June, '15] BORDEN: MOUTHPARTS OF THE THYSANOPTERA 



359 



Obsekvations on Feeding Habits 



The mouthparts of the Thysanoptera are probably used almost 

 entirely for sucking although they have been repeatedly described as 

 intermediate in form between those of sucking and chewing insects. In 

 feeding, the insect begins by a forward and backward movement of 

 the head and by this sort of rasping movement punctures the epidermal 

 cells of the plant tissue. It then lowers its head and begins to suck 

 up the plant juices. It remains here until the punctured cells are 

 nearly emptied when it moves on a bit and repeats the operation. 

 From the structure of the mouthparts it appears that the strong 

 mandible and possibly the hypopharynx are used in breaking the cells 

 of the tissues, while the finer stylets of the maxillae are using in lancing 

 the softer tissues. The tip of the labrum placed over the puncture 

 forms a close connection and the juices are easily sucked up into the 

 mouth. The whole mouth cone is fitted for sucking and most likely 

 the food is almost entirely plant juices. I have made observa- 

 tions on the greenhouse thrips, Heliothrips hoemorrhoidalis and Par- 

 thenothrips dracoenoe on leaves of a greenhouse plant, and also on 

 Euthrips pyri, the pear thrips, on fruit blossoms, as well as Euthrips 

 tritici and Euthrips occidentalis on alfalfa blossoms. The feeding habits 

 of the young are similar to those of the adult. 



Results of Feeding on Deciduous Fruits 



On the deciduous fruits the thrips feed on the tender floral parts 

 (the tips of the petals of the opening buds and later on the inner floral 

 parts including the tender stigma) with very damaging results to the 

 setting of the fruit, where the insects occur in any great numbers. 

 The injured tissues at first turn brown and later black, often resulting 



Explanation of Plate 16 



Fig. 1. Head of Euthrips tritici: a, rudiment of chitinous band to right eye; ht 

 chitinous band to left eye; c, cljrpeus; d, chitinous band under frons; /, man- 

 dible; g, maxilla; h, maxiUary palpus; i, maxiUary stylet; j, labium k, labial 

 palpus; I, labrum; m, hjrpopharynx. 



Fig. 2. Same with mouth parts removed: a, rudiment of chitinous band to right eye; 



h, chitinous band to left eye; c,clypeus; curved spine from chitinous band; 

 e-chitinous band. 



Fig. 3. Tip of labrum, side view. 



Fig. 3a. Tip of labrum, under-side showing stylets in position. 

 Fig. 4. Maxilla: e, part of chitinous band; g, main -part of maxilla; h, maxillary pal- 

 pus; i, maxiUary stylet. 

 Fig. 5. Hypopharynx removed, showing socket and muscular attachment. 

 Fig. 6. Mandible removed. 

 Fig. 7. Labium ventral side. 



Fig. 7a. Labium dorsal side, showing chitinous rod (n). 



