WATER BEETI^S IN RELATION TO PONDFISH CULTURE. 



309 



contains 10 segments, and the last one is armed with two pairs of sharp, curved hooks similar to those 

 on the Dineutes larva. The mouth parts are also similar, the mandibles being sharp-pointed, perfo- 

 rated by a slit near the apex, and hence suctorial. The lateral gills increase in length backwards and 

 contain tracheoles, which give off smaller branches to the gill walls. The legs are long and slender 

 and destitute of swimming hairs. 



Pupation. — According to Miall (1895, p. 39): 



The pupa of Gyrinus is so well hidden that few naturalists have ever seen it. Modeer, quoted by De Geer, says that about 

 the beginning of August the larva creeps out of the water by climbing up the water-plants, and then spins a grayish cocoon 

 pointed at both ends. Inclosed in this cocoon it changes to a pupa and emerges as a perfect insect towards the end of the same 

 month. Modeer adds that the pupa is very liable to the attacks of Ichneumons. 



It hardly seems possible that this larva would depart so far from the custom of the Dineutes larva as 

 to spin a cocoon of silk. The Dineutes cocoon is grayish and pointed at both ends, but it is certainly 

 made of mud pellets, although it looks oftentimes as if it were made of silk. It seems more probable 

 that the Gyrinus cocoon is also made of mud, and the larva would be just as susceptible to the 

 attacks of Ichneumon flies while constructing it. 



Description of the pupa. — This pupa is similar in ail respects to that of Dineutes but is much 

 smaller and entirely white in color. The bases of the first swimming legs project similarly beyond 

 the lateral margins and are at right angles to the body axis. The labrum is very distinct, and the 

 head has a large prominence on either side just above the base of the antenna. 



Habits of the adult. — These gyrinids prefer gently running water and congregate in swarms on the 

 surface of the river (fig. 5, frontispiece), but. careful search has failed to reveal a single larva, pupa, 

 or pupa case around any of the ponds. Hence, except for the food which the adults occasionally 

 furnish to the fish, they do not enter into the ecology of the ponds at all. They fly with ease but like 

 the Dineutes adult can not take flight from the surface of the water. Westwood (Miall, 1895, p. 33) 

 said that he found their food to consist of small dead floating insects, and it thus resembles closely 

 that of Dineutes. Fowler (Miall, 1895, p. 33) remarked that the broad and blunt mandibles indicated 

 a partially vegetable diet, though the sharp and sickle-shaped maxillae favored a different conclusion, 

 and Miall himself (1895, p. 33) added that in captivity the adults feed upon water-plants. Miall also 

 adds an interesting item that these adults when handled give off from the joints of the body a milky 

 fluid that has the odor of cockroaches. The male is capable of producing a squeaking noise by rubbing 

 the imder side of the elytra against the dorsal surface of the posterior abdomen segments. 



Genus BEROSUS Leach. 



Berosus (Leach, 1817, p. 92). 



This is a genus of smallj convex, and elongate beetles, usually of a yellowish 

 color with darker spots on the thorax and elytra. They are herbivorous, both the 

 adults and the larvae feeding on green algae. The antennae of the adults have only 

 seven segments, and the posterior tibiae and tarsi are densely fringed with swimming 

 hairs. 



Berosus striatus (Say). Figs. 96, 97, 99, 101-103, 105, 106, 108, 110. 

 HydroUus striatus (Say, 1825, p. 108). 



Egg cases. — The egg cases are attached to the stem or leaf of some submerged plant. The case and 

 its fag 2 much resemble one of the old-fashioned long-handled warming pans, in which coals were placed 

 for the purpose of warming up a bed before sleeping in it. The case proper is circular or elliptical in 

 outline, about 2 mm. long, 1.5 mm. wide, and 0.33 mm. high, the length being measured continuous 

 with that of the fag. It is surrounded by a narrow band or margin of silk, which fastens it securely to 

 the support. Both the upper and the under surfaces are quite convex. The fag is ribbon-like, from 

 4 to 6 mm. long and about 0.2 mm, wide, and it usually clings to the support, running up from the case 

 toward the surface of the water but never quite reaching it. Each case contained from three to five 

 eggs, which apparently require from 8 to 10 days to hatch. 



> See p. 332. 



48790°— 23- 



