Design, Synthesis and Insecticidal Activity of 3-(Ethylsulfonyl)-Pyridines Bearing Trifluoromethyl-Oxadiazole Fragment

Background: Oxadiazole fragment is one of the most prevalent structures in biochemicals, especially in the research of new pesticides. It is necessary to develop new insecticides with different mode of action for the treatment of insecticide resistance problems. And, it is worth exploring the new active insecticidal lead structures with oxadiazole fragments. Methods: We used a "splicing up" method introducing the trifluoromethyl-oxadiazole moiety to 3-(ethylsulfonyl)-pyridine structure, and replaced the 6-position on the pyridine ring by different substituted amines. Then, a series of novel 3- (ethylsulfonyl)-pyridines containing trifluoromethyl-oxadiazole moiety were designed and synthesized. All these title compounds were confirmed by 1H NMR, 13C NMR and ESI-MS. Results and Discussion: The primary insecticidal activity results indicated that some of them (A1-A7, A10, A13-A14) exhibited good mortality against Mythimna separate at 500 mg/L (80-100%), and compounds A13 and A14 have moderate insecticidal activity against M. separate at 250 mg/L (50-55%). Discussion: The bioassay results showed that the designed compounds did not achieve excellent insecticidal activity by introducing the potential oxadiazole fragment. Therefore, it seems that the special physicochemical properties of the oxadiazole fragment should be considered in fragment splicing-based design. Conclusion: According to the bioassay studies, the results revealed that compounds A13 and A14 which may provide useful information for further design efficient insecticides.

Influence of elevated CO2 on development and food utilization of armyworm Mythimna separata fed on transgenic Bt maize infected by nitrogen-fixing bacteria

Background Bt crops will face a new ecological risk of reduced effectiveness against target-insect pests owing to the general decrease in exogenous-toxin content in Bt crops grown under elevated carbon dioxide (CO2). The method chosen to deal with this issue may affect the sustainability of transgenic crops as an effective pest management tool, especially under future atmospheric CO2 level raising. Methods In this study, rhizobacterias, as being one potential biological regulator to enhance nitrogen utilization efficiency of crops, was selected and the effects of Bt maize (Line IE09S034 with Cry1Ie vs. its parental line of non-Bt maize Xianyu 335) infected by Azospirillum brasilense (AB) and Azotobacter chroococcum (AC) on the development and food utilization of the target Mythimna separate under ambient and double-ambient CO2 in open-top chambers from 2016 to 2017. Results The results indicated that rhizobacteria infection significantly increased the larval life-span, pupal duration, relative consumption rate and approximate digestibility of M. separata, and significantly decreased the pupation rate, pupal weight, adult longevity, fecundity, relative growth rate, efficiency of conversion of digested food and efficiency of conversion of ingested food of M. separata fed on Bt maize, while here were opposite trends in development and food utilization of M. separata fed on non-Bt maize infected with AB and AC compared with the control buffer in 2016 and 2017 regardless of CO2 level. Discussion Simultaneously, elevated CO2 and Bt maize both had negative influence on the development and food utilization of M. separata. Presumably, CO2 concentration arising in future significantly can increase their intake of food and harm to maize crop; however, Bt maize infected with rhizobacterias can reduce the field hazards from M. separata and the application of rhizobacteria infection can enhance the resistance of Bt maize against target lepidoptera pests especially under elevated CO2.

Synthesis and Insecticidal Activity of β-Dihydroagarofuran Acetal Derivatives

To search for improved insecticidal compounds based on β-dihydroagarofuran sesquiterpenoids, forty-four β-dihydroagarofuran acetal derivatives were designed and synthesized. Insecticidal activities and structure-activity relationship of these target compounds were evaluated. Some of the newly synthesized β-dihydroagarofuran acetal compounds were found to show higher insecticidal activity against sixth-instar larvae of Mythimna separate. Especially, compounds 2.2.9, 2.2.10, 2.2.11, 2.3.4, 2.3.6, 2.3.7, 2.5.4, 2.5.7 had great insecticidal activities with lower LD50 than that of the positive control celangulin-V (110.13 μg/g). It deserves mentioning that compound 2.2.11 showed the lowest LD50 (60.33 μg/g) among these compounds. Structure-activity relationship results suggested that the substituent groups of 1-, 6- and 9-positions of the target structures could greatly affect the insecticidal activity. Especially, when the substituent groups of 6-position were n-propyl, n-butyl, allyl, propargyl, o-fluorobenzyl, and p-fluorobenzyl, the compounds showed outstanding insecticidal activities.

Influence of elevated CO2 on development and food utilization of target armyworm Mythimna separata fed on transgenic Bt maize infected by nitrogen-fixing bacteria

Bt crops will face a new ecological risk of reduced effectiveness against target-insect pests owing to the general decrease in exogenous-toxin content in Bt crops grown under elevated CO2. How to deal with this issue may affect the sustainability of transgenic crops as an effective pest management tool especially under future CO2 raising. In this study, azotobacters, as being one potential biological regulator to enhance crops’ nitrogen utilization efficiency, were selected and the effects of Bt maize and non-Bt maize infected by Azospirillum brasilense and Azotobacter chroococcum on development and food utilization of target Mythimna separate were studied under ambient and elevated CO2. The results indicated that azotobacter infection significantly increased larval life-span, pupal duration, RCR and AD of M. separata, and significantly decreased RGR, ECD and ECI of M. separata fed on Bt maize; There were opposite trends in development and food utilization of M. separata fed on non-Bt maize infected with azotobacters compared with the buffer control regardless of CO2 level. Presumably, the application of azotobacter infection could make Bt maize facing lower field hazards from the target pest of M. separate, and finally improve the resistance of Bt maize against target lepidoptera pests especially under elevated CO2.Summary statementElevated CO2 effect on development and food utilization of target armyworm Mythimna separata fed on Bt maize infected by azotobacter, Azospirillum brasilense and Azotobacter chroococcum