EXPERIMENT STATION BULLETINS. 215 



The larval stage of this insect is known as the tobacco-worm 

 or the tomato-worm, depending on the host on which it happens 

 to be feeding at the time. It is a naked, green caterpillar of large size 

 and is feared because of the prominent curved spine at the posterior 

 extremity. It is also found commonly on the potato. When full grown, 

 it sometimes measures three inches in length. The pupal stage is passed 

 in the soil. The pupa is remarkable for the jug-handle form shown in 

 the figure. From this pupa comes the adult moth which is grey in gen- 

 eral color, and is one of the hawk-moths or humming-bird moths so com- . 

 mon about petunias, etc., at dusk. 



REMEDIES. 



This caterpillar is so conspicuous and its work so easily detected thai 

 there is usually little trouble in hand-picking. Paris-green will kill 

 many of them in time but poison works slowly on these large insects 

 and a good deal is required to kill them so that it is best to expedite 

 matters by hand-picking. Then, too, paris-greeu is not safe on tomatoes 

 after the fruit is well started. 



DIRECTIONS FOR PREPARING INSECTICIDES. 



Most insects mav be classified either as chewing insects or as sucking 

 insects. Beetles, grasshoppers, etc., chew their food, while bugs suck 

 theirs by means of long piercing beaks with which they penetrate inside 

 to the juicy parts of the plants. Moths and butterflies suck their food, 

 when in the adult condition, but chew it when in the larval state. Now 

 chewing insects, in many cases, eat foliage, fruit, etc., and if this food 

 be treated with a coating of some arsenical poison, they get the poison 

 in the ordinary course of events, and die. Many chewing insects, like 

 some of the borers, are protected in their burrows and never eat at the 

 surface of the plant except possibly, when just entering the plant. 



Sucking insects are not affected by poisons of this nature, as they 

 draw their supply of food from beneath the surface. With them it is 

 necessary to use some substance like kerosene-emulsion, which kills by 

 contact, but does not injure the plant. Special contact insecticides have 

 been found to work well against special insects and at certain definite 

 times, therefore the best results are obtained by using a variety of kill- 

 ing agents, each suited to a particular purpose. 



While it is necessary to spray evenly and thoroughly with an arsenical 

 poison, like paris-green, it is easily seen that the utmost care is required 

 to obtain good results with a contact insecticide. Most beetles and 

 caterpillars wander about more or less and some of them will find the 

 poison themselves, on the other hand, each insect must be hit by a 

 contact insecticide to be killed. 



As everyone knows, the arsenical poisons are the cheapest when effec- 

 tive, and when nothing prohibits their use. Vegetables well advanced 

 or those which ripen quickly, should not be spraj'ed with permanent 

 poisons like paris-green. Hellebore has the advantage of losing its 



