Toxicity and physiological effects of ajwain (Carum copticum, Apiaceae) essential oil and its major constituents against Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae).

The effects of Ajwain essential oil and its major constituents were investigated against newly fourth instar larvae of Tuta absoluta, a major pest of tomato cropping in Iran and other parts of the world. The study included individual efficacy of each compound and determination of their synergistic or antagonistic efficacy. We also determined the activities of detoxifying enzymes in treated insects. According to the results, the Ajwain essential oil and thymol showed the highest toxicity against T. absoluta larvae (LC50 = 6.14 and 7.72 µL/mL, respectively, and LC30 = 3.05 and 3.57 µL/mL, respectively). The ɤ-terpinene and p-cymene had lesser toxicity compared to other compounds. The larvicidal potency increased by binary mixtures of active constituents, such as thymol + p-cymene and thymol + É¤-terpinene. On the other hand, ɤ-terpinene + p-cymene mixture demonstrated antagonistic effect on the larvae. The esterases and glutathione S-transferases were significantly increased in all treatments. Finally, our results revealed a significant inhibition of AChE activity in the treated larvae by all treatments except for ɤ-terpinene + p-cymene. In vitro experiments representing AChE inhibition with IC50 values were recorded 0.370, 0.457, 0.528, 1.094 and 1.323 µL/mL for thymol + p-cymene, thymol + É¤-terpinene, thymol, ɤ-terpinene and p-cymene, respectively. Thymol demonstrated significant potential as a controlling agent of T. absoluta larvae, both larvicidal, compatible with other compounds with strong AChE inhibition properties. These finding could pave the way for development of new botanicals based on EO constituents which should be completed with preparation of an efficient formulation and field trials.

Effect of thermal stress on the immune responses of Chilo suppressalis walker (Lepidoptera: Crambidae) to Beauveria bassiana.

Temperature is one of the important environmental elements affecting ecological fitness of insects through alterations in physiological systems. In the current study, a comparison was made on the cellular and humoral immune responses of the Chilo suppressalis larvae exposed to thermal stress (34 °C) and optimal rearing temperature (24 °C). Although total hemocyte count increased in the injected larvae by Beauveria bassiana, elevation of hemocyte numbers was significantly different in the larvae exposed to 34 °C for a short-time period compared to long-term exposure and control. A similar trend was observed in plasmatocyte and granulocyte counts as well as phenoloxidase activity. Gene expression of some antimicrobial peptides, including attacin1, attacin2, cecropin1, cecropin2, defensin, gallerimycin, lysozyme and prophenoloxidase-activating proteinase-3, was compared in the larvae exposed to thermal regimes and injection challenges. In all cases, expression of the target genes was relatively higher in the larvae injected by B. bassiana and short-term exposure at 34 °C. The present results confirmed that C. suppressalis could modulate the immune system in response to different thermal stress conditions mainly over a short period.

Effects of α-pinene, trans-anethole, and thymol as the essential oil constituents on antioxidant system and acetylcholine esterase of Ephestia kuehniella Zeller (Lepidoptera: Pyralidae).

The current study aimed to determine the potential effects of three essential oil constituents, α-pinene, trans-anethole, and thymol, on antioxidant system and acetylcholine esterase (AChE) of Ephestia kuehniella Zeller. The 4th instar larvae were initially fed on an artificial diet containing an LC50 concentration of each above-mentioned compounds separately prior to being undertaken for sample preparation and biochemical assays. The significant higher activities of superoxide dismutase, peroxidase and catalase were observed in the treated-larvae at both time intervals. Similar findings were found in the activity of glutathione S-transferase by using both reagents. Although activities of ascorbate peroxidase and glycerol-6-phosphate dehydrogenase increased in the treated larvae by all constituents while glycerol-6-phosphate dehydrogenase showed no statistically different activity among the larvae fed on α-pinene, trans-anethole, and thymol. The concentration of malondialdehyde and the ratio of oxidized (RSSR) to reduced (RSH) thiols showed statistical differences among control and treated larvae except for time interval of 24 h regarding the ratio of RSSR/RSH. Finally, our results demonstrated a significant decrease of AChE activity in the treated larvae by all constituents after 24 h while no statistical differences were found between control and trans-anethole after 24 h. Also, in vitro analysis revealed significant inhibition of AChE representing IC50 values of 0.864, 0.490 and 0.137 µl/ml for α-pinene, trans-anethole, and thymol, respectively. These results determined significant effects of administered constituents on induction of antioxidant system and inhibition of a nervous system component which expand our knowledge on physiological turbulences due to essential oil treatment.

A Laboratory Study on the Modeling of Temperature-Dependent Development and Antioxidant System of Chilo suppressalis (Lepidoptera: Crambidae).

The developmental rates of Chilo suppressalis (Walker; Lepidoptera: Crambidae) were investigated at different constant temperatures of 11, 18, 22, 24, 26, 30, 32, 34, and 36°C to find out temperature thresholds, thermal requirements and larval antioxidant responses. The time to complete immature stages separately reduced by raising the rearing temperature except for eggs which showed no significant differences at 30-34°C. Data analysis by traditional and Ikemoto-Takai linear models determined Tmin of 10.0 and 9.92°C as well as thermal constants of 840.34 and 848.0 DD for the overall immature stages. The models including Analytis, Briere-2, Lactin-2, and Sharpe-Schoolfield-Ikemoto (SSI) calculated Tmin values of 9.15, 9.57, 10.0, and 11.37°C for overall immature stages while Tfast was found to be 33.8, 33.3, 33.7, and 33.0°C, respectively. Tmax was calculated as 35.12, 34.66, 34.56, 36.84, 34.11, and 35.15°C for Analytis, Briere-2, Lactin-2, SSI, Logan-6, and Logan-10. Topt using SSI was calculated as 24.42°C for total developmental time. The larvae exposure to 34°C in the short-term period demonstrated the highest activities of catalase, peroxidase, and superoxide dismutase compared to control (24°C). Activities of ascorbate peroxidase and glucose-6-phosphate hydrogenase also increased at 34°C in the short-term period for all preparations. The larvae exposed to 34°C in short-term period showed the highest amounts of Malondialdehyde and oxidized and reduced thiols (RSSR/RSH) ratio compared to control. These results may be useful to explain potentially ecological performance of C. suppressalis as the major pest of rice in Iran.