PROGRESS IN BIOLOGICAL INQUIRIES, 1924 35 



experimental work. During the past several years more young have 

 been produced at the station each year than were desired for experi- 

 mental purposes. Such young, when about 1 year old, usually were 

 liberated on the marshes in the vicinity of Beaufort. In some years 

 only a few hundred were liberated, but a few times 1.000 or more 

 were liberated. Apparently as a result of these few plantings 

 partly grown diamond-back terrapins have been seen frequently dur- 

 ing the past year by fishermen and others, whereas before they were 

 ■so nearly depleted that such terrapins were seen very rarely or not at 

 all. The apparent results from the limited plantings made are so 

 encouraging that the propagation of diamond-back terrapin for 

 restocking tlie almost depleted grounds seems highly practicable. 



ECOLOGICAL AND OCEANOGRAPHIC STUDIES 



CONTROL OF MOSQUITOES BT MEANS OF FISH 



Experiments and observations on the use of fish, particularly the 

 top minnow {Gambusia affi'nis), as an agency for the control of mos- 

 quitoes have been continued b}' Samuel F. Hildebrand, ichthyologist, 

 assisted by Irving L. Towers, scientific assistant. This work has been 

 conducted in cooperation with the United States Public Health 

 Service and the Board of Health of Augusta, Ga. During the sum- 

 mer of 19'23 a series of experiments was conducted designed to deter- 

 mine the effectiveness of Gambusia as agents for the control of 

 mosquito production in the presence of various types of aquatic 

 vegetation. The experiments were mainly a repetition of the pre- 

 vious year's work, and were contiiuied for the purpose of determining 

 ;the effects upon mosquito control of seasonal variations in tempera- 

 ture and rainfall. Mosquito production throughout the summer of 

 1923 appears to have been much less prolific than during the previous 

 year, and the value of the fish, accprding to the records obtained, was 

 correspondingly smaller. The records, however, have not been criti- 

 cally studied, and it is probable that factors other than seasonal 

 variations in the weather may have contributed to the apparent 

 differences in the effectiveness of Gambusia as agents for mosquito 

 control. 



During June, 1924, experiments again were started which, it is 

 believed, will cast further light upon the true value of top minnows 

 as agents for the control of mosquito production under a variety of 

 conditions. It is admitted by practically all officers engaged in 

 malaria control work in the south that Gambusia are, under certain 

 conditions, of great value, but it is also claimed by some that under 

 other circumstances they are valueless. The experiments that are 

 being undertaken are so selected and arranged that one area which, 

 for example, is overgrown with INIyriophyllum will contain no Gam- 

 busia, while another area similarly overgrown will be stocked with 

 these fish. Weeldy dippings will be made in each area, and the num- 

 ber and size of the immature mosquitoes will be tabulated. Similar 

 experiments have been conducted during previous seasons, and the 

 former work, together with the work now under way, when finally 

 summarized, should do much toward establishing the true worth of 

 ■the top minnoAv under a number of different conditions. 



