EXPERIMENT STATION BULLETINS. 



391 



THE THREE-LINED THRIP {Coleothrips trifasciata, Fitch). 



Oedee HEMIPTERA. 



Family THRIPID^. 



Fig. 10.— The three-lined thrip; 



In June and July these very minute sap 

 sucking insects were common on the celery at 

 the college. The species is our most common 

 one in the heads of clover and is found on 

 onions and various weeds. The individual spec- 

 ?*^5imens are only about one eighth of an inch 

 "long, slender, and prettily marked with three 

 white cross bands along the wings. They were 

 found mostly on the tender central portion of 

 the plants, often hid in considerable numbers 

 between leaves, but as often scattered singly all 

 over the plants. They no doubt assisted the 

 leaf hoppers in making the celery look sickly, 

 but they are so minute that they are not likely 



x^-^^., .^^^-..^^^ .uxx *° ^^ special harm unless very numerous, 

 wings "in natural position on one Should this occur, a Spray of kerosene emulsion 



side and spread on the other. The -n j* • • i i.i • i_ 



line at the side shows the nat. size Will diminish their numbers. 



—(original). 'j'jjg method of preparing the kerosene emul- 



sion may not be well known to all celery-growers, and so it will be given: 

 To two quarts of water add one quart of soft soap or one fourth pound of 

 hard soap, and heat the whole to boiling. When the soap is dissolved, 

 take from the fire, add a pint of kerosene and agitate so thoroughly and 

 rapidly with a force jjump without the nozzle that the mixture will foam 

 like milk when filling the dairyman's pail on a summer's evening. It 

 should be churned in this way until the soap and oil become permanently 

 mixed; that is, until the oil will not rise or appear on standing or when 

 diluted. This will take at least three minutes' rapid work. Stirring with 

 a stick or spoon or slow pumping will not emulsify the soap and oil, 

 though an egg beater may be used for a very small quantity. The emul- 

 sion as first made is too strong and will injure the plants unless diluted 

 before applying. The soft soap emulsion should have as much water 

 added as there is emulsion, and the hard soap emulsion, twice its bulk of 

 water added and well stirred. They are now ready to be applied with a 

 spray pump. The dilute emulsion should be stirred frequently in 

 applying. 



The above is the regular formula. The emulsion can be made in larger 

 quantities in the same proportion, but if made in quantities larger than 

 six or eight times the regular formula, it will be difficult to make a 

 stable emulsion with a small hand force pump. This has been one of the 

 discouraging features in the use of kerosene emulsion. It now seems 

 evident that we can overcome that difficulty in a large measure. The 

 method is to use the soft soap formula, as given above, without the water. 

 The soft soap is heated until it becomes liquid and then, without water, 

 add half as much oil as there has been soap used, emulsifying according 

 to the directions given as above. The emulsion made in this way is as 

 perfect as when used with water and it is so concentrated that it is one 

 third oil, or in other words, the same emulsion in this way occupies less 

 than one half the space that it would when made by the first formula 

 given. An emulsion made in this way, without water, will need to be 

 diluted with four times its own bulk of water before using. 



