54 



Annals Entomological Society of America [Vol. X, 



TABLE III. 



Experiment 6. Relative Resistance of Adult and Nymph. 



It was observed during the various experiments that the 

 nymphs apparently were more resistant than the adults. Two 

 experiments to definitely prove this gave the results shown in 

 the following table: 



TABLE IV. 



TABLE V. 



Experiment 6. Relative Susceptibility of Different Species. 



Experiments were tried to ascertain whether there was any 

 difference in the susceptibility of M . femtir-rubrum, M. bivittatus, 

 D. Carolina and S. curtipennis. In no two experiments did the 

 results accord, so we concluded that, as far as these four species 

 are concerned, differences in susceptibility are individual rather 

 than specific. 



Similar results were obtained when we tried to ascertain 

 whether any one species was more susceptible to a culture 

 obtained from the same species or from a different species. • 



