Chemical profiling and bioactivities of essential oils from Thymus capitatus and Origanum compactum against Tribolium castaneum.

The use of essential oils has emerged as an ecofriendly solution for controlling different pests, particularly insects of stored products. Essential oils (EOs) from Thymus capitatus (TC) and Origanum compactum (OC) have received less attention for these bioactivities. Therefore, our study aimed to assess the repellent, antifeedant and contact toxicity of their EOs against a major stored product pest Tribolium castaneum. Besides, GC-MS was also carried out to determine the compounds responsible for the observed bioactivities. Regarding contact toxicity, LC50 values were 0.58 and 0.35 µL/cm2 for TC and OC after 24 h of exposure, respectively. For the repellent effect, the percentage of repellency (PR) was variable across different concentrations and exposure durations. TC exhibited the best PR (98%) after 3 h of exposure at 0.031 µL/cm2. For prolonged repulsive effect (24 h), TC sustained its repulsive efficacy with a PR of 90% at 0.062 µL/cm2 followed by OC with a PR of 88% at 0.125 µL/cm2. As for the antifeedant effect, both EOs had a significant impact on nutritional indexes, especially the feeding deterrent index and relative consumption rate. OC displayed a notable effect, causing 59% of feeding deterrence at 1.92 µL/pellet. These multifaced effects can be explained by the high content of carvacrol in both EOs (OC: 90% and TC: 78%). These multifaced effects demonstrated through different exposure routes and bioassays promote the use of T. capitatus and O. compactum EOs as a sustainable management strategy to control T. castaneum.

Effect of 20-Hydroxyecdysone, a Phytoecdysteroid, on Development, Digestive, and Detoxification Enzyme Activities of Tribolium castaneum (Coleoptera: Tenebrionidae).

Plants present a delimited reservoir of biologically active compounds. Many plants synthesize several compounds of secondary metabolism, such as alkaloids, terpenoids, phenolics, steroids, etc. Such compounds are generally thought to be involved in plant-insect interactions. Phytoecdysteroids are a class of chemicals that plants synthesize; these compounds are analogues of molting hormones produced by insects. In this work, the effect of the 20-hydroxyecdysone, which is a molecule that belongs to the family of phytoecdysteroids, was tested on an insect pest, Tribolium castaneum (Herbst). Firstly, the effect of this molecule on post-embryonic development parameters was tested after ingestion at 300, 600, 900, and 1,200 ppm. Secondly, the effect of the 20-hydroxyecdysone was also tested on the biological parameters (proteins, alpha-amylase, detoxification enzymes). The results of the post-embryonic parameters test showed an important induction of larval mortality and a significant reduction of pupation and adult emergence rates. On the other hand, the test on the biological parameters showed that the 20-hydroxyecdysone caused a significant decrease in the levels of soluble proteins in treated larvae. In addition, the alpha-amylase activity was significantly inhibited by the ingestion of the phytoecdysteroid. And there was also a disruption of detoxification enzymes. The whole of the disturbances recorded in this work prove that phytoecdysteroids are thought to have potential value on T. castaneum control.