Concentration-dependent effects of spinetoram on nontarget freshwater microalgae: A comparative study on Chlorella vulgaris and Microcystis aeruginosa

The rising global demand for agricultural products is leading to the widespread application of pesticides, such as spinetoram, resulting in environmental pollution and ecotoxicity to nontarget organisms in aquatic ecosystems. This research focused on assessing the toxicity of spinetoram at various concentrations (0, 0.01, 0.1, 0.5, 1.0, and 3.0 mg L-1) on two common freshwater microalgae, Chlorella vulgaris and Microcystis aeruginosa, to shed light on the ecotoxicological effects of insecticides. Our findings demonstrate that M. aeruginosa is more sensitive to spinetoram than is C. vulgaris, with a concentration-dependent reduction in the growth rate observed for M. aeruginosa, whereas only the highest concentration of spinetoram adversely affected C. vulgaris. At a concentration of 0.01 mg L-1, the growth rate of M. aeruginosa unexpectedly increased beginning on day 7, indicating a potential hormetic effect. Although initial exposure to spinetoram improved the photosynthetic efficiency of both microalgae strains at all concentrations, detrimental effects became apparent at higher concentrations and with prolonged exposure. The photosynthetic efficiency of C. vulgaris recovered, in contrast to that of M. aeruginosa, which exhibited limited recovery. Spinetoram more significantly inhibited the effective quantum yield of PSII (EQY) in M. aeruginosa than in C. vulgaris. Although spinetoram is not designed to target phytoplankton, its toxicity can disrupt primary productivity and modify phytoplankton-consumer interactions via bottom-up control mechanisms. This study enhances our understanding of spinetoram's ecotoxicity and potential effects on aquatic ecosystems.

Combined effects of spinetoram and Microcystis aeruginosa on Daphnia pulex offspring: Maternal effects and multigenerational implications

The increasing occurrence of harmful algal blooms (HABs) in freshwater ecosystems detrimentally affect global water environments. Zooplankton's role in controlling HABs is hindered by contaminant exposure, necessitating research into combined stressors' ecological impacts. The response of Daphnia, a freshwater keystone species, to environmental stressors can be influenced by its maternal effects. Here, we investigated the combined effects of the world-widely used insecticide spinetoram and non-toxic HABs species Microcystis aeruginosa on the life-history traits of D. pulex offspring produced from different maternal food conditions. Four maternal groups were established, with each group receiving a specific blend of C. vulgaris (Ch) and M. aeruginosa (Ma) in varying proportions: A (100% Ch), B (90% Ch + 10% Ma), C (80% Ch + 20% Ma), and D (70% Ch + 30% Ma). The offspring from the third brood were gathered, and a 21-day experiment was carried out, involving various feeding groups (AA, AD, BA, BB, CA, CC, DA, and DD). Results demonstrated that grazing on M. aeruginosa by D. pulex induced maternal effects on their offspring, with the continuous exposure group showing an enhanced tolerance to M. aeruginosa. This study also unveiled that spinetoram could interfere with the molting of D. pulex, leading to developmental retardation. The Recovery Group exhibited an intriguing phenomenon: under the influence of both concentrations of the pesticide spinetoram (0.18, 0.35 μg L-1), D. pulex produced more offspring. This might be due to a combined strategy of allocating more energy towards reproduction in response to low-quality food and a potential hormetic effect from low concentrations of spinetoram. Assessing the interplay of combined stressors across multiple generations, encompassing harmful algal blooms (HABs) and environmental pollutants, is essential for predicting population responses to evolving environmental conditions. This understanding is vital for the protection and management of aquatic environments and ecosystems.

Synthesis and activity of spinetoram derivatives

As the second generation commercial product of spinosyns, spinetoram not only has obvious insecticidal effect on vegetable crops, but also can effectively control pests on fruits and nuts. It has been widely used in pest control. In order to find more efficient insecticides, a series of spinetoram derivatives were synthesised. The structures were confirmed by 1H NMR,13C NMR and HRMS, and the insecticidal activity of these derivatives against Plutella xylostella was determined. The insecticidal activity of derivatives against P. xylostella was better than that of the commercially available dihydrazide insecticides. Through the preliminary analysis of the structure-activity relationship of spinetoram derivatives, it was found that the introduction of electron-withdrawing substituents was more likely to produce spinosad compounds with high insecticidal activity, but the position of the substituent had little effect on the insecticidal activity, which was of great significance for the future study of spinetoram derivatization.

Field Efficacy, Sub-lethal, and Biochemical Effects of Certain Biorational Insecticides Against the New Intruder, Spodoptera frugiperda in Bani-Suef, Upper Egypt

Frequent inspections on sorghum and maize crops during seasons of 2021 and 2022 in some regions in Bani-Suef governorate, Egypt, discovered unprecedented invasions of Spodoptera frugiperda (J. E. Smith). Accordingly, our study on Beauveria bassiana and spinetoram was supporter to the Food and Agriculture Organization's tendency in adopting biorational insecticides against S. frugiperda in Egypt. Exposure toxicity of LC25 values at 48 h of B. bassiana were 2.7 × 106 and 5.2 × 106 conidia mL-1 and spinetoram were 0.019 and 0.048 mg L-1 against the 2nd and 4th instar larvae laboratory strain of S. frugiperda, respectively. Sub-lethal effects (LC25) were accomplished on biological parameters against both instar larvae. LC25 of B. bassiana reduced adult emergency (89.91 and 91.05%) more than spinetoram (75.99 and 79.49%) against the 2nd and 4th instar larvae, respectively. The 2nd instar larvae exposed to LC25 of B. bassiana suppressed female fecundity (0.00 eggs) more than spinetoram (19.74 eggs). Enzymatic activity of lipase in hemolymph, fat bodies, and mid-gut of the 4th instars at 48 h showed significant drop in B. bassiana more than spinetoram. Glutathione-S-transferase (GST) levels in hemolymph for both insecticides were equal and exceeded the control. Fat bodies and mid-gut possessed the highest GST activity in B. bassiana followed by spinetoram and the control. Residual efficacy of spinetoram exceled B. bassiana at their field rates under semi-field condition in Bani-Suef along the two seasons of maize crop against both instars. Eventually, B. bassiana alongside spinetoram could afford good control especially on early instar larvae of S. frugiperda.

Sublethal effects of spinetoram and emamectin benzoate on key demographic parameters of fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae) under laboratory conditions

Fall armyworm (FAW) Spodoptera frugiperda, is a serious invasive pest of many crops that causes huge economic losses to agricultural commodities. Insecticides are employed for the management of S. frugiperda. In this study, we investigated the impact of sublethal concentration (LC₁₀) and low lethal concentration (LC₃₀) of spinetoram and emamectin benzoate on S. frugiperda using two-sex life table method. Bioassay results revealed that emamectin benzoate exhibited more toxicity on the 3rd instar of S. frugiperda (LC₅₀ 8.35 × 10^-4 mgL^-1) than spinetoram (LC₅₀ 2.6 × 10^-2 mgL^-1) after 48 h exposure. The total longevity, adult pre-ovipositional period (APOP) and total pre-ovipositional period (TPOP) were prolonged, while pre-adult survival rate and fecundity were reduced at both concentrations of spinetoram and emamectin benzoate. Moreover, the key demographic parameters, including the intrinsic rate of increase (r), finite rate of increase (λ), and net reproductive rate (R₀), were significantly lower in insecticide treated groups as compared to untreated insects. Our findings revealed that the sublethal and low lethal concentrations of both insecticides reduce the survival and reproductive capability of S. frugiperda. These results would be useful to assess the overall effect of both insecticides on S. frugiperda and can provide important implications for the rational utilization of insecticides against S. frugiperda.

Regional differences in susceptibility to spinosyn insecticides registered for Colorado potato beetle management in Canada

The Colorado potato beetle (CPB) is the most economically important pest of Canadian potato, and if left uncontrolled, it can completely consume the crop. In the past decade, the control of CPB has relied heavily on systemic insecticides, principally the neonicotinoids thiamethoxam and clothianidin. Resistance to neonicotinoids in CPB has been well documented in the past 2 decades and mechanisms underlying the resistance better understood. In contrast, resistance to other insecticide classes, including spinosyns (spinosad and spinetoram) and anthranillic diamides (chlorantraniliprole and cyantraniliprole), have not been studied to the same degree in CPB. Spinosyns are the only insecticide certified for organic potato growers in Canada and are frequently applied as a mid-season foliar spray by conventional growers when seed treatments with neoniconitoid or diamide experience control breaks. Improved knowledge on resistance to spinosyns in CPB would allow for the development of regional management strategies. A survey of insecticide susceptibility in CPB populations from 6 potato growing regions between 2018 and 2022 observed: 1) spatial and temporal resistance trends; 2) cross-resistance; and 3) evidence of regional differences in susceptibility to spinosyns. The proportion of populations within each province considered resistant to spinosyns was, in descending order: Québec (16%) > Ontario (14%) > Manitoba (13%) > New Brunswick (9%) > Prince Edward Island (2%) > Alberta (0%). There was a significant change in CPB mortality at the diagnostic concentration (DC = LC₉₀) for spinosad and spinetoram in the 6 provinces but only for year 5 relative to the previous 4 years. Moderate cross-resistance was determined between spinosad and spinetoram with the DC mortality for all populations based on a positive and significant correlation (adjusted R² = 0.3758; P = 1.263e^-13). There was also a positive relationship observed between the number of spinosyn applications (years applied at the sampling location) and declining susceptibility to spinosad (R² = 0.0927; P < 0.002). Cross-resistance was observed between spinosyns and insecticides in the other two classes, the more significant correlation was between spinosad and tetraniliprole (R² = 0.3025; P < 0.0002). In Québec, the greater spinosad use in organic potato farms led to resistance in those CPB populations, but spinosyn resistance at conventional farms was not related to greater application of neonicotinoids and diamides. Spinosyns remain relatively effective, nevertheless growers should be concerned over the increasing cases of reduced susceptibility in conventional potato farms and resistance where organic production occurs. Resistance management should continue to encourage rotation with products from the other classes in season and between years in order to extend spinosyn use for CPB control.

Combined effects of the pesticide spinetoram and the cyanobacterium Microcystis on the water flea Daphnia pulex

Spinetoram is one of the most worldwidely used pesticides for its high insecticidal efficacy and low human toxicity. Following the large usage of spinetoram, the ecotoxicity and environmental risks to aquatic ecosystems have call for urgent study. In the present study, we investigated the combined effects of spinetoram and the harmful alga Microcystis aeruginosa in freshwater, on survival and reproduction of Daphnia pulex. Acute toxicity test of spinetoram resulted in negative effects on survival, with a 48-h LC₅₀ value of 37.71 μg L^-1. Under the long-time exposure to environmentally relevant concentrations (0.18 and 0.35 μg L^-1) of spinetoram and a low composition of Microcystis (30%) in the diet, D. pulex showed both shorter longevity and lower fecundity; the time to first brood also increased. At population level, carrying capacity was highly decreased by spinetoram and Microcystis, whereas a significant decrease of intrinsic growth rate was observed at 0.35 μg L^-1 spinetoram with 30% Microcystis as food. The present study highlighted that pesticide spinetoram had highly toxic effects on D. pulex and could reduce the tolerance of D. pulex to M. aeruginosa, causing great effects on D. pulex population in natural waterbodies.

Insecticide-mediated effects on mating success and reproductive output of Drosophila suzukii

Exposure to sublethal concentrations can have adverse effects on certain individuals, but, can also favor survival and reproduction of others. This study aimed to evaluate the effects of exposing Drosophila suzukii (Matsumura, 1931) (Diptera: Drosophilidae) adults to LC₅₀ of spinetoram and lambda-cyhalothrin and field rate of thiamethoxam on their mating, reproductive output and longevity. The LC₅₀ for lambda-cyhalothrin and for spinetoram were 7.83 and 32.91 ng a.i./cm², respectively. Thiamethoxam, in the concentrations tested, was not toxic to D. suzukii, therefore, we use the recommended concentration for strawberry, 231.25 ng a.i./cm², in the sublethal tests. Insects exposed to LC₅₀ of lambda-cyhalothrin were more likely to mate, but presented shorter copula. Sublethal exposure to thiamethoxam lead to an increase in total fecundity. Among the insecticides tested, spinetoram presented the least expressive effects. Longevity was not affected by any of the tested insecticides. Results presented in this study are relevant to D. suzukii management since the stimulatory effects shown on this pest species can collaborate to outbreaks and insecticide resistance.

Mutation (G275E) of nAChR subunit Foα6 associated with spinetoram resistance in Australian western flower thrips, Frankliniella occidentalis (Pergande)

Western flower thrips, Frankliniella occidentalis is an economically important agricultural pest. It causes damage by feeding and oviposition or indirectly by plant virus transmission. Australian F. occidentalis are resistant to many insecticides including spinosad and the related chemical spinetoram. Spinetoram resistance to F. occidentalis has been recently reported in three different Australian States, however, mechanisms conferring that resistance have not been investigated. To identify the mechanisms underlying resistance to spinetoram in F. occidentalis, we sequenced the genomic region of nicotinic acetylcholine receptor Foα6 in number of spinosad and spinetoram resistant field-populations. We found that a single nucleotide substitution (G to A) in exon 9 of the α6 subunit was present in resistant strains (G275E) and absent from susceptible. By examining field populations we consider the G275E mutation is the major cause of resistance to spinetoram in Australian F. occidentalis. We developed a real-time PCR diagnostic assay to quickly identify resistant alleles in field-populations. The method was used to test spinetoram resistant F. occidentalis collected from Australian cotton during the 2018-2019. Results show thrips tested carried the G275E mutation and the resistance allele was unusually widely distributed. The wide distribution of G275E mutation was not expected because spinetoram is not extensively used in Australian cotton. We speculate resistance may relate to extensive chemical use in crops nearby such as horticulture where thrips are often targeted for control. Our molecular diagnostic assay can provide timely and precise resistance frequency information that can support sustainable chemical use including spinetoram based IPM.

Residue behavior and dietary risk assessment of spinetoram (XDE-175-J/L) and its two metabolites in cauliflower using QuEChERS method coupled with UPLC-MS/MS

Spinetoram (XDE-175-J/L), a new spinosyn-based insecticide, is one of the most widely used bio-pesticide worldwide and its registration for direct application on cauliflower to control Plutella xylostella is currently under review in China. In this study, an accredited method for simultaneous determination of spinetoram and its two metabolites in cauliflower was established and validated using QuEChERS (quick, easy, cheap, effective, rugged, and safe) preparation coupled with ultra-liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The average recoveries using this method were ranged from 74 to 99% with relative standard deviations (RSDs) of 2.4-10.5%. The dissipation kinetics and terminal residues of spinetoram and its two metabolites in cauliflower were studied in Tianjin and Guizhou over two years under open field conditions. The dissipation experiments revealed that spinetoram was swiftly degraded in cauliflower, with the half-lives less than or equal to 4.85 days. The terminal residues of total spinetoram (sum of spinetoram and its two metabolites) detected in cauliflower samples were in the range of 0.009 mg/kg-0.337 mg/kg. Dietary risk assessment study was implemented based on the scientific data of field trials, food consumption and acceptable daily intake (ADI). The estimated long-term dietary risk probability (RQ) of total spinetoram from cauliflower was between 5.79% and 5.91%, indicating that spinetoram was associated with acceptable risk for dietary cauliflower consumption. The results would provide scientific guidance for proper usage of spinetoram in cauliflower field ecosystem.

Influence of Non-lethal Doses of Natural Insecticides Spinetoram and Azadirachtin on Helicoverpa punctigera (Native Budworm, Lepidoptera: Noctuidae) Under Laboratory Conditions

Helicoverpa punctigera (native budworm) is an important pest species in crops across Australia. From the third instar onward, this species causes severe damage to crop plants: therefore, caterpillars need to be managed at an early stage of their development. In our experiment, we raised H. punctigera on an artificial diet, which included different concentrations of the natural insecticides Spinetoram and Azadirachtin. The survival of the larvae, growth and body mass gain was recorded over 17 days. Only caterpillars raised on lowest toxin concentrations survived and molted successfully to the fifth instar, but had slower growth and body mass gain compared to the insecticide-free control group. Caterpillars fed on higher toxin concentrations never molted to the next instar or died in the first few days. To test how the toxins influence physiological conditions including metabolic rate and water loss, surviving fifth instar larvae were exposed to thermolimit respirometry: starting at 25°C following a constant increasing temperature ramping rate of 0.25°C^–1, until reaching the critical thermal maxima (CT_max). Caterpillars raised on a non-lethal dose of insecticides had higher metabolic rates and lost more water compared to the control group. Insects that have seem to consume more energy per mg tissue and have a higher water loss at high temperatures. Non-lethal concentrations of insecticides on pest insects physiology may reduce their impact on crops and may enable more targetted insecticide application.

Susceptibility of fall armyworm, Spodoptera frugiperda (J.E.Smmith), to eight insecticides in China, with special reference to lambda-cyhalothrin

Fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), is the main destructive insect pest of grain crops that occurs in all maize growing regions of the Americas. It has rapidly invaded the Southern China since January 2019. However, the current status of insecticide resistance in S. frugiperda has not been reported in China. In this study, we determined the susceptibility of eight populations of FAW to eight insecticides by an artificial diet incorporation method. The results showed that among eight insecticides, emamectin benzoate, spinetoram, chlorantraniliprole, chlorfenapyr, and lufenuron showed higher toxicity to this pest, while lambda-cyhalothrin and azadirachtin exhibited lower toxicity. Susceptibility of S. frugiperda to indoxacarb was significantly different (10.0-fold for LC₅₀) across the various geographic populations. To investigate the biochemical mechanism of FAW to lambda-cyhalothrin, we performed the synergism tests and the results showed that piperonyl butoxide (PBO) and triphenyl phosphate (TPP) produced a high synergism of lambda-cyhalothrin effects in the two field populations. Sequencing of the gene encoding the acetylcholinesterase (AChE) gene in the two field populations identified two amino acid mutations, all of which have been shown previously to confer resistance to organophosphates (OPs) in several arthropod species. The results of this study provided valuable information for choosing alternative insecticides and for insecticide resistance management of S. frugiperda.

Interaction of HaNPVs with two novel insecticides against Helicoverpa armigera Hubner (Noctuidae: Lepidoptera)

Nucleopolyhedrosis viruses can be utilized for effective management of agriculture pests. Their efficacy can be increased if they are mixed with certain insecticides. In the current study, HaNPV was mixed with two insecticides: spinetoram and emamectin benzoate in various combinations and applied to larvae of H. armigera in laboratory conditions. There were a total of 15 combinations of HaNPV with each of the two insecticides in addition to five doses of HaNPV and three doses of insecticides alone. The synergistic and antagonistic effects of combinations were explored. The results revealed that there was synergistic effect of HaNPV @ 0.5 × 10⁹ PIB/ml × Spinetoram @ 40, 20, 10 ml/100 L of water. In case of emamectin benzoate, synergistic effects were recorded at 1 × 10⁹ PIB/ml HaNPV × emamectin benzoate @ 100 ml/100 L of water. However, 0.5 × 10⁹ PIB/ml HaNPV has synergistic effects with all three doses of emamectin benzoate. The results suggested that HaNPV can be used in combination with spinetoram and emamectin benzoate for the management of resistant population of H. armigera.

Development and validation of a new method for the simultaneous determination of spinetoram J and L in honey from different botanical origins employing solid-phase extraction with a polymeric sorbent and liquid chromatography coupled to quadrupole time-of-flight mass spectrometry

The objective of this study was to propose a novel method to determine residues of the bio-insecticide spinetoram, which is a mixture of two components (spinetoram J and L), in honey from multifloral, rosemary and heather botanical origins; liquid chromatography coupled to quadrupole time-of-flight mass spectrometry was the technique employed. An efficient sample treatment (recoveries between 82% and 95%) involving a solid-phase extraction with a polymeric sorbent has been recommended, and no matrix effect was observed. Chromatographic analysis (4 min) was performed in reverse phase mode by using a fused-core column (Kinetex® EVO C₁₈) with acetonitrile and ammonium formate as the mobile phase components, which was applied in isocratic elution mode. Method was validated according to the current European legislation. Not only was it selective, but it also displayed a wide linear range, good precision (relative standard deviation values lower than 9%) and sensitivity (low limits of detection (spinetoram J, 0.1-0.3 μg/kg; spinetoram L, 0.1-0.2 μg/kg) and quantification (spinetoram J, 0.3-1.2 μg/kg; spinetoram L, 0.4-0.7 μg/kg)). Several honey samples were analyzed with this method and no spinetoram residues were found above the limits of detection.

Effects of spinetoram on the developmental toxicity and immunotoxicity of zebrafish

Our study investigated the effects of spinetoram on the developmental toxicity and immunotoxicity of zebrafish. 10 h post-fertilization (hpf) zebrafish embryos were exposed to several concentrations of spinetoram (0, 5.0 mg/L, 7.5 mg/L, 10 mg/L) for up to 96 hpf, and their mortality, heart rate, number of innate and adaptive immune cells, oxidative stress, apoptosis and gene expression were detected. Studies indicated that the spinetoram exposed zebrafish embryos showed yolk sac edema, slow growth, decreased heart rate, decreased number of immune cells, delayed thymic development and cell apoptosis. In addition, there were also significant changes in oxidative stress related indicators in zebrafish, the content of ROS and MDA and the activity of CAT and SOD increased with the increase of spinetoram concentration. Moreover, we detected the expression of TLR4 related genes including TLR4, MYD88 and NF-κB p65 which were significantly up-regulated in the treated groups. Meanwhile, we also found that pro-inflammatory factors IL-6, IL-8, IFN-γ and CXCL-c1c were up-regulated, but anti-inflammatory factor IL-10 was down-regulated in the treated groups. Briefly, our results show that spinetoram induces the developmental toxicity and immunotoxicity of zebrafish to a certain extent, providing basis for the further research on the molecular mechanism of spinetoram exposure to aquatic ecosystems.

Spinetoram confers its cytotoxic effects by inducing AMPK/mTOR-mediated autophagy and oxidative DNA damage

Spinetoram is one of the most extensively used bio-pesticide in the world. The effects of pesticide in human health are mainly caused by its residue in food. The liver is the direct target of pesticides exposure, however the study of cytotoxicity on human liver cells caused by spinetoram remains unclear. The aim of the present study was to evaluate the cytotoxic effects of the spinetoram in human liver cells in vitro. We demonstrated that spinetoram could inhibit the proliferation of human liver HepG2 cells and induce the oxidative DNA damage. Intracellular biochemical assay indicated that decrease of mitochondrial membrane potential, LC3-II conversion, accumulation of Beclin-1, degradation of p62 and the changes in the phosphorylation of AMPK, mTOR are contributed to the toxic effects of Spinetoram on HepG2 cells. These results showed that the cytotoxicity of spinetoram may be associated with the activity of AMPK/mTOR-mediated autophagy pathway. Meanwhile, the generation of 8-oxodG caused by the spinetoram suggested it has a potential genotoxic effect on human liver cells. We conclude that spinetoram has a significant cytotoxic effect by inducing AMPK/mTOR-mediated autophagy and oxidative DNA damage. This study would provide a theoretical basis for understanding its mechanisms of toxicity and supply an indication for recognizing the safety of spinetoram to human beings.

Evaluation of an 11.2% spinetoram topical spot-on solution for the control of experimental and natural flea (Ctenocephalides felis) infestations on cats in Europe

Spinetoram is the newest member the spinosyn-class of natural products to be commercialized for flea control on cats in the United States under the tradename Cheristin^® for cats. This report describes results from two laboratory studies and a multi-center clinical field trial designed to confirm the efficacy of a topical spot-on solution containing spinetoram (11.2% w/w, 130 mg/mL) against European strains of the cat flea, Ctenocephalides felis. In the laboratory studies, cats were allocated to one of two treatment groups of eight animals each: negative control (mineral oil) or spinetoram, both applied as a topical spot-on at the base of the skull on Day 0. Cats were infested with ∼100 newly emerged, unfed adult fleas on Days -2 or -1, 7, 14, 21, 28 and 35. To calculate efficacy, fleas were counted and removed 48 h after treatment, and 48 h after each subsequent infestation through week 5. Spinetoram treatments provided 100% efficacy through at least day 16 and ≥ 97% efficacy (arithmetic mean) for one month. For the field trial, 23 clinics from Northern and Southern Europe participated in the study that compared the effectiveness and safety of spinetoram and fipronil/(S)-methoprene treatments over a period of two months. There were 258 and 248 evaluable efficacy cases for month 1 and month 2, respectively, with 300 total evaluable cases for safety. Treatments were administered on Day 0 and again on Day 30 (±3 days). The effectiveness of treatments was calculated based on reduction in live flea counts on Days 14, 30, 44 and 60 (±3 days) relative to flea counts obtained on Day 0. Efficacy (geometric mean percent flea reduction) on Days 14, 30, 44 and 60 was 97.0%, 95.0%, 99.3% and 99.1% for spinetoram, respectively, and 86.1%, 80.9%, 92.4% and 92.3% for fipronil/(S)-methoprene, respectively. Spinetoram was deemed non-inferior at all intervals and superior to fipronil/(S)-methoprene at Days 30 and 60. Clinical signs of flea allergy dermatitis (FAD) were markedly improved following spinetoram treatment, as demonstrated through statistically significant reductions in severity of FAD scores for most of the clinical signs when compared to fipronil/(S)-methoprene treatment. There was a lower overall adverse event incidence rate for spinetoram (5.1%) versus fipronil/(S)-methoprene treatment (11.5%).

Effectiveness and residual speed of flea kill of a novel spot on formulation of spinetoram (Cheristin®) for cats

Background

A spot-on spinetoram formulation (Cheristin^®) was developed to eliminate fleas from infested cats. This paper describes three spinetoram studies: two for registration (Studies 1 and 2), and one comparing residual speed of kill (SOK) with topically applied fipronil/(S)-methoprene (FSM) and imidacloprid (Study 3).

Methods

Cats were randomized to treatment based on flea counts from infestations placed within 2 weeks prior to treatment. In Studies 1 and 2, groups were untreated control and spinetoram; in Study 3, groups were untreated control, spinetoram, FSM and imidacloprid, all applied per label on Day 0. Cats were infested the day before treatment. In Studies 1 and 2, counts were completed 48 h post-treatment and after weekly challenges through 5 weeks. In Study 3, infestations were completed weekly through Day 28, with counts 1, 4, 8 and 12 h after treatment or post-infestation (PI). Efficacy was determined on geometric mean flea count reductions compared with controls, and in Study 3 mean flea counts in spinetoram-groups were compared with those in FSM and imidacloprid groups.

Results

In Studies 1 and 2, spinetoram effectiveness was 100% against existing infestations, and at least 96% through Day 37. In Study 3 mean counts were not significantly different from controls in any group until 8 h post-treatment when imidacloprid counts were significantly lower than spinetoram counts, which were in turn significantly lower than FSM counts (P < 0.05). At 1 h PI spinetoram-group counts were significantly lower (P < 0.05) than counts in: controls, all days; imidacloprid, Days 7, 14, and 28; FSM, Days 14 and 28. At 4 h PI, spinetoram mean counts were significantly lower (P < 0.05) relative to: controls, all days; imidacloprid, Days 7, 14 and 21; FSM, Days 7, 14, 21 and 28 (P < 0.05). On multiple occasions, at 8 and 12 h PI, mean counts were significantly lower (P < 0.05) for spinetoram than for imidacloprid and FSM; at no point were FSM or imidacloprid significantly more effective than spinetoram against new infestations. All treatments were well tolerated.

Conclusions

Spinetoram was highly effective for at least 1 month post-treatment and provided more rapid month-long residual SOK than FSM or imidacloprid.

Initial evaluations of the effectiveness of spinetoram as a long-acting, oral systemic pulicide for controlling cat flea (Ctenocephalides felis) infestations on dogs

Spinetoram is a semi-synthetic, spinosyn class natural product derived from fermentation by the actinomycete, Saccharopolyspora spinosa. Based on LD₅₀ (50% lethal dose) values against adult cat fleas (Ctenocephalides felis) using an in vitro contact assay, spinetoram was approximately 4-fold more potent than spinosad. Subsequently, two parallel-arm, randomized block design laboratory studies were conducted to evaluate the effectiveness of orally administered spinetoram against experimental C. felis infestations on dogs, when administered as a single dose or multiple doses over a 6-12h interval. In the first study, 16 mixed-breed dogs were allocated to two treatment groups of eight dogs each, based on pre-treatment flea retention rates: negative (placebo) control; and a single dose of spinetoram at 30mg/kg. In the second study, 32 mixed- and pure-breed dogs were allocated to four treatments groups of eight dogs each, based on pre-treatment flea retention rates: negative (placebo) control; a single dose of 60mg/kg; three sequential 20mg/kg oral doses evenly administered over a 6h period; and three sequential 20mg/kg oral doses evenly administered over a 12h period. In both studies, treatments were administered to dogs in a fed state in order to enhance absorption of spinetoram. Therapeutic efficacy was assessed 24h after treatment and persistent efficacy was assessed 48h after each subsequent flea infestation. The duration of effectiveness was assessed at approximate weekly intervals beginning on Day 5 through Day 56 in the first study, or through Day 105 in the second study. In both studies, treatment efficacy was ≥99% (geometric means) through 44 d, with ≥99% efficacy continuing through 72 d for all three treatments in the second study. Efficacy remained ≥90% for at least 8 weeks with a single 30mg/kg dose; through 13 weeks with three sequential 20mg/kg doses; and through 15 weeks with a single 60mg/kg dose. For all time points and in both studies, spinetoram-treated groups had significantly fewer live fleas relative to their respective negative control group (p<0.05). The pharmacokinetic profile in dogs revealed that the mean plasma concentration of spinetoram required for effectiveness against fleas was maintained for at least 3 months regardless of whether the 60mg/kg total body dose was administered as a single bolus or in three sequential 20mg/kg doses administered over a 6-12h period of time. The results of preliminary in vitro and in vivo studies demonstrate that orally administered spinetoram was well tolerated, and provides long lasting effectiveness against C. felis infestations on dogs.

Sublethal effects of spinetoram on the two-spotted spider mite, Tetranychus urticae (Acari: Tetranychidae)

The two-spotted spider mite Tetranychus urticae is a serious pest of many agricultural crops and ornamental plants. The sublethal effects of a new chemical, spinetoram, on T. urticae were investigated by treating adult females and eggs with LC10 and LC20 in the laboratory. The data were assessed based on age-stage, two-sex life table analysis. The results showed that T. urticae developmental time from egg to adult was reduced and that fecundity was increased by treatment with LC10 and LC20 of spinetoram. The LC10 and LC20 of spinetoram also increased the intrinsic and finite rate of increase and the net reproductive rate and reduced the mean generation time, egg duration, and larval duration whether eggs or adult females were treated. These laboratory results suggest that sublethal or lethal doses of spinetoram may cause outbreaks of T. urticae.

Degradation kinetics of the insecticide spinetoram in a rice field ecosystem

The fate of spinetoram was studied in a rice field ecosystem, and an efficient method for the determination of spinetoram (XDE-175-J and XDE-175-L) in soil, rice straw, paddy water, husk and brown rice was developed. Spinetoram residues were extracted from samples with a salting out extraction procedure. The extracts were diluted with 0.10% formic acid in water and analysed with liquid chromatography tandem mass spectrometry (LC-MS/MS) on a Waters Acquity BEH C18 column. The calibration curve was linear in the range 0.125-100 μg L(-1) and r>0.999. The average recovery was 82.9-89.0% from soil, 78.5-92.1% from rice straw, 93.6-100.3% from paddy water, 79.1-87.9% from brown rice and 72.7-82.9% from husk. The relative standard deviation (RSD) was less than 10%. These results are all within the accepted range for pesticide residue determination. The field test results showed that spinetoram degradation in paddy water, soil and rice straw coincided with C=0.0132e(-1.9685t), C=0.0308e(-0.1018t) and C=0.8530e(-0.6223t), respectively. The half-lives of spinetoram in paddy water, soil and rice straw were 0.35, 6.8 and 1.1 d, respectively. The final residue level was lower than the maximum residue limit (MRL) of 0.05 mg kg(-1) for spinetoram in rice with a harvest interval of 7d. A dosage of 450 mL ha(-1) was recommended, which can be considered safe for human beings and animals. The results of this study will contribute to establishing the scientific basis of the dosage of spinetoram for agricultural fields.