220 * BULLETIN OF THE BUREAU OF FISHERIES. 
things being equal, the more natural the pond and its surroundings can be kept the 
greater will be the likelihood of success. Artificial conditions are usually difficult of 
maintenance and should be established only when necessary. The dragonflies and 
nymphs constitute an important factor in the environment of the ordinary fishpond, and 
even their voracious appetite is accounted for in nature’s methods of equalizing 
things. This is shown by the fact that they eat one another with as much avidity and as 
little compunction as is shown toward any other kind of food. ‘Their removal, therefore, 
would considerably disturb the balance and impose artificial conditions that might be 
difficult to handle. The station is having much success in rearing various kinds of 
fish, among which are the buffalofish and channel catfish, whose breeding is admitted to 
be very difficult. Some of this success may well be due to the maintenance of a natural 
equilibrium in the animal and vegetable life of the fishponds. 
Tillyard (1917, p. 335) has suggested that such an equilibrium may be advanta- 
geously modified without in the least impairing its value: 
Not only are the dragonflies the most powerful determining factor in preserving the balance of 
insect life in ponds, rivers, lakes, and their surroundings, but they do most certainly make war upon the 
flies, mosquitoes, and gnats, which we all desire to see exterminated. I believe that a successful check- 
ing of the mosquito pest in the ornamental waters of parks and gardens could be readily obtained by 
the introduction of species whose larve, as well as the imagines, would prey upon the nuisance. Ifa 
successful planting of a colony of dragonflies in such a position were to be tried, the species selected 
might also be chosen for its coloring, and thus add a new note of interest to the locality. The glorious 
red Orthetrum villosovittatum has now become well established in the Botanical Gardens at Brisbane 
(Australia) and certainly adds a vivid touch of color to its lovely surroundings. 
The suggestions herein contained naturally lead up to the next consideration, which 
seems worthy of a separate heading. 
ODONATES AS DESTROYERS OF Mosourroks, GNATS, AND FLIES.—The quiet waters 
of an artificial fishpond furnish admirable conditions for the breeding of mosquitoes, and 
the screens at their outlets afford similar breeding places for gnats. The mosquitoes 
may include, in the proper geographical localities, both Anopheles and Stegomyia, the 
carriers of malaria and yellow fever. Obviously in a fishpond these pests can not be 
kept down by treatment with an oil film, neither can they be allowed to breed unhindered. 
The consumption of the larve by young fish might furnish an important check, but in 
intensive fish culture very little attention can be paid to the attitude of the fish toward 
mosquito larvee. 
Of the nine ponds in series D at Fairport six were stocked in the spring with fish 
that would not eat mosquito larve. In some of these ponds broods of young fish were 
raised later in the season, but previous to their appearance the mosquitoes could breed 
unhindered by the fish. In at least two of the six ponds no young fish were raised, or 
they were removed before they had time to produce any effect upon insect larve. Here, 
therefore, so far as the fish were concerned, the mosquitoes might hold undisturbed sway 
during the entire season. 
No fish eats adult mosquitoes; when the pupa are once safely transformed into 
imagos they are in no danger of further molestation from that source. Hence if the 
fishpond is to be prevented from serving as a breeding ground for these obnoxious pests 
some other check must be provided. Mention has already been made of the fact that 
the odonate nymph eats mosquito larvae and pupz, and the adult dragonfly is an 
even greater enemy of the mosquito imago. Tillyard (1917, p. 328) stated that he 
