INSECTICIDES 



347 



Figure 139. Penetration of insect tissue by pyrethrins. 

 A, Section of the integument of an untreated Tenebrio mol- 

 itor larva (200 X). B, Section of the integument of a Tene- 

 brio moliloT larva that had been painted on the dorsal sur- 

 face with Sudan III, dissolved in pyrethrum extract. The 

 trichogen cells at the base of the setae were stained red and 

 appear black in the photograph. The hypodermis also 

 stained red and appears as a black line below the trichogen 

 cells (200 X). 



