INSECT ENEMIES OF WESTERN FORESTS 21 



The white fir cone maggot {Lonchaea viridana Meig.) is the com- 

 mon white maggot found so abundantly in w^hite fir and other bal- 

 sam fir cones (fig. 8). These maggots mine through scales and 

 seeds, often causing great damage. The larvae leave the cones as 

 soon as they fall and form small puparia in the ground. Here they 

 overwinter, and in the spring some of them emerge as small, black, 

 shining flies. The great majority of the brood go through a 2-year 

 life cycle, emerging the second spring after pupation. 



CONE BORERS 



The hard, dry cones of certain pines are frequently attacked by 

 the larvae of flatheaded and roundheaded borers which riddle the 

 interior and destroy the seeds. 



The roundheaded cone borer {Paratimia conicola Fisher) has the 

 habit of boring tunnels through the hard pitch and scales of knob- 

 cone pine cones. It works also in the dry limbs of the species. The 

 adults are a rusty reddish brown, and one-half inch in length. 



The flatheaded cone borer {Chrysophana placida Lee.) has been 

 found boring through the hard, dry cones of knobcone and ponde- 

 rosa pine. It also bores in the dead limbs, branches, trunks, and 

 stumps of practically all western pines and firs. In the adult stage 

 it is a small green or greenish-red beetle, about one-half inch in 

 length. 



SEED CHALCIDS 



Seeds of many conifers are attacked by small wasps of the genus 

 Megastigmus {71), which drill through the young green cones with 

 their long ovipositors and lay their eggs within the immature seeds 

 (fig. 9). The small, white, legless larvae feed on and destroy the 

 tissue within the seeds. The normal outer shell is formed later and 

 shows no evidence on the surface that the seed is infested. The 

 feeding habits of these insects are similar to those of the gall makers. 

 In the following spring the larvae reach maturity and emerge as 

 small yellow or nearly black wasps. Each adult leaves a smooth 

 round emergence hole in the seed coat. Some hold over and emerge 

 the second or even the third year. The damage by these seed-in- 

 festing insects is an important factor in seed collecting, and often 

 a high percentage of cleaned commercial seed will be found to have 

 been ruined by these insects. 



There appears to be no practical means of preventing this damage ; 

 but to avoid the introduction of this insect into other countries, in- 

 fested seeds should be fumigated in a tight container with carbon 

 disulphide. As this fumigant has a deleterious effect upon the ger- 

 mination of the seed if used in excessive dosages, not more than 1 

 ounce of fumigant should be used to 100 pounds of seed, and the 

 fumigant should be completely removed by thoroughly aerating the 

 seeds after they have been in the container for 48 hours. Carbon 

 disulphide vapor mixed with air is explosive, and fire should be 



fuarded against. Calcium cyanide may prove to be a more satis- 

 actory fumigant, but which form of it should be used and how it 

 affects the germination of seeds has not yet been fully determined. 

 Since the gas evolved from calcium cyanide is a deadly poison this 

 material should be used with caution, preferably by persons who 

 have had experience with it. 



