116 I'ROCEEDIXGS OF THK KOVAr, SOCIETY OF QUEENSLAND. 



the following facts : — Increased fly activity generally means 

 a decrease in the length of the life-cycle (especially the im- 

 mature stages, owing to favourable conditions of temperature 

 and moisture) and incidentally of the pupal period. For 

 Pycyiosoma mfifacies and P. varipes this latter period is 4| days 

 during the summer months, becoming as low as 3 clays (on 

 an average 4 days) during the most favourable weather (Feb- 

 ruary).^ The egg period of Xasonia in Brisbane during this 

 time is 40 hours. It follows that, of these 3 or 4 days which the 

 fly passes in the pupal stage and during which the chalcid 

 can act against the fly, nearly two days are occupied in the 

 hatching of the parasites egg. Hence, unless the pupae are 

 attacked within 24 to 30 hours after pupation, they are prac- 

 tically safe from destruction by Xasonia ; indeed, we have 

 the paradoxical conception of the pupae of Pycnosoma, during 

 this period, acting as a most efficient chalcid-destroyer — in 

 other words, as a "' Nasonia-trap," in that at least half the 

 chalcid eggs deposited must be Avasted, unless, of course, the 

 wasp will instinctivel}^ refuse to oviposit in advanced pupae. ^ 

 The immunity of Pycnosoma to Xasonia attack was exhibited 

 by the following experiment, carried out in February, 1921. 

 when Pycnosoma spp. are the dominating blowflies in Brisbane. 

 A split sheep's head was placed in a box of soil and allowed to 



killed by this parasite, it should have a marked effect in controlling the 

 increase of the flies, but vuifortiuiately the Chalcid ^^'asp seems to 1k^ 

 dormant at the very time the flies are worst. Very much has yet to be 

 learned of the life-history of both flies and parasites. This tends to 

 show that although it must be a check, yet it cannot in the "light of present 

 knowledge be cla.ssed as an overwhelming check. At Dalmally, in the 

 height of the attack of the present year, Chalcids were not to be found. 

 Then at the end of September they began to show in the breeding cages 

 and are now (December, 1920) breeding in big numbers. Even if the 

 Chalcids be responsible for the abatement of the fly trouble since October, 

 it was quiescent when the principal losses in sheep occurred. We conclude 

 therefore that while Chalcids are certainly a check, they are not, in the 

 light of our present knowledge, important enough to supersede the 

 jetting process." 



3 J. F. lUingworth in an aiticle. •• The Australian Sheep Fly 

 in Hawaii " (Proc. Ent. Soc. Hawaii. 1917 (1918), 3, p. 429 ; Abstr. n 

 Rev. Appl. Ent., B., 6, p. 163) referred to the rapid development there 

 during July. A dead animal was expo.sed on 16th July, larva? hatched 

 out next morning, and three days later entered the soil to pupate, tin- 

 pupal stage occupying about six days. 



* Alt son (1920, p. 224) states that Xa,so7ua .shows preference for 

 pupae between 24 and 72 hours old for oviposition. We have found that 

 the wasp will readily oviposit in living blowfly pupae of any age. 



