The content of tartaric acid in grapes can vary depending on cultivar, ripeness, and environmental conditions; for example, Kliewer et al. reported a tartaric acid content ranging from 3.7 to 13.2 g/L in different cultivars and from 3.4 to 9.2 g/L in early- vs. late-harvested cultivars. The doses used here covered these reported ranges. Each treatment had 20–22 replicates, and each replicate started with 10 D. suzukii eggs from the laboratory culture that were placed in drosophila vials over the diet. The number of developed adults was recorded. A sub-sample of 25 pupae from each treatment was measured for pupal length and width , and the volume of each pupa was estimated based on the formula 2.A separate analysis with 10 different cherry cultivars did not yield a significant effect of the Brix on the percentage of eggs that successfully developed to adults, although we could not rule out the possibility that Brix and other chemical properties may affect other fitness parameters of the developed flies. Many of the differences in chemical traits among different fruits could be attributed to geographic location and differences in environmental and cultivation conditions rather than inherent varietal properties, such as in cherries. In the current study, drainage gutter chemical differences were controlled to some extent, as cherry cultivars used were grown in the same plot with the same fertilization and irrigation regimes. The physical properties of different cultivars did not seem to affect the fly’s oviposition.
The percentage of eggs that developed to adults decreased with the increasing egg density per gram of fruit probably due to intra-specific competition, and this was further confirmed by manipulating the egg density and using the same ‘Bing’ cherry cultivar as the tested host. Females preferred larger fruit for oviposition, which is consistent with the density-dependent survival as the large fruit support higher numbers of fly larvae per fruit. It is well known that many fruit flies employ a variety of fruit characters to assess host quality and tend to be more attracted to larger fruits. Female D. suzukii appears to be able to assess host quality based on fruit size, and this behavior would likely increase foraging efficiency per unit time. Though we recovered very low numbers of D. suzukii from damaged citrus fruits, our laboratory study showed the fly can oviposit into and develop from freshly damaged or rotting navel oranges. Kaçar et al. showed that D. suzukii overwinter in citrus, surviving 3–4 months when fresh oranges were provided as adult food or ovipositional medium, and field-emerged adults from soil-buried pupae could produce and oviposit viable eggs on halved mandarin fruit. Thus, citrus fruit likely play an important role as reservoirs in sustaining the fly populations during San Joaquin Valley winter seasons, and in the spring, those populations may migrate into early season crops, such as cherries. We did not observe grape infestation in our field collections, and our laboratory trials showed a low survival rate of D. suzukii offspring on grapes when compared to other fruits . The oviposition susceptibility and offspring survival could vary among varieties or cultivars due to the variations in skin hardness and chemical properties. For example, Ioriatti et al. demonstrated that oviposition increased consistently as the skin hardness of the grape decreased.
Chemical properties, such as sugar content and acidity levels, may play a role in host susceptibility. In the current study, we found that although table grapes had a tougher skin than raisin or wine grape cultivars tested , females were able to lay eggs into all three types of grapes, often through the fruit surface or near the petiole . The sugar levels of all tested grapes were either equal to or considerably higher than other fruits tested. We also found that tartaric acid concentration negatively affected the fly’s developmental performance. Still, about 20% eggs successfully developed to adults in the diet mixed with the highest tartaric acid, whereas only 4.5% eggs developed from the wine grape cultivar tested. It is thus possible that other unknown chemical traits might also affect larval performance. Overall, our results are consistent with other reported studies that grapes are not good reproductive hosts for D. suzukii .California’s San Joaquin Valley is one of the world’s most important fruit production regions, with a diverse agricultural landscape that can consist of a mosaic of cultivated and unmanaged host fruit crops. Such diverse landscapes result in the inevitable presence of D. suzukii populations that represent a difficult challenge for the management of this polyphagous pest. We showed that only the early seasonal fruits, such as cherries, seem to be at greatest risk to D. suzukii Many of other later seasonal fruits are not as vulnerable to this pest, because either their intact skin reduces oviposition, they ripen during a period of low D. suzukii abundance, or their flesh has chemical attributes that retard survival. However, some of these alternative hosts—such as citrus and damaged, unharvested stone fruit—may act as shelters for overwintering populations and provide sources for early populations moving into the more susceptible crops.
Consequently, area-wide management strategies may need to consider fruit sanitation to lessen overwintering populations, suppressing fall and winter populations by releasing natural enemies, and reducing pest pressure in susceptible crops through ‘border-sprays’ and/or ‘mass trapping’ to kill adults before they move into the vulnerable crop. Alternative and sustainable area-wide management strategies such as biological control are highly desirable to naturally regulate the fly population, especially in uncultivated habitats. An understanding of the temporal and spatial dynamics of the fly populations would be of aid in the optimal timing of the future release of biological control agents to reduce the source populations in the agricultural landscape.The woody plant pomegranate produces colorful flowers and fruits with ornamental and culinary values. Different pomegranate tissues have historically been used for alleviating symptoms or treating various diseases due to the accumulation of a wide diversity of bioactive metabolites . In recent years, pomegranate fruits and juice have been pursued by consumers for their favorable nutritional quality, contributed by the abundant phenolic compounds, e.g., hydrolyzable tannins and flavonoids, in these tissues and products. Genetic variations underlying different metabolite profiles reportedly exist in pomegranate and have been utilized for breeding cultivars with desirable traits. Complementary to the classic breeding approach, new molecular techniques, such as genome editing, can enable targeted modification of key metabolic genes for improved nutritional and commercial quality of pomegranate fruits and products. Among the various genome-editing technologies, Clustered Regularly Interspaced Short Palindromic Repeats /CRISPR-associated protein 9 has gained increasing popularity for its efficiency and ease of use. In this method, a single guide RNA directs the Cas9 nuclease to the target gene sequence upstream of a protospacer adjacent motif. Cas9 creates a break in the double-strand DNA, which is then ligated by homology-directed repair or non-homologousend joining. In general, five genotypes can be obtained from the CRISPR/Cas9-mediated genome editing in a diploid species, including wild type , homozygous mutant , heterozygous mutant/monoallelic , biallelic , and chimera . Initially used for disruption of gene function, there has been rapid advancement in the CRISPR/Cas9 technology for more precise and versatile genome editing. Although CRISPR/Cas9 has been successfully adopted in many plant species , its application has not been reported in pomegranate. In consideration of the time and effort required for transformation and regeneration of pomegranate plants, plastic gutter we chose a hairy root system for testing the feasibility and efficacy of CRISPR/Cas9-mediated genome editing in pomegranate. This is because hairy roots can be induced from different pomegranate explants, accumulate HTs and other phenolic compounds, are transformable, and produce sufficient amounts of tissues for molecular and metabolite analyses within 3 months of transformation. Commerce via global trade and transport provides a mechanism for introduction of invasive species to new territories, extending pest habitats outside of their native regions . Invasive species threaten biodiversity, habitat, nutritious food, clean water, resilient environments, sustainable economies, and human health . Agricultural production systems are continuously challenged by invasive species that attack high-value crops, thereby significantly hampering the ability of food industries to maintain profitability . The geographic range of agricultural crops provides the potential for invasive species to colonize regions on a global scale . Factors that aid expansion include short life cycle, fast growth rate, high plasticity, and resiliency to a wide range of environmental conditions .
Such factors are drivers of rapid evolutionary change, population increase, and global colonization . Practitioners and stakeholders should aim to implement new strategies to manage such new invasive species in agricultural production . Drosophila suzukii Matsumura is an invasive species native to Southeast Asia. Passive transportation is the main reason of the dispersal of this species . It was first detected in North America and Europe in 2008 , and later in South America in 2013 , and Northern Africa in 2017 . The long-serrated ovipositor of D. suzukii enables it to oviposit inside fresh fruit, which creates a challenging management problem . When D. suzukii became established in the U.S. during 2008, the total annual revenue losses for the West Coast berry and cherry industries were estimated at over $500 million . Currently the situation is not changed in term of economic impact . This particular insect is challenging to manage due to its high dispersal potential, ability to survive and adapt to harsh environmental conditions, and ability to attack a wide host range. For these reasons, D. suzukii is a key pest of these fruit industries worldwide. In the last decade, conventional insecticide uses on affected crops significantly increased to manage D. suzukii fruit damage. Typically used insecticides include spinosyns, pyrethroids, and organophosphates . Intensive use of insecticides poses a tremendous risk to non-target organisms such as pollinators, natural enemies, and humans . In addition, frequent insecticide applications likely resulted in resistance development . These factors require development of an IPM program that includes alternatives to conventional insecticides for managing D. suzukii. Non-insecticidal control methods including cladding, irrigation, netting, mulching, pruning, monitoring and mass trapping have been implemented against D. suzukii . While each method provides some relief to D. suzukii pressure, they provide limited reductions in crop damage . Behavioral control of D. suzukii on susceptible fruit indicated promise for industry adoption. The food-grade gum possesses tactile and odorant cues resulting in reduced egg infestation. The food grade gum makes use of physical properties to mimic fruit, resulting in D. suzukii laying their eggs in a soft gel-like substrate, instead of the fruit itself. The food grade gum is a mixture offood-grade ingredients which is highly attractive to D. suzukii and competes with the ripening fruit throughout the season . To the best of our knowledge, the food-grade gum modifies various D. suzukii behaviors, ultimately resulting in a significant decrease in fruit damage. The product diverts D. suzukii away from ripening fruit, which results in significant retention of the pest, keeping it away from fruit. Third, the food-grade gum acts as an egg sink. Since the D. suzukii eggs laid in this medium cannot develop, this translates in a substantial reduction of the pest population growth . The aim of this work was to determine the potential of the foodgrade gum to reduce D. suzukii damage in large-scale commercial open-field and screenhouse fruit production units on blueberry, cherry, raspberry, blackberry, and wine grape. The hypothesis was that food-grade gum would reduce D. suzukii damage in small fruit, tree fruit and grapes under semi-field and small-scale field conditions. These studies were conducted during 2019 and 2020 in California and Oregon in the western United States.In all field trials, GUM dispensers were placed at least 27 meters away from untreated control plots to minimize volatile plume interaction between treatments. In the current study, cotton pads were used to apply ~1.8 g of GUM on each dispenser at the rate of 124 dispensers per hectare under commercial production conditions . Cotton pads were placed directly on the ground close to irrigation drippers to provide adequate daily moisture. Earlier work illustrated that dispensers have a field longevity of 21 days and for this reason, dispensers were therefore deployed 1 to 4 times depending on the duration of crop ripening and susceptibility. In three trials , egg laying data were collected in buffer plots that were located between UTC and GUM plots to determine the active range of released volatiles beyond treated areas.