Imidacloprid-resistant Strain Research Articles

The mode of action of a nitroconjugated neonicotinoid and the effects of target site mutation Y151S on its potency

Neonicotinoid insecticides, such as imidacloprid, are selective agonists of the insect nicotinic acetylcholine receptors (nAChRs) with –NO2 or –CN group in trans-configuration. Previously we reported the excellent insecticidal activity of a series of nitroconjugated neonicotinoids with –NO2 or –CN group in cis-configuration by replacing nitromethylene pharmacophore with a nitroconjugated system. To understand the action mode of these nitroconjugated neonicotinoids, a representative member IPPA152201 was chosen to perform toxicity and pharmacology studies. IPPA152201 showed a comparable toxicity with imidacloprid against Nilaparvata lugens in a susceptible strain and had no significant cross-resistance in an imidacloprid resistant strain. IPPA152201 showed good efficacies on the isolated cockroach neurons (pEC50 = 5.91 ± 0.14) and the evoked responses by IPPA152201 could be blocked by the typical nAChRs antagonists methyllycaconitine citrate (MLA) and dihydro-β-erythroidine (DHβE), with pIC50 of 6.56 ± 0.07 and 6.89 ± 0.12. The efficacy of IPPA152201 on hybrid receptors Nlα1/β2 in Xenopus oocytes and response inhibition by MLA and DHβE were also observed. These data demonstrate that IPPA152201 acts on insect nAChRs as an agonist. In addition, the influence of a Nlα1 mutation (Y151S), which has been linked to the lab-generated neonicotinoid resistance in N. lugens, has been examined. Compared to the wildtype Nlα1/β2, this mutation reduced Imax for IPPA152201 to 63.2% and caused a 1.5-fold increase in EC50, which is much smaller than the effects on imidacloprid. The high insecticidal activity and little influence by Y151S mutation make IPPA152201 to be a potential insecticide to manage N. lugens.

Synthesis and insecticidal activity of 1,2,4-oxadiazole and 1,2,4-thiadiazole derivatives

A series of 5-substituted 1,2,4-oxadiazoles and 1,2,4-thiadiazoles were prepared as muscarinic acetylcholine receptor agonists and evaluated for their insecticidal activity. These derivatives were synthesized through sequential reactions consisting of the condensation of pyridinecarboamides or pyridinecarbothioamides with N,N-dimethylacetamide dimethyl acetal, cyclization with hydroxylamine, quaternization by alkyl halide and reaction with sodium borohydride. All 1,2,4-oxadiazoles and 1,2,4-thiadiazoles synthesized were evaluated for insecticidal activity and their structure-activity relationships are discussed. It was discovered that many compounds were active against representative insects such as Nilaparvata lugens, Nephotettix cincticeps and Aphis craccivora. In particular, it was also found that 3-pyridyl-substituted derivatives of 1,2,4-oxadiazole and 1,2,4-thiadiazole exhibited good insecticidal activity against all the insects tested. Among the compounds evaluated, 3-methyl-5-(1,2,5,6-tetrahydropyridin-3-yl)-1,2,4-thiadiazole (9m-2) showed the highest activity against Nilaparvata lugens, and provided a high level of activity against the imidacloprid-resistant strain. Based on the preliminary binding assay using the binding inhibition of mAChR antagonist [3H]NMS to the nerve-cord membranes as an index of the binding activity, 9m-2 exhibited a range of potencies for the insect muscarinic receptor.

High Performance Liquid Chromatography Assay for p-Nitroanisole o-Demethylation by Cytochrome P450 Enzymes in Musca domestica L.

Abstract A novel sensitive method was developed for measuring p -nitroanisole o -demethylation (PNOD) catalyzed by cytochrome P450 enzymes in crude homogenates of housefly, Musca domestica L., using high performance liquid chromatography (HPLC) with diode array detector. This method is based on the use of liquid-liquid extraction and HPLC with reversed-phase C 18 column and gradient ultraviolet detection at 316 nm. The detection limit ( S/N of 3/1) of p -nitrophenol ( p NP) was 0.1 ng. The relative standard deviation (RSD) of peak area response of the HPLC analysis system was 1.0%. The average recoveries of 0.351, 1.755 and 8.755 μg of p NP added to incubation mixtures ranged from 92.3% to 87.6%, and the RSD of recoveries of three added levels ranged 2.64%–5.90%. The relationships between peak areas and concentration were linear in the range of 9.72–486 ng with good coefficient of determination ( r 2 = 0.9995). This method is sensitive, precise, and reproducible and is also applicable to the assay of p -nitroanisole o -demethylases, which have low catalytic activities, present in other insects or organisms. With this method, the comparison of P450 o -demethylation activity of an imidacloprid-resistant strain with a susceptible strain of M. domestica (L.) was conducted to identify the roles of P450 enzymes involved in housefly resistance to imidacloprid. The results indicated that the resistance mechanism of housefly to imidacloprid was intensely assisted with elevated P450 activities.

MicroRNAs: An exciting and open field calls for extensive study from initial and established investigators

The tobacco whitefly Bemisia tabaci (Gennadius) is an important crop pest which threatens agriculture worldwide. It has evolved resistance to various classes of insecticides. Cycloxaprid is a new-generation neonicotinoid which is a (nitromethylene) imidazole analogue of imidacloprid which is highly efficient for the control of various Hemipteran pests in China. Studies were conducted to determine the baseline susceptibility to cycloxaprid of 18 field samples of B. tabaci collected from 9 geographical locations in China and the possibility of cross-resistance between cycloxaprid and other important neonicotinoids of one laboratory-selected resistant strain. The 50% lethal concentrations (LC50) of cycloxaprid to these 18 samples ranged from 0.84 to 12.17 mg/L. Furthermore, compared with the susceptible laboratory strain, the imidacloprid-resistant strain exhibited a 27.9-fold resistance to imidacloprid and lower level of cross-resistance to acetamiprid (16.3-fold), thiacloprid (13.7-fold) and nitenpyram (16.6-fold), but no cross-resistance to cycloxaprid (1.9-fold). These results demonstrate that cycloxaprid could be one effective alternative insecticide for whitefly management that could reduce imidacloprid selection pressure.

Baseline Susceptibility of Bemisia tabaci B Biotype (Hemiptera: Aleyrodidae) Populations from California and Arizona to Spiromesifen

Susceptibility to spiromesifen, a tetronic acid derivative, was determined for three imidacloprid-resistant strains and 12 geographically discrete natural populations of Bemisia tabaci (Gennadius) (=Bemisia argentifolii Bellows & Perring) (Hemiptera: Aleyrodidae) from California and Arizona by laboratory bioassays. Newly emerged first instars were sprayed with aqueous serial dilutions of spiromesifen and evaluated for toxicity to establish baseline susceptibility data. Interpopulation variability in susceptibility to spiromesifen was observed among the natural populations of whiteflies up to 29-fold; however, there was only 30-fold difference in susceptibility among natural and resistant populations tested. In general, spiromesifen was quite toxic to first instars across most of their geographic range, with LC50 values ranging from 0.210 to 6.08 μg (AI)/ml. The magnitude of variation was smaller among the three-resistant strains. These results suggest that the observed variability reflect natural variation in spiromesifen susceptibility among all the test populations, possibly due to previous exposure to insecticides at each location. The effectiveness of spiromesifen also was evaluated against all immature stages of whiteflies from three field and two resistant strains. Spiromesifen was significantly more active against early instars of whiteflies based on lower LC50 values recorded compared with the fourth instars. Spiromesifen was effective against the resistant strains including a Q-biotype of B. tabaci from Spain, which is highly resistant to neonicotinoids. Results of this study indicate absence of cross-resistance between spiromesifen and more commonly used neonicotinoids. Our findings suggest that spiromesifen should be considered an ideal candidate for whitefly resistance management programs in rotation with other effective chemistries.

Baseline Susceptibility of <I>Bemisia tabaci</I> B Biotype (Hemiptera: Aleyrodidae) Populations from California and Arizona to Spiromesifen

Susceptibility to spiromesifen, a tetronic acid derivative, was determined for three imidacloprid-resistant strains and 12 geographically discrete natural populations of Bemisia tabaci (Gennadius) (=Bemisia argentifolii Bellows & Perring) (Hemiptera: Aleyrodidae) from California and Arizona by laboratory bioassays. Newly emerged first instars were sprayed with aqueous serial dilutions of spiromesifen and evaluated for toxicity to establish baseline susceptibility data. Interpopulation variability in susceptibility to spiromesifen was observed among the natural populations of whiteflies up to 29-fold; however, there was only 30-fold difference in susceptibility among natural and resistant populations tested. In general, spiromesifen was quite toxic to first instars across most of their geographic range, with LC50 values ranging from 0.210 to 6.08 microg (AI)/ml. The magnitude of variation was smaller among the three-resistant strains. These results suggest that the observed variability reflect natural variation in spiromesifen susceptibility among all the test populations, possibly due to previous exposure to insecticides at each location. The effectiveness of spiromesifen also was evaluated against all immature stages of whiteflies from three field and two resistant strains. Spiromesifen was significantly more active against early instars of whiteflies based on lower LC50 values recorded compared with the fourth instars. Spiromesifen was effective against the resistant strains including a Q-biotype of B. tabaci from Spain, which is highly resistant to neonicotinoids. Results of this study indicate absence of cross-resistance between spiromesifen and more commonly used neonicotinoids. Our findings suggest that spiromesifen should be considered an ideal candidate for whitefly resistance management programs in rotation with other effective chemistries.

Assessment of cross-resistance potential to neonicotinoid insecticides in Bemisia tabaci (Hemiptera: Aleyrodidae)

Laboratory bioassays were carried out with four neonicotinoid insecticides on multiple strains of Bemisia tabaci (Gennadius) to evaluate resistance and cross-resistance patterns. Three imidacloprid-resistant strains and field populations from three different locations in the southwestern USA were compared in systemic uptake bioassays with acetamiprid, dinotefuran, imidacloprid and thiamethoxam. An imidacloprid-resistant strain (IM-R) with 120-fold resistance originally collected from Imperial Valley, California, did not show cross-resistance to acetamiprid, dinotefuran or thiamethoxam. The Guatemala-resistant strain (GU-R) that was also highly resistant to imidacloprid (RR=109-fold) showed low levels of cross-resistance when bioassayed with acetamiprid and thiamethoxam. However, dinotefuran was more toxic than either imidacloprid or thiamethoxam to both IM-R and GU-R strains as indicated by low LC50s. By contrast, a Q-biotype Spanish-resistant strain (SQ-R) of B. tabaci highly resistant to imidacloprid demonstrated high cross-resistance to the two related neonicotinoids. Field populations from Imperial Valley (California), Maricopa and Yuma (Arizona), showed variable susceptibility to imidacloprid (LC50s ranging from 3.39 to 115 microg ml(-1)) but did not exhibit cross-resistance to the three neonicotinoids suggesting that all three compounds would be effective in managing whiteflies. Yuma populations were the most susceptible to imidacloprid. Dinotefuran was the most toxic of the four neonicotinoids against field populations. Although differences in binding at the target site and metabolic pathways may influence the variability in cross-resistance patterns among whitefly populations, comparison of whitefly responses from various geographic regions to the four neonicotinoids indicates the importance of ecological and operational factors on development of cross-resistance to the neonicotinoids.

Resistance and cross‐resistance to neonicotinoid insecticides and spinosad in the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae)

The Colorado potato beetle, Leptinotarsa decemlineata (Say), has developed resistance to many insecticides used for its control, recently including imidacloprid, a neonicotinoid compound. Other neonicotinoids are now being deployed to control this pest. A key point in the strategies of resistance management is the monitoring of resistance and cross-resistance. In the summer of 2003, imidacloprid-resistant adult Colorado potato beetles collected from Long Island, New York, USA were bioassayed using topical applications of imidacloprid and nine other neonicotinoids. Compared to a standard susceptible strain, the Long Island beetles showed 309-fold resistance to imidacloprid, and lower levels of cross-resistance to all other neonicotinoids, despite these never having been used in the field, i.e., 59-fold to dinotefuran, 33-fold to clothianidin, 29-fold to acetamiprid, 28-fold to N-methylimidacloprid, 25-fold to thiacloprid, 15-fold to thiamethoxam, 10-fold to nitenpyram, but less than 2-fold to nicotine. In injection bioassays, high resistance to imidacloprid was also found (116-fold). Piperonyl butoxide partially suppressed resistance to imidacloprid, but the resistance level was still over 100-fold, indicating that other mechanisms were primarily responsible for resistance. Low levels of resistance (8- to 10-fold) were found to the nicotinic activator, spinosad, in an imidacloprid-resistant strain collected from the same field in 2004. The cross-resistance seen with all the neonicotinoids tested suggests that the rotation of imidacloprid with other neonicotinoids may not be an effective long-term resistance management strategy. Rotation with spinosad also carries some risk, but it is unlikely that spinosad resistance in this case is mechanistically related to that for the neonicotinoids.

Resistance of aphis gossypii (Homoptera: Aphididae) to fenvalerate and imidacloprid and activities of detoxification enzymes on cotton and cucumber.

Resistance of two strains of cotton aphid, Aphis gossypii Glover, to fenvalerate and imidacloprid were determined on cotton (Gossypium hirsutum L.) and cucumber (Cucumis sativa L.) after resistance selection of one strain to fenvalerate for 16 consecutive generations, and of a second strain to imidacloprid for 12 consecutive generations on cotton in greenhouses. Dose-response and activities of detoxication enzymes of the fenvalerate-resistant strain (R-fenvalerate), the imidacloprid-resistant strain (R-imidacloprid), and a susceptible strain (S) were determined. After 16 consecutive generations of selection, resistance of A. gossypii to fenvalerate increased >29,000-fold and to imidacloprid 8.1-fold. On cucumber. resistance of the R-fenvalerate strain to fenvalerate increased 700-fold and to imidacloprid 3.6-fold. However, the most significant finding in this study was that the R-imidacloprid strain exhibited cross-resistance to fenvalerate, with a resistance ratio of 108.9-fold on cotton and 3:3.5-fold on cucumber, whereas the R-fenvalerate strain did not show significant cross-resistance to imidacloprid on either plant species. Both resistant strains of A. gossypii were more resistant to fenvalerate on cotton than on cucumber, whereas their susceptibility to imidacloprid on otton and cucumber were not significantly different. The response of the S strain to fenvalerate and imidacloprid were similar on cotton and Cucumber. Activities of acetylcholinesterase (AChE) and alpha-naphthylacetate (alpha-NA) esterases of A. gossypii were significantly different among the three strains, with the R-fenvalerate strains having the highest, followed by the R-imidacloprid strain, and the S strain the lowest. The activities of the AChE and alpha-NA esterases for all three strains were also significantly higher on cotton than on cucumber. The resistance mechanism and resistance management strategies for the R-fenvalerate and R-imidacloprid strains of A. gossypii to fenvalerate and imidacloprid on cotton and cucumber are discussed.

Cross-resistance ofAphis gossypii to selected insecticides on cotton and cucumber

Cross-resistance of a fenvalerate-resistant (R-fenvalerate) strain and an imidacloprid-resistant (R-imidacloprid) strain of the cotton aphidAphis gossypii Glover to methomyl, endosulfan and omethoate was determined on cotton and cucumber in the laboratory. The R-fenvalerate strain had been selected for 16 consecutive generations on cotton, and the R-imidacloprid strain for 12. Compared with the susceptible (S) strains, the resistance in the 17th generation of the R-fenvalerate strain to fenvalerate was 29,035-fold on cotton and 700-fold on cucumber, whereas the resistance in the 13th generation of the R-imidacioprid strain to imidacloprid was 4.7-fold on cotton and 3.6-fold on cucumber. The R-fenvalerate strain did not show any cross-resistance to imidacloprid, methomyl or omethoate on cotton and cucumber, but became slightly cross-resistant to endosulfan (RR [resistance ratio] = 5.8 and 7.4 on cotton and cucumber, respectively). On cotton the R-imidacloprid strain became highly cross-resistant to fenvalerate (RR = 108.9) and slightly cross-resistant to methomyl, endosulfan and omethoate (RR = 6.3, 3.0 and 8.5, respectively). In contrast, on cucumber the R-imidacloprid strain became highly cross-resistant to fenvalerate (RR = 33.5) and slightly cross-resistant to methomyl and omethoate (RR = 7.0 and 3.3, respectively), but did not show any cross-resistance to endosulfan. It appears thatA. gossypii of both resistant strains was more resistant to the tested insecticides on cotton than on cucumber, except for imidacloprid —where the resistance on cotton was not significantly different from that on cucumber.

Selection for imidacloprid resistance in silverleaf whiteflies from the Imperial Valley and development of a hydroponic bioassay for resistance monitoring

A field-collected population of the silverleaf whitefly, Bemisia argentifolii, was selected with the nicotinyl compound, imidacloprid, over 32 generations to determine if resistance would develop when maintained under continuous selection pressure in a greenhouse. Resistance was slow to increase at first with low to moderate levels of resistance (RR from 6- to 17-fold) in the first 15 generations of selection. Further selection steadily led to higher levels of resistance, with the greatest resistance ratio at 82-fold, the gradual rise suggesting the involvement of a polygenic system. At the end of the selection, slopes of probit regressions were substantially steeper than earlier, indicating increased homogeneity of imidacloprid resistance in this strain. A hydroponic bioassay featuring systemic uptake of imidacloprid through roots was developed to monitor the changes in resistance to imidacloprid in the selected whitefly strain and in seven field-collected strains from Imperial Valley, California. Six out of seven field-collected strains exhibited low LC50 values (0·002 to 0·512 mg ml-1) compared to the selected resistant strain, with one exception where the LC50 was 0·926 mg ml-1 (RR=15·0). Variation in responses to imidacloprid in the field strains suggest that this technique is sufficiently sensitive to detect differences in susceptibilities of whitefly populations. The imidacloprid-resistant strain showed no cross-resistance to endosulfan, chlorpyrifos or methomyl (RR ranging from 0·4- to 1·5-fold). A low level of cross-resistance was observed to bifenthrin in the IM-R strain at 7-fold. The success of selection for resistance to imidacloprid has serious implications for whitefly control programs that rely heavily on imidacloprid. ©1997 SCI