The relative importance of adult preferences or specialisations of larval physiology in restricting the host range of five species of Dacine fruit flies (Diptera: Tephritidae) was examined, with particular emphasis on their utilization of cultivated fruits. The species; D. tryoni, D. jarvisi, D. cucumis, D. musae and D. cacuminatus differ widely in host range with D. tryoni being highly polyphagous while D. cacuminatus is virtually monophagous. Laboratory experiments showed that larvae of all species survived and developed in many cultivated fruits in which the specialists never occur in the field. By contrast the oviposition preferences and specificity of adult females differed widely between species. Female D. tryoni oviposited in most species of fruit. The specialised species; D. cucumis, D. musae and D. cacuminatus strongly preferred their usual hosts and would not oviposit in novel fruits even in the absence of the preferred host. In contrast, D. jarvisi consistently preferred its main native host but when this was not offered readily accepted cultivated fruits. These differences in preference are consistent with the pattern of infestation displayed by each species in the field. The study indicate that, in general, the occurrence of these species of Dacus in cultivated fruits is constrained more by the behavioural preferences of adult females than by larval specialisations. A genetic change in some aspect of host recognition or acceptance would be necessary for the specialised species to regularly infest cultivated fruits though no change in larval characteristics may be needed. As the types and concentrations of defensive secondary compounds may differ between native and cultivated fruits this conclusion cannot be extended to host shifts among native fruits.

The roles of adult and larval specialisations in limiting the occurrence of five species of Dacus (Diptera: tephritidae) in cultivated fruits.

. 1. An analysis of the number of ovarioles/ovary is presented for fourteen species of Dacus ranging from broad generalists (D.tryoni (Frogg.)) to strict host specialists (D.aglaia Hardy). For eight species data on egg size and the incubation time of eggs is also presented. Interrelationships among these life history variables and their relationships to host specialization were examined.



2. There was a broad positive relationship between the breadth of the natural host range (i.e. excluding cultivated fruits) and ovariole number (and hence potential fecundity). Highly polyphagous species had thirty-five to forty ovarioles/ovary while the specialists ranged from eight to twenty.



3. D.musae (Tryon), a specialist on banana, was an exception having an ovariole number similar to that of the most polyphagous species.



4. There was no clear relationship between egg size and ovariole number across eight species, though monophages were not fully represented in this analysis. Among these eight species there was no significant relationship between wing length and egg length, nor was there any such relationship among individuals within species.



5. There was considerable variation among species in the incubation time (at 25°C) for eggs, ranging from 24 h for D.cucumis French to 53 h for D.cacuminatus (Hering). This variation was only weakly related to egg size, though D.cucumis produced the largest eggs of any species examined.



6. Possible explanations for a relationship between potential fecundity and host range are discussed in terms of the balance between the abundance of host resources for generalists and their predictability for specialists. However, the observed relationship between ovariole number and host range must remain tentative, given that only fourteen species from one genus have been examined. Considerably more data is required for other dacines, for species in other tephritid subfamilies, and for other phytophagous insect groups to determine whether the relationship is generally applicable.

Variation in ovariole number and egg size of species of Dacus (Diptera; Tephritidae) and their relation to host specialization

11 fruit fly species captured at 47 sites in a natural forest area at Cooloola (south-east Queensland) revealed specific patterns of spatial abundance. Although all species were collected throughout the study area, D. bryoniae, D. mayi, D. neohumeralis and D. tryoni were more prevalent (average number caught per trap) in the open Eucalypt forest than the rainforest, whereas C. aequalis, D. absonifacies and D. endiandrae were more prevalent in the rainforest. D. cacuminatus, D. choristus, D. quadratus and D. signatifrons were equally prevalent throughout both forest types. Fly numbers were not distributed randomly throughout the trap sites. The clumped dispersion patterns seemed to be species specific as assessed and summarised by Taylor's Power Law. The exponent (b) relating mean spatial abundance to its variance ranged from 1.6-5.11 for the 11 species captured. Changing patterns of trap catches from one sampling period to another were analysed using correlograms for the 6 most abundant species (D. tryoni, D. neohumeralis, D. endiandrae, C. aequalis, D. cacuminatus and D. mayi). These revealed changing patterns of relative spatial abundance which can be related, in part, to changing population abundance levels. The various spatial patterns recognised are related to each species movement, breeding and feeding behaviour. It is proposed that flies migrate into the rainforest area from distant locations and that the rainforest habitat is an important adult feeding site.

Ecological studies of Eastern Australian fruit flies ( Diptera: Tephritidae ) in their endemic habitat

Fortnightly fruit fly captures for a 2-year period at Cooloola (south-east Queensland) contained 11 species. Three species, viz., D. tryoni, D. neohumeralis and D. endiandrae predominated. The peak trap catches of 7 species corresponded with the peak fruiting times of their major hosts. There was no direct relationship between temperature and rainfall and the variations in population numbers. The host plants of some species do not grow in the Cooloola area and there is evidence that large numbers of flies migrate into the region from other breeding areas up to 100 km away. Pockets of tropical rainforest such as Cooloola could be important adult fruit fly feeding areas even in the absence of larval host plants.

Ecological studies of Eastern Australian fruit flies (Diptera: Tephritidae) in their endemic habitat : I. Temporal variation in abundance.

A newly discovered species of tephritid, Dacus (Bactrocera) opiliae Drew & Hardy, is almost indistinguishable morphologically from the Oriental fruit fly, Dacus dorsalis. and was originally believed to represent an invading population of that species. Breeding by D. opiliae is virtually restricted to the fruit of the native vine Opilia amentacea throughout coastal areas of the Northern Territory and the Kimberleys region of Western Australia. The phenology of the host and aspects of its utilization by D. opiliae are described. Fruit suitable for oviposition is available only for a short period each year from late November to early January. It is shown that D, opiliae is effectively univoltine. Although it was able to infest various cultivated fruits in the laboratory, no evidence of such infestations by natural populations of D. opiliae was recorded during this study and the species seem to present no threat to Australia's fruit-growing industries. Information on host relations of D. jarvisi (Tryon), D. aquilonis (May) and D. tenuifascia (May) is also presented.

The Ecology of Northern Australian Dacinae (Diptera:Tephritidae) I. Host Phenology and Utilization of Opilia amentacea Roxb. (Opiliaceae) by Dacus (Bactrocera) opiliae Drew & Hardy, with notes on some other species.

Changes in trap catches of male Dacus opiliae Drew & Hardy were studied in northern Australia by use of permanently maintained groups of Steiner traps baited with methyl eugenol, an attractant for males of this species. D. opiliae, which is monophagous on a wet-season host species, was common in traps from October to February (wet season) and rare for the remamder of the year. In a second species, D. tenuifascia (May), which is monophagous on a dry-season host, trap catches peaked during the period from August to October after commencement of host fruit production. D. tenuifascia was not absent from traps at any time of the year. Temporal aspects of the seasonal fluctuations of trap catches of D. opiliae could not be explained solely on the basis of increases due to reproduction. Other features, such as the disappearance of D. opiliae from mainland traps during the dry season, were also difficult to explain. It is concluded that changing dispersive behaviour and variable lure response of males. both controlled by environmental variables, may have strongly influenced the observed fluctuations.

Ecology of Northern Australian Dacinae (Diptera: Tephritidae) II*. Seasonla Fluctuations in Trap Catches of Dacus opiliae and D. tenuifascia, and their Relationship to Host Phenology and Climatic Factors

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Ecology of Northern Australian Dacinae (Diptera: Tephritidae) II*. Seasonla Fluctuations in Trap Catches of Dacus opiliae and D. tenuifascia, and their Relationship to Host Phenology and Climatic Factors