Inseticidas via solo, mortalidade do bicho-mineiro-do-cafeeiro, morfofisiologia e metaboloma de coffea arabica L.

Abstract

The alleged bioactivating effect of insecticides that are often used to control leafminers in coffee plantations in Brazil adds another layer to the concern about the inappropriate use of this technology. With this in mind, bioassays were conducted to evaluate whether insecticides traditionally applied via soil provide changes in the morphophysiology, metabolome and control of Leucoptera coffeella in Arabica coffee seedlings. To this end, Catuaí Vermelho IAC 144 coffee seedlings were transplanted into 3.8 L pots. Each treatment consisted of the application of insecticides based on thiamethoxam, dinotefuram, dinotefuram + pyriproxifen, imidacloprid and flupyradifurone according to field recommendations. The control treatment consisted of seedlings treated with water, the design used was completely randomized with 4 repetitions of each bioassay. The seedlings were kept inside entomological cages inside a greenhouse. Every 10, 20, 40, 60 and 80 days after the application of insecticides, a bioassay was carried out, for which 4 seedlings were drawn per treatment in each bioassay, with each seedling being a repetition. Gas exchange was analyzed at 10, 20 and 40 days after insecticide application. In the aerial part, stem diameter, seedling height, number of leaves, leaf area and dry mass yield were evaluated. In the root system, the diameter, number of fine roots, total area, total volume and dry mass yield of the roots were evaluated. An assessment of the coffee miner infestation was also carried out. To evaluate the metabolome, 4 seedlings per treatment were grown under the same conditions for evaluating morphophysiology. At 80 days after insecticide application, leaves from the third pair were collected to evaluate the seedlings' metabolome. Non-target analyzes were conducted on a gas chromatograph coupled to a mass spectrometer. The results indicate that there were no significant differences in the gas exchange of the seedlings at 10, 20 and 40 days after the application of the insecticides. However, the imidacloprid-based neonicotinoid insecticide resulted in reduced seedling height and leaf area at 60 and 80 days after application, with a further decline in stem dry mass observed at 80 days. There was no bioactivating effect on the aerial part of the seedlings with any of the insecticides tested, however the neonicotinoid insecticide containing thiamethoxam 250 g a.i ha-1 demonstrated an increase in root volume and area at 80 days. The insecticides were effective in protecting seedlings throughout the bioassay period, from 10 to 80 days after application. The insecticide based on thiamethoxam 250 g a.i ha-1 exerted a bioactivating effect on the volume and area of the roots of coffee seedlings. Applications of insecticides caused an increase in the expression of free sugars in the seedlings. The insecticides, based on thiamethoxam 250 g a.i ha-1, thiamethoxam 300 g a.i ha-1 and dinotefuram demonstrated different galactose metabolism pathways than control seedlings. Insecticides cause effects on the metabolome of Catuaí Vermelho IAC 144 coffee seedlings.