Studies On Phenylpyrazole Insecticide Resistance Risk Assessment And Cross-Resistance In N. Lugens

The brown planthopper (BPH) Nilaparvata lugens (stal) has been one kind of the most devastating pests of rice in Asia for a long time. Recently, N. lugens outbreaks have occurred more frequently in Yangtze River Delta areas in China. So far, chemical control is still the major method for suppressing N. lugens. However, there is a rapid increase in resistance of N. lugens to the major insecticides such as phenylpyrazole recently. Therefore, it is important to continue to study the susceptibility or resistance to conventional insecticides in BPH in order to provide accordances for insecticide resistance management of the brown planthopper, N. lugens (stal).The aim of this study including:monitoring the insecticides resistance in N. lugens: assessing resistance risk for fipronil by laboratory screen; studying the cross-resistance to three kinds of phenylpyrazole insecticides and testing the toxicity and fertility effects of chlopyrifos to N. lugens.1 insecticide resistance detection and monitoring in N. lugensIn order to establish the strategies of insecticides resistance management, it is necessary to make clear the current situation of resistance of N. lugens to conventional insecticides. The resistance level to several insecticides of 15 populations of N. lugens from nine provinces were examined by dipping methods from 2008 to 2009. The results showed that variation of the resistance level to different insecticides is signifiant in N. lugens. In 2008-2009, the resistance to fipronil were low to medium level (RR=9.0-32.5 -fold) and medium to high level (RR=24.7-44.9 -fold), respectively. And the resistance to fipronil sharply increased with the immigration route variation of N. lugens rapidly. The resistance of imidacloprid was still monitored after prohibition of this medicament. Its resistance level was extremely high (RR=210.1-381.0 -fold). The resistance of N. lugens collected from 6 locations of six provinces in 2009 to thiamethoxam and buprofezin were low to medium level. having rised slowly.2 Resistance risk assessment of fipronil resistance in N. lugensTo assess the resistance risk of fipronil, the resistance selection experiments were conducted in laboratory. Xiaogan population which had been collected in 2007 were selected successively with fipronil in the laboratory. After 18 generations selection, the resistance ratio was increased from 7.5- to 42.8-fold (LC50 value was rised from 0.289 mg a.i./L to 1.646 mg a.i./L), with the resistance ratio increasing by 5.7-fold. The realized heritability (h2) of pre-stage and late stage were calculated by Tabashnik method, the former was 0.0998 (1-9 generation) and the latter was 0.5370 (9-18 generation). h2 was 0.2958 (1-18 generation) in the whole selection process. The result showed that if fipronil was continued to use widely, the resistance to fipronil would rise rapidly;and the speed was increased with the selection pressure positively.3 Cross-resistance of fipronil resistance in N. lugensWhen butene-fipronil and ethiprole have not been used in wide regions, the cross-resistance between butene-fipronil. ethiprole and fipronil were detected with two methods—one was monitoring the resistance by field populations, the other is testing the cross-resistance by laboratory populations selected with fipronil. The result showed that those six field populations which have had medium to high resistance to fipronil (RR=24.7-44.9 -fold) had high level resistance to ethiprole (RR=45.1-96.6 -fold) yet the sensitivity decreased (RR=3.4-4.5 -fold). When the resistance level of selected population had rised by 5.7-fold, the resistance level to ethiprole rised by 4.0-fold,1.5-fold to butene-fipronil. These results confirmed that N. lugens would have high level cross-resistance to ethiprole and low level to butene-fipronil after they had having high level resistance to fipronil.4 Assessment of biological activity and fertility effect of chlopyrifos against N. lugensBecause of the increasing resistance to imidacloprid and fipronil, chlopyrifos has became one of the alternative insecticides to control N. lugens. In this study, the biological activity and fertility effects of chlopyrifos were determined. The results showed that when 3rd instar nymphs were treated with the sub-lethal dose (LC5=0.64mg a.i./L) of pesiticides, there was no significant difference between chlopyrifos treatment and CK when compared by those varibles:egg-production amount, the number of egg masses, and spawning duration of N. lugens. The field population of N. lugens from 2008 to 2009 was susceptible or had a low resistance to chlopyrifos.