842 



ANNUAL REGISTER, 1805. 



*' seasons, but continue to multiply. 

 *' Their enemies, on the contrary, 

 *' exist, but do not multiply, at least 

 *' in the open air, durin^j such peri- 

 *' ods ; and thus the aphis gets the 

 *' start of them, and acquires an as- 

 " cendancy, which once acquired 

 *' is not easily overcome by artificial 

 *' means, upon a large scale at least, 

 *' in the open air. Vain would be 

 " the attempt to clear a hop-garden 

 " of these pernicious vermin, or to 

 " rescue any extensive crop from 

 " their baneful effects. Violent 

 *' rains, attended with lightning, 

 *' have been supposed to be very 

 " efl'ectual in clearing plants of 

 *' them ; but in such case more is to 

 *' be attributed to the plants being 

 *' refreshed and made to grow by 

 *' the rain, of which they stood in 

 " need, than to any destruction of 

 " the aphides themselves, which, on 

 " accurate examination, will be 

 " found to be as plentiful after 

 "such rains as they were before; 

 " nor is wet so injurious to these 

 " insects as many imagine, as is 

 " evident from the following ex- 

 " periment. On the 12th of May, 

 " 1799, I immersed in a glass of 

 " water, the footstalk of a leaf of 

 " considerable length, tali en from a 

 " stove-piant beset with aphides of 

 " a dark lead-colour, which were 

 " feeding on it in great numbers. 

 " On immersion they did not quit 

 " the stalk, but immediatdy their 

 " bodies assumed a kind of luminous 

 *• appearance, from the minute bub- 

 *' bles of air which issued from them. 

 " They were put under water at a 

 " quarter past six in the evening, 

 " and taken out at a quarter past 

 " ten the next morning, having con- 

 " tinued immersed sixteen hours. 

 " On placing them in the sunshine, 

 '• some of them, almost immediately, 

 1 



" shewed signs of life, and three 

 " out of four, at least, survived the 

 " immersion. One of the survivors, 

 " a male, very soon became winged, 

 " and another, a female, was deliver- 

 " ed of a young one. -Many years 

 " before this experiment, with a 

 " view to destroy the alphides, 

 " which infested a plant in my green- 

 " house, I immersed, One evening,the 

 " whole plant, together with the pot 

 " in which itgrew, in a tub of water. 

 " In the morning I took out the 

 " plant, expecting with certainty to 

 " find every aphis dead ; but, to my 

 " great surprise, they soon appeared 

 " alive and well : and thus, in ad- 

 " dition to the other extraordinary 

 " phenomena attendant on these in- 

 " sects, we find that they are capa- 

 " ble of resisting the efiects of ini- 

 " mersion in water for a great 

 " length of time. When taken from 

 " the plant on which they feed, and 

 " kept under water, they do not 

 " survive so long ; their struggling, 

 " in that case, perhaps exhausts t hem 

 " sooner. This part of the subject 

 " might, perhaps, be pushed much 

 " farther : it is sufficient for our 

 " purpose, to have shewn, that wet 

 " is not so hurtful to them as is ge- 

 " nerally imagined." 



" Though no mode of destroying 

 " aphides will perhaps ever be de- 

 " vised on a large scale in the open 

 " air, by artificial means, we can 

 " accomplish it most effectually 

 " when they infest plants in green- 

 " houses and frames, or in any situa- 

 " tion in which we can envelop 

 " them, for a certain time, in clouds 

 " of smoke. Powders or liquids, 

 " however fatal to aphides, must 

 " ever be ineflectual, from the trou- 

 " ble and difficulty of applying them 

 " so that they shall come in contact 

 " with those insects, situated as they 



" usually 



I 



