SEASONAL HISTORY IN THE IMPERIAL VALLEY. 37 
tion. The larvae become much less numerous and require an extended 
period to complete their growth. In 1910 the last larvae in numbers 
were observed in the field on November 20, while one was observed on 
December 1, and three on December 13, and during the first part of 
December these had all changed to pupae or died. The last adult 
appeared on December 27. In 1911 the larvae were not very abundant 
after the first week in October, and the last ones were observed in 
Los Angeles County on November 21. 
NUMBER OF GENERATIONS. 
In the section of the State in which this insect was under observa- 
tion, the first spring generation may commence as early as January 
10 and probably egg-laying by overwintering adults continues for a 
considerable time. As the period of oviposition is quite extended the 
different broods tend to overlap ; still in midsummer there are certain 
periods when the majority of thrips present may be adults or larvae. 
Up to April 1 there is probably one small full generation occupying 
about 56 days. During April and May a second generation will 
develop; then during the four months of June, July, August, and 
September there is one full generation for each month. For the rest 
of the period of the breeding activity we have probably a partial 
brood that extends over 68 to 73 days. 
Thus during the year this insect has a small generation in both the 
early spring and late fall and five full generations during the rest of 
the time, or seven generations a year. 
SEASONAL HISTORY IN THE IMPERIAL VALLEY. 
The observations on the life cycle of this insect for Imperial Valley 
were conducted by Mr. V. L. Wildermuth at El Centro, CaL, in 1910. 
EGG PERIOD. 
Mr. Wildermuth confined adults in vials with fresh sprigs of 
alfalfa and kept the foliage fresh by wrapping the stems in moist 
cotton until the larvae hatched from the eggs. While many eggs were 
secured by this method, large numbers died before hatching, as the 
foliage became too dry, but, as shown in Table XI, the egg stage 
varied from four days in a single case to five days in a lot of 20 eggs 
laid the last day of August. The length of the egg stage at that 
locality was only one-third as great as that observed by the writer in 
Los Angeles County, but this is due in a large measure to the high 
temperature of the Imperial Valley. 
