Yueping He

Electrical penetration graph evidence that pymetrozine toxicity to the rice brown planthopper is by inhibition of phloem feeding.

BACKGROUND Pymetrozine is a valuable novel insecticide for control of sucking insects, including the brown planthopper Nilaparvata lugens (Stål), one of the most serious pests on rice. This study was conducted to elucidate the action mechanisms of pymetrozine on the feeding behaviour of the planthopper. RESULTS The activity test showed that pymetrozine primarily functioned as an antifeedant that caused starvation and death in N. lugens, rather than having neurotoxicity. Pymetrozine-treated insects died at a significantly slower speed than insects treated with starvation. Electrical penetration graph (EPG) data indicated that pymetrozine significantly increased the duration of non-probing periods and had a strong inhibition to phloem ingestion. The inhibition was strongly dose dependent, resulting in a complete suppression of the activity in the phloem region when the pymetrozine concentration was increased to 400 mg L(-1) . Starvation caused by inhibition of phloem ingestion might be a major toxicity mechanism of pymetrozine. EPG data also showed that pymetrozine had no significant effect on stylet movement and duration of xylem sap ingestion. CONCLUSION The study revealed that pymetrozine disturbed the feeding behaviour of N. lugens mainly by increasing the non-probe period and inhibiting phloem ingestion. The inhibition resulted in a slow death similar to starvation.

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.

Influence of Pymetrozine on Feeding Behaviors of Three Rice Planthoppers and a Rice Leafhopper using Electrical Penetration Graphs

ABSTRACT Pymetrozine reportedly inhibits feeding of plant sap-sucking insects, such as aphids and brown planthopper (Nilaparvata lugens (Stål)). By using electrical penetration graph (EPG), this study was conducted to investigate any differential effect of pymetrozine on the feeding behaviors of four major rice sap-sucking insect species, 1) N. lugens, 2) white-backed planthopper (Sogatella furcifera (Horváth)), 3) small brown planthopper (Laodelphax striatellus (Fallén)), and 4) green rice leafhopper (Nephotettix cincticeps Uhler). On pymetrozine-free TN1 rice plants, white-backed planthopper and small brown planthopper showed a significantly less activity in the phloem phases than brown planthopper or green rice leafhopper while green rice leafhopper engaged in relatively more xylem ingestion than brown planthopper, white-backed planthopper, and small brown planthopper. On the plants treated with 100 mg liter-1 of pymetrozine, all four insect species showed significant increases, in total duration of nonprobing and significant decreases in the activities in phloem tissue, while all species showed similar feeding behavior during the pathway and xylem phases. This study revealed that, regardless of whether the insects on untreated plants spent more time feeding on phloem than xylem (brown planthopper) or more time on xylem than phloem (green rice leafhopper) or similar times on phloem and xylem (white-backed planthopper and small brown planthopper), their feeding behavior was disturbed by pymetrozine and exhibited similar patterns of sharp decline in activity in the phloem tissue and a significant increase the nonprobing.

Effect of synergists on susceptibility to chlorantraniliprole in field populations of Chilo suppressalis (Lepidoptera: Pyralidae).

ABSTRACT The Asiatice stem borer, Chilo suppressalis (Walker), an important rice insect pest in China, has developed resistances to several classes of insecticides. To control C. suppressalis, chlorantraniliprole has been introduced as a novel insecticide in rice field since 2008. It is an anthranilic diamide insecticide that binds and activates ryanodine receptors (RyR). The susceptibility of field populations of C. suppressalis to chlorantraniliprole was determined in this study. The hypotheses of equality and parallelism showed that regression lines in the tested five populations were neither equal nor parallel. The Ruian, Cangnan, and Liangyungang populations (RA12, CN12, and LYG12) collected in 2012 had lower LD50 values, whereas the Zhuji populations (ZJ12 and ZJ13) collected in 2012 and 2013 were ≈15 times more tolerant than the RA12 population. To determine the potential mechanisms involved in this tolerance variation, synergism bioassays were performed. Significant differences in susceptibility were found between without synergist and with synergist for the three populations (RA12, LYG12, and ZJ13), based on the tests for the hypotheses of equality. In RA12 and LYG12 populations with chlorantraniliprole, the addition of piperonyl butoxide (PBO) significantly synergized the activity, with synergism ratios of 2.68- and 2.33-fold, respectively, whereas addition of S,S,S-tributyl phosphorotrithioate (DEF) and diethyl maleate (DEM) had no synergist effect. In ZJ13 population with chlorantraniliprole, the addition of PBO and DEF increased synergism ratios by 12.43- and 6.31-fold, respectively, whereas addition of DEM had no significant effect on the toxicity against ZJ13 larvae. These susceptibility and synergism data suggested that detoxification enzymes might be involved in the tolerance variation to chlorantraniliprole in field populations of C. suppressalis.

Host Plant Probing Analysis Reveals Quick Settlement of the Solenopsis Mealybug During Host Shift

ABSTRACT Quantitative feeding behaviors were analyzed by electronic penetration graph technique to evaluate the resources utilization efficiency of the solenopsis mealybug, Phenacoccus solenopsis (Tinsley) (Hemiptera: Pseudococcidae), transferred to a novel host. Both nonphloem and phloem factors were contributed to the host availability during host shift; while only “prephloem” factor was involved with their offspring’s fitness to the transferred host, on which they fed as effectively as their mothers did on the origin host. Different performances on different hosts were supposed to have relations with the diverse phloem components, rather than feeding behaviors. P. solenopsis could try and exploit an efficient stylet pathway to reach the phloem, which would be an importance factor to account for the expansion of the host range and adaptations to different hosts. High efficient feeding behaviors of P. solenopsis in the current study manifested its capability of resource utilization to the novel host, which was suggested to be advantageous for its host shift, and to be the explanation for rapid host shifts associated with its broad host range and quick settlement.