24 MISC. PUBLICATION 273, U. S. DEFT. OF AGRICULTURE 



ous scales, aphids, and bugs. Most of these insects, since tliey are 

 enemies of larger trees as well, will be treated in later discussions. 



While the control of insect pests in forest nurseries is sometimes a 

 difficult matter, the nurseryman, at least, has measures at his dis- 

 posal which would be impractical to use under forest conditions. 

 Some root-feeding insects can be controlled by applying a fumigant 

 to the soil, or by using poisoned baits, but much can be done to avoid 

 injury through regulating cultural methods. Transplant beds which 

 have become heavily infested should be plowed and allowed to re- 

 main fallow for a year. If they are cultivated often enough to 

 prevent the growth of any weeds, most of the insects will have been 

 starved out in a year's time, and the beds can be used again for a 

 short period without serious injury to the transplants. Leaf-feeding 

 insects usually are easily controlled by the use of sprays. 



To protect seedlings from root-feeding insects after they are set 

 out is not so simple, and. so far as is known, no attempt has been 

 made to control soil-inhabiting insects in plantations or forests in 

 the Western States. 



KEY TO DIAGNOSIS OF INSECT INJURY TO SEEDLINGS 



A. Roots of seedlings chewed, injured, or dying. 



1. Rootlets completely bitten off or the bark badly chewed ^ by 



soil-inhabiting insects, appearing as 



a. Curled, white grubs with three pairs of prominent 



legs and with brown heads ^ white grubs, page 24. 



6. Small, curled, white grubs with small brown heads 



but without legs * root weevils, page 26. 



c. Long, slender, hard-shelled, yellow or brown "worms'' 



with feebly developed legs * wireworms, page 26. 



d. Nearly hairless, soft, sluggish, dark-colored caterpil- 



lars working below surface of ground * 



cutworms, page 26. 



2. Tunnels or borings under bark of larger roots 



root bark beetles, page 27. 



3. Large, dark, soft-bodied aphids sucking sap from roots 



root aphids, page 28. 



B. Stems of young seedlings badly chewed or injured." 



1. Stem bitten off, or bark badly chewed — 



a. Nearly hairless, sluggish caterpillars working at 



night cutworms, page 26. 



6. Grasshoppers grasshoppers, page 164. 



2. Borings under bark of larger seedlings bark beetles, page 96. 



C. Leaves of seedlings either chewed, skeletonized, mined, discolored, or 



attacked by leaf-sucking insects defoliators, page 58. 



WHITE GRUBS 



White grubs {29) are probably more common in forest nurseries 

 than any other soil-inhabiting insects. These are the larvae of 

 June beetles (Scarabaeidae), which are widely distributed and feed 

 on the roots of a great variety of plants. The adults are voracious 

 feeders and in the Lake States and elsewhere are often very injurious 

 to the leaves of plants. 



3 Damage meeting this description is done also by root-feeding mammals such as 

 gophers, moles, etc. 



* These characters are not specific and sometimes noninjurious larvae of similar 

 appearance may be confused witli these forms. 



° Similar damage is often done by small animals, such as mice, squirrels, and porcu- 

 pines. 



