320 TEXTBOOK OF ZOOLOGY 



perniciosus Comst. ; the purple scale, Lepidosaphes becki (Newman) ; 

 and the pine scale, Chionaspis pinifoliae Fitch are important scale 

 insect pests. The Cicadellidae or leaf hoppers are represented by the 

 following insect enemies : the sugar-beet leaf hopper, Eutettix tenellus 

 (Baker) ; Delong's leaf hopper, Empoasca filomenta DeL. ; and the 

 grape leaf hopper, Erythroneura comes (Say). Insects of this order 

 are all plant feeders, and they are very numerous ; over sixteen thou- 

 sand species have been described (Fig. 183). 



Order Isoptera. — More than five hundred species of termites, often 

 wrongly called white ants, have been named. Termites are white, 

 soft-bodied, mandibulate insects. They feed principally upon wood, 

 and in the tropics they are one of the most destructive insects known. 

 Termites are social in habits, forming large colonies which are used 

 for years and contain as many as five hundred thousand to a million 

 individuals. The Nevada termite Termopsis nevadensis (Hagen) ; 

 and the western termite, Iteticulitermes Jiesperus Banks, are common 

 and destructive. More will be said of these insects under the dis- 

 cussion of social insects, later in this chapter. 



Order Thysanoptera. — Thrips are very small insects, not more than 

 two to three millimeters in length. They are mostly plant feeders, 

 sucking the juices from the plants. The banded thrip, Aeolothrips 

 fasciatus (L.) and the onion thrip, Thrips idbaci Lindeman are com- 

 mon insect pests. About five hundred species of thrips are known. 



Order Dermaptera. — -The earwigs are small terrestrial, mandibulate 

 insects with a pair of forcepslike appendages at the tip of the ab- 

 domen. The winged species have a short leathery anterior pair of 

 wings which resemble the elytra of some beetles. The small earwig. 

 Labia minor (L.) ; and the toothed earwig, Spongovostox apiceden- 

 tatus (Caudell) are species commonly found in the western United 

 States. 



Hemimetabolous Insects With Incomplete Metamorphosis 



Order Odonata. — The dragonflies and damsel flies are insects with 

 large compound eyes, mandibulate mouth parts, four membranous 

 wings that are finely veined, and a long slender abdomen. The 

 naiads are aquatic and possess a labium which has been highly modi- 

 fied. It can be greatly extended for the catching and holding of 



