9° 



THE STUDY OF INSECTS 



In some species one or both sexes are wingless in the adult state; 

 and in others, short-winged forms occur. The cerci are absent. 



The legs are well developed, but are furnished with very peculiar 

 tarsi. These are usually composed of two segments; the last segment 

 terminates in a cup-shaped or hoof-like end and is usually without claws. 

 Fitted into the cup-shaped end of the tarsus there is a very delicate, 

 protrusile, membranous lobe or bladder, which is withdrawn into the cup 

 when not in use but is protruded when the tarsus is brought into contact 

 with an object. This is one of the most distinctively characteristic 

 features of the members of this order. It was this feature that suggested 

 the name Physopoda which is applied to this order by some writers. 



In one suborder, the Terebrantia, the female has a saw-like ovipositor 

 with which she cuts slits in the tissues of plants and then deposits her 

 eggs therein. In the other suborder, the Tubulifera, 

 the female does not have a saw-like ovipositor and 

 evidently deposits her eggs on the surfaces of objects. 

 The metamorphosis of thrips is interesting because 

 it approaches in some respects the type of com- 

 plete metamorphosis. There is a quiescent stage 

 resembling a pupa preceding the imago (Fig. 141). 



The different species of thrips vary greatly in 

 habits, some being injurious to vegetation, while 

 others are carnivorous, feeding on aphids and other 

 small insects, the eggs of insects, and mites, especially 

 the "red spider." Their most important economic 

 role, however, is that of pests of cultivated plants. 

 The thrips that infest plants puncture the tissue of 

 the plant by their piercing mouth-parts and suck out 



Fig. 141. — Last nym- ,1 

 phal stage of a thrips. tne Sap. 



Suborder TEREBRANTIA 



Among those thrips having saw-like ovipositors are found the more 

 important economic species. The onion thrips, Thrips tabaci, is seriously 

 injurious to onions, and often attacks cucumbers, tobacco, cabbage, and 

 cauliflower. 



The greenhouse thrips, Heliothrips hczmorrhoidalis, is a tropical in- 

 sect, which is often a serious pest in greenhouses; it is also found out 

 of doors in the milder California climate. 



The bean thrips, Heliothrips fasciattis, is a serious pest on oranges, 

 alfalfa, pear trees, and various garden crops in California. 



The orange thrips, Sctrtothrips citri, is a serious orange pest in Cali- 

 fornia and Arizona; it deforms the new growth of foliage and causes 

 scabbing and scarring of the fruits. 



The pear thrips, Tmnothrips inebnsequens , infests pears, prunes, 

 peaches, and other deciduous fruits, both in California and in the East. 

 It infests the opening buds and blossoms, stunting the leaves and blast- 

 ing the blossoms. 



The strawberry thrips, Franklhriella tritici, was first described as a 

 pest of wheat. It is found in the flowers of almost all wild and cultivated 

 plants and is the commonest and most widely distributed of all American 

 species of thrips. It is especially injurious to the strawberry. 



