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Augusto Ramírez-Godoy, María del Pilar Vera-Hoyos, Natalia Jiménez-Beltrán and Hermann Restrepo-Díaz

Asian citrus psyllid [ACP (Diaphorina citri)] is one of the most serious threats to the global citrus (Citrus sp.) culture, and management of ACP has depended primarily on the application of chemical insecticides. The expression of resistance mechanisms to herbivory is a key component in integrated pest management in crop production in which silicon (Si) applications can play an important role in plant–insect relationships. The objective of the current study was to evaluate the application of Si to tahiti lime (Citrus latifolia) plants under natural infestations of ACP. Two experiments were conducted using 15-month-old seedlings and 2-year-old trees, respectively. Treatments were 1) foliar Si sprays (potassium silicate) at a dose of 2 mL·L–1, 2) soil Si application at a dose of 1 kg commercial product per plant, 3) combined soil and foliar applications of Si at the doses just listed, and 4) untreated plants (control). The application of Si treatments to both seedlings and trees affected ACP oviposition, causing a reduction of 60%. Applications of Si did not affect the nutritional status (macronutrients and micronutrients) of plants in either test, except that the foliar concentration of Si tended to be greater in the soil and soil + foliar treatments than in the other treatment in both seedlings and trees. Based on these results, we suggest that Si can be added as a component of ACP integrated pest management programs.

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Augusto Ramírez-Godoy, María del Pilar Vera-Hoyos, Natalia Jiménez-Beltrán and Hermann Restrepo-Diaz

The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, is the most serious threat to the global citrus industry, and its management has depended mainly on the application of chemical insecticides. The application of plant elicitors can contribute to the insect management and also enhance plant physiology. A set of three different experiments was carried out to evaluate the efficacy of foliar applications of synthetic elicitors [salicylic acid (SA), brassinosteroids (Br), chitosan, or thiamine] on the population dynamics of D. citri and their effects on the physiology of Tahiti lime trees. The treatments were as follows: trees were sprayed separately with thiamine, SA, or chitosan at a dose of 100 ppm, respectively; trees were treated with foliar brassinosteroid applications at a dose of 1 ppm; and untreated trees (control). By the end of the experiment, the elicitors reduced (75%) the number of adult psyllids compared with the control, where trees treated with chitosan had ≈0.5 adult individuals accumulated per flush shoot, whereas the control showed around two individuals. Salicylic acid and thiamine also reduced the number of nymphs compared with the control in the 4 weeks after treatment (WAT) (5.5 vs. 10.08 nymphs, respectively). Treatment with synthetic elicitors also caused a 30% reduction in oviposition by D. citri. The foliar applications with Br promoted a greater relative growth rate (RGR) (44 mm·cm−1·d−1) compared with the control treatment and chitosan (24 and 26 mm·cm−1·d−1, respectively). Chitosan sprays favored proline synthesis in both flush shoots and leaves. These results suggest that the use of synthetic elicitors can be considered as a tool to reduce the number of applications of chemical insecticides and decrease the development of resistances by D. citri because these synthetic elicitors showed an efficacy between 40% and 60% in all its stages in field conditions.

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Augusto Ramírez-Godoy, María del Pilar Vera-Hoyos, Natalia Jiménez-Beltrán and Hermann Restrepo-Díaz

Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, is the most serious threat to the global citrus industry, and its management has mainly depended on the application of chemical insecticides. The use of biopesticides can play an important role in regulating this pest. In a first test, two separate experiments were conducted in two different municipalities (Apulo and Jerusalen, Cundinamarca, Colombia) to evaluate the effect of foliar Beauveria bassiana and imidacloprid sprays on ACP populations in 2015 and 2016, respectively. In a second test, two separate tests were carried out in commercial Tahiti lime orchards to evaluate the efficacy of three different commercial biopesticides (Beauveria bassiana and extracts of Sophora sp. and garlic-chili pepper). In test 1, imidacloprid-treated trees showed a reduction (60% and 80%) in cumulative ACP adults in 2016. ACP cumulative nymphs were also diminished by foliar imidacloprid and B. bassiana application, between 40% and 65% in 2015 and 2016, respectively. ACP cumulative eggs showed lower individuals in imidacloprid-treated flushes at 3 and 4 weeks after treatment 9 (WAT) in 2016. In test 2, the results obtained showed ACP adults and eggs unaffected by biopesticide treatments; nymphs were reduced 50% to 75% in trees treated with the three biopesticides in comparison with control trees. All three biopesticides tested can be considered useful tools in integrated pest management (IPM) programs for ACP, since these products reduced immature ACP individuals between 50% and 75% under field conditions.