240 SANITARY ENTOMOLOGY 



the larvae that issue therefrom. During the past summer the larvae 

 emerging from ten masses of Tahanus phaenops eggs were counted. The 

 number per mass ranged from 156 to 385, giving an average of 281 -|- per 

 mass. Larvae from fifteen masses of Tabanus punctifer eggs were counted. 

 The range was found to be from 159 to 701 larvae, — an average of 366 -|" 

 per mass. However, this method of arriving at the number of eggs per 

 mass was very inaccurate in the case of Tabanus punctifer, as practi- 

 cally all these egg masses were, to a greater or less extent, parasitized, and 

 in several of the masses a large per cent of the eggs failed to hatch. 



Larvae from a series of five unidentified Tabanus egg masses collected 

 near Alturas, California, were also counted. Here the range was from 

 326 to 890, — an average of 509 -\- per mass, with no parasitism. 



Mitzmain records that the number of eggs per mass of Tabanus 

 striatus in the Philippines varies from 270 to 425. He observed the 

 oviposition under cage conditions and found that the eggs were deposited 

 at the exact rate of 10 per minute. 



References in literature to the incubation period are extremely scarce. 

 King gives the period for Tabanus kingi as about 5 days, and for Tabanus 

 par as 5 to 6 days. These species occur in the Egyptian Sudan. Neave 

 gives the incubation period of Tabanus corax in Southern Nyasaland as 

 about 5 daj's. Mitzmain determined the period for Tabanus striatus in 

 the Philippines to be from 3 to 5 days. 



In my own experience in the Sierra Nevada Mountains, I have found 

 that the eggs of Tabanus phaenops under laboratory conditions hatch in 

 from 6 to 7 days, while those of Tabanus punctifer require 14 days. How- 

 ever, in one case, a mass of T. punctifer eggs, after being kept a few days 

 in the laboratory, was placed outdoors in the sun, with the result that 

 the incubation period was shortened to 11 days. No doubt if the mass 

 had been kept in the open from the time of oviposition a still shorter 

 incubation period would have been recorded. The eggs of the unidentified 

 species collected near Alturas, California, hatched in from 7 to 8 days 

 under laboratory conditions. 



Usually most of the eggs in a mass hatch at about the same time, but 

 in the case of Tahanus phaenops I have found straggling larva? emerging 

 several hours after the majority of the larvae were in the water at the 

 bottom of the incubation vial. 



LARV^ 



In arranging for the incubation of Tabanus eggs I am accustomed to 

 use a large glass vial with water in the bottom. The egg mass is then 

 suspended in the vial over the water, usually by placing the stem or 

 leaf, to which the mass is attached, against the side of the vial, and press- 



