No abstract

Four populations of Dacus tryoni collected from widely separated regions on the east coast of Australia (Cairns, Brisbane, Sydney, and East Gippsland) were compared in the laboratory to determine how they differed in their adaptations to temperature, and what adaptations have enabled the species to spread into colder areas. The main criteria used for the comparisons were the innate capacity for increase (rm) and its components : speed of development, survival rate, and fecundity. The races were compared at three different temperatures and in two successive years. Differences between the races from Cairns, Brisbane, and Sydney were often large and consistent, and in general they correlated well with differences in the climates of the respective geographic areas. At the lowest temperature the Sydney strain had the highest (rm), while the Cairns strain had the lowest. At the intermediate temperature there were no significant differences between the strains. At the highest temperature the Cairns strain had the highest (rm), while the Sydney strain had the lowest. The strain from East Gippsland behaved in an unpredictable way in most of the experiments, and rarely fitted into the trends set by the other three strains. The major differences appear to have been due primarily to adaptations affecting fecundity. There were also significant differences in the longevity of adults and the survival rates of immature stages, but not in speeds of development. The differences in fecundity may have been related to differences in the proportions of females fertilized in the experimental cages.

The responses of the Queensland fruit fly to food-based lures were studied, with particular emphasis on the importance of ammonia as an attractant or repellent. Certain solutions of ammonium bicarbonate were found to be highly effective attractants for the Queensland fruit fly, provided they were tested in traps in which the retention of the flies did not depend on their contacting the bait solution. The attractancies of such solutions were found to be strongly dependent on concentration and pH, and mean attractancies more than five times that of the commercial protein hydrolysate used as a standard were obtained. Highest attractancies were associated with ammonia evolution rates in the region 5-25 �l ammonia (s.t.p.) h-1 100 ml-1 of solution; rates above 400 �1 ammonia (s.t.p.) h-1 100 ml-1 appeared to be repellent. The addition of a mixture of amino acids to the ammonium bicarbonate solutions under these trap conditions had no significant effect on their attractancy; but the addition of the standard protein hydrolysate to a 0.001 M solution of ammonium bicarbonate, with pH adjusted to 8.5, produced an outstandingly effective lure, with a mean attractancy almost nine times as great as the standard hydrolysate alone at its normal pH of 4.8. Subsequent experiments showed that simply raising the pH of the standard protein hydrolysate to 8.5 caused a similar high attractancy, which could be due in part to the marked rise in ammonia production from endogenous sources. Protein hydrolysate solutions showed pronounced increases in both ammonia production and fruit fly attractancy when microorganisms were allowed to flourish. No such increases occurred when the microorganisms were inhibited with a preservative. Evidence is also presented which indicates that carbon dioxide is mildly repellent to the Queensland fruit fly.

The ecology of a natural population of Dacus tryoni is being studied at an orchard near Sydney, N.S.W. Changes in numbers observed during a single year are described and discussed. Estimates of pupal numbers were based on the weekly total pupal production of a random sample of the fruit trees in the orchard. Parameters of the adult population were measured by means of mark-recapture sampling and analysed by means of three mathematical models. Discrepancies between some of the estimates of numbers given by these models are explained by extensive adult emergence at those times, and the lower survival factors of the young adults. Evidence for the random sampling of adults is presented. The decline of the population towards the end of the season was brought about mainly by (1) high pupal mortality, (2) cessation of pupal production due to diminution and disappearance of larval food, (3) a marked decline in the number of gravid females, apparently in response to diminishing oviposition sites, and (4) a high rate of loss of young adults, presumably by emigration. There was no evidence of overcrowding.

The chemical characteristics of protein attractants for the Queensland fruit fly, Dacus tvyoni, have been investigated.Highly effective commercial fruit fly attractants were found to contain a large proportion of high molecular weight material. Lists are provided of the amino acids present in free and bound form in these hydrolysates. The products found by gas liquid chromatography-mass spectrometry analysis of methylene chloride extracts and head-space volatiles were mainly the primary and secondary products of amino acid degradation, including a number of aldehydes and significant amounts of ethylene. None of these aldehydes nor any of a number of others that may have been present in smaller quantities was found to be active when tested individually for attractancy. Nor did ethylene show any evidence of attractancy under the conditions of these tests. Strecker reagents (such as isatin), which stimulate the formation of amino acid degradation products, caused a temporary and relatively small elevation in attractancy of the commercial hydrolysates.Three enzymatic hydrolysates of a relatively pure protein (bovine serum albumin) were prepared and studied; one, a tryptic digest, was exceptionally attractive to the fruit fly. Analysis of methylene chloride extracts and head-space of these 'model' preparations revealed a number of significant differences between them, but the most important difference in relation to attractancy was found to be the presence of ammonium salts in the trypsin hydrolysate.Subsequent experiments showed that high attractancies could be attained by combinations of amino acid mixtures and ammonium bicarbonate, even though neither had high attractancy (under the particular conditions of these experiments) when tested independently. This apparent synergism was probably due to the attractancy of the ammonia coupled with a feeding stimulus provided by the amino acids.