Mango headspace volatiles trigger differential responses of the mango fruit fly Ceratitis cosyra and its parasitoids.

Before the introduction of Bactrocera dorsalis (Hendel) to sub-Saharan Africa, Ceratitis cosyra (Walker) was economically the most important pest in mango farming. Its native natural enemy, the solitary parasitoid Psyttalia cosyrae (Wilkinson), played a crucial role in C. cosyra bio-control, later complemented by the exotic parasitoids Diachasmimorpha longicaudata (Ashmead) and Fopius arisanus (Sonan) among Integrated Pest Management (IPM) systems. To understand the in situ mango-C. cosyra-parasitoid tritrophic interaction, we assessed the responses of the fruit fly and the three parasitoids to headspace volatiles from various mango conditions. These conditions included non-infested mature unripe mangoes, C. cosyra-infested mangoes, 7th- and 9th-day post-infestation mangoes, non-infested ripe mangoes of three varieties (Kent, Apple, and Haden), and clean air (blank). We also compared the fruit fly's performance in the mango varieties and identified the chemical profiles of mango headspace volatiles. Ceratitis cosyra was attracted to both infested and non-infested mangoes (66-84 % of responsive C. cosyra) and showed superior performance in Kent mango (72.1 % of the 287 puparia recovered) compared to Apple and Haden varieties. Fopius arisanus displayed a stronger attraction to the volatiles of C. cosyra-infested mangoes (68-70 %), while P. cosyrae and D. longicaudata were significantly attracted to the 9th-day post-infestation mangoes (68-78 %) compared to non-infested mango volatiles. Gas chromatography-mass spectroscopy showed substantial quantitative and qualitative differences in volatile profiles among mango treatments. Esters predominated in non-infested ripe, 7th- and 9th-day post-infestation mangoes, while monoterpenes and sesquiterpenes were most dominant in the other treatments. The in situ experiments underscored varying preferences of the species for mango headspace volatiles and their subsequent treatments. These results provide valuable insights for further exploration, specifically in identifying the key volatiles responsible for species responses, to facilitate the development of applicable selective semiochemicals for managing species of African fruit fly.

Dispersal and competitive release affect the management of native and invasive tephritid fruit flies in large and smallholder farms in Ethiopia.

African horticulture is seriously affected by fruit flies, both native and invasive. Novel sustainable control methods need testing against the backdrop of smallholder-dominated farming of Africa. We evaluated the potential of male-specific attractants (parapheromones) laced with insecticide to suppress the alien invasive Bactrocera dorsalis and native Ceratitis capitata. In large-scale guava, methyl-eugenol (ME)-bait stations combined with toxic protein baits suppressed B. dorsalis within 8 months but resulted in a resurgence of the displaced Ceratitis capitata. In smallholder farms, intervention using SPLAT-ME laced with spinosad was surprisingly unsuccessful. Subsequent mark-release-recapture experiments showed high dispersal rates of flies, covering many times a typical farm size, leading to a continuous influx of flies from surrounding areas. Several other factors important for intervention were evaluated. SPLAT-MAT-ME dollops remained attractive for over two weeks, although gradually becoming less attractive than fresh baits. Further, competitive displacement was observed: C. capitata selectively emerged from fruits in which B. dorsalis infestation was low. Finally, we evaluated whether ME could be combined with C. capitata male attractants [trimedlure (TML) and terpinyl acetate (TA)] without affecting attraction. Combining male lures did not affect catches directly, although at very high populations of B. dorsalis attracted to ME interfered with C. capitata trap entry. Although ME-based methods can effectively suppress B. dorsalis, they were not effective at single smallholder scale due to the high dispersive propensity of tephritids. Further, competitive release implies the need for a combination of lures and methods. These observations are important for developing control schemes tailored for African smallholder settings.

Translating olfactomes into attractants: shared volatiles provide attractive bridges for polyphagy in fruit flies.

Tephritid flies are serious fruit pests. Despite clear niche differences, many species show considerable overlap in fruit preferences, of which we here analysed the olfactory correlate. Using the volatiles of four unrelated fruit species, antennal responses were quantified to construct a fruit-odour response database for four tephritid species. Although responses were distinct with a significant niche-correlated bias, the analyses show that the probability of detection of a volatile strongly increased with its sharedness across fruits. This also held for the unrelated fruit fly Drosophila melanogaster (DoOR repository-based analyses). We conjectured that shared volatiles signify 'host' to the fly 'nose' and induce attraction. Indeed, blends of volatiles shared by fruit and detected by all four species were very attractive for tephritid species, more than fruits. Quantitative whole antennal recordings en lieu of, or complementing bottom-up molecular neurogenetic approaches, enables comparative olfactomics in non-model species, and facilitate interpretation of olfaction in evolutionary, ecological, and applied contexts.

Detection of Volatile Constituents from Food Lures by Tephritid Fruit Flies.

Tephritid fruit flies require protein for sexual and gonotrophic development. Food-based lures are therefore widely used in strategies to detect and control fruit flies in the Tephritidae family. However, these baits are attractive to a broad range of insect species. We therefore sought to identify volatiles detected by the fly antennae, with the goal to compose lures that more specifically target tephritids. Using gas chromatography-coupled electroantennographic detection (GC-EAD) we screened for antennal responses of four important tephritid species to volatile compounds from five commercially available protein-based baits. Antennal active compounds were reconstituted in synthetic blends for each species and used in behavioral assays. These species-based blends were attractive in olfactometer experiments, as was a blend composed of all antennally active compounds from all the four species we observed (tested only in Bactrocera dorsalis, Hendel). Pilot field tests indicate that the blends need to be further evaluated and optimized under field conditions.

Identification of host blends that attract the African invasive fruit fly, Bactrocera invadens.

Bactrocera invadens, an invasive fruit fly species in the Afro-tropical region belonging to the Bactrocera dorsalis complex, causes considerable damage to fruit production and productivity. We sought to find attractants from hosts of B. invadens that could serve as baits in traps for monitoring and management of this pest. The attractiveness of volatiles from four different fruit species (mango, guava, banana and orange) at two stages of ripeness (ripe or unripe) was tested in an olfactometer assay. All fruits were attractive against a clean air control. Using hexane extracts of volatile collections of fruits, we demonstrated that male flies preferred the volatiles of ripe guava and orange over unripe fruit extracts. There was a slight difference in preference between females and males; females preferred orange to guava and mango, whereas males preferred mango and guava to orange. Gas chromatography/electroantennographic detection (GC/EAD) and GC/mass spectrometry (GC/MS) were used to identify compounds to which B. invadens antennae were sensitive. GC/EAD recordings from distal and medio-central parts of the fly antenna showed responses to a number of compounds from each fruit species, with esters dominating the responses. Synthetic blends were made for each fruit species using the shared antennally active compounds in ratios found in the extracts. In the olfactometer, B. invadens was most attracted to the banana and orange blends, followed by the mango and guava blends. The synthetic banana blend was as attractive as the volatile collection of banana, although both were less attractive than the fruit. The results demonstrate that composing attractive blends from GC/EAD-active constituents shared by host fruits can be effective for formulating attractive synthetic host mimics for generalist fruit fly species, such as B. invadens.