Figure 1. Plant in bucket ready for placement in the field.
Detection and monitoring for insects and their natural enemies is the foundation of any IPM program. Time and economic constraints often preclude humans from conducting the necessary long periods of field sampling or observations. Other passive sampling methods must be developed.
When the target arthropod is sessile, such as scales and whiteflies, cannot fly such as phytophagous or predatory mites, or can be mechanically confined to an individual plant, then the following sampling method may be appropriate. One option for observing some of the biology and ecology of arthropods and their natural enemies is to use sentinel plants containing the arthropod life stages and placed in the field under natural conditions. Sentinel plants must be provided with water and nutrients and often such sampling requires removal of leaves or periodic exchange of plants. Using sentinel infested plants has the advantage of enabling the scientist to place treatment plants in different types of habitats or vary treatments temporally or spatially.
I developed the bucket technique presented in the accompanying pictures to detect the natural enemies of whiteflies on ornamental plants. The plants will stay in the field indefinitely and the technique has a great deal of scientific utility and is inexpensive to use. For example, whitefly immature stages are sessile and do not move once they settle on the plant. By infesting the plants in the lab and then moving them to the field, the whiteflies are then exposed to natural enemies from the surrounding habitat that easily find them. The species arriving, their arrival time and populations present, etc., can be found by combining this technique with the sail trap. Infested leaves can be removed to the lab to census or rear out the natural enemies that are attracted to the plant.
Directions for Construction and Use:
Decide on the plants and the size of their containers. Purchase some rope, 1 to 2 cm in diameter, that contains a central core made of cotton material. Cut the rope into pieces long enough to fit from the top of the plant surface to the bottom of the bucket as described below. The rope will serve as a wick to water the plants. Obtain a 19 liter plastic bucket with a tight-fitting plastic lid. These can be purchased from a hardware store or scientific supply. Cut a hole in the lid that is smaller than the container of the plants you will be using, such that the plant container fits into the hole leaving 3 to 5 cm or so of the container outside and above the lid. The lid basically forms a collar around the container.
Obtain a stout piece of wire or old coat hanger long enough with some excess to fit through the soil in the pot. Use pliers to put a hook on the end of the wire to hold the rope. Stick the wire (without rope) through the potting soil from the top and down through the ventilation holes in the plant pot at the bottom. Place a loop in the rope and place the loop of rope in the wire hook tip. Then pull the wire with the rope on the hook back through the soil. Adjust the rope so that it is even with the soil line at the top and such that it is long enough to touch the bottom of the bucket when the bucket top containing the plant is placed on the bucket (see images). Several rope wicks for each plant may be needed depending on the conditions.
Fill the bucket with water to a line just below the bottom of the plant when it is in the bucket. This can be done just before placing the apparatus in the field. Depending on the weather conditions, number of wicks, plant species and size, the 3 to 7 liters of water in the bucket will last up to several weeks without refilling. The plant and the infesting arthropods will be exposed to the surroundings under natural field conditions just as if the plant was in the soil.
