In the Australian sheep blowfly, Lucilia cuprina, the number of ovarioles, and hence the maximum number of eggs developed in each ovarian cycle, is a linear function of adult size (headwidth). Field females have a mean headwidth of 3.0 mm (range=2.30–3.50 mm) and a mean potential fecundity/cycle of 232 eggs (range=111–318 eggs). Realised fecundity is influenced by the quality and amount of protein in the adult diet. All field females appear to have the same minimum protein requirement for egg maturation, i.e., whatever their size (potential fecundity) females must obtain sufficient protein to mature at least 110 eggs in order to become gravid. Females whose protein intake exceeds this minimum but falls short of the amount needed for maturation of their full egg complements resorb some of their oocytes and mature the remainder. Since potential fecundity increases with fly size, large females resorb more oocytes than small females under suboptimal protein regimes, i.e., the proportion of oocytes resorbed increases with fly size. Under field conditions, females rarely matured full complements of eggs, which indicates a general shortage of protein‐rich material. The mean reduction in fecundity of field females during these studies was 53.4 eggs/cycle (23.2%). RÉSUMÉ Relations entre la fécondité et la resorption des ovocytes dans des populations de la nature de Lucilia cuprina Wiedemann (Diptera: Calliphoridae) Chez Lucilia cuprina Wied., le nombre d'ovarioles, et ainsi le nombre maximum d'oeufs développés au cours de chaque cycle ovarien, est une fonction linéaire de la taille de l'adulte (largeur de la tête). La largeur moyenne de la tête des femelles de la nature est 3 mm (2,3 à 3,5) et la fécondité potentielle moyenne par cycle de 232 oeufs (111 à 318). La fécondité réelle est influencée par la qualité et la quantité de protéines dans le régime alimentaire. Toutes les femelles de la nature semblent avoir les mêmes exigences minimales en protéines pour la maturation des ovocytes, c'est à dire que quelle que soit leur taille (fécondité potentielle) les femelles doivent obtenir les protéines suffisantes à la formation d'au moins 110 ovocytes pour devenir gravides. Les femelles dont l'absorption de protéines dépasse ce minimum, mais est insuffisant pour permettre la maturation de la totalité de leurs ovocytes, en résorbent quelques uns et conduisent à maturité le reste. Puisque la fécondité potentielle augmente avec la taille des mouches, les grosses femelles résorbent plus d'ovocytes que les petites avec un régime suboptimal en protéines, c'est à dire que la proportion d'ovocytes résorbés augmente avec la taille des mouches. Dans les conditions de la nature, la totalité des ovocytes parvient rarement à maturité, ce qui indique une limitation générale en aliments riches en protéines. La réduction moyenne de la fécondité chez les femelles de la nature a été au cours de cette étude de 53,4 oeufs par cycle (23,2%).

A trap is described for use in population studies on blowflies. It embodies devices for the exclusion of ants and other predators, a screen to prevent blowflies having access to the bait. where they may get drowned and become unsuitable for study, and a screen to exclude large-bodied flies, not needed for study but whose presence in the catches would greatly complicate sorting.The "West Australian" trap first described by Newman and Clark (1926) as a blowfly control measure was standardised for blowfly population studies and employed for mark-recaptureexperiments by Gilmour, Waterhouse and McIntyre (1946). This standardised trap has several short-comings. It allows flies to become lodged in the bait, hindering recovery and identification of marked flies in mark-recapture studies. Increases in labour and material costs over the last 40 years have also made its construction expensive. The trap described here employs the same principles of design as the earlier traps, but flies are excluded from the bait pan. This trap, which is designed for the study of blowfly populations, is easier to repair than the standardised "West Australian" trap. Construction costs are such as to preclude its use in any trapping programme aimed at reducing fly numbers.An exploded view of the trap components is shown in Fig. 1. Fig. 2 gives a vertical section of the assembled trap.

Field populations of Lucilia cuprina (Wied.) in New South Wales were sampled for periods of 3 h on numerous occasions between 1975 and 1982 using West Australian blowfly traps. Ambient temperature, wind speed, relative humidity and solar radiation explained 774% of the within-day deviance of the catches. Temperature alone accounted for 74 9% of this deviance, indicating that the other variables, although significant, did not greatly affect trap catches. As air temperatures increased, log catch rates increased linearly up to 26°C and then remained constant up to 35°C. Wind speeds above 25 m/s caused a linear decline in log catch rates. Log catch rates increased linearly as solar radiation increased and decreased linearly as relative humidity increased. Changes in catch rates with time of day were explained almost entirely by the four weather variables, i.e. there was no evidence that intrinsic behavioural changes with time of day affected catch rates. The combined effects of the four weather variables accounted for 47 1 % of the between-day variation in trap catches. Trap catches that have been standardised, i.e. adjusted to a ' standard ' set of weather conditions, provide relative measures of population size which differ from absolute measures by a constant (unknown) scaling factor.

The stage of egg formation and density of follicular relics enable Lucilia cuprina (Wied.) females to be sorted into 16 ovarian stages, covering the period from emergence to the beginning of the fourth ovarian cycle. The correspondence between the actual age of a fly and its stage of ovarian development was determined at constant temperatures. Where developmental delays were absent, " reproductive age" gave reliable estimates of actual age under both constant and fluctuating temperature regimes. In the field protein shortages and lack of oviposition sites may prolong the time required to complete each ovarian cycle, and flies will be older than their ovaries would indicate. In practice the ovarian stages described provide estimates of minimum age for L. cuprina females.

A wind-oriented bait trap is described for sampling populations of bush fly (Musca i,eiustissima). The trap is less costly than the current "West Australian" blowfly trap, easier to maintain and operate. but samples just as effectively. The trap is baited with a mixture of cattle dung. minced liver, and sodium sulphide. in which blowfly larvae have developed for 2-3 d at 26 C. The function of the larvae is to maintain the attractiveness ofthe bait at a constant level for up to 2 d in the field.