12 N. H. AGRI. EXPERIMENT STATION [Bulletin 243 



feed on the larvse and pupse. Fish and insects are the most important 

 forms and are especially efficient in permanent bodies of water, although 

 the insect enemies also occur commonly in less permanent pools. 



Fish are probably the greatest factor in reducing or preventing mos- 

 quito breeding in permanent ponds and lakes. No mosquitoes are able 

 to breed in ponds properly stocked with fish except in detached or ob- 

 structed pools or vegetation-choked borders and inlets where the fish 

 cannot penetrate. In Rye, in 1928, a series of small, fresh-water pools 

 were under observation, some of which were permanent and others of 

 which dried up during the summer. The permanent pools were well 

 stocked with nine-spined sticklebacks (Pungitius pungitius L.) and no 

 mosquitoes bred in these pools, while the temporary pools, in which the 

 fish did not occur, gave rise to swarms of Aedes vexans. 



The greatest enemy of the salt-marsh mosquitoes, and the only one we 

 have found in New Hampshire, is the killifish {Fundulus heterocUtus L.), 

 also known as the killie or mud minnow. This little fish, which never 

 grows longer than four and one-half inches, is extremely abundant in all 

 kinds of salt marshes, and extends up the creeks into brackish or even 

 fresh water. It is fovmd in clean or dirty water, in large pools or the 

 shallowest depressions, in muddy holes and vegetation-choked ditches; 

 in fact it follows the incoming tide anywhere on the marsh where there 

 is water enough for it to push its way through. It has an insatiable 

 appetite for mosquito larvae and pupse, and wherever it occurs the mos- 

 quitoes are devoured before they can complete their growth. Only in 

 the detached and isolated pools, which are not reached by ordinary 

 tides, can the mosquitoes breed successfully. 



All the important insect enemies of mosquitoes live in fresh water, 

 either during the immature stages (larva, nymph, naiad) or during both 

 adult and immature stages. The predaceous diving beetles (Dytiscidce) 

 live in the water in both stages and readily feed on mosquito larvse. In 

 our observations the larvse of these beetles, called "water tigers", have 

 been the commonest insect enemy of mosquito larvse in New Hamp- 

 shire. The larvse of the water scavenger beetles (Hydrophilidce) occa- 

 sionally feed on mosquito larvae, as do also the nymphs and adults of 

 the black-swimmers (Notonectidce). The naiads of the dragon flies 

 (Odonata) will eat larvae and pupae of mosquitoes, and the actively fly- 

 ing adults sometimes catch adult mosquitoes. 



The larvae of a number of species of mosquitoes are predaceous, and 

 feed on other mosquito larvse. Psorophora ciliata has this habit, but 

 the species is rare in New Hampshire. The larvse of the non-biting mos- 

 quitoes (Subfamily Corethrincc) are predaceous, feeding exclusively on 

 other mosquito larvae. They are, however, not especially common, and 

 we have found them only in cool, shady woodland pools. The members 

 of this subfamily found in New Hampshire are given in the list of spe- 

 cies at the end of this paper. 



