INSECT ENEMIES OF PRINCIPAL CROPS 161 



Experiment with a contact insecticide. — For the sucking 

 insects (preferably plant lice or aphids) add 25 drops of 

 "Black-leaf-40" or other equivalent nicotine preparation 

 to a quart of water (with a little soap added to make it 

 adhere better), and immerse the aphids in it bodily, either 

 by dipping them if they be on twigs, or by applying the 

 liquid to them in a spray. 



Experiment with a fumigant. — Place the insects with their 

 food in a tight box; throw in some calcium cyanide dust and 

 close the lid tightly. Do not open for twenty-four hours. 



Watch the results of these experiments for a few days, 

 and then write up a brief account of them, and their results. 



Observations on Predatory Enemies 



Natural enemies. — Nature's method of keeping these 

 plant destroyers in check is to set some of their predatory 

 enemies upon them. Thus aphids are consumed by the larvae 

 of the lace-wing fly (fig. 32). If one of these larvae (easy to 

 obtain by sweeping low vegetation with an insect net) be 

 placed among a colony of aphids, it will usually begin feeding 

 at once, picking up one aphid at a time on the tips of its long 

 hollow jaw-tubes, and holding it aloft while sucking out the 

 blood and other fluids from its body; then, casting away the 

 empty skin. Other predatory enemies of aphids are syrphus 

 fly larvae and ladybird beetles and their larvae. 



Observations on the habits of any of these may be made by 

 placing them in the midst of an aphid colony, and watching 

 for their attack upon the aphids. An aphid colony on a 



