WATER BEET:LES m RELATION- TO PONDFISH CULTURE. 



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carry six similar spines; the first seven abdominal segments each have four spines; the last segment is 

 unarmed. In addition to these dorsal spines the lateral margins of the first seven abdominal segments 

 are prolonged into spines, which extend outward on the anterior segments and gradually turn backward 

 on the posterior segments. The knoblike prolongations of the posterior coxae and the corresponding 

 indentations of the elytra and wings appear plainly. 



The adult beetle. — General outline oval, the wider end anterior; body strongly convex. Total length, 

 2.5 to 3 mm.; greatest width, 1.5 mm. The head and thorax pale yellow, with a small depression on 

 either side of the thorax near the base. Elytra also yellow, each with five black spots, all rounded, the 

 two median ones more or less fused. The eyes are smaller and not as convex as in other species. 



These beetles swim very poorly, although their hind legs are armed with fringes of long swimming 

 setae; but on the land they walk very well and can run with considerable agility, lifting their body high 

 above the ground on their long hind legs. Like other haliplids they secure their supply of fresh air 

 by means of the posterior coxal plates and lateral grooves in the pleura. They feed exclusively upon 

 filamentous algae. 



This species has been found in every one of the fishponds except 6D and 3F, but was abundant 

 only in the single pond 3D. Both the larvae and the adults furnish excellent fish food and are them- 

 selves too small to menace young fish. 



Genus COPTOTOMUS Say. 



Coptotomus (Say, 1834, p. 443). 



A genus of medium-sized oval dytiscids having the terminal joint of both 



labial and maxillary palps somewhat compressed laterally and notched at the tip. 



The prostemum has an elevated carina and its process is much swollen along the 



middle. The claws of the tarsi are equal or nearly so, are pressed closely together 



and appear like a single claw. There is but a single species found in the Fairport 



ponds, whose life history follows. 



Coptotomus interrogatus (Fabricius). Figures 10-19, 22. 



Dytiscus interrogatus (Fabricius, 1801, p. 267). 

 Coptotomus interrogatus (Say, 1834, p. 443). 



Eggs. — Deposited singly in the stems of various water plants with no preference for any one kind. 

 The eggs hatch in six to eight days. 



Habits of the larva. — This larva swims well, using mainly the fringe of hairs on the lateral margins 

 of the ninth segment and the much denser fringe on the sides of the cerci, propelling itself by a vertical 

 undulatory movement. The le^ assist materially, their length compensating for the scanty fringe of 

 swimming hairs they possess. While swimming, the lateral gills are trailed inertly along the sides of 

 the body. 



Breathing through these gills the larva does not need to come to the surface for an air supply and 

 remains continually beneath the water, crawling about over the vegetation. It eats in true dytiscid 

 style, sucking the juices of its victims through its mandibles. It seems to prefer small damselfly and 

 mayfly nymphs, with an occasional chironomid or beetle larva. In an aquarium it feeds greedily upon 

 Laccophilus larvae and also eats others of its own kind smaller than itself. It is thus cannibalistic, 

 although the notes of Needham and Williamson (1907, p. 486) do not apply, because the larvae they 

 obtained were not those of this species, notwithstanding that the figure they gave has been published 

 as authentic seveml times. 



Desaiption of the larva. — General form spindle-shaped, narrowed anteriorly and posteriorly. Total 

 length, 12 to 14 mm. ; cerci, 2 mm. additional. Greatest width, at the first abdomen segment, 2 to 2.5 mm. 



Head contracted posteriorly to half its anterior width; prothorax one-fourth longer than wide, 

 contracted anteriorly into a long neck, a little wider than the posterior portion of the head. First six 

 abdominal segments diminishing regularly in width backwards, each with a pair of long and slender 

 tracheal gills. Seventh segment reduced abruptly to three-fifths the width of the sixth segment; 

 eighth segment elongate, narrow, tapering to a rounded point, with lateral fringes of long hairs; cerci 

 filiform, as long as the eighth segment and densely fringed with long hairs. General color light brownish 

 yellow, a little darker on the dorsal surface; eyes black. 



