242 



THE AMERICAN NATURALIST [Vol. XLVIII 



be here recorded. The rarity with which the pupae of 

 most species are discovered in collecting suggested that 

 they might not pupate on the food plant of the larvae. 

 Some species of thrips, for example, the pear thrips 

 (Euthrips pyri), are known to pupate in the ground 

 (Moulton, 1912). Since many of the species included in 

 Table I may be found on white clover, which was abun- 

 dant at Douglas Lake, the place of pupation of these 

 species was tested in the following manner. A mass of 

 the flowers of white clover was collected. The flowers 

 were gently squeezed for some time to drive out all the 

 adults. They were then placed in a vessel under cover. 

 After two days, when the flowers were thoroughly dried, 

 they were again gently crushed to make sure that all 

 adults were driven out. At intervals from one to two 

 weeks afterward, 15 adult thrips appeared on the inside 

 of the glass cover. These were of three species, Euthrips 

 tritici, Thrips tutxici and Authotlirips niger. 



I have also frequently observed the pupae of Antho- 

 thrips verbasci in mullein spikes, those of Sericothrips 

 cinrpdatus on white clover, the pupa of Trichothrips tri- 

 dentatus under the bark of the white oak, where the larvae 

 and adults live, and that of an undescribed species on 

 willow galls along with larvae of the same species. I 

 judge from these observations that the majority of thrips 

 pupate on the plants on which the larvae live, and that 

 their rarity in collections is due merely to concealment 

 and sluggish habits. 



Discussion of the Results in Relation to the Life 

 Cycle 



From the data in Table I and the observations given 

 above it is evident that there is considerable diversity in 

 different species with regard to the life cycle, and diver- 

 sity within the same species at different times or in 

 different regions. First, as regards the mode of passing 

 the winter, it would seem that in Euthrips tritici only the 

 females survive that season. The reason for so believing 



