EXPERIMENT STATION BULLETINS. 



125 



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Fig. 2. Onion Tlirips, Thrips tabaci, mature. 

 (Original.) 



those of all true thrips, destitute of claws. 

 The adult winged insect is represented by 

 Fig. 2, shown at rest, with the wings 

 closed, as this is the position in which it is 

 most often seen. The general color is dirty 

 yellow with dusky markings. The feelers 

 are seven jointed, and the size slightly 

 larger than the immature stage. The ex- 

 tremely narrow wings are fringed with long 

 hairs on each side, giving them a feathery 

 apijearance. 



XATURAL ENEMIES. 



Grer/arinida. There are several insects 

 that feed on the tobacco thrips. reducing its 

 ravages, also a parasite, not an insect, that 

 will probaoiy prove to be a gregarinid, was 

 found in many of the dead bodies of this 

 pest. It was noticed that in the breeding- 

 cages, which were rather moist, many of 

 the insects were dying and turning black; 

 on examining one of them in water under 

 a high power of the microscope it was 

 found to be packed completely full of small 

 spherical bodies (Fig. 3). These little 

 bodies, 16 to 20 microns or one twelve hun- 

 dred and fiftieth of an inch in size, had 

 entirely exhausted the body contents of the 

 insects, leaving nothing else in them : they 

 were dark purplish black in color with ec- 

 centric nuclei. One of these spheres, on be- 

 ingr crushed, let out about a dozen smaller 



elongated bodies that answered very well to the description of pseudonavicelli, which 

 are usually contained in the spores of gregarinids. 



Fig. 3. Gregarinida in Onion Thrips. (Original.) 



The disease caused by these parasites seemed to thrive best in moist atmosphere, as 

 in the cages. Owing to the lateness of the season, it was not possible to observe the 

 transformations of this interesting organism and thereby to place it accurately. 



In a bulletin of recent date by Prof. Quaintancc of the Florida Experiment Station, 

 the life-history of the insect is described. According to this bulletin, the average length 

 of time required for the adult to be developed from the egg is sixteen days, thus 

 allowing many generations to mature in a single season. However, it is quite probable 

 that in Michigan the time required is somewhat longer because of the colder climate. 

 In Russia, where the insect first appeared on tobacco, there are said to be three gen- 

 erations during the year. 



A description of this insect and of its work, as well as a r6sum6 of the recent liter- 

 ature on the subject, is given by Mr. Thomas Pergande of the United States Depart- 

 ment of Agriculture at Washington.* 



In this account a large number of plants are said to be attacked; among others 

 cabbage, cauliflower, squash, turnip, catnip, sweet-clover, asd cultivated flowers. It 

 is a serious tobacco pest in Russia. 



• Insect Life, Vol. vii, pp. .392-5. 



