Range and Pasture XIX-5

Big Eyed or Black Grass Bugs

John B. Campbell

Big Eyed Bug

Field Biology

Two genera, Labops and Irbisia, from the family of plant bugs (Miridae) are referred to collectively as big eyed or black grass bugs. They may at times be numerous enough to kill grass plants. They generally do the most damage to introduced grasses seeded for range improvement or to restore farm ground to grassland. Wheat grasses in particular seem to be favored by these bugs. However, the value of these plants often grown for seed production or high quality hay may focus attention on these grasses and infestations of native grasses may be overlooked or ignored. The exception would be where the bugs are numerous enough to cause extensive damage to large acreages of range grass. The big-eyed bugs insert the mouthparts into leaves and suck the juices. As few as two to three nymphs have been reported to kill the leaves of crested wheat grass within a few days. Damage symptoms begin as light colored irregular spots on the leaves. Damaged leaves dry out and die.

Identification (Life Cycle/Seasonal History)

Adults have bulging eyes with whitish buff margins on the wings and light colored markings on the head. The females of the Labops genus have only vestigial hind wings, unlike the Irbisia genus females which have four well-developed wings. Females apparently deposit eggs in the fall in the stems and leaves of plants. The eggs hatch in early spring. Nymphs and adults have similar feeding habits.

Plant Responses and Damage

The damage was discussed earlier. Damaged plants will recover if moisture is adequate and control methods are initiated in a timely manner.

Management Approaches

Research indicates that some grass species or varieties are either tolerant or not as attractive as a host plant as are others. However, there is little money available for host plant resistance research for grasses.

There is evidence that heavy fall grazing or controlled burning may reduce populations if done after the grass bug eggs have been deposited in the plant. Hay harvesting at the appropriate time has been shown to reduce populations of grass bugs on wheat grasses but this is an option only if the grass is being used for hay and not seed production. The reduced tonnage from early hay harvest probably offsets damage from the grass bugs.

Cultural Methods

Heavy fall grazing, burning or early hay harvest are the only known cultural practices that will reduce grass bug populations.

Biological Control

The grass bugs are probably preyed upon by the usual predators and parasites present in a grassland habitat but there is no research indicating a promising biological control agent.

Chemical Control

Most insecticides registered for use on rangeland insects would probably provide control of grass bugs. But generally the use of an insecticide is considered too expensive to be used for control of the big-eyed bugs.

Categories:  Range, Insects, Pasture, Big eyed bugs, Black grass bugs

Date: 12/18/06