The competitive abilities of seven calliphorid and one sarcophagid species were examined by investigation of various Characteristics of their larval growth curves. The relative success of each species is thought to depend to a great extent on the ability of the larvae to attain quickly the minimum weight for viable pupation. The ovoviviparous species (Calliphora nociva Hardy, C. augur (F.) and Parasarcophaga crassipalpis (Macq.)) were found to have the most rapid growth and Chrysomya megacephala (F.), Calliphora nociva and C. augur the highest assimilatory rate during the period of most rapid growth. Further, C. nociva, C. augur, Ch. megacephala and Ch. rufifacies (Macq.) were the species best adapted to pupation at low larval weight, which suggests that their food requirements for successful pupation were less (relative to maximum larval weight) than those of the other species. In this respect, Lucilia cuprina (Wied.) was also well–adapted and Ch. varipes (Macq.) was the least successful species.

For 3 years numbers and species of blowflies breeding in carcasses and on live merino sheep were studied at the University of New South Wales Arid Zone Research Station at Fowlers Gap, to determine which species initiated blowfly strike on sheep and how Lucilia cuprina (Wiedemann) maintained its population throughout the year; particularly whether it could complete its life cycle on carcasses. Larvae taken from struck sheep showed L. cuprina to be the dominant species in >87% of strikes. Native calliphorids, Calliphora nociva Hardy, Calliphora augur (Fabr.), and Calliphora stygia (Fabr.) were present in about 7% of strikes sampled, usually in association with L. cuprina. In a regularly inspected small mob (c. 70) of sheep, incidence of covert strike was higher than incidence of overt strike, supporting the view that a grazier's estimate of flystrike in the flock would almost always be an underestimate. On carcasses, the secondary strike native blowfly, Chrysomys rufijacies (Macquart), was produced in very large numbers. Some native primary strike Calliphora spp. were produced from some carcasses in the colder months, but no L. cuprina was produced from either small or large carcasses (sheep, kangaroos, rabbits) at any time. However, larvae of L. cuprina were recovered from live sheep at all times of the year, indicating that L. cuprina is an obligate parasite of live sheep in the arid zone.

Circadian rhythms of LD50 values to DDT, dieldrin and malathion, topically applied, were determined for houseflies reared under LD 14:10 with “dawn” at 06.00 hr. There was a marked increase in susceptibility at 05.00 hr in each case. With “dawn” at 18.00 hr., DDT LD50 values were lowest at 17.00 hr indicating independence of the flies' “biological clocks” from clock time of day. Flies reared under LD 18:6 and 10:14 also had circadian rhythms of sensitivity to DDT. Mean daily LD50 values were inversely related to photophase length. The ratios of mean daily LD50 to “pre‐dawn” values were greatest for the longer photophases. Flies reared under LD 14:10 until the pupal stage, then DD until testing showed a normal circadian rhythm. Flies reared in total darkness (DD) showed no diel variations in susceptibility. W.H.O. standard strain flies were used for all the experiments. A fully susceptible (Cooper) and a DDT resistant (DEH‐DOV) strain also showed significant circadian rhythms of sensitivity to DDT. ZUSAMMENFASSUNG CIRCADIANRHYTHMEN BEI DER EMPFINDLICHKEIT VON MUSCA DOMESTICA (DIPTERA, MUSCIDAE) GEGENUBER INSEKTIZIDEN Circadianrhythmen der LD 50‐Werte gegenüber DDT, Dieldrin und Malathion ‐ topical angewandt wurden bei Stubenfliegen ermittelt, die bei 14:10 h‐Tag mit “Tagesanbruch” um 6.00 Uhr gezüchtet wurden. In allen Fällen war die Empfindlichkeit um 5.00 Uhr wesentlich erhöht. Bei “Tagesanbruch” um 18.00 Uhr waren die niedrigsten LD 50‐Werte um 17.00 Uhr. Dies weist auf die Unabhängigkeit der biologischen Uhr der Fliegen von der Tageszeit hin. Fliegen, die bei 18:6 oder bei 10:14 LD gezüchtet wurden, zeigten ebenfalls einen Circadianrhythmus hinsichtlich der Empfindlichkeit gegenüber DDT. Die mittleren LD 50‐Werte waren umgekehrt proportional zur Länge der Photophase. Das Verhältnis der mittleren täglichen LD 50‐Werte zu den Vortagesanbruchwerten war am grössten bei längerer Photophase. Fliegen, die bei 14:10 LD bis zum Puppenstadium und anschliessend bei DD bis zur Testung gehalten wurden, zeigten einen normalen circadianen Rhythmus. Bei Züchtung in völliger Dunkelheit zeigten sie keine Tagesschwankungen in der Empfindlichkeit. Für alle Versuche wurde ein WHO‐Standardstamm benutzt. Zwei andere Stämme, einer voll emDfindlich (Cooper), der andere resistent (DEH‐DOV) zeigten ebenfalls signifikante Circadianrhythmen in der DDT‐ Empfindlichkeir.

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