Resistance monitoring and cross-resistance patterns of three rice planthoppers, Nilaparvata lugens, Sogatella furcifera and Laodelphax striatellus to dinotefuran in China.

Three rice planthoppers, brown planthopper, Nilaparvata lugens, white-backed planthopper, Sogatella furcifera and small brown planthopper, Laodelphax striatellus, are important pests of cultivated rice in tropical and temperate Asia. They have caused severe economic loss and developed resistance to insecticides from most chemical classes. Dinotefuran is the third neonicotinoid which possesses a broad spectrum and systemic insecticidal activity. We determined the susceptibility of dinotefuran to field populations from major rice production areas in China from 2013 to 2015. All the populations of S. furcifera and L. striatellus were kept susceptible to dinotefuran (0.7 to 1.4-fold of S. furcifera and 1.1-to 3.4-fold of L. striatellus) However, most strains of N. lugens (except FQ15) collected in 2015 had developed moderate resistance to dinotefuran, with resistance ratios (RR) ranging from 23.1 to 100.0 folds. Cross-resistance studies showed that chlorpyrifos-resistant and buprofezin-resistant Sogatella furcifera, chlorpyrifos-resistant and fipronil-resistant L. striatellus, imidacloprid-resistant and buprofezin-resistant Nilaparvata lugens exhibited negligible or no cross-resistance to dinotefuran. Synergism tests showed that piperonyl butoxide (PBO) produced a high synergism of dinotefuran effects in the DY15 and JS15 populations (2.14 and 2.52-fold, respectively). The obvious increase in resistance to dinotefuran in N. lugens indicates that insecticide resistance management strategies are urgently needed to prevent or delay further increase of insecticide resistance in N. lugens.

The evolution of insecticide resistance in the brown planthopper (Nilaparvata lugens Stål) of China in the period 2012-2016.

The brown planthopper, Nilaparvata lugens, is an economically important pest on rice in Asia. Chemical control is still the most efficient primary way for rice planthopper control. However, due to the intensive use of insecticides to control this pest over many years, resistance to most of the classes of chemical insecticides has been reported. In this article, we report on the status of eight insecticides resistance in Nilaparvata lugens (Stål) collected from China over the period 2012-2016. All of the field populations collected in 2016 had developed extremely high resistance to imidacloprid, thiamethoxam, and buprofezin. Synergism tests showed that piperonyl butoxide (PBO) produced a high synergism of imidacloprid, thiamethoxam, and buprofezin effects in the three field populations, YA2016, HX2016, and YC2016. Functional studies using both double-strand RNA (dsRNA)-mediated knockdown in the expression of CYP6ER1 and transgenic expression of CYP6ER1 in Drosophila melanogaster showed that CYP6ER1 confers imidacloprid, thiamethoxam and buprofezin resistance. These results will be beneficial for effective insecticide resistance management strategies to prevent or delay the development of insecticide resistance in brown planthopper populations.

Cross-resistance to three phenylpyrazole insecticides and A2'N mutation detection of GABA receptor subunit in fipronil-resistant Laodelphax striatellus (Hemiptera: Delphacidae).

BACKGROUND: Laodelphax striatellus (Fallén) is an important pest of crops in East Asia. Over the past decade, phenylpyrazole insecticides, which target the insect GABA receptor, have increasingly been used as alternatives against rice planthoppers. RESULTS: Cross-resistance to ethiprole and butene-fipronil was detected in a laboratory-selected fipronil-resistant strain of L. striatellus (LsFR). Compared with a fipronil-susceptible strain (LsFS), LsFR had obtained a high-level resistance to fipronil (112.1-fold) and moderate resistance to ethiprole (24.5-fold) and butene-fipronil (14.7-fold). For the resistance of field populations, LC50 values of ethiprole were remarkably higher than the other two analogues in Gaochun and Yancheng populations in 2016. Significant correlations were demonstrated between the LC50 values of three phenylpyrazole insecticides (R = 0.944-0.998, P = 0.007-0.016). Additionally, an AS-PCR assay was developed to detect the A2'N mutant GABA receptor in L. striatellus strains or populations. It was noteworthy that mutation frequencies of 19.2 and 3.6% appeared in Lujiang and Gaochun populations in 2016, respectively. Furthermore, there was an extremely significant difference in genomic expression of Lsrdl between the LsFS and LsFR individuals (1.85-fold, F = 26.8, P = 0.0008). CONCLUSIONS: This study could help us better understand the cross-resistance mechanisms in L. striatellus, and be beneficial for proposing effective pest management strategies of phenylpyrazole resistance. © 2016 Society of Chemical Industry.

Expression pattern and pharmacological characterisation of two novel alternative splice variants of the glutamate-gated chloride channel in the small brown planthopper Laodelphax striatellus.

BACKGROUND: Glutamate-gated chloride channels (GluCl) mediate fast inhibitory neurotransmission in invertebrate nervous systems. Although only one GluCl gene was presented in insects, it showed diverse alternative splicing that was speculated could affect channel function and pharmacology. RESULTS: In this study, we isolated GluCl cDNAs from adults of the small brown planthopper (SBPH) Laodelphax striatellus and showed that six L. striatellus GluCl variants (LsGluCl-AS, LsGluCl-BS, LsGluCl-CS, LsGluCl-AL, LsGluCl-BL, LsGluCl-CL) were present in the SBPH. The expression patterns of six variants differed among developmental stages (egg, first- to fifth-instar nymphs, male and female adults) and among the body parts (head, thorax, abdomen, leg) of the female adult SBPH. All the transcripts were abundant in the head of the adult. When expressed in African clawed frog, Xenopus laevis, oocytes, the two functional variants (LsGluCl-AS, LsGluCl-AL) had similar EC50 and IC50 values for L-glutamate and channel blockers picrotoxinin and fipronil. CONCLUSION: This study represents a comprehensive molecular, expression and pharmacological characterisation of GluCl in the SBPH. These findings should be useful in providing more opportunities to discover novel insect control chemicals. © 2016 Society of Chemical Industry.