Mekong BPH Highly Resistant to Fipronil, Imidacloprid & BPMC

by
P.V.Tuong, Director, Southern Pesticide Control & Testing Center
Plant Protection Department, Ho Chi Minh City, Vietnam
P. Garcia, L. Fabellar and K.L. Heong
International Rice Research Institute, Los Baños, Philippines

We evaluated the toxicities of 3 commonly used insecticide active ingredients of brown planthopper populations collected from 3 provinces, Tien Giang, Long An and An Giang,  in the Mekong Delta in 2009. The standardized method developed by the Rice Planthopper Project was used. All 3 populations show similar responses to the 3 active ingredients (Table 1 and Figure 1) implying that there was probably constant migration and mixing of the BPH populations in the provinces. For fipronil, the LD⁵⁰s in Tien Giang and An Giang was significantly different and the relative potency was found to be 2.33.

Table 1: Statistical details of toxicity responses of 3 insecticides on brown planthoppers collected from 3 locations in the Mekong Delta. (* in x1000 nanograms)

Insecticide	Locations	LD50*	Fiducial limits at 95% CL*		Slope (+ se)	Heterogeneity
BPMC	Tien Giang	30.437	21.890	54.325	1.83(0.44)	0.474
	Long An	24.450	18.353	42.190	1.84 (0.42)	0.180
	An Giang	22.939	17.473	34.884	1.81 (0.33)	0.090
Imidacloprid	Tien Giang	2.891	2.225	4.196	1.78  (0.32)	0.057
	Long An	3.077	2.372	4.430	1.79 (0.32)	0.220
	An Giang	3.035	2.294	4.404	1.84 (0.35)	0.200
Fipronil	Tien Giang	3.225	2.347	5.485	1.49 (0.31)	0.183
	Long An	2.068	1.617	2.717	1.87 (0.31)	0.510
	An Giang	1.380	1.039	1.749	1.93 (0.32)	0.520

Using data from Tien Giang we compared the LD⁵⁰s of the 3 insecticides with those obtained from China (Jinhua) Thailand (Ang Thong) and the Philippines reported earlier.  Details for these comparisons are in Table 2.

Table 2:  Statistical details of brown planthopper responses to 3 insecticides in the Philippines, Thailand, China and Vietnam.      (* in x1000 nanograms)

BPMC Population	LD50*	Fiducial limits at 95% CL*		Slope (+ se)	Heterogeneity
Pila, Phil	1.643	0.906	2.257	2.88 (0.43)	1.27
Ang Thong, Thai	1.416	1.101	1.740	2.06 (0.23)	0.52
Jinhua, China	44.792	24.249	61.856	2.46 (0.34)	2.13
Tien Giang, Vn	30.431	21.891	54.347	1.83 (0.44)	0.48

Parallelism Chi Sq. 6.86 p < 0.076. Slopes not significantly different, but Tien Giang significantly different from Pila.

Imidacloprid Population	LD50*	Fiducial limits at 95% CL*		Slope (+ se)	Heterogeneity
Pila, Phil	0.091	0.060	0.1.87	1.06 (0.23)	0.17
Ang Thong, Thai	0.507	0.266	0.749	3.23 (0.46)	2.25
Jin Hua, China	11.597	8.579	14.896	2.23 (0.20)	1.25
Tien Giang, Vn	2.891	2.226	4.193	1.79 (0.32)	0.06

Parallelism Chi Sq  38.8   p < 0.05   Slopes significantly different.

Fipronil Population	LD50*	Fiducial limits at 95% CL*		Slope (+ se)	Heterogeneity
Pila, Phil	0.055	0.020	0.101	1.43(0.23)	1.30
Ang Thong, Thai	0.115	0.059	0.194	1.96 (0.20)	2.75
Jin Hua, China	1.813	1.053	2.989	1.62 (0.17)	2.16
Tien Giang, Vn	3.225	2.349	5.480	1.49 (0.31)	0.18

Parallelism  Chi Sq 4.60  p = 0.203 . Slopes not significantly different.

We found that the Mekong populations were highly tolerant to BPMC, imidaclorpid and fipronil.  The relative potency ratios expressed using LD⁵⁰s for Pila, Philippines, the most susceptible population, are shown in Table 3.

Table 3:  Relative potency ratios with the LD50 of populations in the Philippines as the check of three insecticides in China, Thailand and Vietnam.

Insecticide	Tien Giang, VN	Jinhua, China	Ang Thong, Thai
BPMC	18.58^	27.34	0.86
Imidacloprid	31.77^	127.44^	5.57^
Fipronil	58.64	32.96	2.09

^  Estimated potency ratios because probit lines significantly different

For BPMC the slopes of all the probit lines were not significantly different however Ang Thong and Jinhua the slopes did not differ. Tolerance of the Mekong population was however ~ 19 to 22 times higher than that of the Philippines and Thailand. For imidacloprid, the slopes of the probit lines for China and Mekong were significantly different and thus were not comparable.  The estimated relative potency was x32 that of Pila but much lower than that of China.

Populations in the Mekong were most tolerant to fipronil. They were 58.6 times, 28 times and 1.8 times more tolerant than populations in the Philippines, Thailand and China, respectively. This might be due to long term (about 20 years) of the active ingredient being used for seed dressing rendering longer exposure of the insecticide to BPH. In late 2009, China decided to ban the use of fipronil apparently because of its high toxicity to bees and shell fish (http://www.echinachem.com/English/Information/ShowInfo.aspx?infoid=1218cd23-10cd-4692-80e3-1e267a1794a2 ). Because of the loss in effectiveness of this insecticide and other toxicity factors, continued use of this insecticide, especially as seed treatments, in rice production in the Mekong will need to be carefully reviewed.

In summary the order and folds of tolerance of the three insecticides in three countries were are below (the figures refer to the number of folds difference between two countries):

BPMC	China	1.5x >  Mekong	19x > Philippines	1.2x > Thailand
Imidacloprid	China	4x>  Mekong	6x>  Thailand	6 x> Philippines
Fipronil	Mekong	1.8x > China	16x>  Thailand	2 x> Philippines

Tagged as: imidacloprid, resistance to fipronil