Comparative laboratory efficacy of novel botanical extracts against Tribolium castaneum

Mediterranean Plants as Potential Source of Biopesticides: An Overview of Current Research and Future Trends

The development and implementation of safe natural alternatives to synthetic pesticides are urgent needs that will provide ecological solutions for the control of plant diseases, bacteria, viruses, nematodes, pests, and weeds to ensure the economic stability of farmers and food security, as well as protection of the environment and human health. Unambiguously, production of botanical pesticides will allow for the sustainable and efficient use of natural resources and finally decrease the use of chemical inputs and burden. This is further underlined by the strict regulations on pesticide residues in agricultural products and is in harmony with the Farm to Fork strategy, which aims to reduce pesticide use by 50% by 2030. Thus, the present work aims to compile the scientific knowledge of the last 5 years (2017-February 2023) regarding the Mediterranean plants that present biopesticidal effects. The literature review revealed 40 families of Mediterranean plants with at least one species that have been investigated as potential biopesticides. However, only six families had the highest number of species, and they were reviewed comprehensively in this study. Following a systematic approach, the extraction methods, chemical composition, biopesticidal activity, and commonly used assays for evaluating the antimicrobial, pesticidal, repellant, and herbicidal activity of plant extracts, as well as the toxicological and safety aspects of biopesticide formulation, are discussed in detail. Finally, the aspects that have not yet been investigated or are under-investigated and future perspectives are highlighted.

Cytochrome P450 gene CYP6BQ8 mediates terpinen-4-ol susceptibility in the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

Cytochrome P450 proteins (CYPs) in insects can encode various detoxification enzymes and catabolize heterologous substances, conferring tolerance to insecticides. This study describes the identification of a P450 gene (CYP6BQ8) from Tribolium castaneum (Herbst) and investigation of its spatiotemporal expression profile and potential role in the detoxification of terpinen-4-ol, a component of plant essential oils. The developmental expression profile showed that TcCYP6BQ8 expression was relatively higher in early- and late-larval stages of T. castaneum compared with other developmental stages. Tissue expression profiles showed that TcCYP6BQ8 was mainly expressed in the head and integument of both larvae and adults. The expression profiling of TcCYP6BQ8 in developmental stages and tissues is closely related to the detoxification of heterologous substances. TcCYP6BQ8 expression was significantly induced after exposure to terpinen-4-ol, and RNA interference against TcCYP6BQ8 increased terpinen-4-ol-induced larval mortality from 47.78 to 66.67%. This indicates that TcCYP6BQ8 may be involved in T. castaneum's metabolism of terpinen-4-ol. Correlation investigation between the CYP6BQ8 gene and terpinen-4-ol resistance in T. castaneum revealed that the TcCYP6BQ8 gene was one of the factors behind T. castaneum's resistance to terpinen-4-ol. This discovery may provide a new theoretical foundation for future regulation of T. castaneum.

A comprehensive review on advances in storage pest management: Current scenario and future prospects

Modernization of the agricultural production system led to a significant increase in annual food production intended to meet the ever-growing consumer demand. In many countries, most of the food grains produced is stored for contingency and regular supply. These stored grains, in general, are directly or indirectly infested by insects, resulting in severe grain damages and storage losses, thus, causing a threat to food safety and security. Although a variety of insect management options, such as physical, mechanical, biological, and chemical methods, are available, fumigation has been practiced for decades in storage. However, opportunities for fumigation are narrowing after the phase-out of methyl bromide. Besides, safe food and health concerns paved the path for green chemistry and non-chemical management practices. This review includes the list of stored-grain insects and their detection methods. The different management strategies such as the modern storage structures (hermetic and low-pressure storages), modified or controlled storage atmosphere, application of ozone as fumigant, irradiation, and physical options are presented. Further, the details on sustainable biological options, such as semiochemicals, natural enemies, biopesticides, and entomopathogenic nematodes, are supplemented. The use of inert dusts as grain protectant and in combination with the biological entity is included. Studies on alternative fumigants', novel management options, such as molecular biology tools (RNAi and CRISPR) and nanotechnology in stored grain protection, are also highlighted. This review helps the reader to understand the overall factors affecting grain storage and the different options to manage the insects causing storage losses.

Insect repellent pellets - an application of botanicals against red flour beetle - their antifungal activity during storage and use as potential fumigants

BACKGROUND

The protection of grains from insect infestation is critical during storage. Insect repellent pellets (IRPs) are a potential technique to repel insects by hindering insect movement toward the grains. The basic principle of IRPs is the use of active components found in the oils of lemongrass, eucalyptus, and neem leaves for the controlled release of fumes, thereby avoiding the need for reapplication after a few days. Here, we examined the antifungal activity, the lethal dose, and the repelling effect of IRPs against red flour beetle, Tribolium castaneum, over a 30 day period.

RESULTS

We observed that IRPs possessed antifungal properties and were able to repel the adults of T. castaneum. These insects ultimately died from the fumes if they manage to stay near the IRPs (LD₅₀  = 2 and LD₉₉  = 7 days). The active components (phenol, 2,4-di-tert-butyl-, citral, neral, geraniol, n-hexadecanoic acid) present in IRP during the initial stage were also found after a storage period of 35 days.

CONCLUSION

The active components present in IRPs have antifungal, repellent, and fumigant properties. The IRPs can thus be termed potent botanical insecticides and are an alternative to synthetic insecticides. © 2022 Society of Chemical Industry.

Functional analysis of a cytochrome P450 gene CYP9Z6 responding to terpinen-4-ol in the red flour beetle, Tribolium castaneum

Tribolium castaneum is an agricultural and stored pest found throughout the world. The cytochrome P450 genes of T. castaneum can encode various detoxification enzymes and catabolize heterologous substances, conferring tolerance to insecticides. Herein, we describe the identification of a P450 gene (CYP9Z6) from T. castaneum and investigated its expression profile and potential role in the detoxification of terpinen-4-ol. TcCYP9Z6 expression was significantly induced after exposure to terpinen-4-ol, and RNA-mediated silencing of TcCYP9Z6 increased terpinen-4-ol-induced larval mortality from 47.75% to 63.92%, showing that TcCYP9Z6 is closely related to the detoxification of terpinen-4-ol. The developmental expression profile revealed that TcCYP9Z6 was mainly expressed in late adults and late larvae. Tissue expression profiling revealed that the highest TcCYP9Z6 expression occurred in the head, in both the adult and the larval tissues, followed by the gut in larvae and the antennae in adults. These developmental stages and tissues with high TcCYP9Z6 expression are closely related to the detoxification of heterologous substances. These results indicated that TcCYP9Z6 may play a pivotal role in the detoxification of terpinen-4-ol, which provides support for using TcCYP9Z6 a potential gene for the RNAi-mediated prevention and control of T. castaneum.

Effects of defect action level of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) fragments on quality of wheat flour

BACKGROUND

Tribolium castaneum (Herbst) is one of the most important secondary storage pests of all types of flour and flour-based products. The present study focuses on the fragment producing behaviour of T. castaneum in wheat flour during storage and its effect on the quality parameters and defect action level (DAL) of fragments. The US Food and Drug Administration has set a DAL of 75 insect fragments in 50 g of flour. Box-Behnken design was used to optimize the storage conditions (storage period in days and temperature in degrees Celsius) and insect density (numbers) to keep insect fragments below the DAL.

RESULTS

Optimization results indicated that the presence of single number of adult of T. castaneum is enough to cross the DAL of insect fragments within a storage period of 21 days at a storage temperature of 30 °C. Insect fragments cause perceptible changes in the quality of wheat flour. When sample attained DAL of T. castaneum fragments in wheat flour,the various quality parameters were analysed in that moisture content of wheat flour was 10.8 ± 0.26%, total colour change was 2.052 (ΔE value), T. castaneum progeny emergence was 19.66 ± 1, uric acid was 1.8 ± 0.16 g kg^-1 and microbial count was 7.34 ± 0.5 cfu g^-1 .

CONCLUSIONS

Results from the present study indicate that the presence of even a single adult of stored pest in wheat flour should not be ignored. It is mandatory to determine the threshold level and frequent sampling is required to achieve zero tolerance of stored product insects in food commodities. © 2021 Society of Chemical Industry.