VALUE OF A KNOWLEDGE OF ENTOMOLOGY 



II 



be classified with other orders. Among neuropteroid insects of 

 interest to the farmer are the aphis Hons or young of the lace- 

 winged flies (fig. i6) which are beneficial by feeding on noxious 

 insects and the dragon flies, 

 which also do some good in 

 destroying injurious forms. 



The Coleoptera, Lepidop- 

 tera, Hymenoptera, Neurop- 

 tera and Diptera have what is termed a complete metamor- 

 phosis, which means that they undergo four totally different 

 stages, of egg, larva, pupa and adult or imago. In the remaining 



Fig. 1 6-— A lace-wing with eggs at right 



Fig. 1 7. —Tarnished plant-bug; four stages of nyinphs. Enlarged 

 (After Forbes) 



two orders, Orthoptera and Hemiptera, the metamorphosis is 

 incomplete, which means that in the stages between the egg and 

 the imago the insect undergoes only a gradual change, each 

 successive substage (nymph) after the first being very like the 

 one that precedes or follows it (fig. 17). 



NATURAL ELEMENTS IN THE CONTROL OF INSECTS 



The benefits which the agriculturist reaps from the friendly 

 assistance of various forms of insects which prey upon nox- 

 ious forms is very considerable. Every tiller of the soil 



