INSECTS ON GREENHOUSE PLANTS 213 



grouped in three divisions: the head, which contains 

 the organs of vision, the antennae or feelers, and the 

 mouth parts; the thorax, containing the organs of loco- 

 motion, the legs and wings ; and the abdomen, containing 

 the organs of digestion, respiration and reproduction. 

 Careful examination of each segment of the abdomen 

 shows breathing holes, or spiracles, which connect with 

 air tubes extending to all parts of the body. 



237. Metamorphoses. Many insects in the course of 

 their development pass through four distinct stages of 

 existence. The first is the egg ; the second the larval ; 

 the third the pupal ; and the fourth the mature or adult 

 insect. Attacks made on certain species of insects are 

 the most successful while still in the egg stage. In other 

 species, the pests are exterminated most easily in the 

 larval stages, while in still others, the adult stage is the 

 most opportune time for extermination. Many florists 

 have no knowledge of the changes which insects undergo. 

 These changes are usually spoken of as metamorphoses. 

 Insects which pass through all stages of development are 

 said to have complete metamorphoses. In some insects 

 the changes are less pronounced, and such are said to have 

 incomplete metamorphoses. 



In the larval stage, many insects are voracious feeders, 

 and then it is that much damage is done to florists' crops. 

 The larvae are generally known as worms, grubs, borers 

 or maggots. The most active insects become more or 

 less dormant in a later stage, and often weave a web, or 

 cocoon, about themselves, passing into a stage of apparent 

 rest. Marvelous transformations are, however, going on 

 beneath the cocoon covering, and in due time the com- 

 plete, or perfect insect emerges in a winged form. Some 

 insects pass the entire winter in the cocoon stage. The 



