Fruit Flies: Challenges and Opportunities to Stem the Tide of Global Invasions

Expansion to new habitats and a new commercial host (Malus domestica) by Anastrepha ludens (Tephritidae) likely influenced by global warming

Anastrepha ludens (Mexican fruit-fly) is a highly polyphagous fruit fly species (Tephritidae) attacking wild and commercial fruit from Mexico to Panama. Here we report on a recent habitat and host range expansion as A. ludens lately started to attack apples (Malus domestica) in Mexico, a phenomenon likely influenced by global warming. We document natural infestations in apple-growing regions in the States of Nuevo León and Hidalgo, Mexico where A. ludens has started to attack the cultivars 'Golden Delicious', 'Rayada' and 'Criolla'. No infestations were found in the apple-growing region of Zacatlán, Puebla. To determine apple cultivar susceptibility to the attack of this emerging pest, we ran forced infestation assays in enclosed fruit-bearing branches in all three apple-growing regions and studied the metabolome of all fruit. A clear pattern emerged indicating that the cultivar 'Golden Delicious' was the most susceptible, with 'Criolla' exhibiting complete resistance in one location (Puebla). Although A. ludens can develop in this new host, development rates (egg-adult) and adult emergence were affected when compared with the performance in the natural host 'Marsh' grapefruit. Warmer temperatures and specific secondary metabolites of some apple cultivars are likely contributing to the territorial and host expansion of A. ludens.

Evaluating impacts of radiation-induced sterilization on the performance and gut microbiome of mass-reared Mediterranean fruit fly (Ceratitis capitata) in Hawai'i

Sterile insect technique (SIT) is a useful strategy for preventing and mitigative establishment of invasive insect species. SIT of the pest tephritid Mediterranean fruit fly, Ceratitis capitata (Wiedemann, 1824)WiedemannWiedemann, has been effective in preventing population establishment in vulnerable agricultural areas of the United States. However, irradiation-induced sterilization can have detrimental impacts resulting in reduced performance metrics. Mediterranean fruit fly males reared for SIT have been shown to have differences in their microbiomes relative to other population sources, which has been postulated to be a factor in how well flies compete with wild conspecifics. To identify baseline performance metrics on the effects of irradiation on the gut microbiome of mass-reared flies in Hawai'i, a study was performed to assess performance metrics and microbiome (bacterial 16S rRNA) variation across multiple timepoints. Mediterranean fruit fly pupae were selected from mass-reared trays intended for release, and paired samples were either irradiated or remained as controls and transported to the laboratory for evaluation. Irradiated flies exhibited fewer successful fliers, more rapid mortality rates, and were less active relative to control nonirradiated flies. Contrary to initial expectations, irradiation did not exert substantial impacts on the composition or diversity of bacterial reads. Samples were primarily comprised of sequences classified as Klebsiella and there were low levels of both read and taxonomic diversity relative to other 16S surveys of medfly. Although this study does not demonstrate a strong effect of irradiation alone on the Mediterranean fruit fly microbiome, there are several explanations for this discrepancy.

Mediterranean fruit fly population phenological patterns are strongly affected by elevation and host presence

The Mediterranean fruit fly (medfly) (Ceratitis capitata, Diptera: Tephritidae), is an extremely polyphagous pest that threatens the fruit production and trading industry worldwide. Monitoring C. capitata populations and analysing its dynamics and phenology is considered of outmost importance for designing and implementing sound management approaches. The aim of this study was to investigate the factors regulating the population dynamics of the C. capitata in a coastal and semi-mountainous area. We focused on effects of topography (e.g. elevation), host presence and seasonal patterns of ripening on the phenological patterns considering data collected in 2008. The experimental area is characterized by mixed fruit orchards, and Mediterranean climate with mild winters. Two trap types were used for population monitoring. The female targeted McPhail type and the male targeted Jackson type. Traps were placed in farms located at different elevations and landscape morphology (coastal and semi-mountainous areas). The main crops included citrus, apples, peaches, plums, pears, figs, quinces and apricots. Adult captures were first recorded in May, peaked in mid-summer and mid-autumn and almost ceased at the end of the season (January 2008). Captures in the coastal areas preceded that of highlands by 15 days. Most of the adults detected during the fruit ripening of late stone fruit cultivars (first peak) and citrus (second peak). The probability of capturing the first adults preceded almost three weeks the peak of adult captures either considering the elevation or host focus analyses. The results provide valuable information on the seasonal population trend of C. capitata in mixed fruit Mediterranean orchards and can support the set-up of IPM systems in areas with various landscapes and different hosts throughout the fruit growing season.

Attractancy of a Sesquiterpene, β-caryophyllene to Males of the Oriental Fruit Fly, Bactrocera dorsalis (Diptera: Tephritidae)

The recent discovery of a sesquiterpene, β-caryophyllene (CP) as a male attractant of the guava fruit fly, Bactrocera correcta (Bezzi) (Diptera: Tephritidae) prompted investigations into the attractancy of CP to the Oriental fruit fly, B. dorsalis (Hendel). This is because males of both species of fruit flies are attracted to, and feed on a phenylpropanoid compound, methyl eugenol (ME). Although CP was a more potent attractant than ME for B. correcta, it is not known if males of B. dorsalis are also attracted to CP. The possible attraction of B. dorsalis to CP as a sesquiterpene may indicate its wide host range through its attraction to different groups of plant volatiles i.e., phenylpropanoids and sesquiterpenes. In this paper, we report that males of B. dorsalis were also attracted to, and feed on CP. Subsequently, we conducted a probit regression analysis to determine the quantal response of sexually mature male flies that were attracted to CP in cage bioassays. Therefore, as a measure of male B. dorsalis' sensitivity of CP, the median dose of CP required to elicit a positive response in 50% of the tested B. dorsalis population (ED50) was calculated as 3.7 mg. This value was over 10,000x higher than known ED50 of B. dorsalis' male attraction ME (between 171 and 268 ng). We propose that the attraction of male B. dorsalis flies to CP was much weaker than to ME. Further, we suggest that in any fruit fly surveillance and monitoring programme, application of lures must consider the specificity and potency of each compound to target fruit fly species. The probit regression analysis of male fly quantal response to lure offers such information.

The Global Epidemic of Bactrocera Pests: Mixed-Species Invasions and Risk Assessment

Throughout the past century, the global spread of Bactrocera pests has continued to pose a significant threat to the commercial fruit and vegetable industry, resulting in substantial costs associated with both control measures and quarantine restrictions. The increasing volume of transcontinental trade has contributed to an escalating rate of Bactrocera pest introductions to new regions. To address the worldwide threat posed by this group of pests, we first provide an overview of Bactrocera. We then describe the global epidemic, including border interceptions, species diagnosis, population genetics, geographical expansion, and invasion tracing of Bactrocera pests. We further consider the literature concerning the invasion co-occurrences, life-history flexibility, risk assessment, bridgehead effects, and ongoing implications of invasion recurrences, as well as a case study of Bactrocera invasions of California. Finally, we call for global collaboration to effectively monitor, prevent, and control the ongoing spread of Bactrocera pests and to share experience and knowledge to combat it.