In vitro insecticide resistance patterns in field strains of the sheep blowfly, Lucilia cuprina.

The control of the sheep blowfly relies on the use of insecticides. There have been several reports of in vitro and in vivo resistance to the most widely-used flystrike control chemical, dicyclanil. A recent report also described in vitro resistance to imidacloprid in a strain collected from a single property over three consecutive seasons that also showed resistance to dicyclanil. The present study aimed to use in vitro assays to examine five field-collected blowfly strains to determine if this co-occurrence of resistance to dicyclanil and imidacloprid was present more widely in field strains and to also measure resistance patterns to the other currently-used flystrike control chemicals. Each of the strains showed significant levels of resistance to both dicyclanil and imidacloprid: resistance factors at the IC50 of 9.1-23.8 for dicyclanil, and 8.7-14.1 for imidacloprid. Resistance factors at the IC95 ranged from 16.5 to 53.7, and 14.6-24.3 for dicyclanil and imidacloprid, respectively. Resistance factors were up to 8.5 for cyromazine at the IC95. Resistance to dicyclanil and imidacloprid was suppressed by co-treatment with the cytochrome P450 inhibitor, aminobenzotriazole, implicating this enzyme system in the observed resistances. We discuss the implications of the co-occurrence of resistance to dicyclanil and imidacloprid on insecticide rotation strategies for blowfly control. We also discuss the roles of insecticide resistance, environmental factors (e.g. rainfall), operational factors (e.g. insecticide application technique) and other animal health issues (e.g. scouring / diarrhoea) that together will impact on the likelihood of flystrike occurring at an earlier time point than expected after insecticide application.

Resistance to dicyclanil and imidacloprid in the sheep blowfly, Lucilia cuprina, in Australia.

BACKGROUND: The sheep blowfly, Lucila cuprina, is a myiasis-causing parasite responsible for significant production losses and welfare issues for the Australian sheep industry. Control relies largely on the use of insecticides. The pyrimidine compound, dicyclanil, is the predominant control chemical, although other insecticides also are used, including imidacloprid, ivermectin, cyromazine and spinosad. We investigated in vitro resistance patterns and mechanisms in field-collected blowfly strains. RESULTS: The Walgett 2019 strain showed significant levels of resistance to both dicyclanil and imidacloprid, with resistance factors at the IC50 of 26- and 17-fold, respectively, in in vitro bioassays. Co-treatment with the cytochrome P450 inhibitor, aminobenzotriazole, resulted in significant levels of synergism for dicyclanil and imidacloprid (synergism ratios of 7.2- and 6.1-fold, respectively), implicating cytochrome P450 in resistance to both insecticides. Cyp12d1 transcription levels were increased up to 40-fold throughout the larval life stages in the resistant strain compared to a reference susceptible strain, whereas transcription levels of some other cyp genes (6g1, 4d1, 28d1) did not differ between the strains. Similar resistance levels also were observed in flies collected from the same property in two subsequent years. CONCLUSION: This study indicates that in vitro resistance to both dicyclanil and imidacloprid in this field-collected blowfly strain is likely mediated by cytochrome P450, with Cyp12d1 implicated as the enzyme responsible; however, it remains possible that another P450 also may be involved. A common resistance mechanism for the two drugs has important implications for drug rotation strategies designed to prolong the useful life of flystrike control chemicals. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Serial Metabolic Evaluation of Perihematomal Tissues in the Intracerebral Hemorrhage Pig Model.

PURPOSE: Perihematomal edema (PHE) occurs in patients with intracerebral hemorrhage (ICH) and is often used as surrogate of secondary brain injury. PHE resolves over time, but little is known about the functional integrity of the tissues that recover from edema. In a pig ICH model, we aimed to assess metabolic integrity of perihematoma tissues by using non-invasive magnetic resonance spectroscopy (MRS). MATERIALS AND METHODS: Fourteen male Yorkshire pigs with an average age of 8 weeks were intracerebrally injected with autologous blood to produce ICH. Proton MRS data were obtained at 1, 7, and 14 days after ICH using a whole-body 3.0T MRI system. Point-resolved spectroscopy (PRESS)-localized 2D chemical shift imaging (CSI) was acquired. The concentration of N-Acetylaspartate (NAA), Choline (Cho), and Creatine (Cr) were measured within the area of PHE, tissues adjacent to the injury with no or negligible edema (ATNE), and contralesional brain tissue. A linear mixed model was used to analyze the evolution of metabolites in perihematomal tissues, with p-value < 0.05 indicating statistical significance. RESULTS: The perihematoma volume gradually decreased from 2.38 ± 1.23 ml to 0.41 ± 0.780 ml (p < 0.001) over 2 weeks. Significant (p < 0.001) reductions in NAA, Cr, and Cho concentrations were found in the PHE and ATNE regions compared to the contralesional hemisphere at day 1 and 7 after ICH. All three metabolites were significantly (p < 0.001) restored in the PHE tissue on day 14, but remained persistently low in the ATNE area, and unaltered in the contralesional voxel. CONCLUSION: This study highlights the potential of MRS to probe salvageable tissues within the perihematoma in the sub-acute phase of ICH. Altered metabolites within the PHE and ATNE regions in addition to edema and hematoma volumes were explored as possible markers for tissue recovery. Perihematomal tissue with PHE demonstrated a more reversible injury compared to the tissue adjacent to the injury without edema, suggesting a potentially beneficial role of edema.

Serial Cerebral Metabolic Changes in Patients With Ischemic Stroke Treated With Autologous Bone Marrow Derived Mononuclear Cells.

Purpose: Cell-based therapy offers new opportunities for the development of novel treatments to promote tissue repair, functional restoration, and cerebral metabolic balance. N-acetylasperate (NAA), Choline (Cho), and Creatine (Cr) are three major metabolites seen on proton magnetic resonance spectroscopy (MRS) that play a vital role in balancing the biochemical processes and are suggested as markers of recovery. In this preliminary study, we serially monitored changes in these metabolites in ischemic stroke patients who were treated with autologous bone marrow-derived mononuclear cells (MNCs) using non-invasive MRS. Materials and Methods: A sub-group of nine patients (3 male, 6 female) participated in a serial MRS study, as part of a clinical trial on autologous bone marrow cell therapy in acute ischemic stroke. Seven to ten million mononuclear cells were isolated from the patient's bone marrow and administered intravenously within 72 h of onset of injury. MRS data were obtained at 1, 3, and 6 months using a whole-body 3.0T MRI. Single voxel point-resolved spectroscopy (PRESS) was obtained within the lesion and contralesional gray matter. Spectral analysis was done using TARQUIN software and absolute concentration of NAA, Cho, and Cr was determined. National Institute of Health Stroke Scale (NIHSS) was serially recoreded. Two-way analysis of variance was performed and p < 0.05 considered statistically significant. Results: All metabolites showed statistically significant or clear trends toward lower ipsilesional concentrations compared to the contralesional side at all time points. Statistically significant reductions were found in ipsilesional NAA at 1M and 3M, Cho at 6M, and Cr at 1M and 6M (p < 0.03), compared to the contralesional side. Temporally, ipsilesional NAA increased between 3M and 6M (p < 0.01). On the other hand, ipsilesional Cho showed continued decline till 6M (p < 0.01). Ipsilesional Cr was stable over time. Contralesional metabolites were relatively stable over time, with only Cr showing a reduction 3M (p < 0.02). There was a significant (p < 0.03) correlation between ipsilesional NAA and NIHSS at 3M follow-up. Conclusion: Serial changes in metabolites suggest that MRS can be applied to monitor therapeutic changes. Post-treatment increasing trends of NAA concentration and significant correlation with NIHSS support a potential therapeutic effect.