158 INSECTS AFFECTING VEGETATION 



will be necessary to repeat the spray as often as the lice appear. As 

 in the case of the lice on cherry, the difficulty lies in reaching the lice 

 and not in making a spray that will prove effective. (Bui. 45, Ga. 

 Agr. Exp. Sta.; Bui. 233, Mich. Agr. Exp. Sta.) 



INSECTS AFFECTING THE HOP. 



Hop Merchant. The spiny caterpillar of the hop-merchant is 

 known to all hop growers. After a time, these caterpillars change to 

 the naked pupa? which are marked with golden or silver spots. From 

 these pupae come the adults, very pretty butterflies of a general brown- 

 ish color, marked with darker brown and slate. On the underside of 

 each hind-wing is a silver mark, shaped like a comma, from which 

 the insect takes its Latin name. The eggs are laid in strings on the 

 leaves. Besides hops, the caterpillars feed on elm and nettle. 



The only remedies are hand picking and spraying with arsenical 

 poisons early in the season. After the hops form, no sprays should 

 be applied because of danger from poisoning. 



The Violet-Tip. The violet-tip closely resembles the hop-mer- 

 chant. It is, however, larger and the greys on the wings are apt to 

 take on a more purplish tint. Each hind-wing is marked with a 

 silver spot something like an interrogation mark. The larvae feed 

 on nettle, elm and blackberry as well as on the hop. The treatment 

 is the same as that for the hop-merchant. 



Hop-Louse. Such a fragile creature as an aphid can hardly 

 hope to pass the winter successfully on such a plant as the hop which 

 is spread on the ground during the cold season. For this reason a 

 curious habit has been developed. Late in the season, winged sexual 

 forms are developed from the non-sexual form of the lice that have 

 been feeding on the hop all summer, and these sexual forms lay their 

 eggs on the plum trees, where the eggs are in good high situations, 

 safe for the winter except from birds and other enemies. In the 

 spring, wingless forms are produced at first, and from these, winged 

 females which migrate to the hop to become the parents of the myr- 

 iads of lice which later appear. 



The lesson to be learned from this life-history is very easy to 

 see. Avoid having plum trees, either cultivated or wild, near the 

 hop yards. If it is impossible to do this, then spray the plums with 

 kerosene-emulsion, or tobacco-water just as soon as the eggs hatch, 

 and spray with extreme care so as to hit as many of the lice as pos- 

 sible, before they migrate to the hops. It will be necessary, in many 

 cases, to spray the hops themselves, especially the vines on which the 

 lice first appear, and which serve as centers of infection for the rest 

 of the field. (Bui. 233, Mich. Agr. Exp. Sta.) 



Onion Thrips. Tiniest of all the insects mentioned in this 

 paper, is the onion thrips. A little larger than a printed period 

 and very active, it is so small and quick in its movements, that it is 

 usually overlooked. The injury is brought about by the great num- 

 bers that collect on the plants. On the onion, the thrips prefer 

 the axillary portion of the plant, w r here tw r o leaves join. They 

 scrape the soft material off the leaves, giving them a grey or hoary 



