How Effective is Pneumatic Insect Control?

Results with pneumatic control methods has been highly variable, and the following factors will affect success in the field:

Equipment Factors:
Vacuum equipment will adequately dislodge insects that fly off the plant when disturbed. However, a positive pressure airstream is needed to dislodge insects that cling tightly to the plant (e.g. CPB), since it can be more easily concentrated and directed. Also, a wider airstream will improve dislodging rates, provided airflow velocities can be maintained.

Mechanical shaking at higher travel speeds can improve dislodging rates for insects that do not cling tightly to the plant, and higher travel speeds may also decrease the time for insect escape. However, increasing the travel speed can also result in a higher portion of insects that drop or fall to the ground without capture, thereby lowering capture efficiency.

When vacuum collection is used, a higher airspeed is needed to collect the insects than to dislodge them, and this may decrease the efficiency of vacuum systems in the field. Also, turbulence created by the airflow can contribute to low collection rates with vacuum systems.

Insect Biology:
Adult CPBs on the underside of the leaf, on the edge of the leaf, or grasping the leaf are more difficult to dislodge than those that are not clinging tightly to the leaf or that are walking on the upper surface of the leaf. Therefore, because environmental conditions influence insect position and behavior, they will have an impact on the control rates. At a temperature of around 25C, for example, most of the adult CPBs will be exposed on the upper surfaces of the leaves. At higher temperatures they may be more protected in the shade in the top one third of the plant. The larvae on the other hand, spend more time on the upper surface of the leaves and on the outside of the foliage when the temperatures are lower, as they are exposed to the sun in these locations.

When disturbed, CPB adults "scan" for leaf veins to grip, and this improves their ability to resist removal. Windy conditions may also induce the beetles to increase their hold on the plant. Also, since feeding rate increases with body temperature, ambient temperature may also affect the insects' grip on the plant. The CPB adult will also drop from the plants in response to disturbance and simulate death on the soil (thanatosis). Therefore, equipment vibrations can cause the insects to drop to the ground before the dislodging airstream can direct them to the collection unit. Unless these insects can be collected from or destroyed on the soil surface, control will be ineffective or variable.

Large CPB larvae are mobile and feed over expanded leaves, and are therefore usually less protected on the plant than the small larvae. However, the large larvae may increase their hold on the leaf during feeding by using their mandibles. The small larvae adhere tightly to the plant and are often protected near the top of the plant or in the folds of the leaves, so they are more difficult to dislodge. Once dislodged, however, they do not readily climb back onto the plant. The adults or large larvae climb back onto the plants after they have been dislodged. For control to be effective, they would need to be collected immediately after dislodging.

Crop Canopy:
The crop canopy can interfere with insect dislodging and/or collection as the crop matures. Also, both the placement of the hood within the canopy and the relative distance between the insects and the hood will influence removal and capture rates.