The likely fate of hybrids of Bactrocera tryoni and Bactrocera neohumeralis

Bactrocera tryoni (Froggatt) and B. neohumeralis (Hardy) (Diptera: Tephritidae) are sympatric species which hybridise readily in the laboratory yet remain distinct in the field. B. tryoni mates only at dusk and B. neohumeralis mates only during the day, but hybrids can mate at both times. We investigated the inheritance of mating time in successively backcrossed hybrid stocks to establish whether mating with either species is more likely. The progeny of all backcrosses to B. tryoni mated only at dusk. The majority of the progeny of the first and a minority of the progeny of the second backcross to B. neohumeralis also mated at dusk, but the third successive B. neohumeralis backcross produced flies that mated only during the day. This trend towards dominance of the B. tryoni trait was also reflected in a diagnostic morphological character. We discuss the possible genetic background for these phenomena and propose that unidirectional gene flow might explain how the two species remain distinct in the face of natural hybridisation.     

Attributes pertinent to overwintering potential do not explain why Bactrocera neohumeralis (Hardy) (Diptera: Tephritidae) does not spread further south within the geographical range of B. tryoni (Froggatt)

Abstract  The geographical range of Bactrocera neohumeralis does not extend as far south as that of its sibling species, B. tryoni . However, there was no evidence of any difference between the two species in terms of physiological limitation to southerly spread when comparisons were made of low temperature torpor thresholds of adults, survival time of adults at −4°C and development rates of all stages in either warm or cool regimes. The survival schedule of the two species was similar in the laboratory and also in the moderately cold conditions experienced by caged cohorts that were exposed to winter field temperatures between late April and early November at Richmond, New South Wales (500 km south of the usual southerly limit of B. neohumeralis ). Overwintered cohorts of both species laid similar numbers of eggs in September in terms of eggs per emerged female (an indicator of the reproductive potential). However, because the proportion of B. tryoni surviving to the period of 1–15 September was less than half that for B. neohumeralis , the production per surviving female was more than double in B. tryoni . The possibility of the southerly spread of B. neohumeralis being limited by an Allee effect is discussed.     

Close genetic similarity between two sympatric species of tephritid fruit fly reproductively isolated by mating time

Abstract.— Two sibling species of tephritid fruit fly, Bactrocera tryoni and B. neohumeralis , occur sympatrically throughout the range of B. neohumeralis in Australia. Isolation between the two species appears to be maintained by a difference in mating time: B. tryoni mates at dusk, whereas B. neohumeralis mates during the middle of the day. A morphological difference in humeral callus color also distinguishes the two species. Despite clear phenotypic evidence that B. tryoni and B. neohumeralis are distinct species, genetic differentiation as measured by four markers–nuclear DNA sequences from the white gene and the ribosomal internal transcribed spacer (ITS2), and mitochondrial DNA sequences from the cytochrome b (cytb) and cytochrome oxidase subunit II (COII) genes–is very small. Minor fixed differences occur in the ITS2 sequence, however, in all other cases the two species exhibit a high level of shared polymorphic variation. The close genetic similarity suggests either that speciation has occurred very rapidly and recently in the absence of any mitochondrial DNA sorting or that the sharing of polymorphisms is due to hybridization or introgression. A third species within the tryoni complex, B. aquilonis , is geographically isolated. Bactrocera aquilonis is also genetically very similar, but in this case there is clear differentiation for the mitochondrial loci. The three species form a group of considerable interest for investigation of speciation mechanisms.     

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.     

DNA microsatellite analysis of naturally occurring colour intermediates between Bactrocera tryoni (Froggatt) and Bactrocera neohumeralis (Hardy) (Diptera: Tephritidae)

Abstract  The sympatric tephritid fruit flies Bactrocera tryoni (Froggatt) (Queensland fruit fly) and B. neohumeralis (Hardy) differ in time of mating and for the colour of the humeral callus ('shoulder pad'), which is typically entirely yellow in B. tryoni and typically entirely brown in B. neohumeralis . Field collections in sympatric regions usually include at least 1% of individuals whose humeral calli show mixed patches of yellow and brown ('intermediates'). Over 40 years, a number of studies have debated the possibility that these intermediates are interspecific hybrids. In the present study, we have used microsatellites to show that few if any of these intermediates are hybrids. Instead, most variation humeral callus appears to be confined to one species, B. tryoni . We discuss these results in the context of geneflow between the two species and suggest directions for future research.     

A new family of Strepsiptera parasitizing fruit flies (Tephritidae) in Australia

ABSTRACT. A new family of Strepsiptera (Dipterophagidae) from Australia containing a new genus and species ( Dipterophagus daci ) is described and figured. This is the first species of Strepsiptera to be described as a parasite of Diptera. D.daci is recorded from ten fruit fly species, viz Dacus aquilonis (May), D.bellulus Drew, D.cacuminatus (Hering), D.decurtans (May), D.mayi Hardy, D.neohumeralis Hardy, D.peninsularis Drew, D.tenuifascia (May), D.tryoni (Froggatt) and Dacus sp. n. ( near musae ). Gregarious parasitism (two to six adult parasites per fly) is common.     

The Effects of Selection for early (day) and late (dusk) Mating lines of Hybrids of Bactrocera tryoni and Bactrocera neohumeralis

Bactrocera neohumeralis and Bactrocera tryoni are closely related tephritid fruit fly species. B. neohumeralis mates throughout the day (in bright light) and B. tryoni mates at dusk. The two species can also be distinguished by the colour of their calli (prothoracic sclerites) which are brown and yellow, respectively. The F1 hybrids can mate both in bright light just before dusk and during dusk and have calli that are partly brown and partly yellow. The F2 hybrids have a wider range of callus patterns and mating occurs more widely in the day as well as at dusk. We directly selected hybrid stocks for mating time, creating 'early' (day-mating) and 'late' (dusk-mating) lines. As an apparently inadvertent consequence, the two types of line respectively had predominantly brown and predominantly yellow calli and thus came to closely resemble the original two species in both behaviour and appearance. Lines that were evenly selected (half for day and half for dusk) essentially retained the mating pattern of F2 hybrids. Selection for callus colour alone also affected the distribution of mating times in a predictable way. We propose a genetical model to account for the results and discuss them in the light of the apparent maintenance of species integrity in nature.     

Genetic manipulation of the circadian clock's timing of sexual behaviour in the Queensland fruit flies, Dacus tryoni and Dacus neohumeralis

ABSTRACT. Mating in Dacus tryoni is restricted to dusk, whereas that of a sibling species, Dacus neohumeralis , occurs in the middle of the day. The timing of sexual behaviour in both species is determined by an interaction between a circadian clock and light intensity. In D. tryoni peak mating responsiveness is at the time of dusk, and the optimal light intensity for mating is approximately 91x. In D.neohumeralis peak responsiveness is in the middle of the day, and the optimal light intensity for mating is greater than 10 000 lx. The two species were crossed and the time of mating and response to light intensity of F₁, F₂ and backcross progeny determined. The circadian clock set a mating phase ('gate') as narrow in F₁ flies as in their parents, suggesting the circadian timing mechanism to be common between the two species. The results indicate that the genetic mechanism controlling timing is independent of that controlling response to light intensity, and that both genetic mechanisms are complex.     

REDUCTION IN TRAP CAPTURES OF FEMALE FRUIT FLIES (DIPTERA: TEPHRITIDAE) WHEN SYNTHETIC MALE LURES ARE ADDED

Abstract
Captures of females of 4 species of fruit flies on or in both coloured sticky traps and protein baited traps were reduced by synthetic male attractants. Captures of female Dacus tryoni (Froggatt), Dacus neohumeralis Hardy and Dacus cacuminatus (Hering) were reduced by both cuelure and methyl eugenol, and female Ceratitis capitata (Weidemann) by Capilure®. These effects were sufficient to overcome the normally attractive stimuli of colour and odours associated with yeast.     

THESIS ABSTRACT

Geographical distribution, seasonal abundance and habitat preference of fruit fly species (Diptera: Tephritidae) in South-East Queensland, with special reference to Bactrocera tryoni (Froggatt) and Bactrocera neohumeralis (Hardy) . S. Raghu.     

Aphis migration and the efficiency of the trapping method

Reproducible results were obtained when adhesive traps for aphides were placed at the same height in different parts of a potato field. The total catches in different localities in different seasons can therefore justifiably be compared. During the summer dispersal flights, different species flew at different heights, so traps at one height only are not suitable for comparing the relative abundance of different species. There was less variation in numbers caught on traps at 3–4 ft. above the ground than on traps at 5–6 ft. or at ground-level.
During the first fortnight of July an average of 200 aphides, 1.6% of which were Myzus persicae , was caught on traps in the position of potato plants. Most of these were not potato aphides, but it is suggested that some of them might act as vectors of potato viruses. The number of aphides caught was roughly proportional to the volume of free air space around the traps, and as the foliage increased in density the numbers caught on lower traps decreased in proportion.
Wind-speed records within and above the crop are discussed and it is shown that conditions are often suitable for voluntary aphis flight in and near the crop on relatively windy days. Records of catches on the half-traps facing the wind and on the other halves showed that voluntary flight decreased with increasing height.
Brilliant yellow traps, coated with adhesive grease, caught more aphides than white traps, which in turn caught more than black.     

Enzyme polymorphism and species discrimination in fruit flies of the genus Dacus (Tephritidae).

Sympatric populations of D. tryoni and D. neohumeralis are difficult to completely distinguish taxonomically. Using five pigmentation characters, each of some taxonomic value, a small proportion of individuals cannot be assigned to either species nor definitely classified as hybrids. To aid in species discrimination and hybrid identification gene frequencies in natural populations were estimated at three polymorphic protein loci, an alcohol dehydrogenase (Adh), an octanol dehydrogenase (Odh) and an esterase (E-2). Samples of flies were taken from four sites spread over 1200 miles along the Australian eastern coast. Within each species allelic frequencies at each locus were largely the same at all localities. Consistent differences in gene frequencies between species occurred at all three loci, strongly supporting the hypothesis of two distinct gene pools. The Adh locus best discriminated between species with a unique allele occurring in D. neohumeralis at a frequency of 0-85. None of the loci showed complete differentiation and hence it was not possible to find a quick and easy method to distinguish the species nor to detect field hybrids. Directional selection of laboratory populations for a change in callus colour (the best pigmentation character for separating the species) indicated that at the Adh and E-2 loci frequencies of major alleles were not genetically associated with major genes for callus colour. Thus genotype determination at these loci when considered together with pigmentation characters may be valuable taxonomically for further distinguishing between the species.     

Selected beetle assemblages captured in pitfall traps baited with deer dung or meat in balsam fir and sugar maple forests of central Quebec

Vertebrate dung and carrion are rich and strongly attractive resources for numerous beetles that are often closely linked to them. The presence and abundance of beetles exploiting such resources are influenced by various ecological factors including climate and forest cover vegetation. We studied selected assemblages of coprophilous and necrophagous beetles in Quebec along a 115-km north-south transect in three balsam fir (Abies balsamea (L.) Miller) forest sites and in a fourth forest site dominated by sugar maple (Acer saccharum Marshall), close to the southern fir site. Beetle abundance was estimated using a sampling design comprising replicated pitfall traps baited with red deer meat or dung in each site. A total of 8,511 beetles were caught and identified to family level, 95.7% of which belonged to families with known coprophilous or necrophagous behavior. Meat-baited pitfall traps caught nearly 15 times as many beetles as dung-baited traps. All Histeridae, Hydrophilidae, Scarabaeidae, and Silphidae were identified to species to examine specific diversity variation among sites. For the beetles caught in the meat-baited traps (majority of captures), decreases in abundance and species richness were observed from south to north along the fir forest transect, with evidence of decreasing specific diversity as measured by the Shannon index of diversity. Strong differences in species assemblages were also observed between the southern maple and fir forest sites. The Silphidae and Histeridae were more abundant in the maple forest, whereas the Hydrophilidae and Ptilidae were more abundant in the fir forest.     

A comparison of pitfall traps with bait traps for studying leaf litter ant communities.

A comparison of pitfall traps with bait traps for sampling leaf litter ants was studied in oak-dominated mixed forests during 1995-1997. A total of 31,732 ants were collected from pitfall traps and 54,694 ants were collected from bait traps. They belonged to four subfamilies, 17 genera, and 32 species. Bait traps caught 29 species, whereas pitfall traps caught 31 species. Bait traps attracted one species not found in pitfall traps, but missed three of the species collected with pitfall traps. Collections from the two sampling methods showed differences in species richness, relative abundance, diversity, and species accumulation curves. Pitfall traps caught significantly more ant species per plot than did bait traps. The ant species diversity obtained from pitfall traps was higher than that from bait traps. Bait traps took a much longer time to complete an estimate of species richness than did pitfall traps. Little information was added to pitfall trapping results by the bait trapping method. The results suggested that the pitfall trapping method is superior to the bait trapping method for leaf litter ant studies. Species accumulation curves showed that sampling of 2,192+/-532 ants from six plots by pitfall traps provided a good estimation of ant species richness under the conditions of this study.     

Host preference and host suitability in an egg-pupal fruit fly parasitoid, Fopius arisanus (Sonan) (Hym., Braconidae)

The relative oviposition rate of the parasitoid Fopius arisanus (Sonan) was investigated across three frugivorous tephritid species, Bactrocera tryoni Froggart, Bactrocera jarvisi (Tryon) and Bactrocera cucumis French. Choice and no-choice tests were both used. The suitability of these three species for sustaining larval development and survival to the adult stage was also assessed. Fopius arisanus parasitized all three tephritid species, regardless of the method of exposure, but showed stronger preference for B. tryoni and B. jarvisi over B. cucumis. Superparasitism was extremely rare. Successful development of F. arisanus varied across host species. Bactrocera tryoni yielded significantly more parasitoids than B. jarvisi, but no wasps emerged from B. cucumis puparia. Tests were set up in replicated trials, but results were not homogeneous across trials. We discuss the host relationships of F. arisanus with reference to this variation and in relation to host suitability for larval development.     

Assessment of the diversity and abundance of terrestrial mangrove arthropods in southern New South Wales,Australia

Abstract The diversity and abundance of arboreal and flying arthropods, in three mangrove patches along the south coast of New South Wales, Australia, was investigated to determine the degree of spatial variability in the assemblages among patches. Intercept traps and restricted canopy fogging were used to sample the communities at Minnamurra, Bonnievale and Kurnell. Twelve orders of arthropods were detected, incorporating 252 morphospecies. Abundance, species richness and species composition were very similar across all patches, the variation being much smaller than expected. These findings suggest that the composition of the arboreal and flying fauna associated with mangrove patches are very similar among patches, but preliminary results also showed that species composition could be highly variable within a patch. Variation between the trapping methods was large, as expected . Intercept trapping and restricted canopy fogging techniques were found to sample different suites of species and therefore complement each other well in sampling programs. Cumulative species curves differed between time periods but generally were flatter for intercept traps than for restricted canopy fogging. Results suggested, for a given level of effort, intercept traps caught a more representative sample of the species composition available to them.     

Exploring a new biodiversity frontier: subterranean ants in northern Australia

Although it is common for ant surveys to uncover previously uncollected species, a recent study of subterranean ants in Amazonian Ecuador has indicated that an entire ant fauna may remain largely undiscovered. Here we report on the first systematic investigation of subterranean ants in northern Australia, in order to assess the extent to which the high abundance and diversity of subterranean ants in Amazonia is apparent in tropical Australia. We use a novel sampling technique that combines elements of an attractant bait and a pitfall trap, and allows many traps to be deployed simultaneously. Our main study was conducted at three closely approximated sites in Darwin, where the local ant fauna has been intensively surveyed using conventional (above-ground) sampling techniques. The 720 traps deployed resulted in 421 species records, representing 29 species from 17 genera. Sixteen of these species have cryptobiotic morphology, with four recorded here for the first time. Remarkably, one of these four (a blind species of Solenopsis) was the second most frequently caught species in subterranean traps, with 70 records. Ant abundance, species richness and composition varied markedly between sites, despite site similarity in soils and vegetation. Total ant records were greater in the middle compared with start of the wet season, declined with depth, and were greater after 4 days than one. Sampling at six sites in the Mitchell Falls area of the northern Kimberley region, 1,200 km southwest of Darwin, also revealed several cryptobiotic species new to science, including a new genus record (Pseudolasius) for Western Australia. Our underground sampling has therefore revealed an abundant and diverse subterranean ant fauna in northern Australia, containing many cryptobiotic species not previously collected. We use our results to provide methodological guidelines for most effectively sampling this fauna. Combined with the Amazonian study, our findings indicate that a specialist subterranean ant fauna, including numerous species remaining to be discovered, might be a feature of tropical landscapes throughout the world.     

Is pitfall trapping a valuable sampling method for grassland Orthoptera?

Common methods to assess diversity and abundance of Orthoptera are sweep netting, transect counts and box-quadrat sampling. Pitfall trapping, by contrast, is rarely used, and the value of this method is still being questioned. In 2008, we studied Orthoptera species richness and abundance in five vegetation types along a gradient of dune succession on the Baltic Sea island of Hiddensee (NE Germany) by comparing transect-count and pitfall-trapping data. Using transect counts, 12 species were detected in the study area. With pitfall traps, three chorto- and thamnobiont Ensifera species (C. dorsalis, M. roeselii and T. viridissima) were not caught at all, and it was only in low-growing and sparsely-vegetated grey dunes that all present species were detected. With pitfall traps, the proportion of present species recorded strongly declined with increasing height and density of the vegetation type. Assuming that transect counts are a good proxy for relative Orthoptera densities, densities ascertained by pitfall traps are strongly biased by vegetation structure and locomotive behaviour of the species. More than 80% of all individuals were caught in sparsely-vegetated grey dunes. Frequency patterns of the species also differed. Using pitfall traps, especially chortobiont species were significantly underrepresented. Qualitative and quantitative sampling of Orthoptera using pitfall traps seems only reasonable in habitats with low and sparse vegetation and a high proportion of geobiont species.     

Visual Responses of Adult Asian Citrus Psyllid (Hemiptera: Liviidae) to Colored Sticky Traps on Citrus Trees

The effects of five differently-colored sticky traps in capturing adult Diaphorina citri were evaluated in citrus orchards. Trap catches of D. citri were monitored fortnightly on blue, green, red, white and yellow sticky cards placed on three citrus varieties during D. citri active flight period from April to July in south Texas. Evaluation of mean trap catches of each color by repeated measures analysis of variance produced three separate groups: yellow traps caught significantly more D. citri adults than the other four traps; red and green traps caught significantly more D. citri than blue and white traps, which were not significantly different. Although the number of adult psyllid captured on all trap types significantly increased with time during the trapping period, the performance of traps did not change with time. Trap catches were also significantly influenced by the citrus species; traps placed on lemon trees captured more D. citri than those placed on sweet orange and grapefruit, suggesting that plant preference exhibited by D. citri may influence the performance of traps. The ratio of trap reflectance between the 680 to 700 nm and the 450 nm was significantly correlated with total trap catches in all host species studied. Thus, this index was a good indicator of the attractiveness of adult D. citri to colored traps. Additionally, we compared the reflectance values of young versus mature flush shoots of the three host plants used in this study as related to densities of D. citri recorded in colored traps. We discussed the importance of visual cues in the host finding behavior of adult D. citri.