Australian Fruit Flies Research Articles

Divergent east-west lineages in an Australian fruit fly, (Bactrocera jarvisi), associated with the Carpentaria Basin divide.

Bactrocera jarvisi is an endemic Australian fruit fly species (Diptera: Tephritidae). It occurs commonly across tropical and subtropical coastal Australia, from far-northern Western Australia, across the 'Top End' of the Northern Territory, and then down the Queensland east coast. Across this range, its distribution crosses several well documented biogeographic barriers. In order to better understand factors leading to the divergence of Australian fruit fly lineages, we carried out a population genetic study of B. jarvisi from across its range using genome-wide SNP analysis, utilising adult specimens gained from trapping and fruit rearing. Populations from the Northern Territory (NT) and Western Australia were genetically similar to each other, but divergent from the genetically uniform east-coast (= Queensland, QLD) population. Phylogenetic analysis demonstrated that the NT population derived from the QLD population. We infer a role for the Carpentaria Basin as a biogeographic barrier restricting east-west gene flow. The QLD populations were largely panmictic and recognised east-coast biogeographic barriers play no part in north-south population structuring. While the NT and QLD populations were genetically distinct, there was evidence for the historically recent translocation of flies from each region to the other. Flies reared from different host fruits collected in the same location showed no genetic divergence. While a role for the Carpentaria Basin as a barrier to gene flow for Australian fruit flies agrees with existing work on the related B. tryoni, the reason(s) for population panmixia for B. jarvisi (and B. tryoni) over the entire Queensland east coast, a linear north-south distance of >2000km, remains unknown.

Opiine parasitoids (Hymenoptera: Braconidae) and biological control of fruit flies (Diptera: Tephritidae) in Australia: Past, present and future

AbstractOpiine braconids are parasitoids of the immature stages of frugivorous tephritids. The female wasp lays her eggs into the eggs or larvae of the fruit fly host, where the immature wasp develops before emerging as a next‐generation adult from the now dead host pupal case. In support of a new generation of Australian fruit fly parasitoid research, this paper comprehensively reviews what is known about the Australian fruit fly infesting opiines. Based on the most recent taxonomic revision 11 fruit fly infesting opiine species are documented to occur in Australia, but we consider as doubtful the record forDiachasmimorpha longicaudataand consider the record forFopius illusoriusto be tentative without further collections. We identify that the systematics and taxonomy of the Australian native fruit fly infesting opiines are in urgent need of further work. The history of fruit fly biological control in Australia is comprehensively reviewed, including the export of native Australian opiines for fruit fly control elsewhere in the world. Australia was actively involved in three major classical biological control programmes against fruit flies from the turn of the 1900s until the mid‐1960s. Despite the introduction of 11 opiine species, plus numerous other natural enemies, onlyFopius arisanusestablished in eastern Australia, where in South‐east Queensland it can now cause between 30 and 40% mean parasitism. In addition to the exoticF. arisanus, the native speciesDiachasmimorpha kraussiiandDiachasmimorpha tryonialso cause fruit fly parasitism in agriculturally important crops: both species have also been liberated widely outside of Australia for fruit fly control. Other Australian opiines have not been reared from flies infesting commercial crops and appear biologically restricted to the fruits and environs of Australian east‐coast rainforests. The biology literature forD. tryoniandD. kraussiiis comprehensively reviewed, while forF. arisanus, already reviewed elsewhere, key literature only is covered. Forward looking, we consider the potential for inoculative or inundative releases of opiines in areas where they do not currently occur to be good, while conservation biological control may help to increase the impacts of parasitoids in areas where they are already established.

The responsiveness of Bactrocera jarvisi (Diptera: Tephritidae) to two naturally occurring phenylbutaonids, zingerone and raspberry ketone

The males of different species of Bactrocera and Zeugodacus fruit flies are commonly attracted to plant-derived phenylpropanoids (e.g. methyl eugenol (ME)) or phenylbutanoids (e.g. raspberry ketone (RK)) but almost never to both. However, one particular plant-derived phenylbutanoid, zingerone (ZN), which possesses an intermediate chemical structure between ME and RK, weakly attracts both ME- and RK-responding fruit fly species. Bactrocera jarvisi, an Australian fruit fly species, is weakly attracted to cue lure (an analogue of RK) but strongly attracted to ZN. Here, we investigated the minimum olfactory threshold and optimum sensitivity of B. jarvisi males to ZN and RK as a function of dose, time and sexual maturation. Our results show that B. jarvisi males had a marked preferential response to ZN, with a much lower olfactory threshold and faster response time to ZN than RK. Probit analysis demonstrated that ZN was at least >1600× more potent than RK as a male attractant to B. jarvisi. Although fruit fly male attraction to the phytochemicals is generally associated with sexual maturity, in B. jarvisi immature males were also attracted to ZN. Our results suggest that B. jarvisi males have a fine-tuned olfactory response to ZN, which appears to play a central role in the chemical ecology of this species.

Incorporating evolutionary adaptation in species distribution modelling reduces projected vulnerability to climate change.

Based on the sensitivity of species to ongoing climate change, and numerous challenges they face tracking suitable conditions, there is growing interest in species' capacity to adapt to climatic stress. Here, we develop and apply a new generic modelling approach (AdaptR) that incorporates adaptive capacity through physiological limits, phenotypic plasticity, evolutionary adaptation and dispersal into a species distribution modelling framework. Using AdaptR to predict change in the distribution of 17 species of Australian fruit flies (Drosophilidae), we show that accounting for adaptive capacity reduces projected range losses by up to 33% by 2105. We identify where local adaptation is likely to occur and apply sensitivity analyses to identify the critical factors of interest when parameters are uncertain. Our study suggests some species could be less vulnerable than previously thought, and indicates that spatiotemporal adaptive models could help improve management interventions that support increased species' resilience to climate change.

On the evolution of heightened condition dependence of male sexual displays

The maintenance of genetic variation in male sexual display traits in the face of strong directional sexual selection from female preferences is an ongoing evolutionary conundrum. Condition dependence and the genic capture hypothesis are often cited as theoretical resolutions to this problem, yet little is known about the ability of condition dependence itself to evolve. We set out to test how a suite of cuticular hydrocarbons (CHCs) used in sexual displays are affected by adult diet and the potential for any condition-dependent response to evolve in a laboratory-adapted population of the Australian fruit fly Drosophila serrata. We performed a dietary manipulation within a half-sib breeding design, raising adult males either with or without access to live yeast, a manipulation that had previously shown strong effects on female fitness. Diet had strong phenotypic effects, with males from the different diets producing different CHC blends. The blend of CHCs under sexual selection showed a degree of elevated condition dependence. Regardless of the heightened sensitivity of favoured CHC blends to diet and the presence of genetic variance for the traits, we were unable to detect any genetic variance in the reaction norms for the male dietary response. Our results suggest that there is limited opportunity for males to evolve further condition dependence in response to yeast availability in this population.

Field performance of Lynfield and McPhail traps for monitoring male and female sterile Bactrocera tryoni (Froggatt) and wild Dacus newmani (Perkins)

McPhail traps, baited with protein food lure, are used worldwide for surveillance of many species of fruit flies. Queensland fruit fly (Qfly) Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) is a native Australian fruit fly and normally monitored using Lynfield traps baited with cuelure. On some occasions, McPhail traps with wet food lures are deployed to detect female flies or to find the incursion epicentre. This paper reviews field results on the merits of Lynfield and McPhail traps for detection of male and female Qfly. Following release of equal numbers of sterile males and females, Lynfield traps baited with cuelure captured more Qfly males than protein autolysate or orange concentrate in McPhail traps. Significantly more male than female Qfly were captured in McPhail traps baited with protein autolysate or orange. There was no significant difference between orange concentrate lure and protein autolysate lure in attracting either males or females. Another Australian native fruit fly, Dacus newmani (Perkins), was attracted to cuelure in Lynfield traps but not to either lure in McPhail traps. The data obtained run counter to the reputation of McPhail traps baited with protein autolysate or orange concentrate as a specialist lure/trap combination for female Qfly.

Polyandry and paternity skew in natural and experimental populations of Drosophila serrata

Many species engage in polyandry, resulting in the potential for sexual selection to continue post-copulation through sperm competition and/or cryptic female choice. The relative importance of pre- vs. post-copulatory processes remains unknown for most species despite this information being fundamental for understanding the evolutionary consequences of sexual selection. The Australian fruit fly Drosophila serrata has become a prominent model system for studying precopulatory sexual selection, such as mating preferences and their influence on the evolution of sexually selected traits. Here, we investigated polyandry and the potential for post-copulatory sexual selection in this species using indirect paternity analysis. We genotyped 21 wild-caught and 19 laboratory-reared mothers and their offspring (a total of 787 flies) at six microsatellite loci and found extensive polyandry, with all broods surveyed having at least two sires. Female remating rates were higher than in other Drosophila surveyed to date and no significant differences were found between laboratory and field populations. Additionally, we found evidence for biased sperm usage in several broods of D. serrata. Paternity skew occurred more frequently in broods from the field population than the laboratory one, suggesting differences between the two environments in the level of post-copulatory sexual selection. Our data suggest that D. serrata represents a promising system for studying the interaction between pre- and post-copulatory sexual selection in driving the evolution of sexually selected phenotypes.

Genetic variance in female condition predicts indirect genetic variance in male sexual display traits.

During sexual encounters, individuals often use signals, such as display traits, to attract mates. If individuals alter their display traits with respect to the genotype of potential mates, indirect genetic effects (IGEs) may occur in which the genes of one individual influence the phenotype of another. Although IGEs between related individuals have received much attention, their occurrence between unrelated individuals during sexual encounters has not. Here, we demonstrate that in the Australian fruit fly Drosophila serrata, males assess females by using both visual and olfactory cues, resulting in a rapid plastic response (within minutes) in male cuticular hydrocarbons (CHCs), a display trait that is an important target of mate choice. Several CHCs in males exhibited significant IGEs, and IGEs were inducible on both males reared in the laboratory and on field-caught individuals. A vector describing genetic variance in multiple CHCs in females was found to be almost identical to a vector describing indirect genetic variance in male CHCs, suggesting that males might assess female CHCs during courtship. This vector displayed contributions from all female CHCs in the same direction and of similar magnitude, suggesting that female condition may be the underlying casual trait that males are assessing. Consistent with this interpretation, when measured directly in a separate experiment, genetic variance in female condition accounted for 19.8% of the indirect genetic variance in male CHCs. These indirect genetic effects have the potential to alter the response to selection of male sexual display traits.

Genetic delineation of sibling species of the pest fruit fly Bactocera (Diptera: Tephritidae) using microsatellites.

Using a large set of microsatellites, the genetic relationships between three closely related Australian fruit fly species, Bactrocera tryoni (Froggatt), B. neohumeralis (Hardy) and B. aquilonis(May) were investigated. Bactrocera tryoni and B. neohumeralis are sympatric, while B. aquilonisis allopatric to both. The sympatric species, B. tryoni and B. neohumeralis, were found to be genetically distinct. It is likely that despite differences in mating time between these two species, some gene flow still occurs. In contrast, the sibling species B. tryoni and B. aquilonis were found to be closely related, despite allopatry. The level of genetic divergence was similar to that found within eastern Australian populations of B. tryoni. Consideration of all available genetic data suggests that this similarity is not due to recent (i.e. within the last 30 years) displacement of B. aquilonis by B. tryoni from the B. aquilonis region (north-western Australia). Instead the data suggests that, at least in the areas sampled, asymmetrical hybridization may have occurred over a longer timescale.

Interspecific crosses of Bactrocera tryoni (Froggatt) and Bactrocera jarvisi (Tryon) (Diptera: Tephritidae) in the laboratory

Abstract F 1 progeny from the cross between two species of Australian fruit flies, Bactrocera tryoni (Froggatt) and Bactrocera jarvisi (Tryon), mated with each other in the laboratory to produce viable F2 offspring. F1 and F2 hybrids were morphologically distinct from their B. tryoni and B. jarvisi parents.

Choice of Insecticides in Steiner Traps Affects the Capture Rate of Fruit Flies (Diptera: Tephritidae)

Some Australian fruit flies—i.e., Queensland fruit fly, Dacus tryoni (Froggatt); lesser Queensland fruit fly, Dacus neohumeralis Hardy; solanum fly, Dacus cacuminatus (Hering); and Mediterranean fruit fly, Ceratitis capitata (Wiedemann)—attracted to Steiner traps died outside them. They either succumbed to the insecticide before entering or escaped before being overcome. In a normal trapping program, these flies would fall to the ground and be lost, leading to an observed catch sometimes substantially lower than the actual number of flies attracted. Choice of insecticide used in the trap had a marked effect on number of flies lost and, consequently, on total size of the catch. Dichlorvos was a more effective insecticide for use in traps than malathion, lindane, trichlorfon, or naled.

Ecological studies of Eastern Australian fruit flies (Diptera: Tephritidae) in their endemic habitat : II. The spatial pattern of abundance.

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.