354 



JOURNAL OF ECONOMIC ENTOMOLOGY 



\yo[. 8 



In studjdng this species, the experiments were conducted under 

 laboratory conditions where the temperature varies. Temperature 

 readings during day were between 60-80 degrees and during the night 

 between 40-50 degrees Fahrenheit. Observations were made on 

 forty-seven eggs, twenty-two hatched and transformed into adults. 

 The life cycle according to observations under these conditions re- 

 quired an average period of thirtj^-eight days. 



Explanation of Plate 15 



No. 1. The egg in situ on leaf. (Much enlarged.) 



2. Cocoon. (Much enlarged.) 



3. Pupa. (Much enlarged.) 



4. Larva. (Much enlarged.) 



5. Adult. (Much enlarged.) 



6. Cocoon with top dissected away to show pupa. (Much enlarged.) 



7. Showing pupa encased in cocoon. (Slightly enlarged.) 



TH^: MOUTHPARTS OF THE THYSANOPTERA AND THE 

 RELATION OF THRIPS TO THE NON-SETTING OF CER- 

 TAIN FRUITS AND SEEDS 



By Arthur D. Borden, Pasadena, California 



The asymmetry of the mouthparts of the Thysanoptera has been 

 known for a long time, and a number of papers have been published 

 describing in more or less detail the general characters of the mouth- 

 parts. In the present paper is presented a detailed account of the 

 mouth structure of the thrips based on a considerable comparative 

 stud}^ of the mouthparts. It also includes some observations on the 

 feeding habits and on the damage done by certain of the economically 

 important species. As examples of what serious pests are contained 

 in this group of insects, there need only be mentioned the pear thrips 

 (Euthrips pyri), the wheat thrips {Euthrips tritici), the orange thrips 

 {Euthrips citri), the grass thrips {Anaphothrips striatus), the onion 

 thrips (Thrips tabaci), the tobacco thrips {Euthrips fuscus), the 

 greenhouse thrips {Heliothrips hcemorrhoidalis) , and the bean thrips 

 {Heliothrips fasciatus). Nearly all of these are recognized as pests 

 in the state of California. 



The earliest considerable description I have been able to find of 

 the mouthparts is that of Karl Jordan (1888), on Parthenothrips dra- 

 ccence, a fairly accurate description and quite well illustrated. Then 

 came the account of H. Garman (1890), on Limothrips cerealium, who 

 points out the error in considering the articulated lobes of the maxillae 

 as the mandibles, and suggests that the unpaired organ is truly the 

 mandible. In 1891 J. Bohls published as a doctor's dissertation at 



