Rectal gland volatiles are key mediators of sexual interactions in tephritid fruit flies. We used solid-phase microextraction (SPME) plus gas chromatography-mass spectrometry (GC-MS) and gas ...chromatography-flame ionization detection (GC-FID) to substantially expand rectal gland chemical characterisation of the Queensland fruit fly (Bactrocera tryoni (Diptera: Tephritidae); Qfly). The SPME GC-MS analysis identified 24 of the 30 compounds previously recorded from Qfly rectal glands, plus another 21 compounds that had not previously been reported. A few amides and fatty acid esters dominated the chromatograms of males and females respectively, but we also found other esters, alcohols and aldehydes and a ketone. The GC-FID analyses also revealed over 150 others, as yet unidentified, volatiles, generally in lesser amounts. The GC-FID analyses also showed 49 and 12 compounds were male- and female-specific, respectively, both in single sex (virgin) and mixed sex (mostly mated) groups. Another ten compounds were male-specific among virgins but undetected in mixed sex groups, and 29 were undetected in virgins but male-specific in mixed sex groups. The corresponding figures for females were four and zero, respectively. Most short retention time peaks (including a ketone and an ester) were male-specific, whereas most female-biased peaks (including five fatty acid esters) had long retention times. Our results indicate previously unsuspected diversity of rectal gland volatiles that might have pheromone functions in males, but far fewer in females.
Tephritid fruit flies are amongst the most damaging insect pests of horticulture globally. Some of the key fruit fly species are managed using the sterile insect technique (SIT), whereby millions of ...sterile males are released to suppress reproduction of pest populations. Male annihilation technique (MAT), whereby sex specific lures are used to attract and kill males, is often used to reduce wild male numbers before SIT programs commence, providing released sterile males an increased numerical advantage. Overall program efficacy might be improved if MAT could be deployed simultaneously with SIT, continuously depleting fertile males from pest populations and replacing them with sterile males. However, such 'male replacement' requires a means of suppressing attraction of released sterile males to lures used in MAT. Previous studies have found that exposure of some fruit flies to lure compounds as mature adults can suppress subsequent response to those lures, raising the possibility of pre-release treatments. However, this approach requires holding flies until after maturation for treatment and then release. The present study takes a novel approach of exposing immature adult male Queensland fruit flies (Bactrocera tryoni, or 'Qfly') to raspberry ketone (RK) mixed in food, forcing these flies to ingest RK at ages far younger than they would naturally. After feeding on RK-supplemented food for two days after emergence, male Qflies exhibited a reduction in attraction to cuelure traps that lasted more than 20 days. This approach to RK exposure is compatible with current practises, in which Qflies are released as immature adults, and also yields advantages of accelerated reproductive development and increased mating propensity at young ages.
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•Female Bactrocera tryoni switched from male to fruit-seeking behaviour after mating.•Male sex pheromone was more attractive for virgin females than for mated females.•Fruit cues were ...more attractive for mated females than for virgin females.•EAG responses to pheromones and fruit did not change with female mating state.
In order to reproduce, female tephritid fruit flies need both mates for fertilization and fruit for oviposition. Virgin females are prone to mating and approach males, attracted by their pheromones. Mated females, however, may experience an abrupt reduction of mating propensity and prioritise the search for suitable fruit rather than additional mates. Accordingly, mating in fruit flies may induce a switch in olfactory preferences of females from pheromones to fruit stimuli, and this switch may also be an important mediator of mating-induced sexual inhibition. To test for mating-induced switches in olfactory preference of female Queensland fruit fly, Bactrocera tryoni, we used wind tunnel assays to assess attraction of mated and virgin females to (1) male sex pheromone delivered through a perforated glass sphere or (2) an entire fruit. Electroantennogram (EAG) responses were also used to test for mating-induced changes in olfactory sensitivity to pheromones and fruit odours. Pheromones elicited quicker upwind responses in virgin females than in mated females; during the first six minutes of trials more virgin females than mated females were observed in the upwind end of the wind tunnel where pheromone odours were released. Fruit cues, in contrast, elicited stronger association with the upwind end of the wind tunnel in mated females than in virgin females from the fifth minute onwards. Also, mated females were observed on the fruit for longer periods than virgin females. EAG responses to pheromones and fruit odours were similar in virgin and mated females, indicating that changes in preferences are not a consequence of changes in peripheral sensitivity of antennae to odours but instead appear to be mediated by post-receptor processing. Our results show that mating reduces attraction to male-produced pheromones and increases attraction to fruit stimuli in B. tryoni females. We propose that this behavioural switch from mating stimuli to oviposition stimuli is an important mediator of mating-induced sexual inhibition in this species.
Elastin-like polypeptides (ELPs) are thermoresponsive biopolymers that undergo an LCST-like phase transition in aqueous solutions. The temperature of this LCST-like transition, T t , can be tuned by ...varying the number of repeat units in the ELP, sequence and composition of the repeat units, the solution conditions, and via conjugation to other biomacromolecules. In this study, we show how and why the choice of guest (X) residue in the VPGXG pentad repeat tunes the T t of short ELPs, (VPGXG)4, in the free state and when conjugated to collagen-like peptides (CLPs). In experiments, the (VPGWG)4 chain (in short, WWWW) has a T t < 278 K, while (VPGFG)4 or FFFF has a T t > 353 K in both free ELP and ELP–CLP systems. The T t for the FWWF ELP sequence decreases from being >353 K for free ELP to <278 K for the corresponding ELP–CLP system. The decrease in T t upon conjugation to CLP has been shown to be due to the crowding of ELP chains that decreases the entropic loss upon ELP aggregation. Even though the net hydrophobicity of ELP has been reasoned to drive the T t , the origins of lower T t of WWWW compared to FFFF are unclear, as there is disagreement in hydrophobicity scales in how phenylalanine (F) compares to tryptophan (W). Motivated by these experimental observations, we use a combination of atomistic and coarse-grained (CG) molecular dynamics simulations. Atomistic simulations of free and tethered ELPs show that WWWW are more prone to acquire β-turn structures than FFFF at lower temperatures. Also, the atomistically informed CG simulations show that the increased local stiffness in W than F due to the bulkier side chain in W compared to F, alone does not cause the shift in the transition of WWWW versus FFFF. The experimentally observed lower T t of WWWW than FFFF is achieved in CG simulations only when the CG model incorporates both the atomistically informed local stiffness and stronger effective attractions localized at the W position versus the F position. The effective interactions localized at the guest residue in the CG model is guided by our atomistically observed increased propensity for β-turn structure in WWWW versus FFFF and by past experimental work of Urry et al. quantifying hydrophobic differences through enthalpy of association for W versus F.
The Queensland fruit fly or ‘Q-fly,’
Bactrocera tryoni
(Froggatt) (Diptera: Tephritidae), is Australia’s most damaging insect pest of horticulture. The sterile insect technique (SIT) is being ...developed as a sustainable approach to management of Q-fly. New larval diets are needed for economical production of millions of artificially reared sterile flies that are required for use in SIT. Solid diets that incorporate biological bulking agents present problems of variable quality and waste disposal. Liquid diets emerged as a promising alternative, but these also suffer drawbacks, including separation of components, fermentation and need for cleaning and regular replacement of substrates that support developing larvae. The present study considers whether two promising liquid diet formulations might be improved by incorporating agar (0, 0.25, 0.5, 1.0 and 1.5%) to create semiliquid or gel diets that maintain consistent composition, suppress fermentation, negate the need for supporting substrates and minimize waste. Overall, gel diets containing greater than 0.5% agar outperformed liquid diets (0% agar) and semiliquid diets (0.25% agar) of identical nutritional composition, especially in terms of development rate and productivity. Flies from the two tested diet formulations differed in flight performance, and this likely reflects differences in concentration of wheat germ oil and/or the type of yeast used. Overall, gel diets show great promise for rearing of Q-fly, overcoming many of the constraints of both traditional solid diets and more recently developed liquid diets. There is now a need for larger-scale trials that test and refine these diets for use in operational SIT settings.
Peptide-polymer conjugates are a class of soft materials composed of covalently linked blocks of protein/polypeptides and synthetic/natural polymers. These materials are practically useful in ...biological applications, such as drug delivery, DNA/gene delivery, and antimicrobial coatings, as well as nonbiological applications, such as electronics, separations, optics, and sensing. Given their broad applicability, there is motivation to understand the molecular and macroscale structure, dynamics, and thermodynamic behavior exhibited by such materials. We focus on the past and ongoing molecular simulation studies aimed at obtaining such fundamental understanding and predicting molecular design rules for the target function. We describe briefly the experimental work in this field that validates or motivates these computational studies. We also describe the various models (e.g., atomistic, coarse-grained, or hybrid) and simulation methods (e.g., stochastic versus deterministic, enhanced sampling) that have been used and the types of questions that have been answered using these computational approaches.
Divergence between populations in mating behaviour can function as a potent premating isolating mechanism and promote speciation. However, very few cases of inherited intraspecific variation in ...sexual signalling have been reported in tephritid fruit flies, despite them being a highly speciose family. We tested for such variation in one tephritid, the Queensland fruit fly, Bactrocera tryoni (Qfly). Qfly mating behaviour depends on volatiles secreted from male rectal glands but no role for the volatiles from female rectal glands has yet been reported. We previously detected over 100 volatile compounds in male rectal glands and identified over 30 of them. Similar numbers were recorded in females. However, many compounds showed presence/absence differences between the sexes and many others showed quantitative differences between them. Here we report inherited variation among 24 Qfly lines (23 isofemale lines established from recent field collections and one domesticated line) in the abundance of three esters, two alcohols, two amides, an aldehyde and 18 unidentified volatiles in male rectal glands. We did not find any compounds in female rectal glands that varied significantly among the lines, although this may at least partly reflect lower female sample numbers. Most of the 26 male compounds that differed between lines were more abundant in the domesticated line than any of the recently established isofemale lines, which concurs with other evidence for changes in mating behaviour during domestication of this species. There were also large differences in several of the 26 compounds among the isofemale lines, and some of these differences were associated with the regions from which the lines were collected. While some of the variation in different compounds was correlated across lines, much of it was not, implicating involvement of multiple genes. Our findings parallel reports of geographic variation in other Qfly traits and point to inherited differences in reproductive physiology that could provide a basis for evolution of premating isolation between ecotypes.
Tephritid flies released in sterile insect technique pest management programs are usually marked with fluorescent dyes so that they can be distinguished from wild flies in monitoring traps. Dyes can ...have adverse effects on emergence, quality, and survival, which can impact sterile insect technique (SIT) success, and so it is important to identify dyes and doses that maximize marking efficacy while minimizing deleterious effects on fly quality. This study examines the effects of five fluorescent dye products, Fluoro Pink, Fluoro Orange, Stella Green, Arc Chrome, and Astral Pink applied at four dose levels (1, 2, 3, and 4 g/liter) on Queensland fruit fly. All dye products caused a similar dose-dependent reduction in percentage of adult emergence. Incidence of morphological deformity of emerged adults increased with dose, and this trend was similar for all dye products. No effects of dye product or dose were found on survival rates over the first 35 d of adulthood, although females tended to have higher survival than males. Visibility varied with dose and dye product; 1 g/liter dye was less visible than 2, 3, or 4 g/liter, and Stella green had lower visibility than other dyes. All of the tested dyes except for Stella green were similar in all assessed metrics of fly performance and are recommended for use in SIT programs.
We perform coarse-grained (CG) molecular dynamics (MD) simulations to investigate the self-assembly of collagen-like peptide (CLP) triple helices into fibrillar structures and percolated networks as ...a function of solvent quality. The focus of this study is on CLP triple helices whose strands are different lengths (
i.e.
, heterotrimers), leading to dangling 'sticky ends'. These 'sticky ends' are segments of the CLP strands that have unbonded hydrogen-bonding donor/acceptor sites that drive heterotrimeric CLP triple helices to physically associate with one another, leading to assembly into higher-order structures. We use a validated CG model for CLP in implicit solvent and capture varying solvent quality through changing strength of attraction between CG beads representing the amino acids in the CLP strands. Our CG MD simulations show that, at lower CLP concentrations, CLP heterotrimers assemble into fibrils and, at higher CLP concentrations, into percolated networks. At higher concentrations, decreasing solvent quality causes (i) the formation of heterogeneous network structures with a lower degree of branching at network junctions and (ii) increases in the diameter of network strands and pore sizes. We also observe a nonmonotonic effect of solvent quality on distances between network junctions due to the balance between heterotrimer end-end associations driven by hydrogen bonding and side-side associations driven by worsening solvent quality. Below the percolation threshold, we observe that decreasing solvent quality leads to the formation of fibrils composed of multiple aligned CLP triple helices, while the number of 'sticky ends' governs the spatial extent (radius of gyration) of the assembled fibrils.
Collagen-like peptide heterotrimers are computationally designed to create percolated networks as a function of solvent quality and multifunctional materials of interest to the biomaterials community.
Insects typically host substantial microbial communities (the 'microbiome') that can serve as a vital source of nutrients and also acts as a modulator of immune function. While recent studies have ...shown that diet is an important influence on the gut microbiome, very little is known about the dynamics underpinning microbial acquisition from natural food sources. Here, we addressed this gap by comparing the microbiome of larvae of the polyphagous fruit fly Bactrocera tryoni ('Queensland fruit fly') that were collected from five different fruit types (sapodilla from two different localities, hog plum, pomegranate, green apple, and quince) from North-east to South-east Australia. Using Next-Generation Sequencing on the Illumina MiSeq platform, we addressed two questions: (1) what bacterial communities are available to B. tryoni larvae from different host fruit; and (2) how does the microbiome vary between B. tryoni larvae and its host fruit? The abundant bacterial taxa were similar for B. tryoni larvae from different fruit despite significant differences in the overall microbial community compositions. Our study suggests that the bacterial community structure of B. tryoni larvae is related less to the host fruit (diet) microbiome and more to vertical transfer of the microbiome during egg laying. Our findings also suggest that geographic location may play a quite limited role in structuring of larval microbiomes. This is the first study to use Next-Generation Sequencing to analyze the microbiome of B. tryoni larvae together with the host fruit, an approach that has enabled greatly increased resolution of relationships between the insect's microbiome and that of the surrounding host tissues.
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