Insecticidal activity of Pilocarpus spicatus Saint-Hilaire (Rutaceae) essential oil against the crop pest Dysdercus peruvianus (Guérin-Méneville, 1831) and Oncopeltus fasciatus (Dallas, 1852)

Studies were carried out to evaluate the insecticidal activity of Pilocarpus spicatus Saint-Hilaire (Rutaceae) essential oil (EO) on the development of the Hemiptera Dysdercus peruvianus (Guérin-Méneville, 1831) and Oncopeltus fasciatus (Dallas, 1852). Gas Chromatography/Mass spectrometry analysis revealed a chemical composition with sabinene (32.27%) and sylvestrene (27.26%) as major constituents. Topical and continuous treatment with the pure EO induced 100% of mortality while serial dilutions of the EO induced different levels of lethality in a dose response manner. Median lethal dose (LD50) and lethal dose 90% (LD90) were determined. Malformations in insects and permanent or supernumerary nymphs were often observed after treatments, and the use of scanning electron microscopy allowed the analysis of morphological changes. The different biological effects of P. spicatus EO point out its potential as a rich source of bioactive molecules to be used as an alternative control method against agricultural pest insects.

Effects of nanoemulsion and essential oil from the leaves of Ocotea elegans against Dysdercus peruvianus

The Dysdercus peruvianus Guérin-Méneville is commonly known as the cotton stainer bug. In this study, it was evaluated the insecticide activity and mode of action of the essential oil from leaves of Ocotea elegans Mez and its nanoemulsion against D. peruvianus. Leaves of O. elegans were extracted by hydrodistillation. The essential oil obtained was analyzed by gas chromatography coupled with electron impact mass spectrometry and flame ionization detector. The essential oil toxicity measured by lethal dose 50 (LD50) and survival rate of insects were recorded. Lastly, an assay was carried out to assess the inhibition of the enzyme acetylcholinesterase to determine a possible mechanism of action of insecticidal activity. The sesquiterpene sesquirosefuran was the major compound detected and corresponds to 92% of the components of the essential oil. The nanoemulsion more stable showed hydrophilic lipophilic balance (HLB 11.74), droplet size 92±1.80 nm, and polydispersity index (PDI of 0.215±0.015). After the topical application of the O. elegans essential oil, significant decreases in the survival of D. peruvianus occurred in a dose-response manner with LD50 = 162.18 μg and the survival rate of the nanoemulsion in D. peruvianus was 10.0±5.47, a better value than in pure essential oil. The acetylcholinesterase inhibition presented inhibition concentration (IC50 = 1.37mg/mL) and mixed type of inhibition. This indicates that the essential oil of leaves from O. elegans and its nanoemulsion are promising candidates for use in integrated pest management programs.

Effects of Zanthoxylum caribaeum essential oil against cotton bug Dysdercus peruvianus

Agricultural crops need protection from a variety of different insects popularly known as pests. Some of these pests are becoming increasingly resistant to conventional pesticides, so new control alternatives are needed. In this work, the effects of the essential oil of the plant Zanthoxylum caribaeum on the development of cotton stink bug Dysdercus peruvianus were analyzed. After analysis by chromatography and mass spectrometry, the essential oil of Z. caribaeum presented 54 substances, the main constituents being Sylvestrene, Muurola-4 (14), 5-trans-diene, Isodaucene and α-Pinene. These compounds significantly increased insect mortality and interrupted metamorphosis and molting, often in a dose-dependent manner. In addition, nymphs with deformed legs, wings and antennae were observed. According to the data, the components present in the essential oil of Z. caribeum appear to be promising candidates for the development of green insecticides for use in future integrated pest management (MIP) programs.

De novo transcriptome sequencing and comparative analysis of midgut tissues of four non-model insects pertaining to Hemiptera, Coleoptera, Diptera and Lepidoptera

ABSTRACTDespite the great morphological diversity of insects, there is a regularity in their digestive functions, which is apparently related to their physiology. In the present work we report the de novo midgut transcriptomes of four non-model insects from four distinct orders: Spodoptera frugiperda (Lepidoptera), Musca domestica (Diptera), Tenebrio molitor (Coleoptera) and Dysdercus peruvianus (Hemiptera). We employed a computational strategy to merge assemblies obtained with two different algorithms, which substantially increased the quality of the final transcriptomes. Unigenes were annotated and analyzed using the eggNOG database, which allowed us to assign some level of functional and evolutionary information to 79.7% to 93.1% of the transcriptomes. We found interesting transcriptional patterns, such as: i) the intense use of lysozymes in digestive functions of M. domestica larvae, which are streamlined and adapted to feed on bacteria; ii) the up-regulation of orthologous UDP-glycosyl transferase and cytochrome P450 genes in the whole midguts different species, supporting the presence of an ancient defense frontline to counter xenobiotics; iii) evidence supporting roles for juvenile hormone binding proteins in the midgut physiology, probably as a way to activate genes that help fight anti-nutritional substances (e.g. protease inhibitors). The results presented here shed light on the digestive and structural properties of the digestive systems of these distantly related species. Furthermore, the produced datasets will also be useful for scientists studying these insects.