Utah Pests News Fall 2009

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Common UPPDL Insect Scouting and Submissions

As the insect season begins its decline into the cold winter months ahead, some pests are nearing or just hitting peak injury.  This article covers three pests recovered from scouting expeditions in northern Utah and recent submissions to the UPPDL: dusky sap beetle, Mexican bean beetle, and locust borer.

Dusky Sap Beetle

The dusky sap beetle (Nitidulidae: Carpophilus lugubris, DSB) is a secondary pest of sweet corn and is widely distributed from South America into much of the United States.  In addition to sweet corn, DSB feeds on apple, peach, tomato, pea, yucca, rotting vegetation, discarded fruit and debris from vegetable fields, and on bacterial ooze from trees.

DSB overwinter as adults in decomposing plant material and at the bases of trees and other plants; pupae may also overwinter in the soil.  Adults (shown above alongside a larva on corn kernels) emerge in spring, mate, and deposit eggs in about two weeks.  Eggs develop into adults in about 30-35 days.  Early generations of DSB are usually not problematic, but later generations are often laid on silks or kernels of sweet corn.  Sweet corn becomes especially attractive 10-15 days after silking begins as the corn kernels begin to swell with sugar. DSB larvae—small, cream-colored with brown heads (shown above)—feed upon corn kernels causing minor damage.  Economic losses from DSB are usually because of the presence of larvae in the corn ear, not because of the damage they cause.

Management options:

  • plow under crop debris
  • plant tight, long-husked corn varieties
  • harvest corn immediately when ripe
  • remove damaged and over-ripe vegetables from the area
  • remove or properly compost vegetable debris
  • apply an insecticide (example ingredients include esfenvalerate, lambda-cyhalothrin, zeta-cypermethrin) daily beginning seven days before harvest and continue to three days before harvest.

Mexican Bean Beetle

  Adult MBB (top) are differentiated from beneficial lady beetles by the horizontal rows of 8 black dots on each elytra.  The branched spines of the larva (bottom) begin as solid yellow; the tips of the spines turn black as the larva matures.

Mexican bean beetle (Coccinellidae: Epilachna varivestis, MBB) is a major pest of beans and may be found from Central America, up to the Rocky Mountain States and Southern Canada, and over to New England.  MBB hosts include snap beans, lima beans, soybeans, cowpeas, mung bean, and occasionally black-eye peas, velvet bean, alfalfa, and clover.

MBB is one of two plant-feeding lady beetles (the other being the squash lady beetle, Epilachna borealis).  The other members of this familiar beetle family are beneficial, with both adults and larvae feeding on aphids, mites, scales, etc.  The adult beetles look similar to other lady beetles, but are more yellow-orange turning to a darker bronze as they age (shown on previous page); the larvae are very distinctive, brandishing rows of branched, black-tipped spines. 

MBB overwinter as adults under leaf litter and debris at the edge of fields, along fence rows, or at the bases of trees.  Adults emerge in late May when temperatures become warm enough, and continue through mid-summer.  Adults typically search for garden peas early in the season and then move to beans on which they feed and lay eggs on the undersides of leaves in clusters of 40 or more.  Newly hatched larvae feed gregariously at first, and then disperse into smaller groups to feed.  Larvae pupate on the plants where they have been feeding.  The adults emerge, and search for new bean hosts and overwintering sites.  Peak activity typically occurs in mid July through August.

Management options:

  • eliminate overwintering locations by plowing host material under soil
  • plant bean crop late, or plant early, fast-maturing bean varieties
  • plant more resistant, or less-preferred bean varieties such as Asian long beans
  • exclude beetles by using floating row covers
  • check undersides of bean leaves during summer, and smash MBB eggs and larvae
  • preserve natural enemies by using selective insecticides
  • use insecticide (azadirachtin, esfenvalerate, lambda-cyhalothrin, zeta-cypermethrin, malathion, etc.)

Locust Borer

Locust borer (Cerambycidae: Megacyllene robiniae, LB) is a common pest affecting black locust (Robinia pseudoacacia) and its cultivars, including ‘Purple Robe’. Honeylocust (Gleditsia) is not attacked.  Found throughout North America, LB adults are most abundant in September in Utah, but can occur from August through October.  Presence of adult beetles occurs about the time of goldenrod bloom, on which adults may be seen feeding on pollen.

Adult LB lay eggs on locust bark in the fall.  The eggs hatch and the small larvae bore into the inner bark where they overwinter.  In the spring, when buds begin swelling, larvae bore into the sapwood and then heartwood.  They pupate in mid-summer and emerge from the existing 3-4-inch long tunnel.

  Adult LB (top) are about 1 inch long, black with yellow w-shaped stripes on the elytra, and have long antennae.  Severe infestation (bottom) can weaken trees, making them susceptible to wind damage.

Symptoms include branch failure, water sprouting, swollen areas on the limbs or trunk, oozing in spring, and sawdust-like frass.  Smaller trees may easily break, while larger trees can have deformed growth from multiple branch breakage.

Management options:

  • maintain tree vigor by watering properly and using practices that will minimize stress
  • for small or specimen locust trees, apply insecticide (carbaryl) to the trunk and larger scaffold limbs before egg-laying (about mid-August); re-apply every three weeks through late September
  • in early spring at bud swell, soak the bark and larger branches with carbaryl to target overwintering larvae located just below the bark

-Ryan Davis, Arthropod Diagnostician