Research On Loss Estimation And Economic Threshold Of The Yellow Peach Moth,Conogethes Punctiferalis,on Summer Maize

The yellow peach moth,Conogethes punctiferalis?Guenée??Lepidoptera:Crambidae?,is progressively serious in many areas in China,and causes serious loss to a wide variety of field crops,fruits and forest trees.In recent 20 years,due to the adjustment of planting pattern,climate warming and improper control and management or failure of control,the pest has caused serious loss of maize in Huang-Huai-Hai Region with the decrease of yield and quality,and become an important pest on maize.In this paper,the effects of yield traits and incidence of ear rot diseases caused by Conogethes punctiferalis larvae was researched by natural and artificial infestation methods,and the relation curve between yield loss rate and population density of the yellow peach moth was formulated.The insecticides were screened to control the larvae and the economic threshold of the yellow peach moth on summer maize was worked out.The results can provide an important theoretical basis and guidance for the scientific control of the pest.1.The results showed the yellow peach moth larvae can influence maize yield by shortening ear length,decreasing the number of grains per row of ear and reducing the hundred-grain weight.And yield loss increases with larva density.The yield loss would increase with the larva densities.And the damage of the pest would aggravate the occurrence rate of ear rot.In the natural infestation results,when the larva density was 2 larvae per ear,the hundred-grain weight?33.83 g?was significantly lower than the control group?P<0.05?,and when the larva density was 10 larvae per ear,the ear length?17.87 cm?,the ear diameter?23.80 cm?and the number of grains per row of ear?29.33 grains?were significantly different from the control group?P<0.05?.In artificial infestation results in 2018,when the larva densities were 2 larvae per ear,the number of grains per row of ear?34.45 grains?and the average ear rot rate?57.78%?were significantly different from the control group?P<0.05?.And when the larva density were4 larvae per ear,the ear length?18.02 cm?and the hundred-grain weight?31.48 g?were significantly different from the control group?P<0.05?.In the artificial infestation results in2019,when the larva density were 2 larvae per ear,the number of grains per row of ear?36.38grains?,the hundred-grain weight?29.69 g?and the average ear rot rate?46.67%?were significantly different from the control group?P<0.05?,and when the larva density were 4larvae per ear,the ear length?17.68 cm?and were significantly different from the control group?P<0.05?.And the upper part of the ear usually suffered the most serious damage when the larvae were attached to the top of the ear,the larvae also migrated to the lower middle to harm as the density increases.2.In stomach action efficacy,both the 20%chlorantraniliprole SC and 5%emamectin benzoate WG diluting 5000 and 6000 times,10%cyantraniliprole OD diluting 3000 times had good control efficacy for the pest,with 90%or more in 72h.In the contact action efficacy,5000-and 6000-time dilutions of the 20%chlorantraniliprole SC had good control effectiveness with more than 80%in 72h.Based on the laboratory results,3000,4000 and 5000 times dilutions of20%chlorantraniliprole SC was selected for controlling the pest in the field.The control efficacy of the three treatments was 96.40%,94.1%and 83.4%at 4d,respectively,showing the good control efficacy.The ear length?18.3cm?,grains number per row?35.2 grains?,hundred-grain weight?33.0 g?of the maize ears and the average ear rot rate?17.8%?in 3000-time dilution treatment was significantly higher than that in the control treatment?P<0.05?.3000-time dilution of 20%chlorantraniliprole SC can be selected to control the pest in maize field,and the results can provide sound theoretical bases for controlling the yellow peach moth and the determination of the economic threshold of the pest.3.In the natural infestation method,the relation between yield loss rates and larvae densities was an exponential function model y=0.023394e^0.236901x?R²=0.9876,F=398.6624,P<0.01?.In the artificial infestation method,the relation between yield loss rates and larva densities in 2018 was power function model y=0.017392x^1.1236?R²=0.9958,F=958.4172,P<0.01?and linear function y=0.023562x-0.00819?R²=0.9932,F=588.3026,P<0.01?.The results in 2019 showed that regression curve is power function y=0.031058x^0.8559?R²=0.9975,F=1599.116,P<0.01?and linear function y=0.021965x+0.00842239?R²=0.9946,F=737.4019,P<0.01?.According to several economic threshold models,when only loss recovery was considered,the economic threshold would be 100 larvae per 100 ears and 110eggs per 100 plants with the standard of larva and fertilized eggs,respectively.Taking into account the population dynamics and spatial distribution of yellow peach moth in the summer maize field,it is suggested that when yellow peach moth eggs and larvae in August were monitored in maize field by the appropriate sampling method and when the densities of eggs and larvae reach the economic threshold above,chemical control measures must be taken.