October, '16] , MCGREGOR: BUCCULATRIX THURBERIELLA oOO 



It is very likely that under the most favorable conditions the com- 

 pletion of one generation requires little in excess of two weeks. 



Parasitism 



At least two species of chalcidid flies have been bred from the Buccu- 

 latrix pupae. Twenty cocoons were collected in the field during the 

 last of June and kept under observation in the laboratory. Of. these, 

 16 gave issue to parasites, thus yielding a computed parasitism of 80 

 per cent. Many larvae of the first instar were also being killed at that 

 time by a parasite which attacks them while in the leaf mines. Al- 

 though we have observed a high mortality among individuals of the 

 mining stage, we have been unable to breed perfect adults from such 

 material. During August, again, the parasitism of the cotton leaf- 

 perforator became heavy. No specific determinations of the parasites 

 have yet been made. 



Origin of Pest 



The question has arisen in the writer's mind whether Thurberia or 

 cotton (Gossypium) is the original native host of Bucculatrix thurberi- 

 ella. Domestic and wild cotton were planted in the garden of the 

 Bureau's station at El Centro and germinated at the same time. Thus, 

 plants of the two malvaceous genera, of the same age and condition, 

 were present side by side at the time of the appearance of the cotton 

 leaf-perforator. It seems significant that the Gossypium plants early 

 became heavily infested, while the Thurberia plants (growing immedi- 

 ately adjacent) remained entirely free for weeks. Furthermore, as 

 previously stated, no cotton field in the valley has been found free from 

 the Bucculatrix during June, July and August, which condition is also 

 significant. 



If Thurberia is the native host of the tineid pest one would naturally 

 expect to find this plant occurring in its usual mountainous environ- 

 ment bordering the Valley. Since the prevailing winds at the time 

 of the first appearance of the insect are from the west, it would be 

 natural to suppose that the migrating individuals originally came from 

 wild cotton occurring in the mountains bordering the Valley on the 

 west — provided Thurberia is the native host of the species. With 

 this possibility in view several trips have been taken into the mountains 

 above mentioned, and a very careful search conducted in an effort to 

 establish the occurrence there of wild cotton. Many favorable places 

 were visited at elevations between 2,000 and 4,000 feet, but no trace 

 of Thurberia could be found. In addition, botanists have not re- 

 corded the species from any California point. 



Finally, one point in the biology of the Bucculatrix species is very 

 suggestive. We have reference to the stockade of bristles which are 



