196 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 7 



NOTES ON THE ONION THRIPS AND THE ONION MAGGOT 



By H. T. Fernald and A. I. Bourne, Amherst, Mass. 



The ''Onion Blight" is very common and serious in the onion-raising 

 districts of New England. The trouble is caused by Thrips tabaci 

 Linde., which is widely dispersed over the country, and the loss caused 

 by this insect is often great. 



Studies on this pest extending over a period of about five years 

 have now been completed in Massachusetts, and have given the fol- 

 lowing results: 



The insect passes the winter as the adult in anj^ protected places 

 available. These are generally in the refuse left on the onion field, in 

 rubbish heaps, or at the base of the grasses on uncultivated fields and 

 along roadsides near the onion fields. In spring, soon after the onions 

 come up, the insects leave their winter quarters and pass to the plants, 

 then usually an inch or two high. They locate on the leaves and begin 

 to suck the juices and breed. The effect of the feeding upon the plant 

 is first shown by the leaves attacked, which begin to bend rather 

 sharply downward, bringing the thrips within the protection formed 

 by the bend. This is due to the abstraction of sap from one place 

 while the rest of the leaf is growing rapidly, so that in consequence the 

 injured point is as it were, grown around by the vuiinjured portions. 

 This condition is often evident by the time the plants are three inches 

 high, and increases during the season, while other leaves become in- 

 volved as the insects spread. Dying back from the tips soon appears, 

 and in serious attacks either the entire plant may die or the bulb 

 make only partial growth. 



In testing dift'erent methods of control for this pest, the rather un- 

 usual methods used for raising this crop should be kept in mind. In 

 New England at least, the land is fertilized broadcast and the seed 

 sown in rows by seeders, and covered by a roller behind the seed spout. 

 The rows vary in accordance with the ideas of different growers but 

 their average distance apart is perhaps fourteen inches or less. The 

 seed is sown so closely in the rows that some thinning is usually neces- 

 sary where germination is complete, and a field of vigorous plants 

 cannot be traveled over with a spray pump after these are more than 

 six inches high, without causing serious injury to the leaves which 

 tend to spread out, laterally. Any treatment, therefore, must be 

 while the plants are small, and in some cases at least, the thrips 

 spread to the field after the plants are really too large to permit of 

 treatment without considerable injury. 



The experiments were conducted on river bottom land used almost 



