100 PAUL S. WELCH. 



the excrement and show no evidence of being affected by diges- 

 tion, and (2) greenish, unorganized matter, which represents the 

 remains of the digested parenchymal tissue. 



Even in the very early stages the larvae are active feeders. 

 Larvae, 53/ mm. long, constructed mines 14 mm. long in less than 

 20 hours. Larvae, 7 mm. long, when transferred to new lily 

 leaves completely buried themselves in four hours. Usually 

 but one larva occupies a mine. Several instances were observed, 

 however, in which two were occupying the same mine and in one 

 heavily infested leaf eight larvae of about the same size were 

 found in a single, large mine. The formation of the mine is due 

 primarily to the fact that the larva apparently uses only the 

 parenchyma as food and must get under the epidermis in order 

 to get it. However the mine has an indirect value since it 

 furnishes a protection for the larva during the early and more 

 helpless stages. 



Several days after the mine has been formed the upper and 

 lower epidermis bounding it begin to disintegrate, untimately 

 leaving an ugly hole in the leaf and, in badly infested leaves, 

 producing numerous perforations. The effect on the plant is 

 evident. Not only is the leaf disfigured but in proportion to the 

 number of holes present the leaf surface is also reduced. Many 

 cases were observed in which the infestation was great enough 

 to cause the death of the entire leaf. 



In spite of the fact that in the Douglas Lake region a goodly 

 number of other insects affect the yellow waterlily some of which 

 also produce holes and burrows in the leaves, it is not difficult to 

 identify the work of young Bellura caterpillars. Certain beetles 

 (Donacia) make holes through the leaves in order to deposit 

 eggs but these are distinguished by the circular shape of the holes, 

 and by the rows of eggs or the remains of the eggs on the lower 

 side while the holes made by the larvae of Bellura melanopyga 

 are usually irregular and bear no eggs on the lower margin. The 

 larva of another beetle (Galerucella nymphcea) works on the upper 

 side of the yellow waterlily leaf but instead of making mines it 

 produces irregular trenches on the surface by eating away the 

 epidermis, giving the surface a brownish, etched appearance. 



The Petiole Period. This period begins when the larva quits 



