Mullein bug

Campylomma verbasci

Description. Eggs are 0.8 mm long, white and flask shaped. Mullein bugs develop through five nymphal instars to adults. Nymphs are 0.5-2.5 mm long, yellow, with a pointed head and red eyes. There are several similar insects such as aphids and leafhoppers that can be confused with mullein bug nymphs. Adults mullein bugs are 3 mm long, oval and light green to tan in colour. Antennae are segmented and hind legs have black spots and are spine covered.
Biology. The mullein bug has two major plant hosts, the mullein plant and apple. Occasionally it also attacks pear, grapes, wild rose, serviceberry and oak. The insect overwinters as eggs inserted deep into the bark of one- or two-year-old wood of apple. Eggs begin hatching during bloom and continue to hatch into the petal fall period. Most years the hatch is synchronized with peak emergence at early petal fall, but a cold snap during this time may result in split hatch, making chemical control more difficult.
Nymphs initially feed on plant sap attained from leaf veins, and also sting developing fruitlets. Several weeks after petal fall, nymphs become predaceous and begin feeding on prey such as European red mite and aphids. Nymphs with red bellies are an indication the nymphs have been feeding on mites. Nymphs progress through five instars before becoming adults. Both nymphs and adults are fast moving, and adults are often quick to take flight if disturbed. The adults migrate to mullein plants, common along ditch banks and the sides of roadways in Ontario, where they feed throughout the summer months. Season-long monitoring in apple orchards indicates some mullein bugs remain in the orchard during the summer. During that time they are considered important predators of aphids and mites. In late fall, female mullein bugs return to apple trees and lay overwintering eggs into young wood. There are two to three generations per year.
Damage. During bloom to petal fall period, mullein bug nymphs cause economic losses to certain varieties of apple, particularly Red Delicious and Spartan. Northern Spy, Empire, Cortland, Gala, Jonagold and Golden Delicious are also sometimes affected. McIntosh and other cultivars seem to be largely unaffected, but it is not known whether mullein bug does not generally attack fruit of these cultivars, or if these cultivars are immune to mullein bug stings. Feeding on fruit causes small upraised, reddish bumps on the fruit surface. Fruit often receive multiple stings and the large majority of these abort just prior to or during June drop. Affected fruit that remain on the tree develop small corky warts or bumps surrounded by conical depressions. As affected fruit sizes through the summer, it becomes distorted. If uncontrolled, mullein bug can damage up to 75% of apples in Ontario orchards.

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