Toxicity and sublethal effects of phthalides analogs to Rhyzopertha dominica

Phthalides and their precursors have demonstrated a large variety of biological activities. Eighteen phthalides were synthesized and tested on the stored grain pest Rhyzopertha dominica. In the screening bioassay, compounds rac‐(2R,2aS,4R,4aS,6aR,6bS,7R)‐7‐bromohexahydro‐2,4‐methano‐1,6‐dioxacyclopenta[cd]pentalen‐5(2H)‐one (15) and rac‐(3R,3aR,4R,7S,7aS)‐3‐(propan‐2‐yloxy)hexahydro‐4,7‐methano‐2‐benzofuran‐1(3H)‐one (17) showed mortality similar to the commercial insecticide, Bifenthrin® (≥90 %). The time (LT50) and dose (LD50) necessary to kill 50 % of the R. dominica population were determined for the most efficacious phthalides 15 and 17. Compound 15 presented the lowest LD50 (1.97 μg g−1), being four times more toxic than Bifenthrin® (LD50=9.11 μg g−1). Both compounds presented an LT50 value equal to 24 h. When applied at a sublethal dose, both phthalides (especially compound 15), reduced the emergence of the first progeny of R. dominica. These findings highlight the potential of phthalides 15 and 17 as precursors for the development of insecticides for R. dominica control

Synthesis, insecticidal activity, and phytotoxicity of novel chiral amides

The lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae), is an important pest of stored grains worldwide. Chemical control is the main method used to manage this pest, but the continuous use of insecticides can lead to the selection of resistant R. dominica strains. Thus, there is a constant demand for the development of new insecticide molecules. This study describes the synthesis of 14 chiral amides and evaluation of their insecticidal activity against R. dominica. Their phytotoxicity to wheat (Triticum sativum) seeds is also evaluated. In the screening assay, compounds 8i and 8j caused 100% and 87% mortality of R. dominica. These values did not differ from the mortality caused by Bifenthrin® (75%). Amide 8i presented similar toxicity (LD50 = 27.98 µmol g^−1, CI95 = 25.14–30.71) and speed of action (LT50 = 22 h, CI95 = 19.34–24.66) to amide 8j (LD50 = 29.37 µmol g^−1, CI95 = 27.43–31.09, and LT50 = 19 h, CI95 = 17.05–20.95) against the pest. Both amides inhibited less than 44% of wheat growth.Among the tested amides, only 8i and 8j were effective in R. dominica control and presented no considerable phytotoxicity towards wheat seeds. Therefore, these amides are promising as insecticides for the management of R. dominica

Larvicidal activity of synthetic tropane alkaloids against Ascia monuste orseis (Lepidoptera: Pieridae)

Tropane alkaloids are known to play a role in plant defence. By blocking acetylcholine receptors, they exert insecticidal and deterrent effects against herbivore insects. Carbamates are an important class of chemical insecticides that also inhibit acetyl cholinesterase. The objective of this work was to synthesise a series of tropane alkaloids bearing a carbamate group, and to evaluate their effects against the pest Ascia monuste. The effects of the most active compounds were evaluated on the A. monuste predatorSolenopsis saevissima and on the pollinator Tetragonisca angustula. The synthesis of carbamate‐tropane alkaloids was accomplished in 4–5 steps from commercially available ketones. Results from bioassays showed that compounds 6a, 10a and 14a presented higher activities against second‐instar larvae of A. monuste, with LD50values of 1.01, 3.76 and 1.92 µg substance mg−1 insect, and TL50 values of 7.0, 15.0 and 5.0 h respectively. These compounds were also tested for their selectivity in favour of S. saevissima and T. angustula. Compound 6a, which showed the highest activity against A. monuste, also showed lower toxicity against S. saevissima. Tropane alkaloid derivatives bearing a carbamate group show potential for the development of novel insecticides against A. monuste. © 2017 Society of Chemical Industr

Effects of paracress (Acmella oleracea) extracts on the aphids Myzus persicae and Lipaphis erysimi and two natural enemies

EntomologiaThis study was conducted to evaluate the toxicity of paracress (Acmella oleracea) extracts to the aphids Myzus persicae (Sulz.) and Lipaphis erysimi (Kalt.) (Hemiptera: Aphididae), and the extracts selectivity to the aphid parasitoid Diaeretiella rapae McIntosh (Hymenoptera: Braconidae) and to the predator Orius insidiosus (Say) (Hemiptera: Anthocoridae). We evaluated water and ethanol extracts from A. oleracea. The ethanol extract caused 90% mortality of both aphid species within 70 h and reduced their fecundity, whereas the water extract was inactive. In addition, this extract caused no mortality of the natural enemies. In an attempt to identify bioactive compounds in the ethanol extract, three alkamides, spilanthol, undeca-2E-en-8,10-diynoic acid isobutylamide (compound 2) and (2E)-N-(2-methylbutyl)-2-undecene-8,10-diynamide (compound 3), were isolated and tested on L. erysimi. From the isolated alkamides, spilanthol and compound 2 showed high insecticidal activity against L. erysimi, indicating that they contributed to the observed extract activity. The results of this study demonstrate the potential of the ethanol extract of A. oleracea as a botanical insecticide in the management of aphids in brassicas

Yield losses in transgenic Cry1Ab and non-Bt corn as assessed using a crop-life-table approach

In this study, we constructed crop life tables for Bacillus thuringiensis Berliner (Bt) Cry1Ab and non-Bt corn hybrids, in which yield-loss factors and abundance of predaceous arthropods were recorded during 2 yr at two locations. Corn kernel/grain was the yield component that had the heaviest losses and that determined the overall yield loss in the corn hybrids across years and locations. Yield losses in both corn hybrids were primarily caused by kernel-destroying insects. Helicoverpa zea (Boddie) and Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae) were the key loss factors at one location, while at the other, the key loss factor was the silk fly larvae, Euxesta spp. (Diptera: Ulidiidae). Although the realized yield of corn grains was not different (P > 0.05) between Cry1Ab and non-Bt corn hybrids, the Bt corn hybrid reduced (P < 0.05) the damage by H. zea and S. frugiperda in three of the four field trials, particularly at the location where Lepidoptera were the key loss factors. As expected, no reduction in the abundance of predaceous arthropods was observed in Cry1Ab corn fields. Various species of natural enemies were recorded, particularly the earwig Doru luteipes (Scudder) (Dermaptera: Forficulidae), which was the most abundant and frequent predaceous insect. These results indicate that integration of pest management practices should be pursued to effectively minimize losses by kernel-destroying insects during corn reproductive stages when growing non-Bt or certain low-dose Bt corn cultivars for fall armyworm and corn earworm, such as those producing Cry1Ab or other Cry toxins

Eucalyptus resinifera essential oils have fumigant and repellent action against Hypothenemus hampei

The coffee berry borer Hypothenemus hampei Ferrari (CBB, Coleoptera: Scolytidae) is one of the major pests of coffee causing damage in the field and in warehouses. This pest is mainly controlled with insecticides and repellents. Essential oils (EOs) have been investigated as an alternative to synthetic insecticides, however few studies on the use of EOs to control the CBB have been reported. In this study, the toxicity of essential oils (EOs) extracted from leaves of Eucalyptus and Corymbia species against the coffee berry borer (CBB) was evaluated. Of the eleven species investigated, chemical profiles of EOs of two plants (C. henryi and the hybrid E. alba × E. tereticornis) are reported for the first time. The toxicity of EOs was assessed by contact and fumigation. Fifty compounds were identified in the EOs, with 1,8-cineole, α-pinene, and citronellal being the most common. The EOs were more active by the fumigation route and the oils from E. resinifera caused the higher mortality to CBB. Moreover, the EO from E. resinifera was more toxic (LC50 = 64.72 μL/L) than garlic extract, used as standard, and showed rapid action (LT50 = 4.0 min). The toxic effect of E. resinifera EO towards CBB is due to a synergistic effect involving 1,8-cineole, α-pinene and p-cymene. The EO of E. resinifera was as repellent as the garlic extract to the pest. The potential use of E. resinifera EOs in CBB management is discussed