Pesticide use negatively affects bumble bees across European landscapes

Sustainable agriculture requires balancing crop yields with the effects of pesticides on non-target organisms, such as bees and other crop pollinators. Field studies demonstrated that agricultural use of neonicotinoid insecticides can negatively affect wild bee species1,2, leading to restrictions on these compounds3. However, besides neonicotinoids, field-based evidence of the effects of landscape pesticide exposure on wild bees is lacking. Bees encounter many pesticides in agricultural landscapes4-9 and the effects of this landscape exposure on colony growth and development of any bee species remains unknown. Here we show that the many pesticides found in bumble bee-collected pollen are associated with reduced colony performance during crop bloom, especially in simplified landscapes with intensive agricultural practices. Our results from 316 Bombus terrestris colonies at 106 agricultural sites across eight European countries confirm that the regulatory system fails to sufficiently prevent pesticide-related impacts on non-target organisms, even for a eusocial pollinator species in which colony size may buffer against such impacts10,11. These findings support the need for postapproval monitoring of both pesticide exposure and effects to confirm that the regulatory process is sufficiently protective in limiting the collateral environmental damage of agricultural pesticide use.

Evaluation of acetamiprid and azoxystrobin residues and their hormonal disrupting effects on male rats using liquid chromatography-tandem mass spectrometry

Endocrine-disrupting compounds as pesticides affect the hormonal balance, and this can result in several diseases. Therefore, the analysis of representative hormones with acetamiprid (AC) and azoxystrobin (AZ) was a good strategy for the investigation of the endocrine-disrupting activity of pesticides. Hence, a sensitive and rapid analytical method using liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed. The method was validated for the analysis of AC, AZ, estriol, estrone, progesterone, and testosterone in the serum, testis, and liver of rats. The correlation between the residues of pesticides and the disturbance of the endocrine system was evaluated. The different mass parameters, mobile phase types, analytical columns, injection volumes, and extraction solvents were compared to get the lowest limit of detection of the studied compounds. The detection limits of AC, AZ, estriol, estrone, progesterone, and testosterone were 0.05, 0.05, 1.0, 10, and 1.0 ng/ml, respectively. The method developed was applied to evaluate the changes in these hormones induced by the duration of exposure to AC and AZ in rat testis and serum. The hormones level in rat serum and testis had a significant decrease as they were oral gavage treated with different high concentrations of studied pesticides. Both pesticides were distributed in the body of rats by the multi-compartment model (liver, testis, and serum).

An integrated approach, based on mass spectrometry, for the assessment of imidacloprid metabolism and penetration into mouse brain and fetus after oral treatment

Imidacloprid is an insecticide belonging to neonicotinoids, a class of agonists of the nicotinic acetylcholine receptors that shows higher affinities in insects compared to mammals. However, recent evidence show that neonicotinoids can bind to the mammalian receptors, leading to detrimental responses in cultured neurons. We developed an analytical strategy which uses mass spectrometry with multiple reaction monitoring (targeted approach) and high-resolution acquisitions (untargeted approach), which were applied to quantify imidacloprid and to identify its metabolites in biological tissues after oral treatments of mice. Mouse dams were treated with doses from 0.118 mg/kg bw day up to 41 mg/kg day between gestational days 6-9. Results showed quantifiable levels of imidacloprid in plasma (from 30.48 to 5705 ng/mL) and brain (from 20.48 to 5852 ng/g) of treated mice, proving the passage through the mammalian blood-brain barrier with a high correspondence between doses and measured concentrations. Untargeted analyses allowed the identification of eight metabolites including imidacloprid-olefin, hydroxy-imidacloprid dihydroxy-imidacloprid, imidacloprid-nitrosimine, desnitro-imidacloprid, 6-chloronicotinic acid, 5-(methylsulfanyl)pyridine-2-carboxylic acid and N-imidazolidin-2-ylidenenitramide in plasma and brain. Moreover, analysis of embryonic tissues after oral treatment of mouse dams showed detectable levels of imidacloprid (816.6 ng/g after a dose of 4.1 mg/Kg bw day and 5646 ng/g after a dose of 41 mg/Kg bw day) and its metabolites, proving the permeability of the placenta barrier. Although many studies have been reported on the neurotoxicity of neonicotinoids, our study paves the way for a risk assessment in neurodevelopmental toxicity, demostrating the capability of imidacloprid and its metabolites to pass the biological barriers.

Simultaneous quantification of imidacloprid and its metabolites in tissues of mice upon chronic low-dose administration of imidacloprid

This study aimed to (i) develop a sensitive method for simultaneous detection and quantification of imidacloprid (IMI) and seven of its metabolites in tissue specimens, and to (ii) determine the biodistribution of the IMI compounds in tissues of C57BL/6J male mice; after exposure to 0.6 mg/kg bw/day of IMI (10% of no observable adverse effect level of IMI) through a powdered diet for 24 weeks. We successfully developed a method which was accurate (recoveries were ≥ 70% for most compounds), sensitive (LODs ≤ 0.47 ng/mL and LOQs ≤ 1.43 ng/mL were recorded for all detected compounds, R2 ≥ 0.99) and precise (RSDs ≤ 20%) for routine analysis of IMI and seven of its metabolites in blood and various tissue matrices. After bio-distributional analysis, IMI and five of its metabolites were detected in mice. Brain, testis, lung, kidney, inguinal white adipose tissue and gonadal white adipose tissue mainly accumulated IMI, blood and mesenteric white adipose tissue mainly accumulated IMI-olefin; liver mainly accumulated desnitro-IMI; pancreas predominately accumulated 4-hydroxy-IMI. The desnitro-dehydro-IMI and the desnitro-IMI metabolites recorded tissue-blood concentration ratios ≥ 1.0 for testis, brain, lung and kidney. The cumulative levels of the six detected IMI compounds (Σ6 IMI compounds) were found in the decreasing order: blood > testis > brain > kidney > lung > iWAT > gWAT > mWAT > liver > pancreas. Altogether, this study provided essential data needed for effective mechanistic elucidation of compound-specific adverse outcomes associated with chronic exposures to IMI in mammalian species.

Effect of wall type, delayed mortality and mosquito age on the residual efficacy of a clothianidin-based indoor residual spray formulation (SumiShield™ 50WG) in southern Mozambique

Indoor residual spraying (IRS) is one of the main malaria vector control strategies in Mozambique alongside the distribution of insecticide treated nets. As part of the national insecticide resistance management strategy, Mozambique introduced SumiShield™ 50WG, a third generation IRS product, in 2018. Its residual efficacy was assessed in southern Mozambique during the 2018-2019 malaria season. Using a susceptible Anopheles arabiensis strain, residual efficacy was assessed on two different wall surfaces, cement and mud-plastered walls, using standard WHO (World Health Organization) cone bioassay tests at three different heights. Female mosquitoes of two age groups (2-5 and 13-26 day old) were exposed for 30 minutes, after which mortality was observed 24h, 48h, 72h, and 96h and 120h post-exposure to assess (delayed) mortality. Lethal times (LT) 90, LT50 and LT10 were estimated using Bayesian models. Mortality 24h post exposure was consistently below 80%, the current WHO threshold value for effective IRS, in both young and old mosquitoes, regardless of wall surface type. Considering delayed mortality, residual efficacies (mosquito mortality equal or greater than 80%) ranged from 1.5 to ≥12.5 months, with the duration depending on mortality time post exposure, wall type and mosquito age. Looking at mortality 72h after exposure, residual efficacy was between 6.5 and 9.5 months, depending on wall type and mosquito age. The LT50 and LT10 (i.e. 90% of the mosquitoes survive exposure to the insecticides) values were consistently higher for older mosquitoes (except for LT10 values for 48h and 72h post-exposure mortality) and ranged from 0.9 to 5.8 months and 0.2 to 7.8 months for LT50 and LT10, respectively. The present study highlights the need for assessing mosquito mortality beyond the currently recommended 24h post exposure. Failure to do so may lead to underestimation of the residual efficacy of IRS products, as delayed mortality will lead to a further reduction in mosquito vector populations and potentially negatively impact disease transmission. Monitoring residual efficacy on relevant wall surfaces, including old mosquitoes that are ultimately responsible for malaria transmission, and assessing delayed mortalities are critical to provide accurate and actionable data to guide vector control programmes.

Combined hepatotoxicity of imidacloprid and microplastics in adult zebrafish: Endpoints at gene transcription

Microplastics (MPs) and pesticides are two kinds of ubiquitous pollutants that can pose a health risk to aquatic organisms. However, researches about the combined effects of MPs and pesticides are very limited. A simple combined exposure model was established in this study, adult zebrafish were exposed to 100 μg/L imidacloprid (IMI), 20 μg/L polystyrene microplastics (PS), and a combination of PS and IMI (PS + IMI) for 21 days. The results demonstrated that exposure to PS and IMI inhibited the growth of zebrafish and altered the levels of glycolipid metabolism and oxidative stress-related biochemical parameters. While gene expression analysis revealed that, compared with PS or IMI treatment group, combined exposure caused a greater change in gene expression levels involving the process of glycolipid metabolism (Gk, Hk1, Aco, PPar-α, Cpt1, Acc, Fas, PPar-γ, Apo) and inflammatory response (IL-1β, IL-6, IL-8, TNF-α, IL-10). The results demonstrated that even combined exposure of low concentrations of PS and IMI could cause more severe hepatotoxicity in zebrafish, especially in terms of gene transcription. And more combined toxicity studies are essential for MPs and pesticides risk assessment.

Effects of low-level imidacloprid oral exposure on cholinesterase activity, oxidative stress responses, and primary DNA damage in the blood and brain of male Wistar rats

Imidacloprid is a neonicotinoid insecticide that acts selectively as an agonist on insect nicotinic acetylcholine receptors. It is used for crop protection worldwide, as well as for non-agricultural uses. Imidacloprid systemic accumulation in food is an important source of imidacloprid exposure. Due to the undisputable need for investigations of imidacloprid toxicity in non-target species, we evaluated the effects of a 28-day oral exposure to low doses of imidacloprid (0.06 mg/kg b. w./day, 0.8 mg/kg b. w./day and 2.25 mg/kg b. w./day) on cholinesterase activity, oxidative stress responses and primary DNA damage in the blood and brain tissue of male Wistar rats. Exposure to imidacloprid did not cause significant changes in total cholinesterase, acetylcholinesterase and butyrylcholinesterase activities in plasma and brain tissue. Reactive oxygen species levels and lipid peroxidation increased significantly in the plasma of rats treated with the lowest dose of imidacloprid. Activities of glutathione-peroxidase in plasma and brain and superoxide dismutase in erythrocytes increased significantly at the highest applied dose. High performance liquid chromatography with UV diode array detector revealed the presence of imidacloprid in the plasma of all the treated animals and in the brain of the animals treated with the two higher doses. The alkaline comet assay results showed significant peripheral blood leukocyte damage at the lowest dose of imidacloprid and dose-dependent brain cell DNA damage. Oral 28-day exposure to low doses of imidacloprid in rats resulted in detectable levels of imidacloprid in plasma and brain tissue that directly induced DNA damage, particularly in brain tissue, with slight changes in plasma oxidative stress parameters.

Functional alterations by a subgroup of neonicotinoid pesticides in human dopaminergic neurons

Neonicotinoid pesticides, originally developed to target the insect nervous system, have been reported to interact with human receptors and to activate rodent neurons. Therefore, we evaluated in how far these compounds may trigger signaling in human neurons, and thus, affect the human adult or developing nervous system. We used SH-SY5Y neuroblastoma cells as established model of nicotinic acetylcholine receptor (nAChR) signaling. In parallel, we profiled dopaminergic neurons, generated from LUHMES neuronal precursor cells, as novel system to study nAChR activation in human post-mitotic neurons. Changes of the free intracellular Ca²⁺ concentration ([Ca²⁺]_i) were used as readout, and key findings were confirmed by patch clamp recordings. Nicotine triggered typical neuronal signaling responses that were blocked by antagonists, such as tubocurarine and mecamylamine. Pharmacological approaches suggested a functional expression of α7 and non-α7 nAChRs on LUHMES cells. In this novel test system, the neonicotinoids acetamiprid, imidacloprid, clothianidin and thiacloprid, but not thiamethoxam and dinotefuran, triggered [Ca²⁺]_i signaling at 10-100 µM. Strong synergy of the active neonicotinoids (at low micromolar concentrations) with the α7 nAChR-positive allosteric modulator PNU-120596 was observed in LUHMES and SH-SY5Y cells, and specific antagonists fully inhibited such signaling. To provide a third line of evidence for neonicotinoid signaling via nAChR, we studied cross-desensitization: pretreatment of LUHMES and SH-SY5Y cells with active neonicotinoids (at 1-10 µM) blunted the signaling response of nicotine. The pesticides (at 3-30 µM) also blunted the response to the non-α7 agonist ABT 594 in LUHMES cells. These data show that human neuronal cells are functionally affected by low micromolar concentrations of several neonicotinoids. An effect of such signals on nervous system development is a toxicological concern.

Comparing response of buff-tailed bumblebees and red mason bees to application of a thiacloprid-prochloraz mixture under semi-field conditions

Recent studies have reported interspecific differences in how bee species respond to various stressors. Evaluating the exposure and responses of different bee species to plant protection products is considered an essential part of their risk assessment. This study was conducted to assess the impacts of thiacloprid-prochloraz mixture on buff-tailed bumblebees (Bombus terrestris) and red mason bees (Osmia bicornis) in a worst-case scenario under semi-field conditions. Bumblebee colonies or solitary bee trap nests were confined in tunnels with flowering oilseed rape. The recommended maximum application rates of 72 g thiacloprid/ha and 675 g prochloraz/ha were applied as a tank mixture during bee flight in full flowering oilseed rape. Several parameters such as flight and foraging activity, population parameters, and exposure level were investigated. Our results show adverse effects of the combination of thiacloprid and prochloraz on the reproductive performance of red mason bees. The number of cocoons produced by O. bicornis was significantly reduced in the treatment compared to the control group. Regarding bumblebees, we found no effects of the thiacloprid-prochloraz mixture on any observed parameters of colony development. The maximum detected concentrations of both active substances three days after application were higher in O. bicornis pollen mass compared to B. terrestris stored pollen. We conclude that this worst-case scenario of thiacloprid-prochloraz exposure poses a high risk to solitary bees and thus the use of such mixture should be restricted.

Long-term effects of neonicotinoid insecticides on ants

The widespread prophylactic usage of neonicotinoid insecticides has a clear impact on non-target organisms. However, the possible effects of long-term exposure on soil-dwelling organisms are still poorly understood especially for social insects with long-living queens. Here, we show that effects of chronic exposure to the neonicotinoid thiamethoxam on black garden ant colonies, Lasius niger, become visible before the second overwintering. Queens and workers differed in the residue-ratio of thiamethoxam to its metabolite clothianidin, suggesting that queens may have a superior detoxification system. Even though thiamethoxam did not affect queen mortality, neonicotinoid-exposed colonies showed a reduced number of workers and larvae indicating a trade-off between detoxification and fertility. Since colony size is a key for fitness, our data suggest long-term impacts of neonicotinoids on these organisms. This should be accounted for in future environmental and ecological risk assessments of neonicotinoid applications to prevent irreparable damages to ecosystems.

Effects of the DAG analogue 1,2-dioctanoyl-sn-glycerol (DiC8) on nicotine- and clothianidin-evoked currents through α-bungarotoxin-insensitive nicotinic acetylcholine receptors expressed on cockroach neurosecretory cells

We previously demonstrated that the cockroach α-bungarotoxin-sensitive nicotinic acetylcholine receptors, nAChR1 and nAChR2 subtypes, are differently sensitive to intracellular calcium pathways. Here, using whole cell patch-clamp recordings, we studied the effects of the diacylglycerol (DAG) analogue 1,2-dioctanoyl-sn-glycerol (DiC8) on nicotine- and clothianidin-evoked currents under an α-bungarotoxin treatment. Our results demonstrated that DiC8 reduced nicotine and clothianidin evoked currents. 10 μM DiC8 suppressed the increase in nicotine-induced currents which was brought about by application of 5 mM caffeine or 9 mM Ca²⁺, whereas DiC8 did not affect the decrease in nicotine-induced currents induced by BAPTA. Similarly, bath application of caffeine or 9 mM Ca²⁺ did not change the clothianidin effects, and the amplitude of clothianidin-induced currents was not affected. However, co-application of both 10 μM DiC8 with 9 mM Ca²⁺, caffeine or BAPTA reduced clothianidin current amplitudes. We conclude that nicotine and clothianidin differently modulate nAChR1 and nAChR2 subtypes under DiC8 treatment, and that nicotine activates nAChR1, whereas clothianidin activates both nAChR1 and nAChR2 subtypes.

Efficacy of orally toxic sugar baits against contact-insecticide resistant culex quinquefasciatus

In recent years, attractive toxic sugar bait has been used in the mosquito control in nature, and achieved good control effects. However, the current researches about toxic sugar bait did not focus on whether the wild mosquito population used for control is resistant or not. The purpose of this study was to evaluate the effectiveness of the toxic sugar bait against mosquito resistant populations to test the effects of bait on the control of mosquitoes with different levels of resistance. Boric acid, dinotefuran and deltamethrin were separately formulated into toxic sugar bait to test their anti-mosquito activity against Culex quinquefasciatus. Using the sugar baits formulated with boric acid and dinotefuran, the mortality of Cx. quinquefasciatus resistant populations was significantly higher than that of sensitive populations at the same concentration. Conversely, with the use of sugar baits formulated with deltamethrin, the mortality of Cx. quinquefasciatus resistant populations was significantly lower than that of sensitive populations at the same concentration. The results suggested that toxic sugar baits might have a good application prospect in high resistant mosquito management.

Quantitative elucidation of maternal-to-fetal transfer of neonicotinoid pesticide clothianidin and its metabolites in mice

Neonicotinoids (NNs), a widely used class of systemic pesticides, are regarded as exhibiting selective toxicity in insects. However, NNs are suspected of exerting adverse effects on mammals as well, including humans. To date, only adult male animal models have been subjected to general toxicity studies of NNs; fetuses have yet to be considered in this context. Here, we focused on the NN clothianidin (CLO) for the first quantitative LC-MS/MS analysis of maternal-to-fetal transfer and residual property of once-daily (single or multiple days), orally administered CLO and its metabolites in mice. The results revealed the presence of CLO and its five metabolites at approximately the same respective blood levels in both dams and fetuses. In the dams, CLO showed a peak value 1 h after administration, after which levels rapidly decreased at 3 and 6 h. In the fetuses of each group, levels of CLO were almost the same as those observed in the corresponding dams. The present results clearly demonstrated rapid passage of CLO through the placental barrier. However, metabolite-dependent differences observed in blood pharmacokinetics and residual levels. This is the first quantitative demonstration of the presence of CLO and its metabolites in fetal mouse blood.

Terrestrial adult stages of freshwater insects are sensitive to insecticides

Terrestrial adult stages of freshwater insects may be exposed to pesticides by wind drift, over-spray, contact or feeding. However, studies addressing insecticide effects on freshwater invertebrates focus primarily on the impact of pesticides reaching the streams and potentially harming the aquatic juvenile stages. This is also reflected in the current risk assessment procedures, which do not include testing of adult freshwater insects. In order to assess the potential impact of insecticides on adult stages of freshwater insects, we exposed six common species to the insecticides Karate (lambda-cyhalothrin) and Confidor (imidacloprid). Dose-response relations were established, and LD₅₀ estimates were compared to those of the honey bee, Apis mellifera L. (Hymenoptera: Apidae), which is the standard terrestrial test insect when pesticides are evaluated prior to commercial release. Generally, the tested species were more sensitive to the studied insecticides than the honey bee. In order to examine whether the sensitivity of adult stages of freshwater insects corresponds with the sensitivity of the juvenile stages of the same species, the ranking of the two life stages with respect to the toxicity of Karate was compared, revealing some correspondence, but also some dissimilarities. Our results strongly indicate that terrestrial adult stages of aquatic insects are not adequately protected by current risk assessment procedures.

Rhizobacterial treatments of tall fescue and bermudagrass increases tolerance to damage from white grubs

BACKGROUND

Inoculation of hybrid bermudagrass with plant growth-promoting rhizobacteria (PGPR) can increase plant growth and influence relationships with above-ground herbivores like fall armyworms. However, few experiments have evaluated PGPR applications relative to root herbivory. Root-feeding white grubs cause severe damage to grasses, especially in tall fescue pastures, golf courses, and lawns. Since bacterial inoculants enhance root growth, the goal of this study was to determine if the inoculation of hybrid bermudagrass by rhizobacteria can increase the tolerance of tall fescue and hybrid bermudagrass to damage from white grub feeding, and if PGPR are compatible with neonicotinoid insecticides commonly used for white grub control.

RESULTS

In trials with tall fescue and hybrid bermudagrass, grasses were treated with the PGPR strain mixture Blend 20 or nitrogen or left non-treated and were then infested with Japanese beetle grubs. Grasses treated with PGPR and nitrogen fertilizer produced significantly more top growth than the non-treated grub-infested controls. Tall fescue and hybrid bermudagrass treated with Blend 20 produced root mass similar to or greater than nitrogen fertilized grasses. Both grasses treated with Blend 20 had greater root mass than non-treated infested grass. No treatment negatively impacted grub survival, and weight gains of grubs were similar for all treatments. Bacterial strains were typically compatible with insecticides used to control white grubs.

CONCLUSION

PGPR and nitrogen fertilization stimulate root growth resulting in tolerance of tall fescue and hybrid bermudagrass to white grub infestation. PGPR, acting as biostimulants to increase root biomass on grasses, may have utility for IPM of root herbivores. © 2019 Society of Chemical Industry.

Neonicotinoid seed treatments of soybean provide negligible benefits to US farmers

Neonicotinoids are the most widely used insecticides worldwide and are typically deployed as seed treatments (hereafter NST) in many grain and oilseed crops, including soybeans. However, there is a surprising dearth of information regarding NST effectiveness in increasing soybean seed yield, and most published data suggest weak, or inconsistent yield benefit. The US is the key soybean-producing nation worldwide and this work includes soybean yield data from 194 randomized and replicated field studies conducted specifically to evaluate the effect of NSTs on soybean seed yield at sites within 14 states from 2006 through 2017. Here we show that across the principal soybean-growing region of the country, there are negligible and management-specific yield benefits attributed to NSTs. Across the entire region, the maximum observed yield benefits due to fungicide (FST = fungicide seed treatment) + neonicotinoid use (FST + NST) reached 0.13 Mg/ha. Across the entire region, combinations of management practices affected the effectiveness of FST + NST to increase yield but benefits were minimal ranging between 0.01 to 0.22 Mg/ha. Despite widespread use, this practice appears to have little benefit for most of soybean producers; across the entire region, a partial economic analysis further showed inconsistent evidence of a break-even cost of FST or FST + NST. These results demonstrate that the current widespread prophylactic use of NST in the key soybean-producing areas of the US should be re-evaluated by producers and regulators alike.

Co-encapsulation of imidacloprid and lambda-cyhalothrin using biocompatible nanocarriers: Characterization and application

A well-known strategy for managing pest resistance is application of mixture of pesticides. Conventionally formulated pesticides have several environmental incompatibilities. The use of biocompatible and biodegradable nanocarriers in formulating pesticides could improve environmental protection. In this study, a mixture of imidacloprid and lambda-cyhalothrin was co-encapsulated for the first time using liposomes as nanocarrier to simultaneously deliver these insecticides. Ethanol injection was used to produce self-assembled liposomes. The formed nanoliposomes were coated with different concentrations of chitosan. Nanoparticles were characterized by dynamic light scattering (DLS), scanning electron microscope (SEM) and FT-IR spectroscopy. The encapsulation efficiencies of lambda-cyhalothrin and imidacloprid were about 93% and 51%, respectively. The insecticide carrying liposomes had a size and surface charge of 57 nm and +0.6 mV, respectively. The size and surface charge of the particles produced were increased to 69 nm and +31 mV after being coated with chitosan (0.1%, W/V). In this study, residual activity of technical grade imidacloprid, lambda-cyhalothrin and their mixture and the effect of adjuvants used in commercial and nano formulations of these insecticides on Myzus persicae Sulzer was investigated. The insecticidal effects and duration of residual activity of nano-formulations was correlated with concentration of chitosan in final formulation. In accordance with the life cycle of M. persicae, using the mixture of imidacloprid and lambda-cyhalothrin improves the residual effect over their use alone. The use of lipid nanocarriers makes the improvement even further and can be a better alternative to conventional combination of these insecticides due to their more environmental friendliness.

Neonicotinoid insecticide residues in subsurface drainage and open ditch water around maize fields in southwestern Ontario

Neonicotinoids are widely used class of insecticides. Most are seed treatments and during planting active ingredient may be abraded and lost in fugitive dust. Much of this active ingredient contaminates surface waters, exposing aquatic organism to potential ill effects. This study examines concentrations of neonicotinoids appearing in tile drains and open ditches around commercial maize fields around planting time where neonicotinoid seed treatments had been used. This sample set represents surface water leaving the point of origin, for which data are sparse. Clothianidin was found more often than thiamethoxam and at higher concentrations; at a median concentration of 0.35 ng/mL in tile drain water and almost twice that (0.68 ng/mL) in ditches into which the tiles are draining after applications of 19 g/ha on seed. This concentration reveals a 40 to 50 fold dilution for neonicotinoid residues between the points where they leave the field in which they were applied and when they are found in nearby streams in a similar ecosystem. Our data support that for a no-observed-effect concentration of 0.3 ng/mL for thiamethoxam there would be between a 1.6 and 100-fold margin of safety to mayflies in most streams if fugitive dust on pneumatic planters were properly mitigated.

A study on the long-term efficacy of Seresto® collars in preventing Babesia canis (Piana & Galli-Valerio, 1895) transmission to dogs by infected Dermacentor reticulatus (Fabricius, 1794) ticks

BACKGROUND

An imidacloprid/flumethrin collar (Seresto®) was previously shown to prevent infection with Babesia canis, transmitted by Dermacentor reticulatus, in dogs for up to 1 month after application. The present study evaluated the prevention of transmission throughout the claimed efficacy period of 8 months.

METHODS

Eight animals each were randomly included in groups 1 (negative control) and 2 (Seresto® collar), respectively. Animals in group 2 received the Seresto® collar on Day 0. Tick challenges were performed monthly from the 2nd to the 8th month. Assessment criteria included in situ tick counts 48 hours post-challenge, polymerase chain reaction (PCR) analyses and immunofluorescence assays (IFA). Whenever dogs were diagnosed with babesiosis they were "rescue-treated", excluded and replaced. Consequently, 24 replacement animals were introduced at various time points throughout the study in the control group; thus data for a total of 32 dogs were available in the latter group at study termination.

RESULTS

Acaricidal efficacy for in situ counts was 93% on Day 30, and ranged from 97 to 100% thereafter. No B. canis specific DNA or antibodies were detected in any Seresto®-treated dog at any time. Babesia canis-specific DNA and antibodies were detected in 2-6 of 8 control dogs after each challenge, confirming the validity of the challenge model.

CONCLUSIONS

The Seresto® collar was highly effective against challenges with D. reticulatus ticks for up to 8 months. The high sustained acaricidal efficacy over this period prevented transmission of B. canis, thus fully protecting dogs against infection in this experimental infestation model.

Longitudinal monitoring of anti-saliva antibodies as markers of repellent efficacy against Phlebotomus perniciosus and Phlebotomus papatasi in dogs

A 2-year longitudinal study of enzyme-linked immunosorbent assay (ELISA) antibodies against Phlebotomus perniciosus and Phlebotomus papatasi (Diptera: Psychodidae) sandfly saliva was performed in 32 Beagle dogs treated preventively with an imidacloprid-permethrin topical insecticide in an endemic area in Spain. Dogs were grouped into three sandfly exposure groups according to the time of inclusion in the study. Assays analysed immunoglobulin G (IgG) against salivary gland homogenates (SGH) of both species and recombinant P. papatasi rSP32 and P. perniciosus rSP03B proteins in serum. The dogs were participating in a Leishmania infantum (Kinetoplastida: Trypanosomatidae) vaccine trial and were experimentally infected with the parasite in the second year. No dog acquired natural L. infantum infections during the first year, but most developed anti-saliva antibodies, and median log-transformed optical densities (LODs) were seasonal, mimicking those of local sandflies. This indicates that the repellent efficacy of the insecticide used is below 100%. Multi-level modelling of LODs revealed variability among dogs, autocorrelation and differences according to the salivary antigen and the dog's age. However, dog seroprevalence, estimated using pre-exposure LODs as cut-offs, was relatively low. This, and the fact that dogs did not become naturally infected with L. infantum, would support the efficacy and usefulness of this imidacloprid-permethrin topical insecticide in canine leishmaniasis control.

Acute effect of low-dose thiacloprid exposure synergised by tebuconazole in a parasitoid wasp

Agricultural practices often involve tank-mixing and co-application of insecticides with fungicides to control crop pests. However, natural methods relying on biological control agents such as hymenopteran parasitoids have been shown to be highly effective in suppressing crop pest populations. The current body of insecticide risk assessment data accounting for fungicide co-application is very small, the present study being the first to examine this in a parasitoid wasp. Through low-dose exposure to dry residues of the neonicotinoid insecticide thiacloprid, we examined its mortal and knockdown effect on Aphelinus abdominalis when co-applied with increasing doses of the fungicide tebuconazole. Both of these acute effects of thiacloprid were synergised (toxicity increased to a greater-than-additive effect) by tebuconazole, resulting in significant mortality from low-dose co-applications of tebuconazole, and significant knockdown even without co-applied tebuconazole, the effect increasing as tebuconazole concentration increased. We show the highly toxic effect that a low dose of thiacloprid imposes on A. abdominalis populations, and a synergistic toxicity when co-applied with low doses of tebuconazole. Our work suggests a need for updating pesticide risk assessment methods, accounting for pesticide mixtures, in order to make these risk assessments more field relevant.

Emerald Ash Borer (Coleoptera: Buprestidae) Densities Over a 6-yr Period on Untreated Trees and Trees Treated With Systemic Insecticides at 1-, 2-, and 3-yr Intervals in a Central Michigan Forest

We assessed density of emerald ash borer (Agrilus planipennis Fairmaire) (Coleoptera: Buprestidae) larvae over a 6-yr period by felling and sampling a total of 315 green ash (Fraxinus pennsylvanica Marsh.) trees that were left untreated or treated with imidacloprid, dinotefuran, or emamectin benzoate products at 1-yr, 2-yr, or 3-yr intervals. Our study, conducted across a 32-ha forested area, began soon after emerald ash borer became established and continued through the peak and eventual decline of the emerald ash borer population. Less than half of the 96 trees in the pretreatment sample were infested and larval densities were very low. Densities of emerald ash borer remained low for 3 yr, then increased exponentially, eventually resulting in mortality of most untreated overstory ash. Trees treated with either low or moderate rates of emamectin benzoate applied via trunk injection had few or no emerald ash borer galleries, even 3 yr post-treatment. Basal trunk sprays of dinotefuran applied annually were also effective at preventing larval densities from reaching damaging levels. Average larval densities on trees treated with a trunk injection of imidacloprid were lower but did not differ from untreated trees, regardless of treatment frequency. Larval parasitism was rare, while woodpecker predation was common and accounted for nearly all natural larval mortality, even on trees with very low densities of larvae.

Imidacloprid induced alterations in oxidative stress, biochemical, genotoxic, and immunotoxic biomarkers in non-mammalian model organism Galleria mellonella L. (Lepidoptera: Pyralidae)

Imidacloprid (IMI), a neonicotinoid insecticide, is widely used to control pests in agriculture. We investigated the changes in antioxidant enzyme activities, lipid peroxidation levels, biochemical effects, genotoxic effect, and immunotoxic effect of sublethal doses (0.25, 0.50, 0.75, and 1.00 µg) of IMI at different time periods (24, 48, 72, and 96 h) on a model organism, Galleria mellonella L. The results indicated that there were dose-dependent increases in both antioxidant enzyme activities (SOD and CAT) and MDA levels. Protein content was not affected by IMI at 24th and 48th, whereas it was decreased by the highest dose of IMI (1.00 µg) at 72nd and 96th h. Lipid and carbohydrate contents were reduced with increasing doses of IMI. Micronucleus frequency significantly increased in all IMI doses. All IMI doses caused a significant decrease in THC at 24th, 48th, and 72nd h. Our results can help to illustrate the effects of IMI in target organisms and indirectly may aid to discover potential risk of it on nontarget organisms. Future studies, at molecular levels, will be helpful in understanding the mechanism of action of IMI on these biomarkers.

Effect of long term exposure to sublethal concentration of imidacloprid on some biochemical and haematological parameters of Grass carp and Goldfish

During the present research, C. idella and C. auratus fish were exposed to 2 ppm concentration of imidacloprid for 28 and 24 days, respectively, and the effect on biochemical and haematological parameters was investigated. During the study of biochemical parameters, there occurred significant increase (P<0.05) in the serum levels of ALT and creatinine of imidacloprid exposed groups of both species of fish. The level of serum albumin of imidacloprid exposed groups of both fish species was significantly lower as compared to control group (P<0.05). Serum globulin level in imidacloprid exposed group of C. idella was insignificantly lower as compared to control group, however the serum globulin level of C. auratus was significantly lower than the control group (P < 0.05). The level of total proteins in serum of imidacloprid exposed groups of both fish species was insignificantly lower as compared to control groups (P>0.05). During the study of haematological parameters, TLC of C. idella was insignificantly (P>0.05) higher than control group but the TLC of C. auratus was significantly (P<0.05) higher than control. There was also observed increasing trend in the percentage of neutrophils and lymphocytes of imidacloprid exposed group of each fish species. The platelets count of imidacloprid exposed group of each fish species was significantly (P<0.05) lower than control group. The haemoglobin concentration of imidacloprid exposed group of C. idella was significantly lower than control group (P<0.05). In case of C. auratus, the haemoglobin level of imidacloprid exposed group was insignificantly lower than control group (P>0.05). From the finding of the present research it was concluded that 28 days exposure of C. idella and 24 days exposure of C. auratus to 2 ppm concentration of imidacloprid does not cause mortality however the exposure causes alteration in the normal level of biochemical and haematological parameters.

Assessment of a Density-Based Action Threshold for Suppression of Sugarcane Aphids, (Hemiptera: Aphididae), in the Southern High Plains

In the High Plains, sugarcane aphid, Melanaphis sacchari Zehntner (Hemiptera: Aphididae), colonize grain sorghum, Sorghum bicolor (L) Moench (Cyperales: Poaceae), when it is in reproductive stages and aphid populations increase rapidly. Sugarcane aphid management recommendations based on aphid densities have been implemented in southern United States, but have not been assessed in the High Plains. Therefore, the goal of this work was to validate whether these guidelines can provide effective suppression of the aphids and improve yield. In a 2-y field experiment, sorghum susceptible (DKS44-20) and resistant (DKS37-07) to sugarcane aphids, with and without insecticide (clothianidin) seed treatments, was exposed to natural aphid infestations and treated with a foliar insecticide (flupyradifurone) once sugarcane aphid densities exceeded 50 per leaf. Further, to assess the effects of these tactics on sorghum yield, data were collected from plots that were not treated at the threshold. In both years, foliar insecticide applied at the density-based threshold decreased aphid numbers across sorghum hybrids with and without seed treatments and aphid densities remained below threshold for the remainder of the season. Yield of sorghum depended on sugarcane aphid pressure-when their densities were high (2016), the resistant hybrid with and without the foliar spray outperformed the unsprayed susceptible hybrid, while the susceptible hybrid had higher yields than resistant hybrid when sugarcane aphid pressure was low (2017). Outcomes of this work support the notion that a well-timed foliar application can alleviated losses in yield in sorghum in the Texas Panhandle and potentially other regions of the High Plains.

The effects of imidacloprid combined with endosulfan on IgE-mediated mouse bone marrow-derived mast cell degranulation and anaphylaxis

Low levels of endosulfan are known to stimulate mast cells to release allergic mediators, while imidacloprid can inhibit IgE-mediated mast cell degranulation. However, little information about the effects of both pesticides together on mast cell degranulation is available. To measure the effects, IgE-activated mouse bone marrow-derived mast cells (BMMCs) were treated with imidacloprid and endosulfan, individually, and simultaneously at equi-molar concentrations in tenfold steps ranging from 10^-4 to 10^-11 M, followed by measuring several allergy-related parameters expressed in BMMCs: the mediator production and influx of Ca²⁺, the phosphorylation content of NF-κB in the FcεRI signaling pathway. Then, the effects of the mixtures on IgE-induced passive systemic anaphylaxis (PSA) of BALB/c was detectded. This study clearly showed that the application of equi-molar mixtures of both pesticides with 10^-4-10^-5 M significantly inhibited the IgE-mediated mouse bone marrow-derived mast cells degranulation in vitro and 10^-4 M of them decreased IgE-mediated PSA in vivo, as the application of imidacloprid at the same concentration alone did. Morever endosulfan alone had no remarkable stimulatory effects on any of the factors measured. In conclusion, simultaneous application of equi-molar concentrations of both pesticides generally showed highly similar responses compared to the responses to imidacloprid alone, suggesting that the effects of the mixture could be solely attributed to the effects of imidacloprid.

Evaluation of Alternatives to an Organophosphate Insecticide with Selected Cultural Practices: Effects on Thrips, Frankliniella fusca, and Incidence of Spotted Wilt in Peanut Farmscapes

Peanut growers use a combination of tactics to manage spotted wilt disease caused by thrips-transmitted Tomato spotted wilt virus (TSWV). They include planting TSWV-resistant cultivars, application of insecticides, and various cultural practices. Two commonly used insecticides against thrips are aldicarb and phorate. Both insecticides exhibit broad-spectrum toxicity. Recent research has led to the identification of potential alternatives to aldicarb and phorate. In this study, along with reduced-risk, alternative insecticides, we evaluated the effect of conventional versus strip tillage; single versus twin row seeding pattern; and 13 seed/m versus 20 seed/m on thips density, feeding injury, and spotted wilt incidence. Three field trials were conducted in Georgia in 2012 and 2013. Thrips counts, thrips feeding injuriy, and incidence of spotted wilt were less under strip tillage than under conventional tillage. Reduced feeding injury from thrips was observed on twin-row plots compared with single-row plots. Thrips counts, thrips feeding injury, and incidence of spotted wilt did not vary by seeding rate. Yield from twin-row plots was greater than yield from single-row plots only in 2012. Yield was not affected by other cultural practices. Alternative insecticides, including imidacloprid and spinetoram, were as effective as phorate in suppressing thrips and reducing incidence of spotted wilt in conjunction with cultural practices. Results suggest that cultural practices and reduced-risk insecticides (alternatives to aldicarb and phorate) can effectively suppress thrips and incidence of spotted wilt in peanut.

Effects of co-exposure to imidacloprid and gibberellic acid on redox status, kidney variables and histopathology in adult rats

Data on the individual nephrotoxic effects of imidacloprid (IMI) and gibberellic acid (GA₃) are scarce. Moreover, there is a lack of information about their combined effects on the renal tissue. Our study investigated the effects of IMI and GA₃ separately or together on rats kidney. IMI (64 mg/kg bw) was given for 3 weeks by gavage either individually or in combination with GA₃ (200 mg/L) via drinking water. IMI associated or no with GA₃ increased the levels of kidney malondialdehyde, advanced oxidation protein products, protein carbonyls and metallothionein, plasma creatinine, urea, blood urea nitrogen and lactate dehydrogenase activity. A decline of kidney uric acid level and antioxidant status was also observed. All these changes were supported by histopathological observations. Our results highlighted the role of IMI and/or GA₃-induced nephrotoxicity. Co-exposure to IMI and GA₃ exhibited synergism in biochemical kidney variables and histopathology and antagonism in physical and morphological parameters.

A Meta-analysis and Economic Evaluation of Neonicotinoid Seed Treatments and Other Prophylactic Insecticides in Indiana Maize From 2000-2015 With IPM Recommendations

Corn rootworm remains the key pest of maize in the United States. It is managed largely by Bt corn hybrids, along with soil insecticides and neonicotinoid seed treatments (NSTs), the latter of which are applied to virtually all conventionally (non-Bt) produced maize. Frequently, more than one of these pest-management approaches is employed at the same time. To determine the utility and relative contributions of these various approaches, a meta-analysis was conducted on plant health and pest damage metrics from 15 yr of insecticide efficacy trials conducted on Indiana maize to compare the pest-protection potential of NSTs to that of other insecticides and Bt hybrids. The probability of recovering the insecticide cost associated with each treatment was also calculated when possible. With the exception of early-season plant health (stand counts), in which the NSTs performed better than all other insecticides, the vast majority of insecticides performed similarly in all plant health metrics, including yield. Furthermore, all tested insecticides (including NSTs) reported a high probability (>80%) of recovering treatment costs. Given the similarity in performance and probability of recovering treatment costs, we suggest NSTs be optional for producers, so that they can be incorporated into an insecticide rotation when managing for corn rootworm, the primary Indiana corn pest. This approach could simultaneously reduce costs to growers, lower the likelihood of nontarget effects, and reduce the risk of pests evolving resistance to the neonicotinoid insecticides.

Value of Neonicotinoid Insecticide Seed Treatments in Mid-South Corn (Zea mays) Production Systems

Neonicotinoid seed treatments are one of several effective control options used in corn, Zea mays L., production in the Mid-South for early season insect pests. An analysis was performed on 91 insecticide seed treatment trials from Arkansas, Louisiana, Mississippi, and Tennessee to determine the value of neonicotinoids in corn production systems. The analysis compared neonicotinoid insecticide treated seed plus a fungicide to seed only with the same fungicide. When analyzed by state, corn yields were significantly higher when neonicotinoid seed treatments were used compared to fungicide only treated seed in Louisiana and Mississippi. Corn seed treated with neonicotinoid seed treatments yielded 111, 1,093, 416, and 140 kg/ha, higher than fungicide only treatments for Arkansas, Louisiana, Mississippi, and Tennessee, respectively. Across all states, neonicotinoid seed treatments resulted in a 700 kg/ha advantage compared to fungicide only treated corn seed. Net returns for corn treated with neonicotinoid seed treatment were $1,446/ha compared with $1,390/ha for fungicide only treated corn seed across the Mid-South. Economic returns for neonicotinoid seed treated corn were significantly greater than fungicide-only-treated corn seed in 8 out of 14 yr. When analyzed by state, economic returns for neonicotinoid seed treatments were significantly greater than fungicide-only-treated seed in Louisiana. In some areas, dependent on year, neonicotinoid seed treatments provide significant yield and economic benefits in Mid-South corn.

Toxicokinetics of the neonicotinoid insecticide imidacloprid in rainbow trout (Oncorhynchus mykiss)

Studies were conducted to determine the distribution and elimination of imidacloprid (IMI) in rainbow trout. Animals were injected with a low (47.6 μg/kg), medium (117.5 μg/kg) or high (232.7 μg/kg) dose directly into the bloodstream and allowed to depurate. The fish were then sampled to characterize the loss of IMI from plasma and its appearance in expired water (all dose groups) and urine (medium dose only). In vitro biotransformation of IMI was evaluated using trout liver S9 fractions. Mean total clearance (CL_T) values determined by non-compartmental analysis of plasma time-course data were 21.8, 27.0 and 19.5 mL/h/kg for the low, medium and high dose groups, respectively. Estimated half-lives for the same groups were 67.0, 68.4 and 68.1 h, while fitted values for the steady-state volume of distribution (V_SS) were 1.72, 2.23 and 1.81 L/kg. Branchial elimination rates were much lower than expected, suggesting that IMI is highly bound in blood. Renal clearance rates were greater than measured rates of branchial clearance (60% of CL_T in the medium dose group), possibly indicating a role for renal membrane transporters. There was no evidence for hepatic biotransformation of IMI. Collectively, these findings suggest that IMI would accumulate in trout in continuous waterborne exposures.

Increased survival of honeybees in the laboratory after simultaneous exposure to low doses of pesticides and bacteria

Recent studies of honeybees and bumblebees have examined combinatory effects of different stressors, as insect pollinators are naturally exposed to multiple stressors. At the same time the potential influences of simultaneously occurring agricultural agents on insect pollinator health remain largely unknown. Due to different farming methods, and the drift of applied agents and manure, pollinators are most probably exposed to insecticides but also bacteria from organic fertilizers at the same time. We orally exposed honeybee workers to sub-lethal doses of the insecticide thiacloprid and two strains of the bacterium Enterococcus faecalis, which can occur in manure from farming animals. Our results show that under laboratory conditions the bees simultaneously exposed to the a bacterium and the pesticide thiacloprid thiacloprid had significant higher survival rates 11 days post exposure than the controls, which surprisingly showed the lowest survival. Bees that were exposed to diet containing thiacloprid showed decreased food intake. General antibacterial activity is increased by the insecticide and the bacteria, resulting in a higher immune response observed in treated individuals compared to control individuals. We thus propose that caloric restriction through behavioural and physiological adaptations may have mediated an improved survival and stress resistance in our tests. However, the decreased food consumption could in long-term also result in possible negative effects at colony level. Our study does not show an additive negative impact of sub-lethal insecticide and bacteria doses, when tested under laboratory conditions. In contrast, we report seemingly beneficial effects of simultaneous exposure of bees to agricultural agents, which might demonstrate a surprising biological capacity for coping with stressors, possibly through hormetic regulation.

Usefulness of a topical combination of dinotefuran and pyriproxyfen for long-term control of clinical signs of allergic dermatitis in privately-owned cats in Ile-de-France region

BACKGROUND

The present study assessed the activity of a combination of dinotefuran and pyriproxyfen (Vectra® Felis) for long-term control (3 months) of allergic dermatitis (AD) in privately-owned cats under common household conditions in Ile-de-France region.

METHODS

This was an open pre-treatment vs post-treatment study. Twenty-eight client-owned cats with clinical signs of AD were enrolled in the study. They received topical application of the combination of dinotefuran and pyriproxyfen on days 0, 28, 56 and 84. Two parameters (clinical signs and pruritus severity) were used to assess the animals' condition on days 0, 28 and 84. Fleas were counted if they were observed.

RESULTS

Of the 28 cats initially enrolled, 26 were presented on day 28 and 20 for the final evaluation on day 84. A significant improvement in clinical signs and pruritus was observed in cats for which fleas and/or flea feces were detected on day 0. Globally, the post-treatment AD clinical scores on days 28 and 84 were different from that of the pre-treatment on day 0, with a reduction of 30% and 71%, respectively. For cats with fleas and/or flea feces, the reduction on days 28 and 84 was 33% and 85%, respectively. The improvement of clinical signs and pruritus was not significant in cats with no visible fleas and no flea feces at the beginning of the trial (n = 8).

CONCLUSIONS

The present study indicated that the treatment with a combination of dinotefuran and pyriproxyfen should be considered as useful in controlling fleas on cats without additional environmental treatment and useful for long-term control of clinical signs and pruritus in allergic cats.

Synergy between dinotefuran and fipronil against the cat flea (Ctenocephalides felis): improved onset of action and residual speed of kill in adult cats

BACKGROUND

The cat flea, Ctenocephalides felis felis (C. felis), is a cosmopolitan hematophagous ectoparasite, and is considered to be the most prevalent flea species in both Europe and the USA. Clinical signs frequently associated with flea bites include pruritus, dermatitis and in severe cases even pyodermatitis and alopecia. Ctenocephalides felis is also a vector for several pathogens and is an intermediate host for the cestode Dipylidium caninum. Treatment of cats with a fast-acting pulicide, that is persistently effective in protecting the animal against re-infestation, is therefore imperative to their health. In addition, a rapid onset of activity ("speed of kill") may also reduce the risks of disease transmission and flea allergic dermatitis. The aim of this study was to evaluate the in vitro insecticidal activity and potential synergism between dinotefuran and fipronil against C. felis. A further aim was to evaluate the onset of activity and residual speed of kill of the combination in vivo on cats artificially infested with C. felis.

METHODS

In the first study, the insecticidal activity of dinotefuran and fipronil separately and dinotefuran/fipronil (DF) in combination, at a fixed ratio (2:1), was evaluated using an in vitro coated-vial bioassay. In the second study, the onset of activity against existing flea infestations and residual speed of kill of DF against artificial flea infestations on cats was assessed in vivo. Onset of activity against existing flea infestations was assessed in terms of knock-down effect within 2 h post-treatment and onset of speed of kill assessed at 3 h, 6 h and 12 h post-treatment. Residual speed of kill was evaluated 6 h and 48 h after infestation, over a period of six weeks post-treatment.

RESULTS

In vitro results revealed that the DF combination was synergistic and more potent against fleas than either compound alone. The combination also proved effective when tested in vivo. Efficacy was > 97% [geometric mean (GM) and arithmetic mean (AM)] at 3 h after treatment, and ≥ 99.8% (GM and AM) at 6 h and 12 h post-treatment. At 6 h after flea re-infestations, the efficacy of DF remained ≥ 90.8% (GM and AM) for up to 28 days, and at 42 days post-treatment persistent efficacy was still ≥ 54.3% (GM and AM). At 48 h after flea re-infestations, DF remained almost fully effective for up to 28 days, with efficacies ≥ 99.4% (GM and AM) and was persistently ≥ 93.0% (GM and AM) effective for up to 42 days post-treatment.

CONCLUSIONS

The combination of dinotefuran and fipronil in a single formulation exhibited strong synergistic insecticidal activity against C. felis in vitro, and also proved effective on artificially infested cats. This activity had a rapid onset that persisted for 6 weeks against re-infestations of C. felis on cats. The rapid curative insecticidal effect was observed as early as 3 h after treatment, and as early as 6 h after re-infestations for up to 6 weeks post-treatment. The insecticidal activity profile of DF makes it an optimal candidate for the protection of cats against flea infestations, and possibly also associated diseases.