Mr. CuRTis*s Ohfervatlom on Aphides ^ 



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

 parable injury to certain crops. 



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

 afely dimlniilied ; in very mild winters we know they are very con- 

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

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

 but do not multiply, at lead in the open air, during fuch periods; 

 and thus the Aphh gets the dart of them, and acquires an afcen- 

 dency, which once acquired is not eafily overcome by artificial 

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

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

 refcue any extenfive crop from their baneful efFecls. Violent rains 

 attended with lightning have been fuppofed to be very effedlual in 

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

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

 they ftood in need, than to any deftruftion of the Aphides 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 infe£ls as many imagine, as is evident from the following 

 experiment: On the 12th of May 1799? ^ 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 afTumed a kind of luminous 

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

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

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

 continued immerfed ftxteen hours. On placing them in the 

 fiin-fliine, fome of them almofl immediately Ihowed figns of life, 

 and three out of four at lead furvived the immerfion. One of the, 

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



was 



