Lesser cornstalk borer
Elasmopalpus lignosellus (Zeller)
From: Solomon, J.D. 1995. Guide to insect borers of North
American broadleaf trees and shrubs. Argic. Handbk. 706. Washington, DC:
U.S. Department of Agriculture, Forest Service. 735 p.
Hosts. Black locust, dogwood, tupelo, sycamore, pine,
redcedar, Arizona cypress, and baldcypress. Corn, peanuts, and many other
legumes and grasses are attacked, but plants in the grass family are preferred;
attacks trees only ocassionally (Dixon 1982b, Luginbill and Ainslee
1917).
Range. Throughout the southern half of the United States but
most damaging in sandy soil along the south Atlantic and Gulf Coasts. Also
occurs throughout Central and South America (Luginbill and Ainslee 1917).
Description
Adult. Brownish moth with wingspan of 17 to 25 mm (Luginbill and
Ainslee 1917). Forewings narrow and elongate with oblique distal margins;
yellow ochre to light brown in males and dark brown in females. Hindwings
whitish with gray to brown anterior and distal margins. Head brown to
black.
Egg. Oval, 0.7 mm long by 0.2 mm wide, with sculptured surface;
pale green when first deposited, becoming iridescent crimson at maturity.
Larva. Greenish brown and about 16 mm long when mature.
Head and cervical shield shiny brownish black; body pale green with
longitudinal, somewhat broken white and purple stripes.
Pupa. Pale yellowish green initially, gradually becoming dark
brown, with six hooked spines on abdomen tip, and about 8 mm long.
Biology. Moths emerge during early June in southern Georgia and
are caught almost continually in light traps through Augus (Leuck 1966).
Average life of adults is 10 days, and each female deposits about 125
eggs. Eggs are generally deposited singly on the upper and lower sides of
leaves, at any point along the stem, and in soil just below the surface with
grains of sand adhering to them. Eggs hatch within a week, and early-instar
larvae mine lower branches or begin to feed on stem and roots below the soil
surface (Dixon 1982a). Larvae construct radiating tubelike shelters of
silk, soil, and excrement near the root collar just below the soil
surface. Feeding by larvae on woody tree seedlings is characterized by
surface or subcortical burrowing and girdling and often results in gall-like
swellings and callus tissue around the feeding site (Snyder 1936). Larvae
pass through six instars, and total larvae development requires 13 to 24 days
(Dupree 1965, Leuck 1966). The pupal stage is 8 to 10 days. By late
summer, most life stages are present in infested plants as generations
overlap. The winter is passed in either the larval or pupal stage in soil
and soil litter. It completes two to four generations per year (Dixon
1982b).
Injury and Damage. The first sign of infestation in forest tree
nurseries is wilting foliage. As seedlings begin to die, they may remain
upright or fall over. Removing soil from around the base of the seedlings
reveals larval burrows girdling the stem and gall-like swelling and callus
tissue at wound sites. Sometimes, seedlings are severed just below ground
(Snyder 1936). Close inspection of the soil near feeding sites exposes
small tubes, composed of silk and soil particles, radiating from the injured
seedling. Only one larva is found in a silken tube. Larvae squirm
vigorously when disturbed (Dixon 1982a). When adults are disturbed and
forced to fly during daylight, they fly with short, jerky movements (Dixon
1982a). During the 1930's. 1 to 2% of the black locust seedlings in forest
tree nurseries in Mississippi, Arkansas, and Louisiana and up to 10% of those in
North Carolina nurseries were killed (Snyder 1936). More recently in a
central Florida forest tree nursery, this borer killed about 1 million hardwood
and softwood seedlings and injured as many more (Dixon 1982b). Mortality
of flowering dogwood in the Florida nursery was 70% and the remaining 30%
suffered injury.
Control. Parasites are abundant (Arnaud 1978, Krombein and
others 1979). In Texas, larval mortality from insect parasites ranges from
5 to 9%, and pupal mortality averages about 5% (Johnson and Smith 1981).
Culturally, selected covercrop rotation, late-fall clear-fallowing, proper soil
fertilization, and irrigation will help to ameliorate the factors conductive to
infestation. When such practices fail, granular insecticides can be
incorporated in the soil before covercrops are sown. In serious borer
infestations, insecticides can be applied to nursery beds as soil drenches; this
may have to be repeated several times because adequate exposure of larvae to the
chemical is difficult, as they retreat into their silklined shelters when
disturbed (Dixon 1928b).
Larva(e) seedling injured at root collar with silken feeding tube. James Solomon,
USDA Forest Service. |
Larva(e). James Solomon,
USDA Forest Service. |
Pupa(e). James Solomon,
USDA Forest Service.
|
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