Insect Note #44
Prepared by:
Kenneth A. Sorenson, Extension Entomologist, NCSU
Dated 11/93
Placed on the Web 4/95 by the Department of Entomology, NCSU
Revised: 03/05
Graphognathus spp: Curculionidae, Coleoptera
Whitefringed beetle larvae have been serious pests in recent years
as they feed on the roots of many plants including sweetpotato.
This native of South America was first reported in the United
States in 1936 and in North Carolina in 1942 and has since been
reported on various hosts from New Jersey to Missouri and
throughout the southeast. Whitefringed beetle has been reported
from 48 counties on 25 hosts in NC. The distribution includes
Buncombe, Yadkin, Beaufort and Pender counties. Counties with
reports on sweetpotato include Chatham, Duplin, Greene, Johnston, Lenoir, Nash, Sampson, Wake, Wayne, and Wilson.
Description of Stages
-
Adult
- About 11 mm long and covered with dark gray and
grayish-brown scales. They have 2 longitudinal stripes on the
sides of the body and a marginal band of white hairs. All adults
are females and are incapable of flight. Adults are active in early July through August and early September.
- Egg
- The white, oval eggs are slightly less than 1 mm
long and become pale yellow before hatching. Eggs are laid in
masses on stems and in cracks in the soil, covered with a sticky
secretion and need water to hatch.
- Larva
- The slightly curved, yellowish-white larvae are
legless, have a light brown head, and measure up to 13 mm long.
They occur at the root zone. Larvae appear to pass through the winter.
- Pupa
- Approximately 13 mm in length, the white pupae
gradually darken as they mature in the soil.
Description of Injury
Whitefringed beetles infest over 385 plant species. However,
plants with tap roots and smooth broad leaves are more commonly
damaged. Adults are foliar feeders which leave sawtooth cuts on
outer edges of leaves. Larvae are considerably more
destructive as they feed on underground roots. On sweetpotatoes,
whitefringed beetle damage consists of roughened holes and
characteristic slight surface channels. The damage resembles grub
injury. However, whitefringed beetle damage contains rough ridges
within channels, as a result of larvae possessing no legs or large
mandibles on which to grasp roots. Damage is usually clumped in
one area, while damage to individual sweetpotato roots is rather
extensive.
Life History
Whitefringed beetles usually overwinter as larvae although eggs may
survive in protected areas. By early July, most larvae have
matured and entered the pupal stage. Adults emerge in July and
early August. there are no males, and wingless females produce
eggs without mating. Eggs are laid in small masses (10-20 eggs)
and are usually attached to plant stems and soil clods just below
the soil surface. A single beetle may live 2 or 3 months and lay
600 to 750 eggs. The eggs require moisture and hatch in 2 weeks in
warm, moist soil. The actual number of eggs laid depends on the
host (beetles raised on broadleaf plants lay more eggs than those
raised on grasses). Larvae immediately enter the soil and develop
on the roots of host plants. There is one generation each year.
Control
Bifenthrin (Capture) 2EC preplant banded and incorporated at 19.2 oz. will give some suppression of white fringed beetle and grubs. Sidedress applications and incorporated at 3.2 oz and foliar sprays will help some.
Management
- High fields at risk: in problem fields avoid planting sweetpotatoes and use a long
rotation of corn, cotton, and small grains.
- Control broadleaf weeds, especially sicklepod.
- Place soil baits containing wheat/corn at 6" depths in March
and examine 3 weeks later for whitefringed beetle larvae, white
grubs and wireworms.
- Use tolerant varieties. Beauregard, Regal, or Resisto have
some resistance to soil insects.
- Practice clean cultivation.
- Use preplant and mid-season applications of Capture
- Precipitation or irrigation (about 0.5 inch) immediately
following a soil insecticide application is helpful, however,
avoid excessive irrigation during July and early August which
favors egg hatch and early larval survival.
- Examine plant stems in July for characteristic whitefringed
beetles.
- Use 3 foliar sprays of Sevin, Imidan, Capture, or Thiodan/Phaser every one or two
weeks in late July and early August.
- Use of natural enemies of whitefringed beetles is not possible
at this time.
Second figure not included due to poor quality of reproduction.
The use of brand names and any mention or listing of commercial products or
services in this publication does not imply endorsements by the North Carolina
Cooperative Extension Service nor discrimination against similar products or
services not mentioned. All pesticide recommendations provided in this
publication apply to pest control in North Carolina. Individuals who use
chemicals are responsible for ensuring that the intended use complies with
current regulations and conforms to the product label. Be sure to obtain
information about product usage in your locale and examine a current product
label before applying any chemical. The information presented on pest
biology is based on conditions in North Carolina and may not be applicable
to your locale. For further information, we recommend that you contact the
Cooperative Extension Service office in your county.