1916] Biology of Aquatic Lepidoptera 161 



of N. maculalis uses the holes made by Donacia sp. for the depo- 

 sition of her eggs, thus taking advantage of the work of the 

 female beetle. The eggs of N. maculalis are laid in concentric 

 rows on the lower surface of the leaf, about the circular hole 

 and occupy space not utilized by the eggs of Donacia. Recently 

 deposited eggs of both beetle and moth were frequently found 

 about the same hole, showing that oviposition by the former is 

 sometimes followed shortly by egg deposition by the latter. 

 Recently deposited eggs of N. maculalis were occasionally found 

 about the egg holes of Donacia from which the eggs of the latter 

 had disappeared. The number of concentric rows of N. 

 maculalis eggs varies slightly but in the larger egg masses there 

 are six. The eggs are so placed that the long axes are radial 

 with reference to the hole about which they occur. The number 

 of eggs in a cluster varies rather widely. Frequently, the size of 

 the cluster is determined by the amount of space unoccupied by 

 the eggs of Donacia. In a few instances, the egg mass com- 

 pletely surrounded a Donacia egg hole, eggs of the latter being 

 absent. An examination of a large quantity of these egg masses 

 showed that the number of eggs in each varied from twenty-two 

 to two hundred eighty. 



The act of oviposition was not observed and exact data on 

 this activity are lacking. However, the necessities make it 

 possible to draw tentative conclusions. The female of N. 

 maculalis has no means of making a hole through the leaf and, 

 since the eggs are laid in the above-described manner, she uses 

 the holes provided by some other agency. Even though the 

 writer has failed, in the collections of five summers, to find a 

 single egg mass in the field which was not associated with the 

 egg holes of Donacia, it seems improbable that the female 

 N. maculalis is restricted to them for egg deposition. In the 

 region examined, Donacia is the only animal which makes a 

 small, symmetrical hole through the leaf, a fact which may 

 account for the constant relation between the egg-laying habits 

 of the two species. Similar holes of different origin, if present, 

 might also be used. Since in most of the egg masses there are 

 six concentric rows so arranged that the row most remote from 

 the margin of the hole is four or five millimeters away, the 

 question arises as to the means whereby the female is able to 

 deposit eggs at such a distance from the edge of the hole. An 

 examination of the females of N. maculalis shows that the ter- 



