Field evaluation of glutathione and glutamic acid as host marking pheromones for control of Tephritid fruit flies in a mango orchard in Kenya.

BACKGROUND: Tephritid fruit flies are a major constraint to the global production of horticultural crops. In Africa, an array of native and alien invasive fruit fly species represents a key challenge to the horticultural industry. In an effort to develop a safer management tool for these pests, we previously identified glutathione (GSH) and glutamic acid (GA), as the host marking pheromones (HMPs) of Ceratitis cosyra and Ceratitis rosa, respectively. Here, we report on the effectiveness of these compounds (GSH and GA) in reducing natural fruit fly population infestations in mango orchards. Mango trees at two different agroecological zones in Kenya were sprayed with HMPs, and the fruits sampled periodically and assessed for fruit fly emergence. Fruit fly emergence data were compared to two controls, the positive control using spot spraying of food bait (SS), and the negative control using water (W). RESULTS: The two HMPs and SS substantially decreased fruit fly emergence from the sampled mangoes. GSH and GA treated mangoes showed reduced C. cosyra and C. rosa infestation by ~70-75% relative to control (W), and with variation noted in the pheromone applied and the recovered fruit fly species. The adult emergence in pheromone-treated plants compared favorably with the positive control SS. However, the HMPs had little impact on reducing Bactrocera dorsalis infestation of mangoes. CONCLUSION: The decrease in fruit fly emergence in sampled mango fruits from HMP treated trees corroborate previous laboratory results and support the prospect of using HMPs in the management of African fruit fly species. © 2022 Society of Chemical Industry.

Odor composition of field versus laboratory desert locust populations.

Olfaction plays an important role in the behavioural ecology of the desert locust Schistocerca gregaria (Orthoptera:Acrididae). Different locust life stages and sexes use olfactory cues for different behaviours such as grouping, mating, oviposition, feeding, maturation and gregarization, which can be exploited for management of the desert locust. However, the full spectrum of the chemistry of volatiles released by the desert locust remains unknown. Here, we compared the volatile emissions of different life stages of a natural wild population reared in the laboratory for one generation with those of a population that has been reared in the laboratory for seven generations. Coupled gas chromatography-mass spectrometric analysis was used to identify captured volatiles. Analysis of similarities (ANOSIM) and non-metric multidimensional scaling of the volatile organic compounds (VOCs) showed significant chemo-diversity between different life stages, and sexes for the adults of the two populations. Additionally, chemical analysis showed that nymphs and adults of the field population released ~4- to 40-fold more volatiles, and they were compositionally richer than their laboratory counterparts. These results demonstrate the composition and variation in odors of field and laboratory populations of the desert locust, and that the discriminating odors warrant further investigation to determine their roles in the bioecology and management of this locust species.

Elicitation of Differential Responses in the Root-Knot Nematode Meloidogyne incognita to Tomato Root Exudate Cytokinin, Flavonoids, and Alkaloids.

Root exudates of plants mediate interactions with a variety of organisms in the rhizosphere, including root-knot nematodes (RKNs, Meloidogyne spp.) We investigated the responses of the motile stage second-stage juveniles (J2s) of Meloidogyne incognita to non-volatile components identified in the root exudate of tomato. Using stylet thrusting, chemotaxis assays, and chemical analysis, we identified specific metabolites in the root exudate that attract and repel J2s. Liquid chromatography quadrupole time-of-flight mass spectrometry analysis of bioactive fractions obtained from the root exudate revealed a high diversity of compounds, of which five were identified as the phytohormone zeatin (cytokinin), the flavonoids quercetin and luteolin, and alkaloids solasodine and tomatidine. In stylet thrusting and chemotaxis assays, the five compounds elicited concentration-dependent responses in J2s relative to 2% dimethyl sulfoxide (negative control) and methyl salicylate (positive control). These results indicate that J2 herbivory is influenced by root exudate chemistry and concentrations of specific compounds, which may have potential applications in RKN management.

Identification of Key Root Volatiles Signaling Preference of Tomato over Spinach by the Root Knot Nematode Meloidogyne incognita.

The root knot nematode, Meloidogyne incognita (Kofoid and White) Chitwood, is a serious pest of tomato ( Solanum lycopersicum) and spinach ( Spinacea oleracea) in sub-Saharan Africa. In East Africa these two crops are economically important and are commonly intercropped by smallholder farmers. The role of host plant volatiles in M. incognita interactions with these two commodities is currently unknown. Here, we investigate the olfactory basis of attraction of tomato and spinach roots by the infective second stage juveniles (J2s) of M. incognita. In olfactometer assays, J2s were attracted to root volatiles from both crops over moist sand (control), but in choice tests using the two host plants, volatiles of tomato roots were more attractive than those released by spinach. Root volatiles sampled by solid phase microextraction (SPME) fiber and analyzed by gas chromatography/mass spectrometry (GC/MS) identified a total of eight components, of which five (2-isopropyl-3-methoxypyrazine, 2-(methoxy)-3-(1-methylpropyl)pyrazine, tridecane, and α- and ß-cedrene) occurred in the root-emitted volatiles of both plants, with three (δ-3-carene, sabinene, and methyl salicylate) being specific to tomato root volatiles. In a series of bioassays, methyl salicylate contributed strongly to the attractiveness of tomato, whereas 2-isopropyl-3-methoxypyrazine and tridecane contributed to the attractiveness of spinach. M. incognita J2s were also more attracted to natural spinach root volatiles when methyl salicylate was combined than to spinach volatiles alone, indicating that the presence of methyl salicylate in tomato volatiles strongly contributes to its preference over spinach. Our results indicate that since both tomato and spinach roots are attractive to M. incognita, identifying cultivars of these two plant species that are chemically less attractive can be helpful in the management of root knot nematodes.

Opposing Roles of Foliar and Glandular Trichome Volatile Components in Cultivated Nightshade Interaction with a Specialist Herbivore.

Plant chemistry is an important contributor to the interaction with herbivores. Here, we report on a previously unknown role for foliar and glandular trichome volatiles in their interaction with the specialist herbivore of solanaceous plants, the tomato red spider mite Tetranychus evansi. We used various bioassays and chemical analyses including coupled gas chromatography-mass spectrometry (GC/MS) and liquid chromatography coupled to quadrupole time of flight mass spectrometry (LC-QToF-MS) to investigate this interaction between cultivated African nightshades and T. evansi. We show that, whereas morphologically different cultivated African nightshade species released similar foliar volatile organic compounds (VOCs) that attracted T. evansi, VOCs released from exudates of ruptured glandular trichomes of one nightshade species influenced local defense on the leaf surface. VOCs from ruptured glandular trichomes comprising mainly saturated and unsaturated fatty acids deterred T. evansi oviposition. Of the fatty acids, the unsaturated fatty acids accounted for >40% of the oviposition deterrent activity. Our findings point to a defense strategy in a plant, based on opposing roles for volatiles released by foliar and glandular trichomes in response to attack by a specialist herbivore.

Development and assessment of plant-based synthetic odor baits for surveillance and control of malaria vectors.

BACKGROUND: Recent malaria vector control measures have considerably reduced indoor biting mosquito populations. However, reducing the outdoor biting populations remains a challenge because of the unavailability of appropriate lures to achieve this. This study sought to test the efficacy of plant-based synthetic odor baits in trapping outdoor populations of malaria vectors. METHODOLOGY AND PRINCIPAL FINDING: Three plant-based lures ((E)-linalool oxide [LO], (E)-linalool oxide and (E)-ß-ocimene [LO + OC], and a six-component blend comprising (E)-linalool oxide, (E)-ß-ocimene, hexanal, ß-pinene, limonene, and (E)-ß-farnesene [Blend C]), were tested alongside an animal/human-based synthetic lure (comprising heptanal, octanal, nonanal, and decanal [Blend F]) and worn socks in a malaria endemic zone in the western part of Kenya. Mosquito Magnet-X (MM-X) and lightless Centre for Disease Control (CDC) light traps were used. Odor-baited traps were compared with traps baited with either solvent alone or solvent + carbon dioxide (controls) for 18 days in a series of randomized incomplete-block designs of days × sites × treatments. The interactive effect of plant and animal/human odor was also tested by combining LO with either Blend F or worn socks. Our results show that irrespective of trap type, traps baited with synthetic plant odors compared favorably to the same traps baited with synthetic animal odors and worn socks in trapping malaria vectors, relative to the controls. Combining LO and worn socks enhanced trap captures of Anopheles species while LO + Blend F recorded reduced trap capture. Carbon dioxide enhanced total trap capture of both plant- and animal/human-derived odors. However, significantly higher proportions of male and engorged female Anopheles gambiae s.l. were caught when the odor treatments did not include carbon dioxide. CONCLUSION AND SIGNIFICANCE: The results highlight the potential of plant-based odors and specifically linalool oxide, with or without carbon dioxide, for surveillance and mass trapping of malaria vectors.