Sciaridae 399 



Family sciaridae 



CULTURE METHODS USED FOR SCIARA 



Helen B. Smith, Johns Hopkins University 



Methods of collecting. Sciara is collected most easily in greenhouses. 

 The flies are usually found on the window panes, not in the sun. They 

 may be captured by inverting a glass vial over them and then gradually 

 inserting a piece of paper or cardboard between the window pane and the 

 vial, so as to force them into the vial. Cotton may be used to stopper the 

 vial. 



Culture medium. Sciara is usually cultivated in pair matings in glass 

 vials 1 inch wide and 4 inches high. Mass-cultures may be grown in 

 half pint milk bottles. The vials or bottles are sterilized and filled to a 

 depth of about 1 inch with plain agar medium made by heating approxi- 

 mately 2 parts of agar in 3 of tap water, by measure. When the agar 

 has solidified, finely ground sterilized straw is sprinkled into the vials to 

 insure a dry surface. The vials are plugged with cotton. Frequently 

 small quantities of ground straw are added to the agar medium before it 

 is poured into the vials ; this serves to make the substratum more porous, 

 but is not essential. 



Feeding. Many different types of food have been tried with varying 

 degrees of success. The most satisfactory one thus far used is a mixture 

 of equal parts of poultry yeast, powdered mushroom, and ground straw. 

 The latter serves to prevent the formation of an impervious surface 

 layer on the cultures. When small larvae are visible (usually 10 days 

 after the parent flies have been placed in the vial) a small quantity of 

 food mixture is sprinkled on the surface. This is soon eaten up and 

 the supply must be replenished about every second day until pupation 

 begins. Practice alone will demonstrate what quantity of food is re- 

 quired. In general it is better to feed sparingly rather than abundantly, 

 for if cultures are given too much food, the larvae fail to eat all of it, 

 and the excess remains on top of the culture as a loose mixture to drop 

 out when one attempts to remove the flies that have hatched. Although 

 this culture method is by no means perfect as yet, it is adequate and 

 reliable for present purposes. 



Temperature and moisture conditions. Sciara is resistant to cold; 

 the only effect of low temperatures is to retard the rate of development. 

 The larvae are very susceptible to heat, however, and 29 C. is lethal if 

 maintained more than a short time. Higher temperatures are imme- 

 diately lethal. In the laboratory the cultures are kept in an incubator 

 with a temperature range of 2 2°-24° C. Moisture conditions are regu- 

 lated by placing a large flat pan of water on the lowest shelf of the 



