THE TURNIP APHIS 157 



When fresh drops are observed upon a leaf, it is instructive to 

 place a piece of paper or a glass slip on the same spot. It 

 will generally become sprinkled with honey-dew before long, 

 and thus will show that th« sugary fluid does not exude from 

 the leaf, but is dropped from above. Moreover, the drops do 

 not grow steadily, as we should expect them to do if they 

 exuded from the plant, but increase only by running together. 



These slow-moving and almost defenceless creatures have 

 many insect-enemies. Lady-birds and their larvEE, the lace- 

 wing fly (Chrysopa), and the Syrphus-larva, subsist entirely 

 upon them. It is a curious sight to watch the blind and 

 footless Syrphus-larva looping over a bush in search of aphids, 

 exploring every leaf, dropping fearlessly from leaf to leaf, or 

 from a leaf to the ground, and holding up a captured aphis in 

 the air while it devours it. But for these checks to the 

 increase of aphids, it may be doubted whether the plants on 

 which the higher animals depend for food would survive at all. 



Ants often run about plants which are infested by aphids, 

 and have been seen to attack and drive off the aphis-eaters. 

 The aphis can also defend itself to some small extent by 

 pointing its tubes towards the enemy, and discharging the 

 fluid upon his face or jaws. The fluid rapidly coagulates, and 

 may clog the jaws to such a degree that the assailant retires to 

 rub them clean. But it is not common for the aphis to escape 

 in this way. 



The following remedies for aphids have been tried with fair 

 success : — 



(i) Syringing with soft soap and petroleum. Boil one part 

 of soft soap in eight parts of water. Add one part of petroleum, 

 and mix. Keep this as a stock solution. For use, dilute one 

 part of the stock solution with sixteen parts of water. 



(2) Syringing with resin-soap and petroleum. Resin-soap is 

 made by boiling four parts of resin with three parts of washing 

 soda, and fifty parts by weight of water. Boil until all is 

 dissolved. For use, dilute one part of the solution with nine 

 parts of water. 



Single sprays, for example, of rose-bushes, may be quickly 

 cleared of aphids by bending them down into a basin of hot 

 water. The water should be just too hot for the finger. 

 Momentary immersion in such water will kill aphids without 

 injuring the spray. 



