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Ivermectin (Iv) is widely used to control Rhipicephalus annulatus infestations in cattle in Egypt. However, increasing resistance to ivermectin necessitates alternative approaches. This study aimed to address this resistance by investigating the interactions between ivermectin and essential oil components (EOCs)-carvacrol, cinnamaldehyde, D-limonene, trans-anethole, and thymol-against four R. annulatus tick isolates collected from Beni-Suef, El-Minia, and El-Fayoum. The larval immersion test was conducted using various ivermectin concentrations (3, 1.5, 0.75, 0.38, 0.19, 0.09, 0.045, 0.025, and 0.0125 mg/mL) prepared in EthTX1 %. Additionally, EOCs were tested at different concentrations (20, 10, 5, and 2.5 mg/mL) prepared by dilution in 5 % ethyl alcohol and EthTX 1 %. Ivermectin and each EOC were tested individually against the isolates. Subsequently, the LC50 of ivermectin was combined with the LC50 of each EOC in a 1:1 ratio to evaluate potential synergistic effects. All EOCs demonstrated significant toxicity against the isolates. The combination of carvacrol and thymol with ivermectin increased mortality, but the combination index (CI) exceeded one for all isolates, indicating no synergism. Similarly, while D-limonene, cinnamaldehyde, and trans-anethole also resulted in high mortality rates, including up to 100 %, no synergism was observed (CI > 1). However, these three EOCs exhibited CIs close to 1, suggesting an additive effect when combined with ivermectin. In conclusion, combining ivermectin with certain EOCs, particularly D-limonene, cinnamaldehyde, and trans-anethole, may offer an effective tool for controlling cattle ticks. Developing topical or pour-on formulations of ivermectin-EOC combinations could be an integral part of integrated management strategies to combat resistance to macrocyclic lactones like ivermectin. Further studies, including tests on adult ticks and field trials, are needed to evaluate the efficacy of these combinations., Competing Interests: Declaration of Competing Interest The authors declare that the research was conducted in the absence of any commercial or financial relationships., (Copyright © 2024 Elsevier B.V. All rights reserved.)

The house fly, Musca domestica (Linnaeus) (Diptera: Muscidae), is a significant threat to human and animal health and is also resistant to a variety of insecticides. Plant-derived benzoates are known to have insecticidal activities against various insects. In this study, the larvicidal, pupicidal, and adulticidal activities of benzoate derivatives (benzyl alcohol BA, benzyl benzoate BB, and methyl benzoate MB) were assessed and investigated for their effects on larval structure and acetylcholinesterase activity. Six concentrations (2.5 to 100 mg/mL) of benzoate derivatives were applied to larvae and pupae through the residual film method and topical application, respectively. Meanwhile, concentrations from 0.625 to 50 mg/L air were applied to adult flies through a fumigation assay. BA and MB achieved promising results against larvae with LC 50 values of 10.90 and 11.53 mg/mL, respectively. Moreover, BA killed 100% of the larvae at a concentration of 25 mg/mL, and MB achieved the same effect at a concentration of 50 mg/mL. Regarding the pupicidal activity, MB showed a percentage inhibition rate (PIR) of 100% at a concentration of 100 mg/mL, while the same effect was achieved by BA at a concentration of 50 mg/mL. Meanwhile, BB did not show any effect on the larvae or pupae at any of the tested concentrations. Moreover, the scanning microscopy observations on the treated larvae by BA and MB estimated flaccid and deformity in the larva body with a shrunken cuticle. Additionally, both BA and MB suppress nerve signal transmission by inhibiting acetylcholinesterase. In conclusion, the results of this study indicate that BA and MB may be useful in control housefly populations. These substances cause severe muscular relaxation and deformities in insects., (© 2024. Sociedade Entomológica do Brasil.)