Insects and Parasitic Diseaes : 97 



ments both sexes lived for equally long periods. Sweet and Seddon 

 (1917, p. 11), whose observations in this direction were admittedly 

 incomplete, observe that " . . . it is worthy of record that the 

 last surviving * ticks ' were males. 



Influtnce of seasonal conditions on viahility. — Experiments car- 

 ried out in the winter (Juno), and again in late spring (November) 

 show that the adult " tick " survives outdoor longer in winter than 

 in summer. In the first of these experiments (No. 15) the " ticks " 

 were placed on the natural surface of the soil in a sheep-yard and 

 covered only by a wire-gauze cage. The cage was exposed to all 

 prevailing weather conditions excepting i\\Q direct force of the 

 wind from one direction, and from the sun's rays during the after- 

 noon. During the winter all of the ** ticks " (ten females) died in 

 nine days; in the early spring, Avhen the average temperature w^as 

 about 10°F. higher, thirty *' ticks " of both sexes all died within 

 five days. In the second experiment (No. 17) in which the " ticks '* 

 were kept on the lawn in a dish of sheep-pen sweepings upon which 

 rested a piece of tree trunk, all of the *' ticks " (ten females) died 

 in el,even days in winter; in the spring, when the average tempera- 

 ture was about 8°F. higher, all of the ** ticks '' (forty-six males and 

 females) died in six days. 



6. To determine the period of viability of the pupa when removed 

 from the host. 



Experiment No. 19. 



Eight pupae extruded during the morning of May 28th were 

 kept on moist filter paper and incubated at 34° C. In all six young 

 flies were produced on eighteenth and nineteenth days. The re- 

 maining pupae (two) were found to be dead. 



Thus 75% of the pupa|e remained viable, and produced young 

 flies in eighteen to nineteen days from date of extrusion. 



Experiment No. 20. 



Twenty pupae of unknown ages, collected on November 27th, wer^ 

 placed in a dry Petri dish and incubated at 33 °C. One young fly, 

 emerged on seventh day, one on eighth day, threes on tenth day, and 

 one on eleventh day. The remaining fourteen were found to be 

 dead when examined on December 31st. 



Thus 42.8% of the pupae remained viable, and produced young 

 flies seven to eleven days after their removal from the host. 



