Jin-Cai Wu

Pesticide-induced susceptibility of rice to brown planthopper Nilaparvata lugens

The effects of rice plants treated with various pesticides (jingganmycin, bisultap and methamidophos) on feeding, survival rates and population growth of Nilaparvata lugens Stål (Homoptera: Delphacidae), susceptibility of the treated rice plants and amounts of free amino acids and sucrose were studied. Experiments indicated that the effects of the tested pesticides were dependent on nymphal age, pesticide and their dose and time after application. Jingganmycin at 75 g a.i. ha−1 significantly increased the N. lugens population. Both jingganmycin and bisultap increased the survival rate of N. lugens nymphs. The feeding rate of the insects was also affected by the pesticide application, but the effect varied between nymphal age and time after application and lasted no longer than 15 d. Results clearly indicated that pesticide application increased the susceptibility of rice plants to N. lugens. Although the free amino acids in rice plants did not change with the pesticide treatments, the concentration of sucrose significantly decreased 5 d after application and the C/N ratio significantly decreased in jingganmycin treated plants 5 d and 10 d after application.

Cultivar and Insecticide Applications Affect the Physiological Development of the Brown Planthopper, Nilaparvata lugens (Stål) (Hemiptera: Delphacidae)

Abstract Nilaparvata lugens (Stål) (Hemiptera:Delphacidae) is a serious migratory pest of rice in Asia. Pest resurgence often occurs because of insecticide overuse. Using both susceptible (TN1) and moderately resistant (Xieyou 963) cultivars, we studied the effect of foliar insecticides on the percentage of brachypterous adults, female reproductive rate, and crude fat and soluble sugar contents in third- and fifth-instar nymphs and adults. The percentage of brachypterous adults and reproductive rate of adult females developed from nymphs that fed on insecticide-treated plants varied significantly with rice cultivar, type of insecticide, and its concentration. Feeding on susceptible plants increased the percentage of brachypterous adults and reproductive rate of adult females. Also, deltamethrin increased brachypterous production relative to imidacloprid and triazophos. The highest reproductive rate was on plants treated with triazophos. All insecticide treatments in both cultivars resulted in increase of soluble sugar contents in third- and fifth-instar nymphs and adults developed from nymphs feeding on insecticide-treated rice plants. This effect was stronger on the susceptible cultivar. Changes of crude fat content after N. lugens feeding on insecticide-treated plants were related to its feeding duration. Crude fat content in adult developed from nymphs feeding on treated plants was significantly higher that on control plants. These studies showed that plant and insecticide influences on physiological ecology of this planthopper will influence its population dynamics under commercial production of rice in Asia.

Selective insecticide-induced stimulation on fecundity and biochemical changes in Tryporyza incertulas (Lepidoptera: Pyralidae).

Abstract The use of selective insecticides in rice, Oryza sativa L., fields often causes resurgence of nontarget pest insects. This study was conducted to investigate the effect of two selective insecticides, buprofezin and imidacloprid, on Tryporyza incertulas (Walker), a nontarget pest. After larval feeding on rice plants treated with each insecticide, fecundity, ovary protein content, and titer of juvenile hormone III (JHIII) in the resulting female moths were determined with ‘Xiushui 63’ rice susceptible to T. incertulas and ‘Zhendao 2’ moderately resistant to T. incertulas. The fecundity of females developed from larvae that fed on the insecticide-treated Xiushui 63 plants was stimulated compared with that of moths from larvae that fed on rice plants that were not treated with either insecticide. There was no stimulating effect in females from larvae that fed on insecticide-treated Zhendao 2 plants. The weight of fourth instars (final instars) that fed on the insecticide-treated Xiushui 63 rice plants was significantly greater than that of control, increasing by 50.3 and 46.7% for 60 and 112.5 g (AI) ha−1 buprofezin, and by 23.7 and 19.5% for 15 and 37.5 g (AI) ha−1 imidacloprid treatments, respectively. Ovary protein content in adult females developed from larvae that fed on the rice treated with the high dose of buprofezin was significantly higher than that in control. For the high and low doses of imidacloprid during the second instar, and the low dose of imidacloprid during the fourth instar, JHIII titers in female adults were also significantly higher than that in control, increasing by 152.81, 90.52, and 114.19%, respectively.

Comparisons of stimulatory effects of a series of concentrations of four insecticides on reproduction in the rice brown planthopper Nilaparvata lugens Stål (Homoptera: Delphacidae)

The rice brown planthopper, Nilaparvata lugens (Stål) (Homoptera: Delphacidae), is the type of insect pest whose resurgence is induced by pesticides. Outbreaks of the pest frequently occur in Asia. We investigated the effects of series of concentrations of four insecticides, imidacloprid, buprofezin, deltamethrin and triazophos, on the durations of the preoviposition (DPP) and oviposition period (DOP), female longevity (LOF), realized fecundity (RFE) and egg hatchability of N. lugens on two rice varieties: TN1 and Xieyou 963. DPP, DOP, LOF, NLE and hatchability varied with insecticide type, concentration, number of applications, and rice variety. For imidacloprid and buprofezin, RFE and hatchability decreased, DPP increased, and DOP and LOF lessened significantly with increasing concentration. In contrast, for deltamethrin and triazophos, DPP and DOP shortened, and LOF, RFE and hatchability increased significantly with increasing concentration. Increase in the number of applications for the four insecticides amplified the effects on these life-history variables. For example, three successive sprays of deltamethrin significantly increased RFE compared to a single spray under the same concentrations and rice variety. Additionally, rice variety also showed a significant influence on the variables. For example, RFE on TN1 significantly increased compared to on Xieyou 963 under the same concentrations and spray times. There were significant correlations between each index and insecticide concentrations for four insecticides on both rice varieties except in the case of hatchability for a single spray of buprofezin on TN1 and for LOF for a single spray of deltamethrin on TN1. Our findings have important implications for the understanding of mechanisms of N. lugens resurgence, and for management of the pest in commercial rice production.

Molecular basis for insecticide-enhanced thermotolerance in the brown planthopper Nilaparvata lugens Stål (Hemiptera:Delphacidae).

Climate change is likely to have marked ecological effects on terrestrial ecosystems, including the activities of insect pests. Most attention has focused on the increasing geographical ranges of pests; however, if extrinsic factors enhance their thermotolerance, populations may express increased voltinism and longer daily and annual activity periods. These changes in pest populations have the potential for severe consequences, including increased crop losses and decreased food security at the global level. The brown planthopper (BPH) Nilaparvata lugens Stål (Hemiptera: Delphacidae) is a serious pest of rice crops in temperate and tropical regions of Asia. It is often present in rice microclimates at temperatures close to its maximum thermotolerance. Recent BPH outbreaks in tropical Asia are considered to be associated with excess use of pesticides and increasing temperature. This study tested whether exposure to sublethal concentrations of triazophos (tzp), an insecticide widely used in Asian rice production, enhances thermotolerance of BPH. Tzp exposure (40 ppm at 40 °C) significantly decreased mortality (from 94% in controls to 50% at 48 h post‐treatment) and increased lethal mean time (LT50) of adults by 17.2 h. To investigate the underlying molecular mechanism of this tzp‐enhanced thermotolerance, we selected Hsp70 and Arginine kinase (Argk) for detailed study. Transcripts encoding both proteins in third‐instar nymphs and brachypterous adult females were up‐regulated, compared with controls, after exposure to tzp. RNAi silencing of both genes demonstrated that Hsp70 and Argk are essential for survival and tzp‐increased thermotolerance. We propose that tzp induces thermotolerance in BPHs by increasing the expression of genes that act in cell protection mechanisms. The significance of our proposal relates to the importance of understanding the influence of sublethal concentrations of insecticides on pest biology. In addition to its influence on thermotolerance, tzp also enhances BPH reproduction. We infer that exposure to a pesticide stressor can produce cross‐tolerance, that is, increased tolerance to one stressor also increases tolerance to other stressors, including temperature. Aside from needing a better understanding of these effects in nature and in other pest/cropping systems, we suggest that pest management programmes can be improved with better understanding of the influences of stressors, including increased environmental temperatures and sublethal concentrations of insecticides, on pest biology.

Proteomic analysis of insecticide triazophos-induced mating-responsive proteins of Nilaparvata lugens Stål (Hemiptera: Delphacidae).

The brown planthopper, Nilaparvata lugens (Stål) (Hemiptera: Delphacidae), is a classic example of a resurgent pest induced by insecticides. It has been demonstrated that triazophos treatment causes an increase in the content of male accessory gland proteins (Acps) that can be transferred to females via mating, influencing female reproduction. However, the mechanism of this type of insecticide-induced Acps in males and the subsequent stimulation of reproduction in females are not well understood. To identify changes in the types of Acps and reproductive proteins in mated females, we conducted a comparative proteomic analysis. Six samples were categorized into four different groups: (1) untreated unmated males compared to treated unmated males (UUM vs TUM); (2) treated unmated males compared to treated mated males (TUM vs TMM); (3) untreated unmated females compared to treated unmated females (UUF vs TUF); (4) treated unmated females compared to treated mated females (TUF vs TMF). Protein expression changes among the four different groups were examined by two-dimensional gel electrophoresis (2-DE) and liquid chromatography tandem mass spectrometry (LC-MS/MS). Of the 500-600 reproducibly detected protein spots on each gel, 107 protein spots were differentially expressed between the four different groups. Of the 63 proteins identified by LC-MS/MS analysis, 38 were up-regulated and 25 were down-regulated in the four different groups. Some novel proteins related to fecundity were observed including spermatogenesis-associated protein 5, testis development protein NYD-SP6, arginine kinase, actin-5C, vitellogenin, and ovarian serine protease nudel. The elevated expression of novel fecundity proteins in six samples of N. lugens females and males due to exposure to triazophos was confirmed by quantitative real-time PCR (qRT-PCR). The results suggest that these proteins may participate in the reproductive process of N. lugens adult females and males. Our findings fill a gap in understanding the relationship between insecticide-treated males and the stimulated reproduction of N. lugens females.

Effects of herbicides on rice resistance and on multiplication and feeding of brown planthopper (BPH), Nilaparvata lugens (StÅl) (Homoptera: Delphacidae)

Two-way effects of herbicide on rice resistance and multiplication and feeding of the rice brown planthopper (BPH), Nilaparvata lugens (Stål) were studied. Four of 11 herbicides tested, butachlor, metolachlor, oxadiazon and bentazone, had significantly stimulating effects on multiplication and feeding of BPH. Multiplication times (N 1/N 0) of BPH on the rice treated with the four herbicides were 674, 367, 322 and 311, respectively, while that of N. lugens on the untreated plants was 159. The results of measurements of honeydew production by BPH indicated that the feeding rates of the brown planthoppers increased when the insects fed on the plants treated with bentazone, quinclorac, oxadiazon and quinclorac. Survival rates of N. lugens first to third-instars rose on the rice plants treated with butachlor, bentazone, but that of the fourth and fifth instars were not affected. Furthermore, all of those herbicides tested led to a decline of rice resistance, i.e. the injury scales of the treated plants were larger than that of the control under the same pest stress. Based on their effects on rice resistance and on BPH, the herbicides tested can be divided into two categories, one affecting rice resistance and BPH multiplication, the other affecting rice resistance only.

Effective duration of pesticide-induced susceptibility of rice to brown planthopper (Nilaparvata lugens Stål, Homoptera: Delphacidae), and physiological and biochemical changes in rice plants following pesticide application

The effective durations of pesticide-induced susceptibility of rice to brown planthopper (BPH), Nilaparvata lugens (Stål) (Homoptera: Delphacidae), and physiological and biochemical changes in rice plants following pesticide applications, were studied. The effective duration of the herbicide butachlor on the susceptibility of rice variety Zhengdao 2 to BPH exceeded 16 days. The difference in damage rating between rice plants with pesticide treatments and control plants gradually decreased with days after treatment (DAT). There was a significant correlation between damage rating and DAT. The number of rice tillers at 3 – 10 DAT and plant heights at 7 – 10 DAT declined on Zhengdao 2 with the butachlor treatment. On the other hand, there were no effects of butachlor on damage rating, number of rice tillers and plant height for Xiushui 63. This might be related to tolerance of Xiushui 63 to butachlor. For Zhengdao 2, the fungicide jingganmycin and the insecticide bisultap had a significant influence on BPH damage, number of rice tillers and plant height. In contrast to butachlor, jingganmycin and bisultap had a significant effect on BPH damage to Xiushui 63. However, these two pesticides had no significant effect on the number of rice tillers and plant height of Xiushui 63. In general, the effective duration of butachlor on rice plants was greater than jingganmycin and bisultap. Oxalic acid content and photosynthesis in rice plants declined significantly after jingganmycin and bisultap treatments. These findings are consistent with those of pesticide-susceptibility of rice to BPH. Pesticide-induced susceptibility of rice resistance to BPH counteracts the role of varietal resistance in integrated pest management.

Insecticide-Induced Changes in Protein, RNA, and DNA Contents in Ovary and Fat Body of Female Nilaparvata lugens (Hemiptera: Delphacidae)

ABSTRACT The widespread use of insecticides is known to cause resurgence in Nilaparvata lugens (Stål) (Hemiptera: Delphacidae) populations, a serious insect pest of rice, Orzya sativa L., crops in Asia. The current study investigated insecticide-induced changes in protein, RNA, and DNA levels in the ovary and fat body of adult female N. lugens. Potted rice plants were sprayed with different concentrations of imidacloprid, triazophos, and detamethrin. The results showed that all three insecticides caused a significant increase in protein and RNA contents in the ovary and fat body of adult females developed from nymphs fed on treated plants compared with those from on untreated plants, although there was no significant effect on DNA content. In general, protein and RNA contents in both ovary and fat body increased linearly with insecticide concentrations or days after emergence (DAEs) when they were applied. There was a significant correlation between protein content and RNA content in both ovary and fat body. In addition, the relationship between ratios of RNA to protein in ovary and fat body of adult female N. lugens and insecticide concentrations showed a significant positive correlation for most DAEs of imidacloprid and several DAEs of triazophos and deltamethrin treatments. These findings suggest that RNA in both ovary and fat body was more sensitive to insecticides and that the insecticide-induced changes in RNA content in turn influence protein synthesis in ovary and fat body. Consistently, RNA-to-protein ratios in ovary and fat body were ≈0.42 in all treatments and controls.

Effects of two pesticides, TZP and JGM, on reproduction of three planthopper species, Nilaparvata lugens Stål, Sogatella furcifera Horvath, and Laodelphax striatella Fallén

Three planthopper species, the brown planthopper (BPH), Nilaparvata lugens Stål, the white-backed planthopper (WBPH), Sogatella furcifera Horvath, and the small brown planthopper (SBPH), Laodelphax striatella Fallén, often co-occur in rice grown regions of China. The present investigation examined effects of two pesticides, triazophos (TZP) and jinggangmycin (JGM) (a fungicide), on reproduction of BPH, WBPH, and SBPH. The results showed that TZP stimulated the fecundity of the three planthopper species. Interestingly, JGM stimulated the fecundity of BPH but suppressed the fecundity of WBPH. In addition, TZP and JGM had a significant effect on the preoviposition period (PVD), the oviposition period (OPD), and the longevity of adult females (LAF) of BPH and WBPH. Based on these findings, to avoid resurgence occurrence of planthoppers, we suggest that the application of TZP should be banned in rice fields, that JGM should be used to control rice sheath blight at the early growth stages of rice (with WBPH occurrence and without BPH occurrence).