^6 THE APPI.l-: LEAF HOPPER 



This gives a total of 1,117, or an average of 51 young per gen- 

 eration in Series B, and the average number of young produced by 

 the first form of each generation of the three above series, D. C and B, 

 is 50. 



Obtaining these results has called, as indicated by the table, for 

 a large number of individual experiments in the insectary, 17 in the 

 case of D, 20 in the case of C, and 11 in the case of B, and has de- 

 manded most careful and painstaking etTort. As stated above, D was 

 started from an egg collected in the river gorge near St. Anthony 

 Park. Series B and C were started from eggs hatched early in the 

 insectarv. D shows a greater prolificacy than either B or C. This 

 may be Awq to the fact of a longer period in the egg, more natural 

 conditions, etc. The table shows that reproduction during July and 

 August was somewhat more rapid than in the earlier part of the 

 season. 



It nuist l)e borne in mind that in the above breedings we have 

 taken only the fir>t individuals in each generation. If it were pos- 

 sible to com])ute tlie entire number of lice coming from a single stem 

 mother with which we started in each series, the sum total would be 

 enormous, be_\"ond belief. 



To give an idea of the prolificness of plant lice of all kinds, we 

 quote from Reaumer's statistics, from which it is shown that a single 

 stem mother, in one season of uninterrupted breeding, may give rise 

 to 5,'>04,*)00,000. To appreciate what an enormous number this is, 

 we quote frtnu one of Dr. Felt's Reports the following illustration: 

 "If these individuals were ranged four abreast, the usual arrangement 

 of a marching column of human beings, and each file closely behind 

 the other, we would have an army long enough to encircle the globe 

 at the ecjualor, and enough would remain to stretch across this conti- 

 nent. In other words, an army 17 r>^l miles long." Fitch, for- 

 merly entomologist of Illinois, estimated the number of aphids (cherry 

 aphids) living at one time on a small cherrv tree to be 12,000,000. 



The eminent Huxley has vividly demonstrated this wondrous 

 fecundity, after careful calculation, estimating that in ten generations 

 of uninterru])ted breeding of plani: lice, starting from one individual, 

 there would result a mass of organic matter equal to the bulk of 

 500,000,000 human beings, or about the i)opulation of the Chinese 

 Empire. Fortunately, climatic conditions and parasitic and predaceous 

 enemies kee]i ])lant lice in check. 



