246 RECORD OF CURRENT RESEARCHES RELATING TO 



reproduction of the Aphis, but it does not appear to be necessary to 

 tbe life of tbe insect. 



During December, 1879, the temperature reached — 11° to — 12° C, 

 and not only did not the subterranean Phylloxera in any way suffer, 

 but on the plants and trees in the garden were gathered various 

 species of Aphis, all stiffened by the cold, and often covered with snow 

 or boar-frost, but alive. 



When these were taken into a temperature of 8° to 10'', in two or 

 three days all began to produce young. Suspended only by the cold, 

 the generative faculty, or rather the gemmation, was by no means 

 extinct. 



The author therefore concludes that the hibernating Pseudogynes 

 of those species of Aphis which reproduce indefinitely, suffer very 

 little from the cold, and are capable of resisting very low temperatures. 



Destruction of Insect Pests by means of Fungi.* — Professor E. 

 K. Lankester, in a summary of two recent papers on this subject, says 

 that insect pests such as the Phylloxera and the Colorado beetle, are 

 about to receive a check at the hands of the same class of scientific 

 students as have already reformed surgery by the knowledge 

 obtained of Bacteria, as well as improved the silk, beer, wine, and 

 other manufactures. The application of knowledge of natural facts 

 is in this case a very remarkable one ; for it is proposed to make use 

 of our recently acquired knowledge of diseases due to Bacteria — not 

 that we may arrest such diseases, but that we may promote them. 

 Insect pests are to be destroyed by poisoning them not with acrid 

 mineral poisons which damage plants as well as the insects, but by 

 encouraging the spread of the disease-producing Bacteria which are 

 known to be fatal to such insects. 



Professor Hagen, of Cambridge, Mass., has called attentionf to the 

 old practice of destroying greenhouse pests by the application of 

 yeast. He conceives that this method may be ajiplied to other insect 

 pests. He imagines that the yeast-fungus enters the body of the 

 insect on which it is sprinkled and there produces a growth which is 

 fatal to the insect's life. It is a well-known fact that insects are very 

 subject to fungoid diseases, and it is also ascertained that the applica- 

 tion of yeast to the plants frequented by such insects favours their 

 acquisition of such disease. 



Professor Elias Metschnikoff, the celebrated embryologist, has 

 however made some investigations on this subject and given an expla- 

 nation of the possible value of yeast application,! different and more 

 satisfactory than that which Professor Hagen appears to adopt. 



The general result of the most accurate investigations of the beer- 

 yeast fungus (Saccharomyces cerevisice), is entirely opposed to the notion 

 that it can enter an insect's body and produce a disease. Beer-yeast 

 is beer-yeast and appears always (or within experimental limits) to 



* 'Nature,' xxi. (1880) p. 447. 



t ' Destruction of Obnoxious Insects — Phylloxera, Potato-beetle, Cotton- 

 worm, Colorado Grasshopper, and Greenhouse Pests — by application of the 

 Yeast Fungus,' Cambridge, 1879. 



X 'Zool. Anzeiger,' iii. (1880) p. 44. 



