Survival and demography of the tomato borer (Tuta absoluta) exposed to citrus essential oils and major compounds

Abstract

The tomato borer, Tuta absoluta (Meyrick, 1917) (Lepidoptera: Gelechiidae) is a global pest that have dispersed quickly over the countries. That pest shows high level of resistance to insecticides commonly used. Therewith the evaluation of essential oils toxicity it’s important for development of new insecticide molecules. In this study we evaluated the lethal and sublethal effects of Citrus aurantifolia (lime), Citrus aurantium (petitgrain) and Citrus aurantium bergamia (bergamot) essential oils and its major compounds against T. absoluta. Therefore, the EOs were solubilized in acetone at 100 μg μL-¹ and 1 μL of that solution were applied to the mid-dorsal abdominal region of 2º instar larvae using a microsyringe (Hamilton 50 μL). The survival was assessed every 12 h up to a total of 72 h; in all experiments in this study, the control treatments consisted of 2º instar larvae exposed to only 1 μL of acetone. The lethal time 50 (LT50) of larvae exposed to petitgrain and lime EOs was 13.57 h while those treated with bergamot had LT50 of 19.34 h. For chemical characterization, EOs were submitted to gas chromatography analysis coupled to mass spectrometry (GC-ME) and the major compounds were identified. Results show lime EO had 44.74% of alpha-terpinol; petitgrain and bergamot have 55.45% and 58.12% of linalyl acetate respectively. To determine the median lethal dose (LD50), six doses of EOs were used based on arithmetic progression and previous experiments, being them, 100; 75; 55; 41.3 and 31.6 and 17.3 μg μL-¹. The LD50 of the EOs for lime, petitgrain and bergamot were 33.75, 38.78 and 35.05 μg μL-¹, respectively. To determine the toxicity of the major components, solutions were used in the concentration equivalent to LD50 in the OEs; 16.2 μg μL-1 (alpha-terpineol) and 25.8 μg μL-1 (linalyl acetate). After applying a 1 μL aliquot on the dorsal abdominal region of 2º instar larvae, survival was assessed for a period of 72 h. The majority compounds showed toxicity lower than that found in EOs, not being able to eliminate half of the tested population. To life table analysis, the 2º instar larvae were exposed to 1 μL of the LD50 of the EOs and evaluated daily. The treatments reduced the duration of larval instars, duration of the pupal period, fertility, oviposition and egg viability. As a result, there was a reduction in the population growth parameters of T. absoluta. Thus, in this study it was proved that the EOs of C. aurantifolia (lime), C. aurantium (petitgrain) and C. aurantium bergamia (Bergamot) cause lethal effects in T. absoluta. When EOs were used in sublethal doses, they affected reproductive and demographic parameters of this pest.