Essential Oils in Urban Insect Management-A Review

Essential Oils as Bioinsecticides Against Blattella germanica (Linnaeus, 1767): Evaluating Its Efficacy Under a Practical Framework

Concerns about the negative effects of traditional insecticides and increasing insecticide resistance have prompted the exploration of botanical alternatives like essential oils (EOs). The registration of biocides is a mandatory procedure, and some regions have established a special status for compounds that meet specific low-risk criteria, which includes certain EOs. This study aimed to evaluate and compare the efficacy of sixteen EOs, both registered as low-risk biocides and/or standard biocides, against the German cockroach, Blattella germanica. A topical application was performed with undiluted EOs (15 µL) on the dorsal surface of awake cockroaches. The results showed significant variations in efficacy, as follows: thyme, sweet orange, and lavender oils were the most effective, achieving 100% mortality within 24 h and a less than 30 s knockdown effect. In contrast, linseed and cottonseed oils were the least effective, resulting in 70% and 40% 24 h mortality. Remarkably, some EOs registered as low-risk biocides performed as well as the ones registered as standard biocides, suggesting that this category does not have to always be at odds with efficacy. Future research should adopt practical, application-driven approaches to ensure bioinsecticides balance performance and safety, meeting both regulatory and consumer demands.

Protective effects of Lavandula stoechas and Thymus numidicus essential oils against deltamethrin-induced hematological and biochemical toxicity in female rabbits

Recent studies have shown that essential oils (EOs) extracted from medicinal and aromatic plants have herbicidal and/or insecticidal properties, helping to mitigate the toxicity experienced by living organisms exposed to pesticides. Moreover, the primary compounds isolated from these EOs also have the potential to reduce pesticide-induced damage. The present work aimed to evaluate the protective effects of Thymus numidicus (TNEO) and Lavandula stoechas (LSEO) against Deltamethrin-induced toxicity in female rabbits. The results obtained by GC/MS analysis showed that monoterpenes and oxygenated monoterpenes were the main components of the EOs extracted from the aerial parts of Thymus numidicus and Lavandula stoechas. The use of the pesticide Deltamethrin caused significant damage to the liver and kidneys (p < 0.05), together with blood disorders, signs of restlessness and tremors. However, females treated with TNEO showed better tolerance than the group treated with LSEO. The combination of both oils showed more pronounced protective effects. This suggests a potential synergistic effect in reducing deltamethrin-induced toxicity.

Impact of plant monoterpenes on insect pest management and insect-associated microbes

The fight against insect pests primarily relies on the utilization of synthetic insecticides. However, improper application of these chemicals can lead to detrimental effects on both the environment and human health, as well as foster the development of insect resistance. Consequently, novel strategies must be implemented to address the challenges stemming from the prolonged use of synthetic insecticides in agricultural and public health environments. Certain strategies involve the combination of crop protectants, which not only enhance insecticidal effectiveness but also reduce application rates. Plant-based natural products emerge as promising alternatives for insect management. Monoterpenes, which are abundant plant compounds produced through the activation of various enzymes, have attracted significant attention for their effectiveness in insect control. Notably, they are prolific in fragrance-producing plants. This review explores the plant defense, insecticidal, and antimicrobial characteristics of monoterpenes against insect pests, shedding light on their potential modes of action and possibilities for commercialization. Emphasizing their role as targeted and environmentally safer, the review highlights the practical viability of monoterpenes within integrated pest management programs.

Common Home Remedies Do Not Deter Argentine Ants, Linepithema humile (Hymenoptera: Formicidae), from a Preferred Harborage

In two laboratory trials, natural products, including freshly picked leaves from spearmint, rosemary, and tansy plants, a water extract from soybean plants, peels from a common cucumber, and 1% peppermint oil in hexane, were placed in a moist harborage preferred by Argentine ants, Linepithema humile (Mayr), and the number of ants entering the harborage after two and four hours was counted. None of the recommended home remedies (tansy, cucumber, or soybean extract) deterred ants from an attractive, moist harborage in either trial, even when the quantity of these treatments was increased 4- to 10-fold. Freshly picked leaves from rosemary and spearmint plants deterred ants from harboring, and the 1% peppermint oil was the most deterrent of all treatments.

Insecticidal Activity of Essential Oils and Their Synergistic Effect on Improving the Efficacy of β-Cypermethrin against Blattella germanica

We screened the contact activity of 32 commercial essential oils (EOs) and their synergistic effect with β-cypermethrin against Blattella germanica. Results showed that the most effective EOs against B. germanica were from Illicium verum, Syzygium aromaticum, and Cinnamomum camphora, with LD50 values of less than 500 μg/insect. The most potent synergistic effects of β-cypermethrin on B. germanica were from Dysphania ambrosioides and Mentha canadensis. Both oils have a co-toxic factor of 133.33. The results of the major compound testing of the EOs showed that trans-anisaldehyde and thymol have the best insecticidal activity against B. germanica, with LD50 values of 141.30 and 138.61 μg/insect, respectively. The compounds with the best synergistic effect on β-cypermethrin were γ-terpinene and linalool at a concentration of 0.5%. The co-toxic factors for γ-terpinene and linalool were 150 and 133.33, respectively, which were similar to the synergistic effect observed with 2% piperonyl butoxide.

Influence of molecular descriptors of plant volatilomics on fumigant action against the three major stored product beetle pests

Plant volatilomics such as essential oils (EOs) and volatile phytochemicals (PCs) are known as potential natural sources for the development of biofumigants as an alternative to conventional fumigant pesticides. This present work was aimed to evaluate the fumigant toxic effect of five selected EOs (cinnamon, garlic, lemon, orange, and peppermint) and PCs (citronellol, limonene, linalool, piperitone, and terpineol) against the Callosobruchus maculatus, Sitophilus oryzae, and Tribolium castaneum adults. Furthermore, for the estimation of the relationship between molecular descriptors and fumigant toxicity of plant volatiles, quantitative structural activity relationship (QSAR) models were developed using principal component analysis and multiple linear regression. Amongst the tested EOs, garlic EO was found to be the most toxic fumigant. The PCs toxicity analysis revealed that terpineol, limonene, linalool, and piperitone as potential fumigants to C. maculatus (< 20 µL/L air of LC50), limonene and piperitone as potential fumigants to T. castaneum (14.35 and 154.11 µL/L air of LC50, respectively), and linalool and piperitone as potential fumigants to S. oryzae (192.27 and 69.10 µL/L air of LC50, respectively). QSAR analysis demonstrated the role of various molecular descriptors of EOs and PCs on the fumigant toxicity in insect pest species. In specific, dipole and Randic index influence the toxicity in C. maculatus, molecular weight and maximal projection area influence the toxicity in S. oryzae, and boiling point and Dreiding energy influence the toxicity in T. castaneum. The present findings may provide insight of a new strategy to select effective EOs and/or PCs against stored product insect pests.

Coconut fatty acids exhibit strong repellency and week-long efficacy against several urban pest arthropods of the southwestern United States

BACKGROUND

The southwestern United States is home to a variety of arthropods including Turkestan cockroaches, Blatta lateralis (Walker); hematophagous kissing bugs, Tritoma rubida (Uhler); and Arizona bark scorpions, Centruroides sculpturatus Ewing. These arthropods cause medical concern when they become established around homes and/or invade indoors. Traditionally, the management of these pests has relied primarily on the use of chemical insecticides; however, they offer poor prospects for control owing to their lack of efficacy as well as the effects of insecticides on humans and the environment. Botanical repellents are an option that has not been fully investigated for the management of these pests. Here, we investigated the behavioral responses of common urban pests of the southwestern USA to recently discovered coconut fatty acids (CFAs), to establish the potential use of these compounds as repellents.

RESULTS

Fresh residues of CFA mixture (CFAm) and their constituents caprylic acid, capric acid, capric acid methyl ester, lauric acid, and lauric acid methyl ester, tested at a concentration of 1 mg cm-2 , strongly repelled all arthropods. The repellent activity of CFAm lasted for at least 7 days, and the addition of lavender oil, used as an odor-masking agent, did not decrease this effect. Concentrations of CFAm ten times lower (0.1 mg cm-2 ) still repelled Turkestan cockroaches, and concentrations 100 times lower (0.01 mg cm-2 ) repelled T. rubida and scorpions.

CONCLUSIONS

CFAm and some of their constituents are efficacious, economical, and logistically feasible for inclusion in integrated pest management programs for these important urban pests of the southwestern USA. © 2023 Society of Chemical Industry.

The prevalence of Wolbachia in multiple cockroach species and its implication for urban insect management

Cockroach management relies heavily on the use of conventional insecticides in urban settings, which no longer provide the anticipated level of control. Knowledge of cockroach endosymbionts, like Wolbachia, might provide novel avenues for control. Therefore, we screened 16 cockroach species belonging to 3 families (Ectobiidae, Blattidae, and Blaberidae) for the presence of Wolbachia. We mapped the evolution of Wolbachia-cockroach relationships based on maximum likelihood phylogeny and phylogenetic species clustering on a multi-loci sequence dataset (i.e., coxA, virD4, hcpA, and gatB) of Wolbachia genes. We confirmed the previous report of Wolbachia in 1 Ectobiid species; Supella longipalpa (Fab.), and detected the presence of Wolbachia in 2 Ectobiid species; Balta notulata (Stål) and Pseudomops septentrionalis Hebard, and 1 Blaberid species; Gromphadorhina portentosa (Schaum). All cockroach-associated Wolbachia herein detected were clustered with the ancestor of F clade Wolbachia of Cimex lectularius L. (bed bugs). Since Wolbachia provision C. lectularius with biotin vitamins that confer reproductive fitness, we screened the cockroach-associated Wolbachia for the presence of biotin genes. In toto, our results reveal 2 important findings: (i) Wolbachia is relatively uncommon among cockroach species infecting about 25% of species investigated, and (ii) cockroach-associated Wolbachia have biotin genes that likely provide nutritional benefits to their hosts. Thus, we discuss the potential of exploring Wolbachia as a tool for urban insect management.

Gel Carriers for Plant Extracts and Synthetic Pesticides in Rodent and Arthropod Pest Control: An Overview

Insecticides and rodenticides form the basis of integrated pest management systems worldwide. As pest resistance continues to increase and entire groups of chemical active ingredients are restricted or banned, manufacturers are looking for new options for more effective formulations and safer application methods for the remaining pesticide ingredients. In addition to new technological adaptations of mainstream formulations in the form of sprays, fumigants, and dusts, the use of gel formulations is becoming increasingly explored and employed. This article summarizes information on the current and potential use of gel (including hydrogel) and paste formulations against harmful arthropods or rodents in specific branches of pest management in the agricultural, food, stored product, structural wood, urban, medical, and public health areas. Due to the worldwide high interest in natural substances, part of the review was devoted to the use of gels for the formulation of pesticide substances of botanical origin, such as essential or edible oils. Gels as emerging formulation of so called “smart insecticides” based on molecular iRNA disruptors are discussed.