FOREST PROTECTION 27 



case should a remedy be attempted by one who is not fully 

 informed as to the life history and food-habits of the insect 

 enemy, and with the remedy to be used. In either event 

 more damage than benefit may result. For instance, trap- 

 trees may often be successfully used against certain insect 

 pests; but unless destroyed at the proper time, just before 

 the emergence of the adults, the numbers of the enemy will 

 be increased rather than diminished. The advice of a com- 

 petent Forest Entomologist should be obtained wherever pos- 

 sible. 



C. INSECT ANATOMY. 



I. The body of an adult insect is divided into three regions. 



a. The head consists of a single segment, and bears 

 exteriorly a pair of antennce, a pair of compound eyes, 

 the ocelli, which vary in number and are often absent, 

 and the mouth parts, consisting of the labrum, two 

 mandibles, two maxillce, and the labium. Maxillary 

 and labial palpi are also present, sometimes so modi- 

 fied however as to be not easily recognizable. The 

 difference between "biting" and "sucking" mouth 

 parts is important both in classification and as re- 

 gards methods of treatment. 



b. The thorax consists of three segments, the prothorax, 

 the mesothorax, and the metathorax. Each segment 

 bears a pair of legs, and the mesothorax and meta- 

 thorax normally bear the fore and hind wings. The 

 legs are also segmented, the joints bearing the fol- 

 lowing names: The segment attached to the thorax 

 is called the coxa, then come in order the trochanter 

 (sometimes made up of two short segments), the femur, 

 the tibia, and lastly the tarsus made up of several 

 segments on the last of which are borne the claws. 

 The wings are composed of two membranes held to- 

 gether by supporting rods called veins, or nerves, and 

 are sometimes covered with hairs or scales. In the 

 case of the Coleoptera, the fore wings (Elytra) are 

 hard and leathery, and the veins are absent. 



c. The abdomen consists of several segments, some or 

 all with stigmata or breathing pores. The external 

 reproductive organs are usually borne on the last or 

 anal segment of the abdomen. In certain species 

 an ovipositor (laying-tube), or a saw-like instrument 

 assists the female in oviposition. 



