INSECT ENEMIES OF WESTERN FORESTS 27 



leaving a visible sign, and the small, white, legless larvae develop 

 within the seed coat, completely consuming the cotyledons. The 

 full-grown larvae leave the seed late in the fall or winter to pupate 

 in the ground, from which they emerge as adult weevils late in 

 June and throughout July. Sometimes over 60 percent of the seed 

 crop is thus destroyed. This weevil has been reared from Oregon 

 ash in Oregon and Washington. 



In the Southwest forest trees belonging to the family Legumino- 

 sae — such as cat's claw (Acacia), mesquite (Prosopis), horsebean 

 {Parkins onia) , palo-verde (Cercidium), and locust (Robinia) — 

 frequently have their seeds infested and destroyed by the small, 

 white, curled, legless grubs of species of bean weevils of the genus 

 Bruchus. The adults are small, stout, brown to black beetles about 

 y 8 inch long. 



INSECTS INJURIOUS TO FOREST NURSERIES 



A forest nurseryman must guard against insect enemies of 

 young trees, as well as against damping-off, rodents, heat injury, 

 and unfavorable soil conditions. Young seedlings in seed and 

 transplant beds are frequently damaged by root-feeding insects, 

 which are able to inflict more injury at this stage than later, after 

 trees have become established and have developed larger root sys- 

 tems. The stems of young seedlings may be attacked above ground 

 by cutworms, grasshoppers, leafhoppers, aphids, and various bark- 

 chewing beetles ; and the leaves may be fed upon by caterpillars, 

 sawflies, and various scales, aphids, and bugs. 



In western forest nurseries, white grubs, strawberry root 

 weevils, seed-corn maggots, cutworms, symphylids, grasshoppers, 

 and aphids are some of the pests that have been particularly 

 troublesome. But in general these nurseries have been more fortu- 

 nate than those in the East in escaping insect pests (107) . 



Although the control of insect pests in forest nurseries is some- 

 times a difficult matter, the nurseryman has measures at his dis- 

 posal which would be impractical to use under forest conditions. 

 Most root-feeding insects can be controlled by applying a soil 

 fumigant, or by using poisoned baits, but much can be done to 

 avoid injury through regulating cultural methods. Certain new 

 soil fumigants, such as D-D (dichloropropane-dichloropropylene) 

 and ethylene dibromide have largely taken the place of the older 

 soil fumigants, such as carbon disulfide, chloropicrin, calcium 

 cyanide, dichloroethyl ether, paradichlorobenzene, and naphtha- 

 lene. Transplant beds that have become heavily infested should be 

 plowed and allowed to remain fallow for at least a year. If they 

 are cultivated often enough to prevent the growth of 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 



