Liezhong Chen

Dynamics of Yeast-like Symbiote and Its Relationship with the Virulence of Brown Planthopper, Nilaparvata lugens Stal, to Resistant Rice Varieties

Abstract Abundance of the yeast-like symbiote (YLS) in brown planthopper (BPH), Nilaparvata lugens Stal, collected from rice fields in China and obtained from International Rice Research Institute (IRRI), was monitored. The role of YLS in nymph survival rate, development and adult reproduction, and activities of transaminases in BPH on different resistant rice varieties were examined. Also, the relationship between YLS and virulence shifts of BPH to resistant rice varieties was discussed. The results indicated that the virulence of BPH populations to resistant rice varieties was strongly related to the abundance of YLS in 5th instar nymphs and brachy-pterous females of BPH field populations at Nanning in South China and Hangzhou in East China, showing the more abundance of YLS in BPH, the higher virulence of BPH to resistant rice varieties, while no obvious differences in YLS abundance were monitored between three BPH biotypes. Numbers of YLS reduced significantly in female adult of BPH biotype 1 fed on resistant rice varieties IR26, Mudgo and ASD7, compared with that fed on susceptible rice variety TNI. The lowest YLS abundance of BPH from field population was found in 2nd generation successively fed on resistant varieties, and the number of YLS was resumed at 4th generation when the BPH has adapted the resistant varieties. The markedly lower nymphal survival rate, adult fecundity and activities of alanine and aspartic transminase, and significantly longer nymph duration in the three aposymbiotic biotypes than in the symbiotic ones were recorded on both susceptible and resistant rice varieties. However, the much greater differences between aposymbiotic and symbiotic BPH were found on the inadaptable resistant rice varieties than that on the fitness resistant rice varieties. Those results implied that YLS in BPH should play a crucial role in the virulent shift of BPH populations to resistant rice varieties.

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

BACKGROUNDnPymetrozine 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.nnnRESULTSnThe 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.nnnCONCLUSIONnThe 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.

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.