Leaf beetles and flea beetles
Leaf beetles (family Chrysomelidae), including smaller species named flea beetles, chew and feed on foliage and in some species roots and stems of various plants. Over 430 species of leaf beetles occur in California, but most are not pests.
Identification
Adult leaf beetles are oblong to oval and have threadlike antennae. The coloration of some leaf beetles blends with the color of leaves. Other species are brightly colored and contrastingly marked so they are easy to observe on foliage. Adult leaf beetles are generally less than 1/3 inch long. Adult flea beetles are smaller and commonly about 1/16 inch (1.5 mm) long.
Flea beetles are usually blackish or a dark, shiny metallic color. Adults frequently jump when disturbed, which is the source of their common name. Larger species of leaf beetles may drop from foliage when disturbed. Several common species are pictured and sometimes discussed at the links below.
Asparagus beetle. Crioceris asparagi and spotted asparagus beetle (C. duodecimpunctata) adults chew asparagus ferns or the growing tips of spears. Larvae chew on ferns or inside their berries.
Grape bud beetle. Glyptoscelis squamulata adults chew and feed in grape buds. This kills buds and causes terminal dieback, distorted regrowth, and reduced fruit yield. Larvae chew on grape roots, but their damage is not important.
Elm leaf beetle. Xanthogaleruca luteola as adults and larvae chews and feeds on leaves of elms and zelkova. It can entirely defoliate trees when it is abundant.
Eucalyptus tortoise beetles. Chrysophtharta m-fuscum and Trachymela sloanei adults and larvae chew foliage of various eucalyptus species. They can almost entirely defoliate infested trees.
Imported willow leaf beetle. Plagiodera versicolora adults and larvae chew foliage of cottonwood, poplar, and willow.
Klamathweed beetle. Chrysolina quadrigemina and St. Johnswort beetle (Chrysolina hyperici) adults and larvae chew foliage of Hypericum. These beetles were deliberately introduced to control weedy St. Johnswort, an exotic rangeland weed that is toxic to livestock.
Palestriped flea beetle. Systena blanda adults chew pits in the underside of leaves and larvae chew roots. Hosts include artichoke, carrot, corn, eggplant, pepper, sugar beet, and cole crops such as broccoli, Brussels sprouts, cabbage, and cauliflower.
Potato flea beetle. Epitrix cucumeris hosts include corn, pepper, potato, sugar beet, and tomato. Adults chew and pit leaves and are the important source of damage. Larvae chew and feed on roots, which is generally not important on well established (older) plants. They can also chew on germinating seeds, seedlings, and potato tubers, which can cause important damage.
Tamarisk or cedar leaf beetle. Diorhabda elongata adults and larvae resemble those of elm leaf beetle. D. elongata was deliberately introduced to control weedy Tamarix species. These plants infest riparian areas, consuming much water and crowding out native plants, which reduces habitat for wildlife.
Tobacco flea beetle. Epitrix hirtipennis adults chew pits in leaves and sometimes fruit. Larvae chew on roots, stems, and potato tubers. Hosts include eggplant, potato, and tomato.
Tuber flea beetle. Epitrix tuberis adults feed on leaves and larvae feed on potato roots, stems, and tubers. Other hosts include bean, lettuce, radish, spinach, sugar beet, tomato, and crucifers such as cabbage and cauliflower.
Western spotted cucumber beetle. Diabrotica undecimpunctata undecimpunctata adults chew foliage and larvae chew on and in roots and stems of bean, corn, and cucurbits such as cucumbers and melons.
Western striped cucumber beetle. Acalymma trivittatum adults chew foliage, and larvae chew on and in roots and stems. Hosts include bean, corn, and cucurbits such as cucumbers and melons.
Life cycle
Leaf beetles develop through four life stages: egg, larva, pupa, and adult. After hatching from eggs that are generally laid on host foliage, the larvae develop through three increasingly larger instars. Pupation commonly occurs on the ground near the base of host plants. Overwintering is typically as adults in protected places. Most species of leaf beetles including flea beetles have several generations per year.
Damage
Adult leaf beetles chew and feed on foliage and cause ragged leaves and sometimes premature drop of foliage. Adult flea beetles cause pits and small holes in leaves and cause the immediately surrounding tissue to become bleached or whitish. Heavy feeding can kill seedings.
Leaf beetle larvae chew all the way through foliage or scrape the foliage, giving leaves a windowpanelike appearance. Larvae of flea beetles generally feed on or inside roots or stems. Adults and species with foliage-feeding larvae leave dark feces (excrement) on infested leaves. Heavy larval feeding can kill germinating seeds and seedlings.
When melons and vegetables are fed upon, especially the underground parts, plants can become more susceptible to various plant pathogens. Cucumber beetles can vector various plant viruses that cause cucurbit diseases. When potato tubers are infested by flea beetles the potatoes can become inedible.
Solutions
Provide good growing conditions and proper cultural care to keep plants vigorous so they are more tolerant of pest damage. Control weeds near valued plants because cucumber beetles and flea beetles feed on various weeds and can move from these alternative hosts to feed on melons and vegetables.
When growing melons and vegetables susceptible to cucumber beetles and flea beetles, covering plants with fine screening or mesh cloth before the seedlings emerge or immediately after transplanting can exclude these pests. Hold the covering above the surface of plants, such as by using hoops or stakes. Exclusion is of greatest importance when plants are young. Depending on the host and beetle species, covers can be removed once plants become well established.
Where damage is intolerable, beetles on foliage can be reduced by directly spraying the insects with insecticidal soap. Host foliage can be sprayed with a pyrethroid, such as bifenthrin, or spinosad, which have some residual persistence. Applying a systemic neonicotinoid such as imidacloprid can control both adults and root-feeding larvae. Check product labels before use to ensure the target crop or site is listed. Some insecticides cannot be applied to food crops. Except for insecticidal soap, these insecticides can be toxic to bees and parasitoids and predators of pests. Do not apply them to plants that are flowering or wait until evening when honey bees are no longer active.
Adapted from the publications linked above and Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide 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).
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