Síntese, atratividade e eficácia de encapsulados sobre Atta sexdens (Hymenoptera: Formicidae)

Abstract

Leaf-cutting ants (Hymenoptera, Formicidae, Attini) are defoliation pests of great agronomic importance The most effective control method is chemical, by using granulated baits containing sulfluramide as standard active ingredient. Therefore, the objective of this work was to develop an encapsulated based on chitosan and tapioca, compatible with the attractive ingredient (citrus pulp) and with the active ingredient (sulfluramide). For the synthesis of the encapsulates 30 mL of the chitosan solution, 6 mL of tapioca solution, 6 mL of acetone solution with sulfluramide and finally 3 g of citrus pulp were gradually added under constant stirring. The final solution was dripped in NaOH (1 mol) and after the precipitation process the encapsulates were subjected to Petri dish drying at 24°C for 2 days. In order to confirm the presence of sulfluramide in the encapsulated, Fourier Transform Infrared Spectrometer (FTIR), X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) were performed. According to the characterizations made by FTIR, XRD and SEM, the presence of sulfluramide was confirmed in the synthesized encapsulated. To evaluate the attractiveness and the incorporation, the behavioral acts were observed regarding the foliar and encapsulated disks: to hold them on the fungus; lick its surface; puncture them into smaller fragments; pleating or gripping its edges; deposition of fecal fluid; incorporation in the fungus garden and deposition of hyphae on the newly incorporated fragments. There was rejection in the loading and the incorporation of encapsulated based on chitosan and tapioca in comparison to leaf discs. The most frequent behavioral acts in the processing of the encapsulated were: licking (21.53%), holding the encapsulated (21.41%) and loading the encapsulated (18.57%). The caste that most acted in the processing of encapsulated were the gardeners (50.59%). To evaluate the accumulated mortality of Atta sexdens workers were supply encapsulated without sulfluramide (ESA); encapsulated with 2% (m/v) sulfluramide (E2%); commercial bait Mirex™ (IGC). For that, evaluations were done at 1, 2, 3, 5, 7, 9, 11, 14, 17 and 21 days after treatment application, and the mortality was accounted per day. Mortality averages were corrected for the Abbott formula. The symptoms of intoxication corresponded to: t = tremors; l = slow movements; f = difficulty in moving legs; d = paralyzed front legs; p = paralyzed hind legs; i = all legs paralyzed, but antennas and gaster with normal movements; g = general paralysis. The non-parametric test Kruskal-Wallis was used for the analysis of the data at significance level (p<0.05), followed by test Student-Newman-Keuls. It was observed that in ESA the symptoms increased until the eleventh day, where the registered mortality rates were 64%. The E2% treatment presented symptoms from the first day and the 14th day all the workers were in dead. The treatment IGC, as in E2%, presented marked symptoms from the first day. On the ninth day of evaluation, it already had 100% of workers dead. Comparing the treatments between each other the mortality of E2% and IGC were significantly higher than in ESA. The encapsulated proved to have allowed the intoxication of workers causing mortality in the same proportion as the granulated baits.