DD Screens for Insect Capture: History
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Subjects: Agronomy
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The double-charged dipolar electric field screen (DD screen) has a strong attractive force that captures insects entering its electric field. The DD screen is useful for capturing small insects that pass through a conventional insect net, and unique derivatives of this screen have been invented to trap various insect pests on-site in a greenhouse.

  • aphid
  • attractive force
  • electrostatic field
  • electrostatic soil cover

1. Construction of DD Screens and Their Insect-Capturing Ability

Based on the arrangement of insulated conductor wires, DD screens are classified into three types: the single-layered type, possessing oppositely charged insulated conductor wires arranged alternately (Figure 4A); two-layered type; and three-layered type, possessing oppositely charged insulated conductor wires arranged in an offset configuration (Figure 4B,C). The two- and three-layered types have a shorter distance between insulated conductor wires than the single-layered type (Figure 4) and therefore create a stronger force when the same voltage is applied due to the higher potential difference.
Figure 4. Three types of DD screens for capturing insect pests and the static electric fields formed by the DD screens. (A) A unit of the single-layered DD screen, where oppositely charged insulated conductor wires are arrayed alternately. (B,C) Two- and three-layered DD screens. Two or three oppositely charged SM screen units were combined in an offset arrangement with the oppositely charged insulated conductor wires.
Toyoda et al. [52] discussed the insect-capturing ability of DD screens, in which they determined the appropriate voltage setting for capturing all insect pests tested. The assay was conducted by blowing the insects toward the screen. Incidentally, the screen was charged with the same magnitude of negative and positive voltage. Therefore, the actual potential difference was twice the difference between the voltages listed in the table. 
When an insect enters this field, there are two ways that it can be captured. The first is that the insect invades the space near the negatively charged insulated conductor wire (negative pole). Here, the insect is deprived of free electrons, electrified, and thus attracted to the negative pole. This is the same phenomenon that occurs in the static electric field (discharge-mediated positive electrification) of the SD screen. The second is the case in which the insect enters the space of the positive pole. In this case, the insect receives electrons and is electrified negatively for attraction to the pole (charge-mediated negative electrification).

2. Practical Application of DD Screens

2.1. Grounded and Ungrounded Circuits for Charging

In the usual electric circuit (grounded circuit) configuration for voltage charging of the DD screen, a negative voltage generator pumps negative charge from the ground and supplies it to the insulated conductor wires while a positive voltage generator pushes free electrons from the linked insulated conductor wires to the ground to generate positively charged insulated conductor wires. From the viewpoint of electricity movement, the same amount of electricity can be returned to the ground from the conductors.
In the ungrounded circuit, the free electrons of the insulated conductor wires are supplied directly to the other insulated conductor wires by the voltage produced by the two generators. Therefore, an electric field screen with this circuit has no need for a grounded line. For this reason, the placement of the electric field screen is freely selectable, allowing portability of the electric field screen.

2.2. Diversification of DD Screens

The bamboo blind-type electric field screen is a single-layered type of screen that was devised to reduce construction costs, particularly for practical applications involving a plastic hoop greenhouse [36]. This screen can be hung easily anywhere and can be positioned at the openings of lateral-side plastic film roll-ups. Although it is not possible to prevent the entry of pests completely, this approach is useful for greatly diminishing the interior pest population.
An electrostatic flying insect catcher (electrostatic racket) is a two-layered apparatus used to capture flying pests directly [30]. This apparatus is carried by the greenhouse attendant during ordinary plant care checks and is used to capture flying insects quickly (as they appear). It is possible to reduce the pest population significantly with the continued diligent use of this device. The apparatus can be used in various facilities, such as food-processing factories, warehouses, and facilities that provide meals, in which the use of insecticides is strictly regulated or prohibited.
An electrostatic cabinet (two-layered type) system was designed for use inside facilities, including greenhouses [35]. The entire structure has a simple design. The frame is furnished with two electric field screens, which are installed on opposite faces of the frame for better ventilation. The door of the cabinet and the remaining faces are covered with reinforced plastic film. The electrostatic cabinet can be set up affordably compared to more involved greenhouse screen installations. The cabinet can also be used as a cultivation facility for specific plants that should be protected from pests or as a pest-free laboratory and workroom.
An electrostatic nursery shelter (three-layered type) is an apparatus used to raise healthy plant seedlings [34]. The shelter is designed so that it can be installed in a greenhouse that is not furnished with electric field screens. The reason for using the three-layered type screen is to prevent the entry of pests as well as pathogen spores [54]. Because the structure is simple, its size can be easily modified to the scale needed for seedling cultivation. To obtain better ventilation, the screens can be installed on opposite faces of the shelter, along with a small axis fan.

2.3. Yellow-Coloring of DD Screen for Attracting Phototactic Insect Pests

Many insects are attracted to a particular type of light (or color). The researchers utilized this characteristic in the capture method. The following experiments were conducted to examine whether this behavior could be applied to enhance the capture capability of the DD screen. Although the DD screen was able to capture insects entering the static electric field of the screen, it did not attract distant insects.
Nonomura et al. [33] used a single-layered DD screen backed with a yellow board, gray board, or gray net to examine the effects of better light reflection for bringing out insect photoselectivity. As insects attracted by the color plate were captured by the insulated conductor wires of the screen, the feasibility of this method was evaluated by counting the number of insects trapped. As a control, DD screens with a gray-colored board and gray net were also used. These three screens were placed in a greenhouse where numerous whiteflies were present. The results showed, as expected, that whiteflies were preferentially trapped by the screen with the yellow-colored board [33].
Takikawa et al. [31,32] used a yellow-colored insulated conductor to fabricate a colored DD screen. For this purpose, the conductor metal wire in the insulator coating was changed to water. Because water conducts electricity, the transparent polyvinyl chloride tube filled with charged water was similarly electrified and produced an electric field in the space surrounding the tube. Two-layered, yellow-colored DD screens were constructed by pairing two identical yellow-colored SM screen units. In this screen, the yellow-colored tubes of the two units were arranged in an off configuration. The yellow-colored DD screen was highly effective at attracting and trapping whiteflies, thrips, and leaf miners distant from the apparatus in the greenhouse [31]. The wide selection of commercially available watercolors is useful for constructing devices with the coloration most suitable for attracting phototactic insect pests.

This entry is adapted from the peer-reviewed paper 10.3390/agronomy13010023

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