282 BULLETIN OF THE BUREAU OF FISHERIES. 



Reighard (1894) has expressed in a table "a part of the imperfectly known relation- 

 ships existing between the various groups of plants and the invertebrate animals on the 

 one hand and the fishes on the other." One of the great gaps in the chain of relations 

 therein expressed is a lack of definite knowledge concerning the role of the higher plants. 



Some definite research in this direction has been begun. Recent investigations 

 on the food habits of aquatic insects have shown that the larger aquatic plants do 

 serve as forage materials. According to Hart (1895), the larvae of Nymphula sp. {Para- 

 ponyx), an aquatic lepidopterous insect, feed voraciously on Potaniogeton natans. Need- 

 ham (1907) mentions the presence of Nymphea advena in the diet of Chironomus albis- 

 tria, and Morgan (1912) found that the higher plant tissues formed an important part 

 of the stomach content of May-fly larvae. In view of these investigations the leaves 

 and other edible parts of Potamogeton were closely scrutinized for evidences of their 

 use as food. In my own investigations the first indication that the living tissues of 

 Potamogeton was being eaten was seen in the young growing tips of P. crispus, which 

 had been transferred from a pond to an aquarium in the laboratory. The leaves of 

 several plants were mined by a small larval form which proved to be a chironomid 

 (midge). The characteristic leaf mine is shown in figure 72. Miss Tilbury (1913), 

 who was working in the Cornell laboratory on the feeding habits of the midge, taking 

 advantage of this observation, reared her species, Chironomus cayugm Johannsen, 

 mainly on P. crispus and entirely on Potamogeton. 



On examining the leaves of other Potamogetons it was found that practically all 

 species were foraged upon to a greater or less extent. Lar\'al depredations were most 

 common on P. Rohhinsii. In this plant the aquatic lepidopterous lar\'a Nymphula sp. 

 (Paraponyx) is the chief herbivore, and so voracious is its appetite that a large proportion 

 of the growing tips are constantly being defoliated in the manner shown by figure 68. 

 Portions of the leaf are cut out also by the larva, applied together by means of silk, 

 and used as a protective case or retreat during the larval and pupal stages. Nymphula 

 sp. is by far the most conspicuous larva feeding upon P. Rohhinsii, yet other important 

 smaller forms are numerous. The limy incrustation that accumulates very freely on 

 P. Rohhinsii offers apparently especial inducements to certain case-making insects, as 

 midges and caddis flies. Such larvae are exceedingly numerous on this species of plant, 

 and the limy incrustation is the chief material used in the construction of the cases. 



A few of the chironomid larv-ae that were common on P. Rohhinsii collected at North 

 Fairhaven in October were segregated and fed exclusively on this Potamogeton. They 

 passed successfully through the pupal and adult stages and proved to be the midge, 

 Chironomous aberrans. The larval and pupal stages have been hitherto unrecognized 

 in the life history of this species." 



The leaves of P. amplifolius were conspicuously mined by the dipterous larva 

 Hydrellia sp. (Ephydridae). The pupae were collected on the leaves August 6. Several 

 flies and their parasites were reared from them, emergence occurring between August 16 

 and 20. The larva makes a wide, irregular mine through the leaf, and in each case under 

 observation pupates at the end of the mine toward the base of the leaf blade where the 

 edges naturally roll together and form a protecting furrow (fig. 73). Nymphula sp. 

 (Paraponyx) is also common on this Potamogeton and many of the young leaves are eaten 

 by them. Oftentimes the larva cuts out a portion of the leaf for its case with the neat- 



" Determinations of dipterous larvae have been made by Prof. O. A. Johannsen; of caddis-fly larvae, by Mr. J. T. Lloyd. 



