Proba Bug

Proba bug is a native insect that occurs on coyote brush, Baccharis pilularis, a common shrub on coastal mountain range hillsides from Oregon to Los Angeles. In the central coast, coyote brush commonly grows along highways next to the artichoke fields. Proba bug can be a major pest of artichokes that are grown both as perennial and annual crops.

Adults are about 0.2 inch (0.5 cm), uniformly light brown, and lack any obvious marks on their body, unlike lygus bugs, which have a prominent yellow, triangular-shaped marking at the base of the forewings. The newly hatched nymphs are pale greenish-yellow, somewhat similar to small aphids with the exception that the proba nymphs move faster with their overly long legs. The second- and third-instar nymphs are reddish-brown, and the fourth- and fifth-instar nymphs exhibit light and dark alternate bands on the abdominal segments.

Proba bug is active throughout the year in the central coast growing districts; however, because of low temperatures during winter, the insect develops very slowly and causes minimal damage at this time. As air temperature begins to rise in March, the bug becomes more active. Proba bug nymphs quickly molt into adults, and egg laying occurs following mating. A large number of eggs are laid in the artichoke leaf petioles and hatch in 20 to 30 days. Soon after hatching, the nymphs start feeding on young leaves.

Proba bug nymphs and adults feed mainly on the very young leaves that are in the frond stage. As they feed with their piercing-sucking mouthparts, they inject a toxin into the plant that results in the death of the leaf tissues around feeding wound. As the developing leaves expand, the feeding punctures turn into brown, necrotic spots that fall off, leaving the leaf with a shot hole appearance. In a severely infested artichoke field, affected leaves are abnormally small and light yellow; as the leaves age, they turn brown. The damage to the artichokes by the proba bug is very similar to that caused by lygus except that proba bug is more aggressive in its feeding habit.

Proba bug also feeds at the base of the young artichoke bud, causing it to turn partially or completely black and rendering it unmarketable.

In the past, the use of organophosphate and chlorinated hydrocarbon insecticides kept this insect out of artichoke fields. Cancellation of most of these insecticides has resulted in the resurgence of proba bug as a pest of artichoke in recent years. The destruction of any nearby coyote brush shrubs and stalk removal following harvest helps to manage this pest.

Naturally occurring predators that feed on the nymphal stages of proba bug include bigeyed bugs (Geocoris spp.), damsel bugs (Nabis spp.), minute pirate bugs (Orius tristicolor), and several species of spiders.

Cut bare stalks at the base and remove them from the field or disc them under at harvest. This practice, called stumping, will kill the immature stages (eggs and nymphs) that would otherwise reinfest plants. Remove any coyote brush in the immediate vicinity of the field, as it may harbor a large number of proba bugs.

Biological and cultural controls are acceptable for use on organically certified crops.

Monitor the crop for the physical symptoms of damage in March. When the damage is evident, determine the proba bug population level by sampling the shoots during the vegetative phase and the fruiting terminals during the production phase of the crop at weekly intervals. To sample the vegetative shoots, cut one off at ground level and shake it vigorously in a 5-gallon white bucket. Count all the dislodged proba bugs. To sample the semi-exposed terminal fruiting bud, cut the productive shoot off just below the lower secondary bud and vigorously shake it in the bucket. Sample a total of 10 to 15 shoots. A population level of three nymphs per shoot is considered the treatment threshold. If not treated, the crop can suffer 20 to 30% loss of yield due to leaf damage and more if fruiting shoots are attacked.