42 PROCEEDINGS ENTOMOLOGICAL SOCIETY 



all came from Gatun. Mansonia titillans occurred also in a lot 

 from Miraflores. The explanation of the appearance of these 

 mosquitoes in numbers is that the creation of the lakes at Gatun 

 and Pedro Miguel has furnished an extensive habitat for Pistia 

 and thereby abundant opportunity for Mansonia and Aedeomyia 

 to breed. 



In the discussion of Mr. Knab's paper Mr. Busck said that 

 the eradication of certain species of mosquitoes as well as of many 

 other insects on the Canal Zone was no more than could be ex- 

 pected as a natural result of the canal work and the sanitary 

 measures in connection therewith. As the large trees with their 

 host of water-bearing, mosquito breeding plant parasites are cut 

 down and the bamboo swamps are drained, the shady habitat 

 and characteristic breeding places of very many species of mosqui- 

 toes are entirely abolished and the extermination within the Canal 

 Zone of such species is necessarily effected. 



It is more noteworthy that certain other species of mosquitoes 

 hitherto absent, or at least rare on the Zone, should have become 

 established and abundant in spite of the constant warfare against 

 mosquitoes by the Sanitary Department. But such is certainly 

 the case with the two species Mansonia titillans and Aedeomyia 

 squamipenms. 



The reason for this lies in their peculiar biology, closely asso- 

 ciated with and dependent upon the water-plant, Pistia, which 

 make the larva? of these species practically unaffected by any 

 of the hitherto used control measures. 



The Pistia formerly occurred only sparingly and in small colo- 

 nies, mainly in the so called "Black Swamp," but the plant has 

 now enormously increased, due to the greatly enlarged open areas 

 of water, especially by the formation of the Gatun Lake, which 

 now covers the Black Swamp. Large floating islands of Pistia 

 now occur and afford unlimited breeding possibility for the two 

 mosquito species which attach themselves to the roots of the 

 Pistia. The effect was particularly noticeable on the part of the 

 lake which was formerly the Trinidad River and where Aedeomyia 

 squamipennis, unknown hitherto from the Canal Zone, this sum- 

 mer came by the hundreds every night, attracted by my acetelyn 

 lamps and white sheets. 



