84 -Wr» CiRTis's OhfervatioHS on ApbiJes^ 



iifoal means of diminution fall in preventing them from doing irre- 

 parable injury to certain crops. 



In fevere winters we have no doubt but Aphidei are very confider- 

 ably diminillied ; in very mild winters we know they are very con- 

 fiderably increafed ; for they not only exift during fuch feafons, 

 but continue to multiply. Their enemies, on the contrary, exift, 

 but do not multiply, at Icaft in tlie open air, during fuch periods ; 

 and thus the A[>h'n gets the ftart of them, and acquires an afcen- 

 dency, which once acquired is not eafily overcome by artificial 

 means, upon a large fcale at leafl-, in the open air. Vain would be 

 the attempt to clear a hop-garden of thcfe pernicious vermin, or to 

 refcue any extenlive crop from their baneful efFefts. Violent rains 

 attended with lightning have been fiippofed to be very efFeftual in 

 clearing plants of them ; but in fuch cafe more is to be attributed to 

 the plants being refrcHied and made to grow by the rain, of which 

 they ftood in need, than to any deftruftion of the ^A/Vi?j' them- 

 felves, which, on an accurate examination, will be found to be as 

 plentiful after fuch rains as they were before ; nor is wet fo injurious 

 to thefe infeds as many imagine, as is evident from the following 

 experiment: On the 12th of May 1799, I immerfed in a glafs-of 

 water the footftalk. of a leaf of confiderable length, taken from a 

 flove plant, befet with Aphides of a dark lead colour, which were 

 feeding on it in great numbers. On immerfion they did not quit 

 the ftalk, but immediately their bodies affumed a kind of luminous 

 appearance from the minute bubbles of air which iflued from them. 

 They were put under water at a quarter part fix in the evening, 

 and taken out at a quarter paft ten the next morning, having 

 continued immerfed fixteen hours. On placing them in the 

 fun-lliine, fome of them almoft immediately ihowed figns of life, 

 and three out of four at leaft furvived the immerfion. One of the 

 furvivors, a male, very foon became winged, and another, a female, 



was 



