At least 74 species of katydids (family Tettigoniidae) are present in California. Most are not pests because they chew only a small amount of foliage before moving to another plant. Forktailed bush katydid (Scudderia furcata) can be a pest because it chews young fruit in addition to leaves. Angularwinged katydid (Microcentrum retinerve) and broadwinged katydid (Microcentrum rhombifolium) are other common species.
Katydid adults are relatively large, slender, leaf-mimicking insects. They resemble grasshoppers, but have more slender antennae that are nearly as long or longer than the body. The nymphs are wingless and nymphs of forktailed bush katydid and some other species have antennae that are black and white banded. Adults and nymphs are easily overlooked on plants because the body of many species is green and somewhat shaped like a leaf. Some katydid species are brown or tan.
Eggs of forktailed bush katydid are oval shaped and about 1/8 inch (3 mm) long. They occur inserted into the edge of leaves where they appear as oval swellings of the leaf edge. Angularwinged katydid, broadwinged katydid, and some other katydid species line up their eggs on twigs or elsewhere in single or double overlapping rows. The eggs are disklike, gray, and about 1/5 inch long.
Adults of forktailed bush katydid are about 1-1/8 inches long. Adult angularwinged katydids are about 1-4/5 inches long. Adult broadwinged katydids are about 2-1/4 inches long. The body shape of adult forktailed bush katydids resembles that of a grasshopper. The angularwinged katydid and broadwinged katydid have a distinctly humped back as both adults and nymphs; the adult wings are more broad than those of forktailed bush katydid. The top of the thorax of an adult broadwinged katydid has a small tooth on the front, center margin of the pronotum that distinguishes this species from the similar looking adults of angularwinged katydid.
Katydids develop through three life stages: egg, nymph, and adult. They overwinter as eggs.
Eggs of the broadwinged katydid and forktailed bush katydid hatch in late March through May. The adults appear in midsummer and continue to lay eggs during June and July. A small percentage of forktailed bush katydid eggs will hatch in July and August, producing a second generation of nymphs and adults.
Eggs of the angularwinged katydid hatch in late May. Adults are present in summer and females lay eggs during this time. Angularwinged katydid and broadwinged katydid have only one generation per year.
Katydid adults and nymphs chew holes in foliage. Smaller nymphs feed in the middle of the leaf, creating small holes. Larger nymphs and adults chew and feed on the leaf edge. Because the katydids chew on only one or a few leaves before moving elsewhere to feed, leaf chewing by these insects is not important to plant health.
Aside from foliage, nymphs of forktailed bush katydid also feed on young fruit of citrus and stone fruits. In blueberry and pear, both adults and nymphs will feed on fruit. In blueberry the adults are the most important fruit-chewing stage.
Katydids tend to take one, small bite out of a fruit before moving on to another feeding site. Therefore a few forktailed bush katydids may damage a large number of fruit. The feeding wounds generally heal over, but as the fruit grow the wounds enlarge into brownish, gray, or tan, slightly sunken patches that appear corky and are generally circular. Sometimes katydid feeding on young fruit causes it to grow distorted and the affected fruit may drop. Note that certain other insects such as cutworms and earwigs can also cause shallow, circular scars on fruit.
The feeding injury is generally small and easily overlooked until the fruit grow. Katydids are commonly no longer present by the time fruit grow large enough for the injury to become apparent. Generally no control is recommended for katydids on home fruit bushes and trees. Because the internal quality of fruit is little or not at all affected by katydids, efforts to control them may not be warranted.
Because katydids are rarely abundant on plants, the few that are observed can be caught and crushed or otherwise disposed of. Unlike the day-active grasshoppers, katydids rest during the day and feed at night. Adults at night sometimes come to lights and can be relatively easy to capture in the early morning when they are cool and lethargic.
Where katydid injury to fruit has previously been unacceptable, after petal fall when fruit are small, the bush or tree can be sprayed with spinosad. Adding horticultural oil to the mix can increase the efficacy persistence of spinosad. Note that spinosad is toxic to honey bees and certain beneficial predators for at least several hours after it is applied. Do not apply spinosad to plants while they are flowering.
Adapted from Integrated Pest Management for Citrus, Integrated Pest Management for Stone Fruits, and Pests of the Garden and Small Farm: A Grower's Guide to Using Less Pesticide, University of California Statewide Integrated Pest Management Program (UC IPM).