Synergistic interaction between carvacrol and Bacillus thuringiensis crystalline proteins against Cydia pomonella and Spodoptera exigua

Abstract

The aim of our study was to determine the usefulness of mixtures of carvacrol and Bacillus thuringiensis crystalline proteins Cry against pests of two different species: Cydia pomonella L. (Lepidoptera: Tortricidae) and Spodoptera exigua Hübner (Lepidoptera: Noctuidae). The novelty of our work lies in showing the interactions between carvacrol and bacterial toxins against insect pests. Moreover, we have demonstrated that carvacrol applied via ingestion exerts toxicity against lepidopteran caterpillars. We have shown that the botanical compound and Cry proteins act in synergy and their mixtures are most effective in reducing the number of L1 and L3 larvae when B. thuringiensis toxins constitute up to 0.1% and 0.05% of the mixtures, respectively. Carvacrol and crystalline proteins act in synergy in these combinations and have the potential to be effective in protecting crops against lepidopteran pests. The nature of the interaction between the components depended on the proportion of their concentrations in the mixture. Mixtures containing Cry toxin concentrations equal or higher than 20% caused lower observed mortality of insects compared to the expected one. Furthermore, we showed that crystalline proteins of B. thuringiensis MPU B9, carvacrol and their mixture did not affect the morphology of insect haemocytes, and additionally, had no effect on the immune system.

Botanical biopesticide combination concept—a viable option for pest management in organic farming

“…Recently, carvacrol, a monoterpenoid phenol, extracted from aromatic plants (oregano) also shown synergistic effects with Bt against Cydia pomonella when mixed in the ratio of 1:25,000 and 1:50,000 (Bt: carvacrol) causing 1.5 and 1.9 times higher mortality, respectively. The ratio of 1:1000 and 1:2000 also showed 1.5-and 1.8-folds higher mortality of Spodoptera exigua than expected (Konecka et al 2020). Some of the succesful synergistic interactions between botanicals and EPB are shown in Table 1.…”

“…Insect immune system is a major target for botanical and microbial pesticide combinations (Konecka et al 2020). The fitness of a plant extract for combining with a microbial insecticide depends on qualitative and quantitative variations of secondary metabolites, which might affect the microbes (Ribeiro et al 2012).…”

“…The synergism of neem and Btk may be due to the direct effect on enzyme regulation of the insect larvae (Bandyopadhyay et al 2014). Carvacol, a plant-based extract from many aromatic plants, acted earlier (inhibitory effect on acetylcholinesterase activity), before the rupture of midgut cells by Bt (Konecka et al 2020). Azadirachtin causes several effects on insects, viz., growth disruption, feeding, oviposition disruption, reduction in fitness, and fecundity, thus making it more susceptible to microbial infection (Defago et al 2011).…”

Synergistic Field Crop Pest Management Properties of Plant-Derived Essential Oils in Combination with Synthetic Pesticides and Bioactive Molecules: A Review

“…A study indicated that the essential oil compound carvacrol ( Figure 3 ) was able to synergistically interact with the crystalline proteins produced by Bacillus thuringiensis MPU B9 and MPU B54 strains to mediate larvicidal activity against Cydia pomonella (Linnaeus)(codling moth) and S. exigua (beet armyworm moth). The best synergistic larvicidal action was observed at a 1:25000 (MPU B54 protein to carvacrol) concentration ratio, which induced a 96.7% (±3.33%) mortality rate [ 122 ]. A similar study elucidated that EOs from A. indica containing azadirachtin and Sinapis alba were synergistically active against crop pests, like Spodopteraexigua (Hübner), C. pomonella and Dendrolimus pini (Linnaeus), when used in combination with bacterial crystalline toxins of B. thuringiensis MPU B9 isolate.…”

Synergistic and additive interactions of Shewanella sp., Pseudomonas sp. and Thauera sp. with chlorantraniliprole and emamectin benzoate for controlling Spodoptera litura (Fabricius)

“…To achieve pollution-free agricultural output and good compatibility with the environment, we may utilize new chemical pesticides at lower doses coupled with entomopathogenic bacterial strains. Combined treatments of insecticide and biological agents can be more efficient than individual constituents because of their different modes of action, which may also delay the development of resistance 19 . Entomopathogenic bacteria appear to be compatible with a wide spectrum of chemical insecticides and can result in synergism when applied in combination even at low pesticide doses 20 – 22 .…”