Scale‐appropriate spatial modelling to support area‐wide management of a polyphagous fruit fly (Diptera: Tephritidae)

Control of mobile pests frequently requires area‐wide management (AWM) that spans commercial and non‐commercial habitats. Spatial modelling of habitat suitability can guide investment and implementation of AWM, but current approaches rarely capture population drivers, including local foraging, at an appropriate spatial resolution. To support the development of AWM for the fruit fly pest, Bactrocera tryoni (Tephritidae), we developed a habitat suitability model for the three premier fruit‐growing regions in south‐eastern Australia (~34,780 km²). Expert elicitation and published literature was used to develop a Bayesian network to model the drivers of B. tryoni habitat suitability, as determined by the ability of populations to persist and increase. The effect of uncertainty was tested through sensitivity analysis. The model was then linked with spatially explicit data (at 10 m resolution) to generate risk maps, using moving windows to capture local foraging movement. Habitat suitability was most strongly influenced by host availability within a distance of 200 m. Climate stress, and soil moisture for pupation, was also limiting. Experts were uncertain regarding the relative importance of drivers of host availability (host preference, host density, fruit seasonality), but this did not greatly affect model outputs. Independent trapping data supported model predictions, but their value was limited as traps were placed almost exclusively in optimal or suitable habitat. Amenability to AWM, when assessed as the ratio of suitable or optimal habitat that was under non‐horticultural versus horticultural land‐uses, differed by region (0.15–1.17). However, risk‐mapping did identify where ratios were locally most favourable (lowest). Also, predominantly local dispersal by B. tryoni suggests AWM for pest suppression could be applied at a landscape‐scale. Results show that a relatively simple model could capture the multi‐scale drivers of population dynamics and the complexity of landscapes sufficiently to guide AWM of a mobile pest.     

Optimizing methyl‐eugenol aromatherapy to maximize posttreatment effects to enhance mating competitiveness of male Bactrocera carambolae (Diptera: Tephritidae)

Methyl‐eugenol (ME) (1,2‐dimethoxy‐4‐(2‐propenyl)benzene), a natural phytochemical, did enhance male Bactrocera carambolae Drew & Hancock (Diptera: Tephritidae) mating competitiveness 3 d after ingestion. Enhanced male mating competitiveness can significantly increase the effectiveness of the sterile insect technique (SIT). ME application to mass reared sterile flies by feeding is infeasible. ME application by aromatherapy however, would be a very practical way of ME application in fly emergence and release facilities. This approach was shown to enhance mating competitiveness of B. carambolae 3 d posttreatment (DPT). Despite this added benefit, every additional day of delaying release will reduce sterile fly quality and will add cost to SIT application. The present study was planned to assess the effects of ME‐aromatherapy on male B. carambolae mating competitiveness 1DPT and 2DPT. ME aromatherapy 1DPT or 2DPT did enhance mating competitiveness of B. carambolae males whereas ME feeding 1DPT and 2DPT did not. Male mating competitiveness was enhanced by the ME aromatherapy irrespective if they received 1DPT, 2DPT or 3DPT. ME aromatherapy, being a viable approach for its application, did enhance mating competitiveness of male B. carambolae 1 d posttreatment as ME feeding did 3 d after ingestion.     

Identification,mRNA Expression,and Functional Analysis of Chitin Synthase 1 Gene and Its Two Alternative Splicing Variants in Oriental Fruit Fly,Bactrocera dorsalis

Two alternative splicing variants of chitin synthase 1 gene (BdCHS1) were cloned and characterized from the oriental fruit fly, Bactrocera dorsalis (Hendel). The cDNA of both variants (BdCHS1a and BdCHS1b) consisted of 5,552 nucleotides (nt), with an open reading frame (ORF) of 4,776 nt, encoding a protein of 1,592 amino acid residues, plus 685- and 88-nt of 5′- and 3′-noncoding regions, respectively. The alternative splicing site was located between positions 3,784-3,960 and formed a pair of mutually exclusive exons (a/b) that were same in size (177 nt), but showed only 65% identity at the nucleotide level. During B. dorsalis growth and development, BdCHS1 and BdCHS1a were both mainly expressed during the larval-pupal and pupal-adult transitions, while BdCHS1b was mainly expressed during pupal-adult metamorphosis and in the middle of the pupal stage. BdCHS1a was predominately expressed in the integument whereas BdCHS1b was mainly expressed in the trachea. The 20-hydroxyecdysone (20E) induced the expression of BdCHS1 and its variants. Injection of dsRNA of BdCHS1, BdCHS1a, and BdCHS1b into third-instar larvae significantly reduced the expression levels of the corresponding variants, generated phenotypic defects, and killed most of the treated larvae. Furthermore, silencing of BdCHS1 and BdCHS1a had a similar result in that the larva was trapped in old cuticle and died without tanning completely, while silencing of BdCHS1b has no effect on insect morphology. These results demonstrated that BdCHS1 plays an important role in the larval-pupal transition and the expression of BdCHS1 in B. dorsalis is regulated by 20E.     

Facilitation in Ovipositional Behavior of Bactrocera tryoni Flies

Mature female Queensland fruit flies, Bactrocera tryoni Froggatt, released into canopies of field-caged trees containing host fruit, did not discriminate between fruit having or lacking two resident conspecific females when selecting fruit on which to alight. When released individually onto a fruit, mature females showed no greater or lesser propensity to initiate boring with the ovipositor into fruit having or lacking a resident female engaged in pre-ovipositional or post-ovipositional behavior. However, boring propensity of introduced females was significantly enhanced or facilitated when released onto fruit on which a conspecific female was in the act of ovipositing. Introduced females were significantly more prone to initiate boring into high-ranking fruit (nectarines) than low-ranking fruit (lemons) and to do so when having a high rather than a low egg load. Neither fruit type nor egg load of introduced females had a significant effect on the occurrence of encounters between introduced and resident females, on the occurrence of contests, or on the propensity of introduced females to initiate boring in the presence of a resident female. Among introduced females, there was a consistent trend to initiate boring earlier in the presence than in the absence of a resident female. We discuss circumstances, likely to be narrow, under which boring propensity of an intruding female might be facilitated in the presence of a resident female.     

Does previous experience enhance foraging on a particular host in a polyphagous frugivore?

Prior oviposition or feeding experience with a host plant has been proposed to improve foraging efficiency for polyphagous insect herbivores. Many laboratory-based experiments have attributed certain modified behavioural responses, such as an improved ability to locate a host, as evidence for the benefits of learning. However, few studies have considered the negative ramifications of learning, particularly under field conditions rather than laboratory conditions. In the current study, using the polyphagous fruit fly Bactrocera tryoni (Froggatt) (Diptera: Tephritidae), we explore both the positive and negative consequences of modified host selection resulting from prior oviposition experience. In field cage experiments, prior oviposition experience on a given host increased the selection of that host despite its abundance and its suitability for offspring development. For example, in a field cage that contained significantly more blueberry (poor larval host) than guava (good larval host), prior experience on guava resulted in more flies selecting and accepting guava than did naïve flies (a presumed positive foraging outcome). However, the opposite also held, that prior experience on blueberry led to increased blueberry use, even when guava was more abundant. In unrestrained flies, prior experience dramatically improved recapture rate with flies locating the training fruit. The results highlight the potential benefits of learning, but also identify that learning can be a disadvantage if prior experience on a poor host leads to flies repeatedly using that host over a more suitable host.     

Relationship between female body size and demographic parameters inBactrocera Malaysian A (Diptera: Tephritidae)

The effect of body size, as measured by the head width, of the female Bactrocera sp. Malaysian A (kept separately in sexual pairs) on the demographic parameters was investigated in the laboratory under ambient conditions of 28–30°C, 78–85% RH and natural photoperiod. Body size was shown to influence significantly all the demographic parameters. The expectation of life of females at eclosion from pupae was respectively for head widths of 1.6, 1.8, 1.9, 2.0 and 2.1 mm: 76.2, 73.4, 73.8, 102.4 and 115.2 days. The mean number of eggs laid per female in its life time was respectively: 86.4±48.7, 181.8±56.1, 229.7±72.6, 364.3±69.4 and 477.5±109.3 which was significantly different from one another (F=3.73,P<0.05) especially the two smaller sizes from the two larger sizes. The regression line for total eggs laid (Y) against head width (X) was Y=785.2X−1208.7 (R²=0.35,P<0.001). The net reproductive rate (R₀) was respectively 15.8, 34.0, 43.5, 66.9 and 88.8 eggs, while the intrinsic rate of increase (r) was respectivley 0.0435, 0.0538, 0.0670, 0.0665 and 0.0711. The results confirm that for mass rearing purposes, larger females which produce more offspring are to be preferred.