Knowledge of pest biology and phenology is fundamental to successful IPM programs. With the increased emphasis on environmental conservation and human health, census of natural enemies is often also of interest. The decision making required for IPM must be based on reliable biological information that can only be developed through the use of proper quantitative sampling methods. Efficiently sampling of plant foliage for arthropods often presents a difficult challenge. No single method is adequate for all target species or plant host. Many insects and mites are too cryptic, small or soft bodied to find, handle, census or remove in the field and for these species foliage is usually returned to the lab and examined under a stereomicroscope. Sweep nets or beat "jarring" sheets may be used to collect some target species. Sweep nets present a problem because they are very inefficient, but they also collect unwanted plant debris and venomous non-target insects such as bees or wasps. Beat sheets are useful only for species that are slow moving or that exhibit "thanotopsis" (playing dead) such as weevils.

For those cases where the sampling objective is to find out the presence and relative numbers of as many of the insects present as possible, a vacuum device may be a more appropriate method. One of the best known early models of a vacuum sampler still in use today was invented in California to sample alfalfa and other herbaceous crops by a Mr. E. Dietrick and is known as the D-vac. Other models are also available from suppliers. Most are self-contained motor-driven backpack models containing a long tube with a net bag over the end to collect the insects.

Sampling pecan foliage.

Here I describe a do-it-yourself vacuum sampler suitable for sampling tree/shrub foliage that is cheap and easy to make and use. This model collects the insects inside a large vial and is very useful for collecting the cryptic life immature stages and adults of most predacious insects. I found its efficiency to exceed 99% in removing the insects present on foliage. The actual collecting head can be changed according to the size and type of foliage being sampled. I used a 4-inch piece of PVC for crape myrtle branches and a 5 gallon bucket for pecan terminals. It also requires a portable generator to power the electrical motor of the vacuum cleaner. While the extension cord requirement is a limitation, unlike a backpack motor, portable generators can be used for other purposes besides sampling insects.

Materials List:

• 5 gallon plastic bucket - (head)
  
• 4-inch (10.16 cm) diameter PVC pipe 10 inches long (base pipe) with one female type expanded end
  
• 4-inch diameter PVC pipe 15" long (head)
  
• PVC step-down joint - 4 to 2-inches (or the diameter of vacuum cleaner hose)
  
• a plastic commode flange
  
• some aluminum window screen (funnel)
  
• two heavy plastic funnels (4 inch (17.6 cm) diameter)
  
• two plastic vials - 250 ml and top
  
• small 3 inch swatch of cloth
  
• four 3/4 inch carriage bolts with nuts and lock washers
  
• caulk - "Liquid Nails"
  
• small sheet metal screws
  
• small upright portable vacuum cleaner (3-4 watt rating)
  
• industrial electrical extension cord of 15-25 m in length
  
• portable generator with enough output wattage to power the vacuum cleaner
  
• cutting tool

Insect vacuum sampler.

Construction Directions: (from the vacuum cleaner end toward the head).
Attach the vacuum cleaner hose to the 2-inch end of the PVC step-down with duct tape. The 4-inch end will attach by friction to the collecting head of choice: bucket or PVC pipe.

PVC Pipe Collecting Head:
Use the 4-inch funnel, the 15-inch piece of PVC, and a 250 ml vial to form the head as follows. Cut a hole in the vial lid wide enough so that it fits over the funnel to a depth of 1 to 2 inches and glue together. Cut a hole in the bottom of the vial leaving only a narrow rim with enough space to attach a swatch of cloth. This will serve as the collecting device and allow the vacuum air with the insects to flow from the collecting head through the funnel and through the collecting vial. Mount the funnel with the collecting vial inside the 15-inch PVC tube such that it extends out of the bottom just enough to handle but leaving enough room to tightly attach the 4-inch end of the step-down joint. (Note: The picture shows two extra short pieces of PVC (one for each type of collecting head) used between the step-down joint and the PVC piece housing the collecting vial. These are not necessary of the vials on the funnels are placed properly.)

Operation:
The foliage is placed inside the PVC and shaken vigorously to dislodge the insects into the air stream which are then carried into the collecting vial. Once the sample is taken, detach the step-down joint from the head and open the vial to survey the contents. Repeat.

Five Gallon Bucket Collecting Head:
Cut a hole in the bottom of the bucket so that the commode flange fits snugly through the hole when placed inside the bucket but allow the rim of the bucket bottom to remain such that four bolts can be used to attach the flange permanently to the bucket bottom. Also, add some caulk around the junction of the flange and the bucket bottom for an airtight seal when they are bolted together. Cut the window screen into a funnel large enough to cover the base diameter of the bucket and place it inside the bucket so that it fits into the hole in the commode flange. Use caulk, duct tape and small screws if you like to attach the screen funnel permanently inside the bucket. Attach the 4x10-inch PVC piece to the commode flange outside the bucket bottom (the commode flange connecting end should be 4 inches in diameter so that the female end of the PVC fits over it snugly). Construct a 4-inch funnel and 250 ml vial as described above with holes and cloth. Place the funnel and the vial inside the 4-inch PVC such that the vial extends out far enough to turn but allows the step-down joint to fit tightly over the regular end of the PVC tube. Operation: Same as described above with the 4-inch PVC pipe head.