Effect of citrus peel chemicals on Bactrocera tryonilarval survival

Queensland fruit fly, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) is a major horticultural insect pest in Australia which significantly limits domestic and international market access for Australian horticultural produce. Citrus is one of the industries seriously affected by the fruit fly problem in Australia. This research investigated the effect of citrus peel essential oil chemicals on B. tryoni larval survival in five different commercially important Citrus species and cultivars as a way of better understanding fruit susceptibility. The fruits used were Murcott Mandarin, Navel orange, Eureka lemon, Valencia orange and yellow grapefruit. The essential oils of each citrus type were extracted using hydrodistillation and then mixed, at different concentrations, with artificial larval diets to which B. tryoni eggs were added. Surviving larvae were counted after five trial days. The same process was repeated for six essential oil components. Regression analysis of increasing oil concentration against larval survival showed that the crude oil blends of Navel orange, Eureka lemon and yellow grapefruit had significant negative effects on B. tryoni larval survival, but no such effects were seen for Murcott Mandarin and Valencia orange. Of the individual essential oil fractions, only D-limonene had a significant effect on B. tryoni larval survival, with this chemical being highly toxic at very low concentrations. The results of this study open up opportunities for incorporating B. tryoni resistance mechanisms into citrus through minor peel property changes which would not impact on the eating attributes of the fruit.

Protein feeding of Queensland fruit fly Bactrocera tryoni and cucumber fly Zeugodacus cucumis (Diptera: Tephritidae) on non-host vegetation: effect of plant species and bait height

Perimeter-baiting of non-crop vegetation using toxic protein baits was developed overseas as a technique for control of melon fly, Zeugodacus (Zeugodacus) cucurbitae (Coquillett) (formerly Bactrocera (Zeugodacus) cucurbitae), and evidence suggests that this technique may also be effective in Australia for control of local fruit fly species in vegetable crops. Using field cage trials and laboratory reared flies, primary data were generated to support this approach by testing fruit flies' feeding response to protein when applied to eight plant species (forage sorghum, grain sorghum, sweet corn, sugarcane, eggplant, cassava, lilly pilly and orange jessamine) and applied at three heights (1, 1.5 and 2 m). When compared across the plants, Queensland fruit fly, Bactrocera tryoni (Froggatt), most commonly fed on protein bait applied to sugarcane and cassava, whereas more cucumber fly, Zeugodacus (Austrodacus) cucumis (French) (formerly Bactrocera (Austrodacus) cucumis), fed on bait applied to sweet corn and forage sorghum. When protein bait was applied at different heights, B. tryoni responded most to bait placed in the upper part of the plants (2 m), whereas Z. cucumis preferred bait placed lower on the plants (1 and 1.5 m). These results have implications for optimal placement of protein bait for best practice control of fruit flies in vegetable crops and suggest that the two species exhibit different foraging behaviours.

Modified atmosphere packaging effects on the postharvest quality of papaya fruit

Export of Fijian papaya (Carica papaya) fruit to destinations such as New Zealand has increased significantly over the last several years. Shipment by sea rather than air is the preferred method, given the capacity for larger volumes and reductions in cost. Long shipping times, however, can compromise fruit quality, although the use of modified atmosphere packaging (MAP) may provide a viable solution for extending fruit storage life. In a collaborative ACIAR project, Australian and Fijian researchers investigated the potential of using MAP to extend storage life of a Fijian papaya ('Fiji Red') fruit based on simulated sea transport conditions. Fruit were packed in one of three MAP environments within cartons, consisting of either a (1) Low Density Polyethylene (LDPE) bag with 10 g of KMnO4, (2) Polyamide Film (PF) bag with macro-perforations or (3) without a bag (control fruit). Fruit were held for 1, 2 or 3 weeks at 10°C before being unpacked, ripened and assessed for quality. On day 6 after outturn, fruit with the highest overall quality were those held in LDPE bags. LDPE fruit generally coloured up faster at outturn than PF or control fruit, had less overall moisture loss and scored high in flavour. Headspace carbon dioxide and oxygen concentrations within the LDPE bags were also near recommended levels for maintaining optimum storage-life quality. The LDPE bag provided the most suitable conditions for long term storage of fresh papaya fruit and is therefore the recommended MAP type for use with sea freight export out of Fiji.

Citrus as a component of the Mediterranean Diet

Citrus are native to southeastern Asia, but are present in the Mediterranean basin for centuries. This group of species has reached great importance in some of the Mediterranean countries and, in the case of orange, mandarin and lemon trees, they found here soil and climatic conditions which allows them to achieve a high level of fruit quality, even better than in the regions where they came from. Citrus fruits are present in the diet of the peoples living on the Mediterranean basin, at least since the time of the Roman Empire. In the 20th century they became the main crop in various agricultural areas of the Mediterranean, playing an important role in the landscape, in the diet of the overall population, and also in international trade. They are present in the gardens of palaces and monasteries, but also in the courtyards and orchards of the poorest families. Their fruits are not only a refreshing dessert, but also a condiment, or even a major component of many dishes. Citrus fruits have well-documented nutritional and health benefits. They can actually help prevent and cure some diseases and, above all, they are essential in a balanced and tasty diet.

3,5,6-trichloro-2-pyridinyloxyacetic acid as effective thinning agent for fruit of 'Montenegrina' mandarin.

2016

Sexual selection in a tropical fruit fly : role of a plant derived chemical in mate choice

The specific mechanisms by which selective pressures affect individuals are often difficult to resolve. In tephritid fruit flies, males respond strongly and positively to certain plant derived chemicals. Sexual selection by female choice has been hypothesized as the mechanism driving this behaviour in certain species, as females preferentially mate with males that have fed on these chemicals. This hypothesis is, to date, based on studies of only very few species and its generality is largely untested. We tested the hypothesis on different spatial scales (small cage and seminatural field-cage) using the monophagous fruit fly, Bactrocera cacuminata. This species is known to respond to methyl eugenol (ME), a chemical found in many plant species and one upon which previous studies have focused. Contrary to expectation, no obvious female choice was apparent in selecting ME-fed males over unfed males as measured by the number of matings achieved over time, copulation duration, or time of copulation initiation. However, the number of matings achieved by ME-fed males was significantly greater than unfed males 16 and 32 days after exposure to ME in small cages (but not in a field-cage). This delayed advantage suggests that ME may not influence the pheromone system of B. cacuminata but may have other consequences, acting on some other fitness consequence (e.g., enhancement of physiology or survival) of male exposure to these chemicals. We discuss the ecological and evolutionary implications of our findings to explore alternate hypotheses to explain the patterns of response of dacine fruit flies to specific plant-derived chemicals.