Resistance to diamides, a new class of insecticides, in the smaller tea tortrix honmai Yasuda (: ) in tea fields of Prefecture,

Toru Uchiyama and Akihito Ozawa

Tea Research Center, Shizuoka Res. Inst. of Agric. and For., 1706-11 Kurasawa, Kikugawa, Shizuoka 439-0002, Japan Correspondence email: [email protected]

Summary We conducted a 6-year study (2006–2011) for investigating the susceptibility of the smaller tea tortrix Adoxophes honmai Yasuda to the diamide insecticides, namely, flubendiamide and chlorantraniliprole in the Shimada-Yui tea fields in the Makinihara area of , Japan. The corrected mortality of the populations to the two diamide insecticides at 10 days after treatment at 2000 dilution (representing an ordinary dose) indicated that mortality after practical application of the insecticides at this dose was limited.

The LC50 values of flubendiamide showed a rapid annual increase from 2007 (16.2 ppm) to 2011 August

(161 ppm), exceeding the registration dose of 100 ppm from 2010 onward. Further, the LC50 values of chlorantraniliprole increased sharply from 2010 (25.3 ppm) to 2011 August (98.8 ppm), exceeding the registration dose of 50 ppm in 2011. In the pest control calendar, the accumulation adoption number exceeded LC50 at 10 days after the release of A. honmai larvae by three and two times, respectively, for flubendiamide and chlorantraniliprole.

Introduction Shizuoka Prefecture is the most important tea-producing district in Japan. However, in recent years, the smaller tea tortrix Adoxophes honmai Yasuda has begun to cause serious damage to tea leaves. The reduced effect of diacylhydrazine (DAH) analogs insect growth regulators (IGRs) at controlling in A. honmai was initially observed by tea famers in around 2004. We investigated the susceptibility of A. honmai to DAH analog IGRs in tea fields in the area of Shizuoka Prefecture. Consequently, we elucidated the level of resistance of A. honmai to DAH analog IGRs from 2005 onward (Uchyama et al., 2013, Fig. 1). In addition, over the same timeframe, we investigated the susceptibility of A. honmai to diamide insecticides, which is a new class of insecticide with different chemistry, which had previously been reported to have excellent controlling effect on lepidopteran pests, including A. honmai. To our knowledge, the current study is the first to report a high level of resistance by Fig. 1. Annual changes in the LC resistance ratio of A. honmai to two diamide insecticides, namely, 50 Adoxophyes honmai larvae to 4 insect growth regulator flubendiamide and chlorantraniliprole, based on the (IGR) insecticides. Tested populations were collected data collected from 2006 to 2011. annually from tea fields at Shimada-Yui in Shizuoka Prefecture, Japan. Dotted lines indicate regression lines. Materials and methods . From 2006 to 2011, seven successive populations of A. honmai were collected from adjoining tea fields in Shimada-Yui, located in the Makinohara area of Shizuoka Prefecture, Japan. More than 20 adult females were collected from each A. honmai population to obtain egg masses. The insects were reared in groups, on an artificial diet (Insecta LFS, Nihon-Nosan Kogyo Co. Ltd., Yokohama, Japan), in an insectary at 25 °C under a 16-h light:8-h dark photoperiod. F1 or F2 larvae were used for the bioassays. A susceptible strain (Kanaya) to the insecticides was used as a control.

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Leaf dipping bioassay. The leaf dipping bioassay method was used to test the susceptibility of A. honmai to the two diamide insecticides, namely, flubendiamide and chlorantraniliprole. The insecticides were mixed with tap water to generate 4–6 serial dilutions. The tea leaves were collected from the tea field of our center where pesticides are not used. The leaves were dipped in the insecticide solution for 10 s and dried on paper. Then, 6–7 treated leaves were transferred to a styrol cup containing a layer of filter paper. Afterward, ten 2nd or 3rd A. honmai instar larvae were placed in the cups, which were covered using a cap. All treatments were repeated three times. The cups were stored at 25 °C and a 16L:8D h photoperiod. Larvae were scored for mortality after eight and 10 days.

Results and discussion 1. The corrected mortality of flubendiamde at 10 days after treatment by using 2000 and 8000 dilutions were both lower in August 2011 than in 2007 for the Shimada-Yui A. honmai populations (Table 1). The corrected mortality of chlorantraniliprole was also lower at 10 days after treatment by using the above two dilutions in August 2011 than in 2010 (Table 1). The corrected mortality of A. honmai for the two diamide insecticides at 10 days after treatment by using the 2000 dilution (representing an ordinary dose) indicated

Table 1. Effect of two diamide insecticides against the 2nd and 3rd Adoxophyes honmai instar larvae. Corrected mortalityc [%] (N d) Insecticides b Days after Susceptible a Dilution Shiamada-Yui population (Formulation , %AI) release strain 2006 2007 2008 2009 2010 2011 June 2011 August (Kanaya) Flubendiamide 2,000 8 90.0f (30) 90.3 (30) 73.5 (26) 84.7 (30) 24.3 (31) 16.7 (30) 21.5 (30) 100 (30) (W, 20)e 10 ―g 96.8 85.2 92.7 52.5 34.1 32.0 100 8,000 8 86.7f (30) 45.2 (30) 14.8 (28) 38.8 (30) 0 (28) 3.70 (26) 0 (29) 100 (29) 10 ― 51.6 26.2 46.0 15.3 7.41 0 100 Chlorantraniliprole 2,000 8 ― ― ― ― 72.0 (29) 36.7 (30) 20.9 (27) 100 (30) (F, 10) 10 ― ― ― ― 72.0 45.6 21.9 100 8,000 8 ― ― ― ― 22.6 (30) 3.33 (30) 0 (29) 100 (30) 10 ― ― ― ― 27.1 10.4 0 100 a W: Wettable powder, F: Flowable. b Upper numerals are ordinary dose of each insecticide. c Corrected mortality by method of Abbott(1925). d Number of larvae tested. e Formulation of flubendiamide at 2011 June and August is 18% flowable by formulation change; therefore, 18% flowable was adjusted to same %AI of wettable powder. f g This data is on 7 days after release. No data. 200 2011 that the mortality after practical application of this Flubendiamide August dose was limited (Table 1). 150 Chlorantraniliprole 2011 2010 August 2. The LC50 values of flubendiamide showed a rapid 100 annual increase from 2007 (16.2 ppm) to 2011 August (161 ppm), exceeding the registration dose of 100 ppm 50 2008 (ppm) at 10 days after release after days at 10 (ppm) from 2010 onwards (Fig. 2). The LC50 values of 50 2007 chlorantraniliprole also rose sharply from 2010 (25.3 LC 2010 2009 0 ppm) to 2011 August (98.8 ppm), exceeding the 0 1 2 3 4 registration dose of 50 ppm in 2011 (Fig. 2). In the The accumulation adoption number pest control calendar, the accumulation adoption to the pest control calender Fig. 2. The relationship between the number of times number exceeded LC50 at 10 days after the release of A. that the accumulation adoption number exceeded LC50 honmai larvae by three and two times, respectively, for at 10 days after the release of Adoxophyes honmai flubendiamide and chlorantraniliprole (Fig. 2). larvae on the pest control calendar for two diamide insecticides. The pest control calendar is compiled by References the agricultural cooperative association that has Uchiyama, T., Ozawa, A., Yoo, J. (2013) jurisdiction over Shimada-Yui. Susceptibility and resistance to diacylhydrazine

2 analog insect growth regulator insecticides in the smaller tea tortrix, Adoxophyes honmai Yasuda (Lepidoptera: Tortricidae), collected in tea fields in Shizuoka prefecture, Japan. Jpn. J. Appl. Entomol. Zool. 57:85-93 (in Japanese with English abstract)

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