INSECTS ON GREENHOUSE PLANTS 215 



sucking insects have hard, outer body-coverings, which 

 act as a means of defense from contact poisons. 



As before noted, insects breathe through minute open- 

 ings in the segments of the abdomen. Anything which 

 closes these produces suffocation. Certain gases are, 

 therefore, as injurious to insect life as are poisonous gases 

 which enter the lungs of human individuals through the 

 nostrils. 



A study of structure and habits reveals the fact that 

 there are four principal methods of combating insects: 

 first, by poisoning with substances taken into the diges- 

 tive system through the mouth : second, producing death 

 with irritating chemical substances which destroy the 

 skin and the tissues beneath; third, by suffocation 

 through closing the breathing pores of the body ; fourth, 

 by poisoning with gases which are taken into the body 

 through the breathing pores. 



241. List of pests commonly found in greenhouses. 



(a) Chewing. 



(1) Exterminated by hand picking or arsenical poisons. 



Leaf Rollers, Archips, various species. 



(2) Exterminated by freezing the soil in winter, or by 



removing them from the soil. 



White Grubs, Lachnosterma, various species. 



(3) Exterminated by trapping with poisoned bait, or by 



hand picking. 



Cutworms, various genera and species. 

 (6) Sucking. 



(1) Exterminated by water sprays and salt solutions. 



Red-Spider, Tetranychus bimaculatus Harvey. 



(2) Exterminated by tobacco fumes. 



. ,. I Myzus persicae Sulz. 

 Green Aphis | N 4 taro P phora rosfe Linn< 



Black Aphis, Nectarophora chrysanthemicolens 

 Wahl. 



(3) Exterminated by tobacco dust in soil. 



Blue Aphis, Aphis middle tonii Thos. ( ?) 



