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.


CONCLUSIONS
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.
State Key Laboratory Breeding Base for Zhejiang Sustainable Pest and Disease Control, Institute of Plant Protection and Microbiology, Zhejiang Academy of Agricultural Sciences, Hangzhou, China.
Yueping
Y
He
Li
L
Chen
Jianming
J
Chen
Juefeng
J
Zhang
Liezhong
L
Chen
Jinliang
J
Shen
Yu Cheng
YC
Zhu
D000818:Animals; D004594:Electrophysiology; D005247:Feeding Behavior / Q000187:drug effects; D006430:Hemiptera / Q000737:chemistry / Q000187:drug effects* / Q000502:physiology*; D007306:Insecticides / Q000633:toxicity*; D012275:Oryza / Q000469:parasitology*; D052585:Phloem / Q000469:parasitology*; D010935:Plant Diseases / Q000469:parasitology*; D014227:Triazines / Q000633:toxicity*
D007306:Insecticides; D014227:Triazines; C480311:pymetrozine