Efficacy Tests of Nine Insecticides on Tetranychus truncatus Ehara

Yinghao MA Aixue ZHANG Dayong JIN

Abstract ［Objectives］ This study was conducted to screen out pesticides that are highly effective against Tetranychus truncatus Ehara.

［Methods］ Nine kinds of pesticides were used to control pests on soybean. A petri dish efficacy test was first performed in laboratory, then a leaf efficacy test was performed in a greenhouse, and finally, three kinds of agents with good efficacy in the two tests were selected for field control tests.

［Results］ The indoor and outdoor test results showed that abamectin was the best agent, which showed efficacy higher than 96%, followed by bifenthrin, whose efficacy was higher than 93%. It can be seen that abamectin is the best choice for the prevention and control of T. truncatus , and bifenthrin can also be used according to the situation.

［Conclusions］ This study provides a theoretical basis for the control of T. truncatus .

Key words Tetranychus truncatus Ehara; Pesticides; Efficacy; Control

Received: February 5, 2020Accepted: March 28, 2020

Supported by the Cooperative Project Between the People餾 Republic of China and the Republic of Korea (413090094).

Yinghao MA (1997-), male, P. R. China, master, devoted to research about agricultural pest control technology.

*Corresponding author. E-mail: jindy@ybu.edu.cn.

Tetranychus truncatus Ehara has a very complex diet. It mainly harms soybean, corn and other food crops and vegetables such as eggplant and kidney bean, and even harms jujube, apple and other fruit trees, and its damage is spread all over the country［1-3］. In recent years, T. truncatus has been particularly harmful in the Northeast region, and its damage loss rate has reached 10%-30%［4］. With the warming of the global climate, the growth and development of T. truncatus has been provided with favorable environmental conditions, and the time to harm crops has been prolonged. In some areas, T. truncatus has caused disasters, which even caused crop failure［5］.The mite sucks the juice of plant leaves with a stab-sucking mouthpart, which seriously affects the photosynthesis of plants. The lightly damaged leaves show small yellow-white spots, and the severely damaged leaves have continuous spots thereon forming patches, lose green color entirely, and even wither and fall. Because of their small size, fast reproduction and damage to the back of the leaves, many pesticides have unsatisfactory control effects［6］.

In recent years, after high-toxicity high-residue pesticides have been eliminated, banned or restricted, how can we screen out agrochemicals with good effects and low residues has become an urgent problem to be solved［7］. Therefore, an efficacy and control test was carried out on 9 kinds of agrochemicals to experimental populations of T. truncatus , both indoors and outdoors, aiming to screen effective acaricides against T. truncatus and to provide a basis for its control.

Materials and Methods

Test materials

Test agents

Nine kinds of pesticides were purchased from the market and tested. The information of the pesticides is as follows:

Test mites

T. truncatus individuals were collected on the weeds in the greenhouse of Agricultural College, Yanbian University, and then reared with potted cowpea leaves in the laboratory for testing.

Test methods

Laboratory petri dish efficacy test

A layer of 1 cm thick absorbent cotton was spread in a petri dish with a diameter of 15 cm, and then a layer of filter paper was spread. Water was added to the petri dish to the height of the sponge. Fresh and clean soybean leaves were collected in a greenhouse, and laid on the filter paper with the back side facing up. There should be no gap between the leaves and the filter paper. One soybean leaf was placed in each petri dish, and then 30 adult mites were attached to the soybean leaf with a fine brush. After diluting each agent at a recommended concentration, the leaves with mites thereon were sprayed with a small sprayer. The number of live mites was investigated before and 1, 3 and 5 d after the application of pesticides, for the calculation of the death rate. Each agent was set with three repetitions, and water was used as a control check (CK).

Greenhouse pot test

In the laboratory efficacy test, agents with efficacy higher than 90% on the 5﹖h d was selected for further testing on potted soybeans in a greenhouse. Plastic pots with a diameter of 25 cm were selected, and 30 pots of soybean were planted. When the soybean plants grew with 5 leaves, 50 mites were attached to the soybean leaves in each pot with a fine brush. After diluting each agent at a recommended concentration, the leaves with mites thereon were sprayed with a small sprayer. The number of live mites was investigated before and 1, 4 and 7 d after the agent application, for the calculation of the death rate. Each agent was set with three repetitions, and water was used as a control check (CK).

Field soybean efficacy test

In the field test, three pesticides whose efficacy was more than 95% on the 7﹖h d were used for further efficacy test in the field. The soybean field in front of the greenhouse of the Agriculture College of Yanbian University was selected as a test field. It was divided into 20 plots in randomized block arrangement. There were 5 soybean plants in each plot (1 m×2 m) , and about 100 mites were connected to the leaves of each soybean plant. After investigating the number of pests on the 2﹏d d, the three kinds of agents were mixed with water at regular ratios and sprayed. Investigation was performed before and 1, 4 and 7 d after agent application for the calculation of the death rate and corrected death rate. Each treatment was repeated 5 times, with clear water as a CK.

Calculation methods

Death rate (%)=(Number of live pests before spraying-Number of live pests after spraying)/Number of live pests before spraying×100%

Corrected rate (%)=(Death rate in treatment-Death rate in control)/(1-Death rate in control)×100%

The data was subjected to variance analysis using SPSS11.5, and multiple comparisons were performed using Duncan餾 new complex range method.

Results and Analysis

Laboratory test results

The results of the laboratory petri dish efficacy test are shown in Table 2.

As shown in Table 2, there were differences in the efficacy of the nine different pesticides on T. truncatus at 1, 3 and 5 d after application. At 1 d after application, the agents with efficacy higher than 85% were abamectin, pyridaben spirodiclofen and thiamethoxam. There were five agents with efficacy higher than 90% at 3 d after application: abamectin, pyridaben spirodiclofen, thiamethoxam, bifenthrin and abamectin spirodiclofen. And 7 d after application, the agents with efficacy higher than 90% were abamectin, pyridaben spirodiclofen, thiamethoxam, bifenthrin, chlorfenapyr and abamectin spirodiclofen.

In the laboratory test, the 6 agents with efficacy higher than 90% on the 7﹖h d were further used for the pot test in a greenhouse.

Greenhouse test results

The results of the greenhouse pot test are shown in Table 3.

As shown in Table 3, there were also differences in the efficacy of six different pesticides on T. truncatus at 1, 4 and 7 d after application. Five agents with efficacy higher than 85% at 1 d after application were abamectin, bifenthrin, thiamethoxam, chlorfenapyr and pyridaben spirodiclofen. The drugs with efficacy higher than 90% at 4 d after treatment were abamectin, bifenthrin, chlorfenapyr and pyridaben spirodiclofen. The drugs with efficacy higher than 95% at 7 d after application were abamectin, bifenthrin and thiamethoxam.

In the greenhouse test, the three drugs with efficacy higher than 95% on the 7﹖h d were further used in the field efficacy test.

Field test results

The results of the field efficacy test are shown in Table 4.

Data in the same column followed by the same letter was not significantly different at the 5% level.

As shown in Table 4, there were also significant differences in the efficacy of the three pesticides on T. truncatus at 1, 4 and 7 d after application. Only abamectin showed efficacy higher than 90% at 1 d after application, and its efficacy was 92.14%; abamectin and bifenthrin showed efficacy more than 90% at 4 d after application, which was 93.68% and 91.88%, respectively; and only abamectin exhibited efficacy higher than 95% at 7 d after application, which reached 96.19%, while the efficacy of bifenthrin also reached 93.29%, and that of thiamethoxam was only 88.46%.

Conclusions and Discussion

The results of the indoor and outdoor agent screening tests showed that abamectin had the best field efficacy among the 9 pesticides. The efficacy was 92% on the 1﹕t d after its application, and reached 96% at 7 d after the application, showing excellent fast-acting property and high efficiency. The next was bifenthrin, the efficacy of which also reached 91% on the 4﹖h d after application and 93% on the 7﹖h d after application, also showing good quick-acting property and high efficiency.

It was found in the tests that in the peak period of T. truncatus , its population was large and its reproduction speed was fast. In order to improve the control effect and reduce the damage of crops, fast-acting and highly-effective agents must be selected. It can be seen that in production, abamectin is the first choice to control T. truncatus , followed by bifenthrin.

Agricultural Biotechnology2020

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Editor: Yingzhi GUANGProofreader: Xinxiu ZHU