IO4 PAUL S. WELCH. 



the leaf-feeding period. The percentage of idioblasts was large 

 and they showed no indication of having been affected by the 

 digestive process. The majority of the idioblasts were intact. 

 Some showed signs of fragmentation, due to the initial action of 

 the mandibles when the plant tissue was removed. Examination 

 of the excrement also showed that, except for a short time when 

 the larva is cutting away the epidermis and surrounding tissue 

 in starting a new burrow, all of the material which is excavated 

 passes through the alimentary canal of the larva and is subjected 

 to the digestive process. Thus it is evident that the length of a 

 burrow is a criterion of the amount of food material which has 

 been taken from the plant. The larva is a voracious feeder, 

 eating during both day and night, and large quantities of plant 

 tissue are consumed. 



Effect on the Food Plant. The effect of the larva is such that 

 infested plants are doomed. During the latter part of July and 

 early August hundreds of leaves showed incisions converging 

 towards the midrib and more especially towards the attachment 

 of the petiole. Many leaves turned yellow and disintegrated, 

 due to one or both of two causes: (i) eating in the region of the 

 attachment of the petiole almost or entirely severed the connection 

 of the leaf. with the petiole; (2) the removal of the greater part 

 of the substance of the petiole and the occasional eating through 

 one side produced a more or less complete separation of the leaf 

 from the rootstalk. 



It thus appears that these larvae produce havoc in the beds of 

 Nymphcea americana and are a serious enemy since they not only 

 disfigure the leaves but also actually cause the destruction of the 

 same. They also destroy the flowers to some extent. In fact, 

 of the goodly number of insects found on TV. americana in the 

 Douglas Lake region, the Bellura larvae are usually the worst 

 enemy. Fortunately the rootstalks seem to suffer but little 

 from their attacks. 



Other Plants as Food. Observations and experiments showed 

 that under normal conditions these larvae use only the yellow 

 waterlily as food. In the field none were found feeding on the 

 white waterlily (Castalia odorata) notwithstanding the fact that 

 in many cases Nymphcca americana and Castalia odorata occurred 



