The overall goal of this procedure is to establish an objective method of quantifying damage to cotton plants caused by two-spotted spider mites using an active multispectral optical sensor. This method can help answer key questions in agricultural entomology, such as which insecticides are best able to control spider mites in cotton. The main advantage of this technique is that it providers researchers an objective metric for evaluating spider mite damage on cotton while saving time and valuable human resources.
We first had this idea for this method for evaluating different insecticides on cotton for efficacy against two-spotted spider mites. To begin the protocol, grow not genetically modified, or not BT cotton plants to four to five true leaf stage in plastic trays in a greenhouse. Next, transfer spider mite colonies from the pinto beans onto the young four to five true leaf stage cotton plants.
Transfer three masses of spider mites for lightly infested plant. Place a pan under the pinto bean leaf tip containing two-spotted spider mite, or TSSM masses. Cut the pinto bean leaf tips with scissors allowing TSSM masses to fall into the pan.
Turn the pan upside down over the cotton plants and tap the TSSM masses onto the plants. Then randomly spread the three masses of the TSSMs onto the cotton plant. For medially infested plants, transfer 20 masses by placing a pan under the pinto bean leaf tip containing the TSSM masses.
Cut the pinto bean leaf tips with scissors and allow them to fall into the pan. Turn the pan upside down over the cotton plants and tap out TSSM masses onto 100 cotton plants raised in the greenhouse. Transfer 40 masses for heavily infested plants.
Then collect 40 masses in a pan. Prior to assaying damage, infect cotton plants with two-spotted spider mites as described in the text protocol. Horizontally mount the optical sensor onto the greenhouse frame approximately seven feet above the floor.
Set the distance between the scanner and the plant canopy at 36 inches. Use a carpenter's level to ensure that the sensor is horizontally level. When scanning the test plants, it is critical that the scanner be placed a fixed distance from the crop canopy and that the background is uniform.
Next place uninfested trays of cotton plants on a wheeled push cart. Activate the sensor switch and slowly push the cart under the sensor until the tray completely passes the sensor head. Once the tray has completely passed the sensor, turn off the switch and retract the cart.
Then, repeat the scan for a total of three replications for all trays of cotton. Transmit the normalized difference vegetation index or NDVI values from the scanning and store them onto a pocket PC.Then download them to a computer in text format. This graph uses normalized difference vegetation index or NDVI values to demonstrate the differences in plant vigor between noninfested control plants which increased vegetative growth in contrast to the TSSM infested plants which degraded in health over time.
Mean separation of the treatments revealed no definable difference in percent reduction in NVDI between treatment categories and the control until day five when infestation classes significantly deviated from the control and further deviated over time. While attempting this procedure, it is important to remember to maintain a consistent height of the optical sensor above the target canopy and to ensure a consistent background. After it's development, this technique paved the way for researchers in the field of agricultural entomology to evaluate the effect of insecticides against two-spotted spider mites on cotton.
The use of multispectral active optical sensor to evaluate insecticidal efficacy for control of spider mites in cotton is more efficient than subjective damage ratings for scoring treatment differences.
