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Differential impacts of pesticides on Euschistus heros (Hem.: Pentatomidae) and its parasitoid Telenomus podisi (Hym.: Platygastridae).

ABSTRACT: Euschistus heros (Fabricius) (Hemiptera: Pentatomidae) primarily attack the pods and seeds of soybean plants, causing severe economic losses in Neotropical Region, and chemical control is essential to avoid these losses. Thus, insecticides more effective against this pest and less toxic to Telenomus podisi Ashmead (Hymenoptera: Platygastridae) - the main biological control agent of E. heros - should be used. In this report, we studied the differential acute impacts of pesticides used in Brazilian soybean against E. heros and T. podisi and evaluated their sublethal effects on the parasitoid to identify effective pesticides towards the pest with less harmful effect to the natural enemy. The LC₅₀ of the insecticides to E. heros ranged from 1.20 to 533.74 ng a.i./cm²; the order of toxicity was thiamethoxam + lambda-cyhalothrin > acetamiprid + fenpropathrin > zeta-cypermethrin > acephate > imidacloprid. All pesticides were classified as slightly to moderately toxic to T. podisi based on the risk quotient. The exposure of T. podisi females to imidacloprid and the insecticide pre-formulated mixtures reduced the emergence of the offspring parasitoids by up to 40% whereas zeta-cypermethrin and the insecticides pre-formulated mixtures reduced offspring survival. The preferred order of choice of insecticides for the management of E. heros according to agronomic, toxicological, and environmental feasibility was the following: thiamethoxam + lambda-cyhalothrin > zeta-cypermethrin > acetamiprid + fenpropathrin > acephate > imidacloprid. Our study provides important and pioneer information to select insecticides for effective control of E. heros with lower impacts on T. podisi.

SUBMITTER: Pazini JB

PROVIDER: S-EPMC6483992 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Over the past few years, the use of RNA interference (RNAi) for insect pest management has attracted considerable interest in academia and industry as a pest-specific and environment-friendly strategy for pest control. For the success of this technique, the presence of core RNAi genes and a functional silencing machinery is essential. Therefore, the aim of this study was to test whether the Neotropical brown stinkbug Euschistus heros has the main RNAi core genes and whether the supply of dsRNA could generate an efficient gene silencing response. To do this, total mRNA of all developmental stages was sequenced on an Illumina platform, followed by a de novo assembly, gene annotation and RNAi-related gene identification. Once RNAi-related genes were identified, nuclease activities in hemolymph were investigated through an ex vivo assay. To test the functionality of the siRNA machinery, E. heros adults were microinjected with ~28 ng per mg of insect of a dsRNA targeting the V-ATPase-A gene. Mortality, relative transcript levels of V-ATPase-A, and the expression of the genes involved in the siRNA machinery, Dicer-2 (DCR-2) and Argonaute 2 (AGO-2), were analyzed. Transcriptome sequencing generated more than 126 million sequenced reads, and these were annotated in approximately 80,000 contigs. The search of RNAi-related genes resulted in 47 genes involved in the three major RNAi pathways, with the absence of sid-like homologous. Although ex vivo incubation of dsRNA in E. heros hemolymph showed rapid degradation, there was 35% mortality at 4 days after treatment and a significant reduction in V-ATPase-A gene expression. These results indicated that although sid-like genes are lacking, the dsRNA uptake mechanism was very efficient. Also, 2-fold and 4-fold overexpression of DCR-2 and AGO-2, respectively, after dsRNA supply indicated the activation of the siRNA machinery. Consequently, E. heros has proven to be sensitive to RNAi upon injection of dsRNA into its hemocoel. We believe that this finding together with a publically available transcriptome and the validation of a responsive RNAi machinery provide a starting point for future field applications against one of the most important soybean pests in South America.

Dataset Information

Differential impacts of pesticides on Euschistus heros (Hem.: Pentatomidae) and its parasitoid Telenomus podisi (Hym.: Platygastridae).

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