INSECTICIDES 



349 



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Figure 140. Effect of pyrethrum concentrate on nerve 

 ganglia. A, Cross section of the ventral nerve ganglion of 

 Tenebrio molitor larva killed by decapitation and stained 

 with toluidine blue (1350 X). B, Cross section of the ventral 

 nerve ganglion of Tenebrio molitor larva that had been killed 

 with pyrethrum extract and stained with toluidine blue 

 (1350 X ) . Note the vacuolated tissue with dark stained mar- 

 gins; the violet stained areas in the lower part of the photo- 

 graph appear black. 



