THE CITBUS THRIPS. 21 



deposition was secured in two experiments, in which the insects 

 oviposited at the rate of 0.7 egg each per day. This is probably 

 below the normal rate in the field in summer. The largest number 

 of eggs occurring in the ovisac at one time and developed suffi- 

 ciently to be observable with the ordinary powers of the microscope 

 is five, and it is improbable that more than this number would 

 develop and be deposited in one day. In 1911, of 1,050 female 

 thrips collected monthly from April to October, inclusive, developed 

 eggs were absent from 644, which may have oviposited just before 

 captivity and were therefore not taken into account. In the remain- 

 ing 406 insects there were 493 eggs, an average of 1.2 each. The 

 percentage of thrips with only one egg visible was 80.7 per cent; 

 with two eggs present, 17.1 per cent; and with more than two, but 

 2 per cent. It may be inferred from these data that on an average 

 a single specimen will not deposit more than one egg per day, 

 though the number will vary slightly with the character of the 

 season and the quality and amoimt of food. Earely as many as 

 five may be deposited. 



It would seem that in cool seasons such as 1911 the citrus thrips 

 will deposit, on an average, only from 26 to 70 eggs in the course of 

 her life, and this is believed to be one of the chief reasons for the 

 relatively light infestation of thrips in that season as compared with 

 such seasons as 1908 and 1909. In such exceptionally favorable 

 seasons as the last mentioned it is possible that a large proportion 

 of the insects might live the maximum of 49 days and deposit the 

 maximum of 5 eggs each per day, making a total of 245 eggs for the 

 individual. 



DURATION OF THE LIFE CYCLE. 



The duration of the life cycle was determined by two methods, 

 viz, by the complete rearing of individual specimens through all 

 the stages and by adding together the number of days in the egg, 

 larval, and pupal stages. Owing to difficulties in handling only a 

 comparatively small number of insects (13 to be exact) were carried 

 through all the stages. From this record, obtained in May and early 

 June, 1911, a maximum life cycle of 31 days, minimum of 28 days, 

 and average of 29.8 days were secured. From the abundant data 

 assembled in determining the duration of the separate immature 

 stages the life cycle was found to be 33.9 days in May and early 

 June and 29.1 days in September, months in which the weather was 

 moderately cool ; and in the period from June to September, during 

 the hot weather, it was 15.2 days. The data are given in detail in 

 Table VI. The figures do not take into account the three or four 

 days between emergence and the first oviposition, which should be 

 added for the complete life cycle. 



