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1. Longyou County Plant Protection and Quarantine Station of Zhejiang Province, Longyou 324400, China; 2. Quzhou City Plant Protection and Quarantine Station of Zhejiang Province, Quzhou 324000, China

Abstract In recent years, the occurrence of riceChilosuppressalis(Walker) in Longyou County of Zhejiang Province has increased year by year and has become aggravated. This poses a great threat to the safety of rice production. In order to curb the recurrence momentum of riceC.suppressalis, according to the dynamic monitoring and field system survey of riceC.suppressalisin Longyou County since 2015, the causes of the annual increase of riceC.suppressalisin recent years were analyzed, and the recurrence area ofC.suppressaliswas introduced, and finally some prevention and control measures were put forward.

Key words Chilosuppressalis(Walker), Causes of recurrence, Prevention and control measures

1 Introduction

Longyou County is located in the western area of Zhejiang Province, in the middle of the Jinqu Basin. In recent years, the rice planting area of the whole Longyou county is about 21 333 ha. The area of early, middle and late rice varieties accounts for 24.6%, 48.6% and 26.8%, respectively. Thus, Longyou County is a typical single harvest and double harvest mixed planting area.Chilosuppressalis(Walker) is one of the main pests of rice in Longyou County, and it occurs 3 to 4 generations annually. After 2015, due to the long-term use of pesticides such as Chlorantraniliprole (C18H14BrCl2N5O2), the level of resistance toC.suppressalishas increased significantly, combined with changes in rice varieties, evolution of farming systems, changes in climatic conditions,etc. The base ofC.suppressalishas rebounded significantly, and the damage has increased year by year. In 2017, the area of riceC.suppressaliswas 44 667 ha, the area of control was 46 667 ha, the loss of rice in the field was 3%-5%, and the loss of rice caused by serious field was greater than 20%. In view of this situation, we sorted the data of many years on the occurrence and control of riceC.suppressalisin Longyou County, analyzed the causes of the recurrence of riceC.suppressalisin recent years, and proposed a series of comprehensive prevention and control measures forC.suppressalis.

2 Causes of recurrence of RiceC.suppressalis in recent years

2.1Greatincreaseofthedrugresistance,gradualincreaseofresidualnumberafterwinter,significantincreaseinrecentthreeyearsIn recent years, the level of resistance to pesticides such as Chlorantraniliprole and other pesticides has increased significantly (in 2017, the inspection results of Longyou County indicated that the resistance ofC.suppressalisto Chlorantraniliprole was up to 317.12 times) and the effect of warm winter, the residual number after winter increased year by year. According to the residualC.suppressalisnumber results of Longyou Station in Daluding Village and Liantang Village of Rashi Town, Wukan Village in Mohuan Township, Shilipu in Donghua Residential Area, Shandi Village and Houting Village in Longzhou Residential Area, Zhitang Village and Yaotang Village in Hengshan Town in April 16, 2018, the weighted average of the residual number ofC.suppressalisafter winter in the whole county was 2 297, 2 597, 3 636, and 5 256 heads in 667 m2land in 2014-2017, respectively. The residual number ofC.suppressalisafter winter was gradually increased, especially recent three years; in 2016-2018, the residual number ofC.suppressalisafter winter was 1.4 times, 2.02 times, and 2.42 times of that in 2015.

2.2Largenumberofemergingmothsinthewinteringgeneration,largemothpeaknumber,andlongmothpeakdayDue to increase in residual number after winter and high temperature in early spring, the number of emerging moths in wintering generation gradually increased, the moth peak number was large and moth peak day was long, leading to gradual aggravation of first generationC.suppressalisin early season rice. According to monitoring ofC.suppressalissex attractant system in Liucun Village in Longzhou Residential Area, the quantity of wintering generation emerging moths trapped in 5 trays in peak day was 239 pieces in 2018, 195 pieces in 2017, and 90 pieces in 2016; the total moths of wintering generation emerging moths trapped in 5 trays was 3 768 pieces in 2018, 2 297 pieces in 2017, and 1 223 pieces in 2016. The number of days with more than 80 pieces of the wintering generation emerging moths trapped in 5 trays was 19 in 2018, 10 and 2 in 2017 and 2in 2016, as shown in Fig.1.

2.3Longdurationofthefirstandsecondgenerationof"mediummoths"andextremedisuniformfieldstateThe duration of the first and second generation of "medium moths" in emergingC.suppressalis(the number of moths daily trapped in 5 trays was 40-80 pieces) was long. According to monitoring ofC.suppressalissex attractant system in Liucun Village in Longzhou Residential Area, the average number of the first and second generation of emerging moths daily trapped in 5 trays was 39 and 30 pieces, respectively; the number of days for "medium moths" (the number of moths daily trapped in 5 trays was 40-80 pieces) was 23 and 7 d; the average number of the first and second generation of emerging moths daily trapped in 5 trays in 2017 was 27 and 7 pieces, respectively; the number of days for "medium moths" (the number of moths daily trapped in 5 trays was 40-80 pieces) was 4 and 0 d (Fig.2 and Fig.3); the state of moths in the field was extremely disuniform, the coexistence of moths, eggs, larvae and pupa was very common, so the difficulty in prevention and control was great (the comparison of field hazard peaks ofC.suppressaliswas illustrated in Fig.5 to Fig.7). According to the survey of residual number after the treatment of the first and second generation of riceC.suppressalisin the field in 2018, the ratio of second, third, fourth, fifth and sixth years and pupa was 17∶53∶16∶4∶7∶3; the survey of residual number after the treatment of the third generation of riceC.suppressalis, the the ratio of third, fourth, fifth and sixth years and pupa was 52∶28∶12∶4∶4.

Fig.1ComparisonofwinteringgenerationChilosuppressalistrappedbysexattractantin2016-2018

Fig.2ComparisonofthefirstgenerationofChilosuppressalistrappedbysexattractantin2017-2018

2.4Obvioustailpeakofthefirstgenerationmothsandhighpeakofthethirdgenerationofmoths,andaccelerationofgenerationprocessDue to the influence of the warm winter and high temperature in early spring, the high peak of wintering moths in the year of 2018 was 15 days earlier than in 2017 (Fig.1). In 2017 and 2018, the tail peak of the first generation moths ofC.suppressaliswas obvious in the early season rice, and the quantity of moths was larger than the front peak, and the tail peak mainly threatened the the single harvest paddy field in the single harvest and double harvest mixed area, and it had serious damage to the single harvest paddy field where only one time of prevention was carried out or it was no time for prevention and control (Fig.7). In 2017 and 2018,C.suppressaliscompleted two complete generations in the early season rice (Fig.2). In 2017, the high peak of third generation moths ofC.suppressaliswas obvious and in large quantity. The trend of continuous cropping late season rice finishing the fourth complete generation was obvious (Fig.4). As a result,C.suppressaliscaused serious damage to late season paddy field where no prevention and control measures were carried out or it was no time for prevention and control (Fig.6).

Fig.3ComparisonofthesecondgenerationofChilosuppressalistrappedbythewavepeakofsexattractantin2017-2018

Fig.4ComparisonofthethirdgenerationofChilosuppressalistrappedbythewavepeakofsexattractantin2016-2017

2.5Manyvarietiesofrice,diversifiedcultivationmethods,unevengrowthperiod,manybridgesandfields,andabundanthostsAccording to the incomplete statistics of the Longyou County Seed Station, there are more than 50 varieties of rice planted in Longyou County in recent years. The rice varieties are complicated, the growth period is uneven, the bridge fields are increased, and the foods ofC.suppressalisare rich. From late May to mid-September, there are almost all rice in the growth stage such as tillering stage and rupturing stage, which is very favorable for the spawning of imagoes ofC.suppressalisand larvae making irregular short tunnels in the rice stem. Besides, the promotion of thick-stem large panicle super rice varieties, diversification of cultivation methods, coexistence of single harvest and double harvest rice mixed planting, transplanting rice, direct seeding rice, shoot culture rice, and reclaimed rice further aggravated the occurrence and harm ofC.suppressalis.

Fig.5ComparisonofwavepeaksofhazardsofChilosuppressalistoearlyseasonpaddyfieldin2016-2018

Fig.6ComparisonofwavepeaksofhazardsofChilosuppressalistocontinuouscroppingpaddyfieldin2015-2017

Fig.7ComparisonofwavepeaksofhazardsofChilosuppressalistosingleharvestpaddyfieldin2015-2017

3 Prevention and control measures forC.suppressalis

3.1StrengtheningadministrativepromotionandimplementingpropagandaandtechnicaltrainingIn 2017, Longyou County People’s Government Office issued theNoticeonImplementingthePreventionandControlofC.suppressalis(Long Zheng Ban Fa[2017]No. 34), carried out the TV propaganda ofC.suppressalis"pouring water to kill larvae", to strengthen the popularization of the technical measures of "pouring water to kill larvae" forC.suppressalis. In addition, Longyou County held trainings of comprehensive prevention and control technology for riceC.suppressalis. to further implement the key technical measures for comprehensive prevention and control ofC.suppressalis.

3.2StrengtheningthedynamicmonitoringoftheoccurrenceofC.suppressalis,promptlyprovidingwarningandguidanceforpreventionandcontrolOn the basis of improving and standardizing the systemetic observation of the observation site forChilosuppressalissex attractant in Liucun Village of Longzhou Residential Area and Wangjia Village of Hu Town, three new sets of Ningbo Newcom digital monitoring instruments and two sets of Beijing Ecoman remote control systems for remote control ofC.suppressalis, to constantly improve the pest monitoring information level, promote regional forecasting process and provide a scientific basis for accurate forecasting and prevention and control ofC.suppressalis.

3.3Strengtheningregionalcomprehensivepreventionandcontrol,andtakingvarioustechnicalmeasures

3.3.1Cleaning stubble and tillage, pouring water to kill larvae, and reducing the base number ofC.suppressalispopulation. It is recommended to implement low stubble harvesting, reduce rice pile height as much as possible during late rice harvesting, carry out rice pile smashing, reduce the amount of wintering insects; according to the monitoring situation of regionalC.suppressalis, implement tillage and put the residual stubble and straws into soil for winter idle paddy field and manure field, pour water to submerge for 7-10 d, so as to kill wintering generation larvae and reduce the base number ofC.suppressalispopulation.

3.3.2Planting Vetiveria zizanioides (L.) Nash to attractC.suppressalisto reduce the amount of eggs in the field. It is recommended to plant V. zizanioides (L.) Nash along two sides of tillage roads of the paddy field to attractC.suppressalis, the spacing should be 3-5 m, to trap theC.suppressalisand reduce the amount of eggs in rice.

3.3.3Setting traps in a large area to attract and kill adultC.suppressalisin the whole process. From the wintering generation adultC.suppressalisemerging stage, it is recommended to useC.suppressalissex attractant to trap and kill adult maleC.suppressalis; use the sex attractant in a large area, set 15 set attractants for one hectare of paddy field, and adopt the same method for non-paddy field; the setting height of sex attractant should be 50-80 cm above the ground, and adopt long-term attractant chips with effect longer than two months, and promptly replace the attractant chips.

3.3.4Properly adjusting the prevention and control strategies, and using pesticides in a scientific and precise manner. It is recommended to take prevention and control measures in accordance with the different base number ofC.suppressalispopulation in different regions. For example, for double harvest rice in single harvest and double harvest mixed planting regions with large base

number ofC.suppressalispopulation, it is necessary to take strict control ofC.suppressalis, attach great importance to the prevention and control of fourth generation ofC.suppressalis; for single harvest rice in single harvest and double harvest mixed planting regions with large base number ofC.suppressalispopulation, it is necessary to focus on the prevention and control of two key points of front and tail peaks of the second generation ofC.suppressalis, to reduce the base number of the third generation ofC.suppressalis. Finally, it is recommended to select the appropriate pesticide, strictly control the pesticide application volume and times, and strengthen the rotation of pesticides, to slow down the drug resistance ofC.suppressalis.