onions and other susceptible crops, whether grown in 

 new or in old land. Observations tend to demonstrate that in 

 some localities, at least, it makes little diflference as to the 

 previous crop. 



The life-cycle has been found to require under the 

 most favourable conditions about three weeks. Thus a dozen 

 or more generations might be produced during a season. 

 'Besides onions and related plants, this thrips attacks 

 cabbage, cauliflower, parseley, cucumber, melon, pumpkin, 

 squash, kale, turnip, tomato, seed beets, blackberry and 

 strawberry. Of ornamental plants, it does much injury 

 to carnations and roses and more or less injury to 

 aster, blanket flower (Gaillardia), honeysuckle (Lonicera), 

 daisies, nasturtium, narcissus, mignonette, candytuft (Iberis), 

 four-o'clock (Mirabillis), and cone flower or golden glow 

 (Eudbeckia). Very serious injury is frequently committed 

 to cucumbers and carnations in greenhouses, the damage 

 sometimes amounting to the destruction of entire plantings. 



•Kerosene emulsion, whale-oil or fi.sh-oil soaps, and 

 tobacco or nicotin extracts are recommended for use, their 

 application being commenced early in the season. The 

 importance of clean methods of field management, including 

 the destruction by burning of culls, tops, and injured plants 

 after the crop is gathered, is emphasized. Investigations in 

 Texas and Indiana have shown the following formulas to 

 give the most successful results: (1) Nicotin-sulphate 3-2 oz,, 

 cresol soap 3 pints, and water 50 gallons; (2) nicotin sulphate 

 4'3 oz , whale-oil soap 4 lb, and water 50 gallons. When 

 spraying is once begun it should be continued at intervals of 

 from seven to ten days, in case there is no heavy rainfall 

 during this period, and no surrounding breeding host for the 

 species. The spraying should, as a rule, be continued up 

 to three or four weeks of harvest time. In spraying for 

 thrips, the nozzles should be held well down upon the 

 plants and the spray applied with as much force as possible. 



'Where setts are used considerable injury may be pre- 

 vented by dipping them about a week before planting in 

 nicotin sulphate at about the same strength as used for 

 spraying, and then giving two dippings in the same insecticide 



at planting time, or in almost any other of the solutions 

 mentioned, including kerosene emulsion. Since this thrips 

 displays preference toward cabbage and cauliflower, neither 

 of these two crops should be grown contiguous to onions. ' 



ARSENATE OF LEAD. 



Arsenate of lead, as an insecticide, has not up to the 

 present time found extensive favour in the West Indies, but 

 in many places it is largely used instead of Paris green and 

 London purple. 



The chief advantage in the use of arsenate of lead lies 

 in its insolubility. It was first developed as an insecticide 

 in response to the need for a substance which might be used 

 at greater strength, without injury to the foliage of plants, 

 than could either of the others mentioned, for the control of 

 insects, which were not killed by these when applied in 

 mixtures strong enough to scorch the plants. In addition, 

 arsenate of lead possesses exceptional powers of adhesion to 

 the foliage of plants. 



Paris green and Loudon purple are ordinarily used at 

 the rate of 1 lb. to 150 gallons of water, and from that 

 strength to 1 Bb. in 100 gallons. The addition of lime to 

 neutralize the soluble arsenious acid has been practised, 

 usually with good results, but these are not alwaj-s uniform. 

 Arsenate of lead was for a nuQiber of years only sold in the 

 form of a paste. In this form it could only be used as a spray, 

 and the objection made to the material in that form referred 

 to the large amount of water which it contained, increasing 

 the cost of freight, and also to the fact that the paste dried 

 out to a considerable extent. This drying out affected the 

 strength of the material so that it was often impossible, 

 under field conditions, to prepare mixtures of uniform 

 composition. 



To remedy these defects a dry, powdered form of arsenate 

 of lead has been prepared, and this, during the last few years, 

 has come to be largely used. It is stated to possess the 

 advantages of the wet form and, in addition, to be without 

 its disadvantages. 



In certain of the West Indian islands where Paris green 

 and London purple have been used in large amounts for the 

 control of the cotton worm, it has been found that labourers 

 .sometimes object to the work of applying the poisons because 

 of the irritating effects on the skin, and that light showers 

 easilj' wash the poison off the leaves. 



It is likely that arsenate of lead would bo without these 

 objections, but it might be somewhat slower in its action 

 on the cotton worm than either of the others. In the case 

 of heavy and repeated applications, there would be less danger 

 of scorching the leaves by arsenate of lead. 



The dry form of arsenate of lead, therefore, would seem 

 to be worthy of trial by cotton growers, especially in 

 localities where light showers frequently interfere with the 

 application of Paris green and London purple, or where 

 difficulty has been experienced in getting labourers to use 

 them. 



USE OF NAPHTHALENE IN THE 

 CONTROL OF FLEAS. 



The following note relating experience in the use of 

 naphthalene for the control of fleas may be of interest to 

 readers of the Agricultural Nen's: — 



'A few years ago I read of an instance in the United 

 States in which a new house became infested with fleas before 



