SCIENCE. 



[Vol. XXI. No. 521 



SCIENCE: 



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NOTES FROM THE CORNELL INSECTARY. 



BY M. v. SLINGEBLAND, CORNELL UNIVERSITY, ITHACA, N Y. 



II. — Some Observations Upon Plant-Lice 



Moke than three-quarters of a century ago Kyber, a German 

 observer, published under a similar title the results of experiments 

 which not only confirmed the earlier observations of Bonnet and 

 De Geer, but which also threw increased light on the generation 

 and development of Aphids. Kyber found, for instance, that by 

 keeping the insects in a warm room a series of agamic generations 

 was produced which extended through four years without the 

 intervention of the sexual forms. However, no record was kept 

 of the number of generations produced during the time. In 1779, 

 thirty-sis years before Kyber's experiment. Bonnet had carried 

 Aphis sanibuoi through nineteen generations without commerce 

 with the male insect. From these and similar experiments a la w 

 has been educed, which we dare not deny, that "under certain 

 circumstances a female Aphis may, without coupling, continue 

 propagating to infinity, provided that the necessary conditions 

 for the development of young — food and heat — are not want- 

 ing." 



April 2, 1890, nearly two years and ten months ago, the writer 

 isolated a nymph recently born of a wingless agamic female 

 plant-louse, and since that time the experiment has been con- 

 tinued and is now in progress in the green-house at the Insectary 

 of the Cornell Agricultural Experiment Station. The icsect is 

 probably Myzus achyrantes Monell, one of the "green-flies" of 

 florists, which is always to be found in considerable numbers 

 upon the varieties o( Achyrantes grown in the Insectary; at one 

 time it also attacked buckwheat and radishes growing in the 

 green-house. 



The experiment has been conducted in the following manner: 

 The flrst nymph was isolated by placing her on a small plant 

 known to be free from Aphids, and this plant was kept in a cage 

 made by placing the flower-pot in a large saucer partly filled with 

 sand, and then placing over the plant and pot a glass cylinder, 

 which sank for a slight distance into the sand, and was covered 

 with Swiss muslin at the top. The nymph was examined daily, 

 and when she became a mother two or three of her young would 

 be isolated in similar cages. When these daughters of the original 

 mother became mothers themselves, their young would also be 

 isolated, and so on. Not all of the young of each parent were 

 allowed to live, and sometimes, to save cages, a mother would be 

 removed to give place to one of her daughters; usually, however, 

 a mother would not be destroyed until some of her daughters be- 

 came mothers, for it frequently happened that some of the nymphs 

 first isolated died before becoming mothers. In some cases the 

 mother was left undisturbed, the young being removed and 

 counted every day or two, to see how long she would live, how 

 many nymphs might be born of a single mother, and whether 

 there was any diminution in the reproductive power as generation 



after generation passed by without the male element again entering 

 into the case. Great care has been taken to insure the isolation of 

 the nymphs; when there was any doubt as to the pedigree of the 

 nymph, she was immediately replaced by one of known pedigree. 

 Nothing but wingless agamic females have thus far been pro- 

 duced in the cages. "Winged forms are sometimes seen, in April 

 especially, on the other Achyrantes plants in the Insectary. The 

 following table has been prepared to show the number of the 

 generations, the rapidity with which they have been produced, 

 and many other interesting points which have been brought out 

 during the two years and ten months that the writer has cared 

 for these little creatures — my pets, as I call them. 



Let me point out a few of the most interesting facts to be 

 gleaned from an examination of the above table Sixty-two gen- 

 erations have been produced thus far, or nearly two (1.8) genera- 

 tions a month on an average. The extremes were in the 13th and 

 14th generations, when it took a month for a generation to de- 

 velop; and in the 46th, 47th, and 48th generations, which were 

 all produced within a month. 



This difference was due to the fact that the plants had become 

 old, stunted, and pot-bound when the 13th and 14th generations 

 of the Aphids wei-e produced, while in the other case the plants 

 were young and vigorous. It was also found that this difference 

 in the plants produced not only the retardation of development of 

 the Aphids, but there was also a very marked difference in their 

 size and reprpductive power. On these stunted plants it takes 

 from two to three times as long for the nymph to develop, it does 

 not attain more than one-third the size, and less than one-third 



