128 Observatiofis on the Habits o/Oscinella frit 



The larvae used in Exps. 1 and 2 were practically fully grown and 

 it is not understood why they failed to pupate^. Later in the season, 

 under similar conditions, flies emerged freely above ground. In Exps. 4 



^ .Saturation of the soil would not kill the larvae for some time although it would prob- 

 ably hasten the rotting of the host plants and thus deprive the larvae of food. The subjoined 

 notes illustrate the resistant powers of the immature stages to an unfavourable environ- 

 ment. 



Larvae. Larvae of various ages (a full grown larva averages 3 mm. in length) were col- 

 lected in the field and submerged, 1 in. deep, in dishes holding about an ounce of water, 

 the dishes not being covered. The water supply was not renewed. A few larvae after sub- 

 mersion were removed and bred to the adult stage in young oat tillers. 



On 16. 6. 20 six larvae were submerged and they were removed after 9 days, being then 

 placed on young oat tillers. One larva died on the 10th day and another on the 13th day 

 after submersion, but the other four were successful in completing metamorphosis. Pupa- 

 tion took place in 12, 12, 14 and 17 days and emergence of the adult in 29 (?), 44 (chalcid), 

 33 ((J) and 29 (?) days respectively. In another case a larva underwent ecdysis after 27 days 

 submersion, but then failed to pupate. 



The larvae were quiescent when submerged, but became active when removed from 

 the water. Death was assumed when no sign of mandibular movement was visible under 

 the microscope. 



Ten larvae deprived of food and moisture lived for the minimum, maximum and average 

 periods of 1, 4 and 2-9 days respectively, at room temperature. 



Puparia. Twenty-four puparia were taken from oat stems on 28. 6. 20 and divided into 

 batches A and B. 



A. Twelve were placed in a dry chimney cage and gave 100 per cent, emergence by the 

 end of 14 days. 



B. Twelve were held submerged by cotton wool under water. No emergence took place 

 by the end of 23 days and the water was then removed. After 32 daj's one female emerged. 

 Three larvae failed to pupate, therefore emergence equalled 11-1 per cent. 



The immature stages therefore exhibit considerable powers of endurance. Even the 

 very young larvae are not readily killed. On 3. 6. 20, fifteen larvae varying in size from 

 0-15 to 0-8 mm. were placed 2 inches from the base of a clean oat plant, on the surface of 

 the soil. After 2 days three larvae were recovered, two from tillers and one from a hole, 

 gnawed in the stem 1^ inches above the soil. The remainder were caught by the greased 

 rim of the pot. When migrating from one tiller to another or from plant to plant, the 

 time of exposure in the field would be short, as they are capable of moving on damp soil 

 at the rate of 1 inch per minute. 



