ZHAO Xiu-Mei，ZHANG Shu-Quan，LUO Bao-Jun，QU Zhong-Cheng，LI Min，WANG Li-Da，WU Lin-Lin，LI Qing-Chao(Qiqihar Sub-academy of Heilongjiang Academy of Agricultural Sciences，Qiqihar，Heilongjiang 161006，China)

1 Introduction

Heilongjiang province is not only major grain producing area but also green agricultural production and processing base in China．Maize，whose area is the largest in Heilongjiang province，was grown 4.712 million hectares in 2009 and 5.2318 million hectares in 2011．The good harvest will play an important role in solving grain safety in China and achieving 50 billion kgs of gain yield in Heilongjiang province．

Ostrinia furnacalis is a pest，which caused the most serious economic losses for maize in Heilongjiang province．In general，estimates of yield losses by ostrinia furnacalis range from 5%to 10%，and 20%to 30%in some particular years．The yield losses are over 1.5 billion kgs，annually．The maize quality and grade were influenced seriously.

Longjiang county of Qiqihaer city was key demonstration county of environmental－friendly biocontrol against ostrinia furnacalis，and took on the demonstration project of controlling Ostrinia furnacalis by means of Trichogramma dendrolim in 46.7 thousand hectares of maize area．The control efficacy was determined by the correction parasitism rate，average control effect and restoration yield loss rate．Therefore，a scientific basis can be provided by this study for evaluating control efficacy of Trichogramma dendrolim against Ostrinia furnacalis

2 Materials and methods

2.1 Trichogramma dendrolim cards

Trichogramma dendrolim cards were produced by the Qiqihaer branch of Heilongjiang academy of agricultural sciences.

2.2 The experimental site and time

The experiment were conducted in the Dongsheng village of Longjiang county of Qiqihaer city in 2009 and 2010.

2.3 Date and frequency of Trichogramma dendrolim cards used

The date and frequency were determined according to adult emergence processing of Trichogramma dendrolim and the dynamic changes of insect pests lured by black light trap．When pupation rate of winter generation Ostrinia furnacalis reached 20%of total number，theTrichogrammadendrolim cardswere placed in the field at the first time after 10 days．Then the Trichogramma dendrolim cards were placed in the field at the second time after 7 days．The Trichogramma dendrolim cards were placed in the field twice a year．In 2009，Trichogramma dendrolim cards were placed on July 8 and July 15，respectively．In 2010，Trichogramma dendrolim cards were placed on July 5 and July 12，respectively.

2.4 The number of Trichogramma dendrolim and application method

The total number of Trichogramma dendrolim used was 225 thousand per hectare，and 60%at the first time，40% at the second time．The Trichogramma dendrolim cards are cut into small pieces according to the number of Trichogramma dendrolim needed，and placed in 223 m2per spot at 45 spots per hectare．A healthy corn leaf was cut into two pieces along the middle pulse．The card were placed on the half leaf，then lightly rolled into roller form towards the stem，pinned tightly with the toothpick or thread at last.

2.5 Control efficacies and evaluation methods

2.5.1 Investigation of correction parasitism rate

The number and parasitism rate of eggs were investigated in Trichogramma dendrolim district and control district in the field respectively，and were investigated on the seventh day after Trichogramma dendrolim cards were placed in the field at the last time，then parasitism rate was corrected according to calculating．Random samples were taken at 5 spots according to checkboard sampling，and 20 eggs of ostrinia furnacalis were investigated at a spot．After they were cultured in the petridish for 2 to 3 days，the number of parasitism eggs(egg mass became black)was recorded．The control district were set up in maize field beyond 400 meters against wind from the treated district，and investigation method was the same as above

Parasitism rate% =number of parasitism egg masses/number of total egg masses×100

Correction parasitism rate% = (parasitism egg masses in Trichogramma dendrolim district－parasitism egg masses in control district)/(1－parasitism rate in control district)×100

2.5.2 Investigation of average control effect

The maize plants were investigated in Trichogramma dendrolim district and control district through anatomical stem before maize was harvested in the last ten－ day period of September．The reduction rate of wounded plants，insect population and wormhole were calculated．Random samples were taken at 5 spots according to checkboard sampling，and 20 plants were investigated at a spot.

Rate of wounded plants(%)=The number of wounded plants/the total number of plants×100

Reduction rate= (The rate of wounded plants in control district－rate of wounded plants in Trichogramma dendrolim district)/The rate of wounded plants in control district×100

Average control effect= (The reduction rate of wounded plants+The reduction rate of insect population+The reduction rate of wormhole)÷3

2.5.3 Determination of restoration yield loss rate

The maize wound was divided into 4 wounded parts including spike top，spike below，spike stalk and stem，and the wounded plants were investigated according to wounded parts，then multiplied by the yield of wounded parts．The results were loss rate of yield．The loss rates of yield were constants in different wounded parts．

The loss rates of yield of spike top was 11.4%，spike below was 32.1%，spike stalk was 13.0%，stem was 5.84%.

The loss rates of yield= spike top loss rate of yield×wounded rate of spike top+spike below loss rate of yield×wounded rate of spike below+ spike stalk loss rate of yield×wounded rate of spike stalk+stem loss rate of yield×wounded rate of stem.

Restoration yield loss rate=yield loss rate of control－yield loss rate treated with Trichogramma dendrolim．

3 Results

3.1 Correction parasitism rate

The correction parasitism rate against ostrinia fur-nacalis egg masses in Trichogramma dendrolim district were 71.75%in 2009，73.57%in 2010，respectively．The results showed the parasitism of Trichogramma dendrolim against ostrinia furnacalis was more effective(Table 1)．

3.2 Average control effect

The results showed that the reduction rate of wounded plants was 67.08%，the reduction rate of insect population was 64.75%，the reduction rate of wormhole was 65.73%and the average control effect was 65.85%，respectively in 2009(Table 2)．The results showed that the reduction rate of wounded plants was 69.65%，the reduction rate of insect population was 71.24%，the reduction rate of wormhole was 69.83% and the average control effect was 70.24%，respectively in 2010(Table 2)．

3.3 Restoration yield loss rate

The results revealed that the restoration yield loss rate was 6.78%in 2009 and 7.97%in treated district(Table 3)．

3.4 Benefit analysis

The results showed that it was significant in benefit of using Trichogramma dendrolim to control ostrinia furnacalis．According to 600 kg per 667 m2of maize yield，the restoration yield loss rate was 6.78%，the restoration yield loss was 40.68 kg/667 m2，The price of maize was 1.3 yuan/Kg，The benefit increased was 52.88 yuan/667 m2，the input was 1.90 yuan/667 m2．Input and output ratio was 1∶27.8，respectively in 2009(Table 4)．

The restoration yield loss rate was 7.97%，the restoration yield loss was 47.82 kg/667 m2，the price of maize was 1.4 yuan/per Kg，the benefit increased was 66.95 yuan/667 m2，the input was 2.00 yuan/667 m2．Input and output ratio was 1∶33.5，respectively in 2010(Table 4).

Table 1 Survey of using Trichogramma dendrolim to control ostrinia furnacalis egg parasitism rate

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Table 4 Efficacy survey of using Trichogramma dendrolim to control ostrinia furnacalis

4 Discussion

The results of evaluation on field control efficacy of Trichogramma dendrolimi against Ostrinia furnacalis showed that the correction rates of Ostrinia furnacalis egg mass parasitism were 71.75%and 73.57%，the average control effect were 65.85%and 70.24%，the restoration yield loss rates were 6.78%and 7.97%，input－ output ratio at 1∶27.8 and 1∶33.5 in Longjiang county of Heilongjiang province in 2009 and 2010，respectively．The technology is a integration of advanced，practical，environmental safety，efficient biocontrol measures，embodies the“public plant protection，green plant protection”fully，has significant economic，social and ecological benefits．It is of farreaching significance to control corn borer damage effectively，ensure maize production and food security，improve the quality of maize and develop the ecofriendly agriculture.

China Plant Protection Manual．Corn pest control volumes．Chinese Agricultural Technology Extension and Service Center，2007．Beijing:China Agriculture Press.

Wu JX，2002．Agricultural Entomology．Beijing:China Agriculture Press.

Zhao XM，Zhang SQ，Li WY，2010．The control efficacy measurement and evaluation of Trichogramma against control corn borer in the field．Crops magazine，2:93 －94