THE CITRUS 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 amount 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. 
