Jinliang Shen

Inheritance, fitness cost and mechanism of resistance to tebufenozide in Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae)

BACKGROUND Tebufenozide has been used as a key insecticide for controlling beet armyworm, Spodoptera exigua (Hübner). To evaluate the risk of resistance evolution and to develop a better resistance management strategy, a field-collected population was selected with tebufenozide in the laboratory. Thereafter, the inheritance and fitness cost of tebufenozide resistance in S. exigua were investigated. RESULTS After being selected with tebufenozide for 61 generations, S. exigua developed a 92-fold resistance to the chemical. The degrees of dominance for the reciprocal cross progeny were - 0.2698 and - 0.2785. The resistant strain had a relative fitness of 0.71, with substantially lower rates of larval survival, pupal weight, pupation and oviposition per female, and prolonged larval and pupal duration. PBO significantly increased the toxicity of tebufenozide (SR = 2) against resistant insects, and DEM and DEF also showed synergism with tebufenozide. CONCLUSION Tebufenozide resistance in S. exigua was inherited as autosomal, incompletely recessive and controlled by more than one gene. Development of the resistance may cost significant fitness for the resistant population. Mixed-function oxidases might play an important role in tebufenozide resistance in S. exigua. This study provided valuable information for further understanding tebufenozide resistance and for facilitating the development of resistance management strategies.

Resistance Allele Frequency to Bt Cotton in Field Populations of Helicoverpa armigera (Lepidoptera: Noctuidae) in China

Abstract Resistance evolution in target insects to Bacillus thurningiensis (Bt) cotton, Gossypium hirsutum L., is a main threat to Bt cotton technology. An increasing trend of population density of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) has been observed since 2001 in Qiuxian County (Hebei, China), where Bt cotton has been planted dominantly since 1998. This region was selected in 2006 and 2007 for estimating frequency of gene alleles conferring resistance to Bt cotton by screening the F1 progeny from single-pair cross between field-collected male and laboratory female of the Bt-resistant strain of H. armigera (F1 screen). F1 offspring from each single-pair line were screened for resistance alleles based on larval growth, development, and survival on Bt cotton leaves for 5 d. Two-year results indicated that ≈20% of field-collected males carried resistance alleles. The conservative estimate of the resistance allele frequency was 0.094 (95% CI, 0.044–0.145) for 2006 and 0.107 (95% CI, 0.055–0.159) for 2007. This is the first report of resistance allele frequency increase to such a high level in the field in China. Long-term adoption of Bt sprays, dominant planting of single-toxin–producing Bt cotton, and lack of conventional cotton refuge system might accelerate the resistance evolution in the region.

Using an F2 screen to monitor frequency of resistance alleles to Bt cotton in field populations of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)

BACKGROUND In an effort to control the most devastating cotton pest, Helicoverpa armigera (Hübner), in Qiuxian County (Hebei, China), Bt cotton has been planted almost exclusively since 1998 in this area. Owing to the high insecticidal selection pressures in this region, monitoring of Bt resistance in H. armigera is necessary so that proactive actions can be implemented before field control measures fail. From 2003 to 2005, an F(2) screen was conducted in order to monitor Bt resistance in H. armigera populations collected from this area. RESULTS The F(2) screen showed that 15 out of 278 isofemale lines carried resistance alleles to Bt cotton. The resistance allele frequency in field populations of H. armigera ranged from 0.0119 to 0.0297, with an overall frequency of 0.0146 and a 95% confidence interval of 0.0084-0.0225 for the 3 year period. This value is greater than the value reported from 1999 (P < 0.05). CONCLUSION A fluctuating but overall increase in resistance allele frequency was detected in the field populations of H. armigera in Qiuxian County from 1999 to 2005. To prevent further increases in Bt resistance frequency in this pest, it is necessary to introduce Bt cotton expressing multiple Bt toxins and integrate this technology with other tactics for management of this key pest.

Differential Resistance and Cross-Resistance to Three Phenylpyrazole Insecticides in the Planthopper Nilaparvata lugens (Hemiptera: Delphacidae)

ABSTRACT Cross-resistance to two fipronil analogs, butene-fipronil and ethiprole, was detected in fipronil-resistant field populations and a resistant laboratory strain of the planthopper Nilaparvata lugens (Stål) (Hemiptera: Delphacidae), although the two analogs have not been used widely in rice-growing areas in China. The results showed that six field populations with 23.8–43.3-fold resistance to fipronil had reached a higher level of cross-resistance to ethiprole (resistance ratio [RR] = 47.1–100.9-fold) and had a minor level of cross-resistance (RR = 3.4–8.1-fold) to butene-fipronil. After 10 generations of selection, the RR to fipronil increased from 7.3-fold to 41.3-fold. At the same time, the insect increased cross-RR to ethiprole from 16.3-fold to 65.6-fold, whereas it had only minor increase in cross-resistance to butene-fipronil from 2.8-fold to 4.0-fold. These results confirmed that fipronil-resistant N. lugens could develop a higher level of cross-resistance to ethiprole, although it still maintained a lower level cross-resistance to butene-fipronil. Our data suggest that ethiprole is not a suitable alternative for controlling N. lugens, once the insect has developed a high level resistance to fipronil. Further investigation is necessary to understand the cross-resistance mechanisms in N. lugens.

Regression Analysis of Dynamics of Insecticide Resistance in Field Populations of Chilo suppressalis (Lepidoptera: Crambidae) During 2002–2011 in China

ABSTRACT To understand the evolution of insecticide resistance in the Asiatic rice borer, Chilo suppressalis (Walker) (Lepidoptera: Crambidae), in field, regression analysis based on a linear or nonlinear model was adopted for analyzing resistance dynamics to six insecticides of two field populations of the Lianyungang (LYG) and Ruian (RA) populations during 2002–2011. For the low-level resistance population, LYG population, sustained susceptibilities to abamectin and fipronil were seen for 10 yr; a polynomial curve regression model showed an increase in resistance to chlorpyrifos; exponential growth models fit to the resistance dynamics to triazophos and deltamethrin, and a sigmoidal growth curve for monosultap. For the high-level multiple resistance population, RA population, a slight increase from susceptible to a minor resistance to abamectin could be modeled by apolynomial cubic equation; an exponential growth model fit to the increase of resistance to fipronil from 8.7-fold to 33.6-fold; a sine waveform model fit to the vibrating tendency of resistance to chlorpyrifos; the dynamics of resistance to triazophos could be modeled by two combined curves, with a polynomial growth model and a sine waveform model; the high level of resistance to monosultap could be modeled with a sine waveform model; and a significant linear growth relationship of the resistance to deltamethrin of the RA population overyears was found. Then, the relationship between dynamics of resistance development to insecticides among the field populations of C. suppressalis and the application history of pesticides for controlling rice borers was discussed.

Molecular characterization and developmental expression of the gene encoding the prothoracicotropic hormone in the beet armyworm, Spodoptera exigua.

Prothoracicotropic hormone (PTTH), a neuropeptide hormone stimulating the prothoracic glands to synthesize ecdysone, plays an important role in regulating postembryonic development in insects. The cDNA encoding PTTH was isolated and sequenced from the beet armyworm, Spodoptera exigua (Spe). The deduced amino acid sequence is composed of a signal peptide, a peptide (65 amino acids) of unknown function, and a mature PTTH molecule (111 amino acids). The Spe-PTTH shows similarities (45.5%–70.3%) to other known PTTHs reported in Lepidoptera species, but 7 cysteine residues and the hydrophobic regions were conserved. Whole-mount immunocytochemistry by using an antiserum against recombinant Helicoverpa armigera PTTH showed that Spe-PTTH was synthesized in two pairs of neurosecretory cells in the S. exigua brain. Northern blot analysis demonstrates the presence of a 1.2-kb transcript in the brain. The Spe-PTTH mRNA is detectable at high levels at the wandering larval stage, early pupal stage, and pharate adult stage, suggesting that the Spe-PTTH gene might be correlated with molting, metamorphosis, and reproduction.

Cloning and expression of the gene encoding the diapause hormone and pheromone biosynthesis activating neuropeptide of the beet armyworm, Spodoptera exigua †

Diapause hormone (DH) and pheromone biosynthesis activating neuropeptide (PBAN), two important insect neuropeptides, regulate insect development and sex pheromone biosynthesis, respectively. DH-like immunoreactivity has been detected in the suboesophageal ganglion (SG) of pharate adult of Spodoptera exigua (Spe) by using an antiserum against Helicoverpa armigera DH. A full-length of Spe-DH-PBAN cDNA was obtained based on reverse transcription-PCR and rapid amplification of cDNA ends strategies. The open reading frame of this cDNA encodes a 197-amino acid precursor protein that contains DH, PBAN, and three other SG neuropeptides, all of which share a conservative C-terminal pentapeptide motif FXPR/KL (X = G, T or S). Northern blot analysis demonstrates the presence of an 800 bp transcript in the SG. The Spe-DH-PBAN mRNA is detectable at high levels at larval and adult stages, suggesting that Spe-DH-PBAN gene might be correlated with larval development and sex pheromone biosynthesis in moths.

Superfamily of genes encoding G protein-coupled receptors in the diamondback moth Plutella xylostella (Lepidoptera: Plutellidae)

G protein‐coupled receptors (GPCRs) are the largest and most versatile superfamily of cell membrane proteins, which mediate various physiological processes including reproduction, development and behaviour. The diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae), is one of the most notorious insect pests, preferentially feeding on cruciferous plants. P. xylostella is not only one of the worlds most widespread lepidopteran insects, but has also developed resistance to nearly all classes of insecticides. Although the mechanisms of insecticide resistance have been studied extensively in many insect species, few investigations have been carried out on GPCRs in P. xylostella. In the present study, we identified 95 putative GPCRs in the P. xylostella genome. The identified GPCRs were compared with their homologues in Bombyx mori and Drosophila melanogaster. Our results suggest that GPCRs in different insect species may have evolved by a birth‐and‐death process. One of the differences among compared insects is the duplication of short neuropeptide F receptor and adipokinetic hormone receptors in P. xylostella and B. mori. Another divergence is the decrease in quantity and diversity of the stress‐tolerance gene, Mth, in P. xylostella. The evolution by the birth‐and‐death process is probably involved in adaptation to the feeding behaviour, reproduction and stress responses of P. xylostella. Some of the genes identified in the present study could be potential targets for the development of novel pesticides.

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.

A Modified F1 Screening Method for Detecting Resistance Gene Alleles to Bt Cotton in Helicoverpa armigera (Lepidoptera: Noctuidae)

Large-scale cultivation of Bt cotton places high selection pressure on target insects and, consequently, may prompt resistance evolution in pest populations. To better monitor Bt-resistance allele frequency in field populations, a modification of the F1 screen was developed to screen F1 progeny derived from single pair mating between field-collected males and laboratory resistant females (designated as F1 screen). This method was used to survey a field population of Heliocoverpa armigera (Hubner) for resistance alleles at the same loci in the resistant strain. After treatment of the F1 progeny derived from more than 260 single pair mating lines with Bt cotton, there was no clear separation of resistant genotypes from susceptible genotypes based on survival rates which demonstrated a linear distribution within a certain range. We further analyzed larval growth data of the F1 progeny and found a correlation between larval body weight and survival rate. The maximum correlation was obtained when F1 larval bod...