92 ALFRED E. CA:MER0X. — EXPERIMENTS ON THE MANGOLD FLY. 



would not be well advised to keep his land as clean as possible of these weeds, but 

 that there is no evidence available that P. bicolor will migrate from docks to mangolds 

 and beets. Therefore the removal of docks for the specific purpose of preventing 

 mangolds and beets from being attacked by the dock fly rather misses the mark. 



Conclusions. 



It would appear from the foregoing experiments that the following conclusions 

 might be considered to have been tentatively established : — 



1. P. hjoscyami reared on belladonna will oviposit and complete its life-history 

 on mangolds if belladonna be absent. Why this same species did not oviposit on the 

 leaves of sugar-beet was not discovered. 



2. P. hyoscyami reared on mangold leaves did not oviposit on those of the very 

 closely allied sugar-beet. All that can be inferred from the experiment is that the 

 species when reared on the leaves of the mangold will more readily oviposit on those 

 of the same plant than on sugar-beet. 



3. P. bicolor reared on dock does not oviposit and complete its life-history on the 

 leaves of the mangold or sugar-beet. It may also be safely asserted that neither does 

 P. hyoscyami reared on mangold or sugar-beet leaves oviposit on those of the dock. 



4. Where weeds and cultivated plants have their leaves similarly blotched and 

 blistered by leaf-mining maggots, one must make a careful examination of the insects 

 before stating that the damage is due to one and the same agent. The author believes 

 that hasty and immature judgment has led to the commonly accepted error that the 

 maggot (P. bicolor) which mines in the leaves of the dock also attacks those of 

 mangolds. That the insect which blisters the leaves of the common weed, goosefoot 

 {Chenopodiion albiitn), is identical with the P. hyoscyami which causes similar injury 

 to mangold leaves, there is no doubt. In how far there may be a migration, if any, 

 of the insects between the two plants has not been experimentally estabhshed. 



The author desires to acknowledge many valuable suggestions made by Dr. A. D. 

 Imms during the progress of these experiments and to express his indebtedness to 

 Professor S. J. Hickson. 



