DIPTERA 



159 



ing from the pupal stage of most insects. The pupa of Anopheles has a 

 narrower and more pointed head and much shorter and wider breathing 

 tubes than those of Culex. 



Mosquitoes flourish alike in the heated moist regions of the tropics and 

 in the frigid regions of ice and snow. Many species have their haunts and 

 breeding-places in fresh water, others breed abundantly and some perhaps 

 exclusively in brackish water. They are found even in arid regions far 

 from water, where it is probable they lay their eggs in the ground. So, 

 go where we will, we cannot escape them, we must fight them. 



Fig. 131. Wheat plant, showing injuries by Hessian fly: a, Egg of Hes- 

 sian fly; b, larva; c, flaxseed; d, pupa or chrysalis; e, female, natural size; 

 /, female; g, male; h, flaxseed or pupal stage between the leaves and stalk; 

 i, chalcidid parasite; all enlarged except wheat stem and e. (After Riley, 

 Burgess, and Trouvelot.) 



A very easy and successful way of getting rid of mosquitoes in a pond 

 which will sustain fish is to stock it with such fish as the " top-minnow," 

 sun-fish, and stickleback, whose young especially feed upon the larvae. 

 Dragon-flies also should be encouraged and protected, since their nymphs 

 feed upon the larvae of mosquitoes, and the adults are voracious feeders 

 upon the mosquitoes. In fact, if it were not for the dragon-flies, life in the 

 Hawaian Islands would be almost intolerable on account of the hordes of 

 mosquitoes. Pools and marshes should be drained, or, if the pool or mud- 



