The redberry mite, Acalitus essigi, was found on Himalaya berry in California in 1921. It was subsequently reported on blackberry in California and Washington. It causes the well-known redberry disease, which forms an interesting and attractive contrast as a result of the mite feeding on the fruit between the drupelets and around the core. Infested berries show swollen, brilliant red or pink and greenish drupelets among unaffected purple or maroon drupelets. Some berries
have entirely red drupelets. Affected berries remain red or green and do not ripen normally. Often berries of late maturing varieties are seriously infested.