INSECTS AFFECTING

SWEETPOTATOES

Agriculture Handbook No. 329

Agricultural Research Service

UNITED STATES DEPARTMENT OF AGRICULTURE

In Cooperation With

Clemson University Agricultural Experiment Station

CONTENTS

Page

Wireworms 2

Cucumber beetles 5

Systena 10

Sweetpotato flea beetle I4

Notoxus calcaratus IQ

Grubs ig

Sweetpotato leaf beetle 20

Sweetpotato weevil 22

Other insects 24

Injury from causes other than insects 25

List of insects that attack sweetpotatoes 27

Literature cited 28

Washington, P.C. j^^^^^ j^^^ ^^^^

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 Price 25 cents

INSECTS AFFECTING SWEETPOTATOES

By F. P. CtJTHBEBT, JR., Entomologist, Entomology Research Division

At least 18 species of insects feed on the edible

roots of sweetpotatoes. The crop grows during

the summer and fall when populations of most

insects are highest and development is most rapid.

Therefore, the roots are often attacked from the

time they begin to enlarge in June or July until

harvest in October or November. Even when the

best available control measures are used, few crops

are produced that are entirely free of insect-feeding scars. Insect attacks lower the quality of

sweetpotatoes by marring their appearance, providing entry points for decay organisms, causing

waste when the roots are prepjared for cooking, and

sometimes by causing objectionable tastes. Eoots

that contain either insects or their excrement are

usually unfit for human food.

The control of soil insects became difficult when

some developed resistance to broad-spectrum chlorinated hydrocarbon insecticides and recommendations of other insecticides were withdrawn because of residue hazards. Injury by some insects

became more prevalent when new varieties of

sweetpotatoes were introduced that were more

susceptible to attack than older varieties.

The large number of insects involved and

their resistance to insecticides make their effective control by any one method unlikely. Therefore, the responsible species must be identified

whenever possible. The purpose of this handbook

is to provide growers and agricultural workers

with descriptions of the insects, the injury they

cause to sweetpotatoes, and pertinent information

of their importance, distribution, seasonal history,

and habits.

Most examples of plant injury illustrated in this

publication were photographed from plants

grown and infested with a specific insect species

under controlled conditions, in order to accurately

relate the type of injury to the insect causing it.

In the laboratory, large numbers of the test insects were caged for a short time with sweetpotato

plants to provide examples of damage to foliage

and fresh injury to roots. In the field, individual

sweetpotato plants were grown in sterilized soil

within large concrete pipes buried in soil. The

pipes were sealed on the bottom and caged at the

top to exclude contaminant insects. Specific insects were then introduced during the growing

season, and the roots were harvested at the normal

time to provide examples of root injury after the

feeding scars had healed and had been altered

in appearance by growth of the root.

Sometimes a grower is unaware of insects until

harvesttime, when he discovers the crop damage

they have caused. An attempt is then made to

identify the insect responsible by the appearance of

the feeding scars. A few of the insects produce

characteristic scars that can be accurately identified. However, injury by many of the most harmful insects on harvested roots is so similar in

appearance that an accurate identification cannot

be made. Eecent injury is easier to identify than

old injury that has been altered by root growth,

soil rots, or secondary insect attack.

A natural inclination of some growers is to

consider the depth of insect holes an important

characteristic and it sometimes is. However, the

relative depth of the holes can be drastically

altered by the growth of the root. Early-season

feeding scars that do not penetrate the cortex

flatten out and leave only unsightly blemishes on

the root. A scar that penetrates the cortex becomes deeper, in almost direct proportion to the

increase in diameter of the root through growth.

Thus two scars that differed only slightly at the

start may differ several inches in depth by harvest

(fig. 1). , When grown side by side, sweetpotato

varieties with a thin cortex will have more deep

holes from early season injury than varieties with

a thick cortex. Injury by some insects may differ

in appearance on different varieties of sweetpotatoes or on the same variety grown in soils of

different types.

Examine roots from several plants at frequent

intervals during the growing season to learn what

insects are damaging a crop of sweetpotatoes.

If injury is found, search the surrounding soil for

larvae or pupae and the soil or foliage for adult

insects. Many of the adult beetles feed on sweetpotato foliage, and their presence can often be

detected by the type of leaf injury.

1
AGRICULTURE HANDBOOK 329, U.S. DEPARTMENT OF AGRICULTURE

FIGURE 1.—Appearance at harvest of Insect injury early in the season that: penetrated the cortex (deep hole

left-center) ; did not penetrate the cortex (shallow scar right-center). (XI)

WIREWORMS

Several kinds of wireworms feed on sweetpotatoes. The southern potato wireworm, Conoderus

falli Lane, is probably the most injurious one in

the Southeastern States. Cuthbert and others

HY discussed this species as a pest of white

potatoes. The adult beetles are dark brown, about

a quarter of an inch long (fig. 2), and are found

near the soil surface under leaves and trash in

sweetpotato plantings. The adults do not feed on

sweetpotato plants.

The eggs (fig. 3) are laid in the soil from late

spring to early fall. They are small and often

concealed by particles of earth that adhere to

them. The eggs hatch in 5 days during midsummer, but may take several weeks during cool

weather in the spring or fall.

' Italic numbers in parentheses refer to Literature

Cited, p. 28.

Sweetpotatoes are injured by the larvae, which

hatch from eggs laid in the soil during the summer and early fall. The larvae (fig. 4) are white,

cream, or yellowish gray with reddish-brown

heads and tails. They are smooth, shiny, and relatively hard bodied. ' When full grown they are

VQ to % inch long. In midsummer when temperatures are high and food plentiful the larval stage

may last only 30 days. It may last as many as

340 days under less favorable conditions. When

fully grown, the larvae change to pupae in earthen

cells under the ground. The pupae (fig. 5), which

are slightly larger than the adult beetles, are white

when first formed but soon change to creamy yellow. The pupae become adults in 5 to 19 days.

Usually two generations of this wireworm occur

each year.

Injury by southern potato wireworm larvae

usually consists of fairly small irregularly shaped

f
INSECTS AFFECTING SWEETPOTATOES

FIGURE 2.—Adult of the southern potato wireworm (Conoderus fallí). (X 11)

FIGURE 3.—Eggs of the southern potato wireworm ( Conoderus falli). (X 15)

holes. If growth cracks or other breaks in the

skin are present the holes may be concentrated in

these, otherwise the holes are scattered at random

over the surface of the root (fig. 6). The original

holes are usually less than a quarter of an inch

deep and seldom as much as a half of an inch but

may be considerably deepened by later growth of

the root. New feeding holes have ragged edges

and usually contain chewed root fiber (fig. 7).

Thisis a good diagnostic character.

Southern potato wireworms usually attack

sweetpotatoes late in the season. Consequently,

they produce less "healed-hole" injury (early season injury that has been healed over) than either

Dlahrotica (p. 5) or Systena (p. 10) larvae. The

larvae frequently invade the feeding scars made

by other insects. Wireworm holes are commonly

found in the shallow tunnels produced by sweetpotato ñea beetle larvae. Wireworm holes also

provide an ideal environment for decay organisms

and are frequently invaded by them.

The tobacco wireworm, Oonoderus vespertinus

(Fabricius), a widely distributed pest of tobacco,

also damages sweetpotatoes in areas where it is

abundant. Rabb (9) studied the biology of the

tobacco wireworm in North Carolina. The adults

FIGURE 4.—Larva of the southern potato wireworm {Conoderus falli). (X 10)
AGRICULTURE HANDBOOK 329, U.S. DEPARTMENT OF AGRICULTURE

are similar in size and shape to those of the southem potato wireworm but distinctively inarked

with areas of light and dark brown. The immature stages are also very similar.

Only one generation of the tobacco wireworm

occurs each year. The eggs, which are laid during

the summer, hatch into larvae in 1 to 3 weeks.

Pupation takes place during the late spring and

summer of the following year. Most overwintered

larvae have pupated before sweetpotato roots begin to enlarge ; therefore injury is probably caused

by larvae from eggs laid during the current year.

The gulf wireworm, Oonoderus amplicoUis

(Gyllenhal), is an important pest of sweetpotatoes in the coastal plains of the South Atlantic and

Gulf states. Cockerham and Deen (^) studied its

biology in Alabama. All stages are very similar

in appearance to the southern potato wireworm.

The life cycle is approximately the same as that

of the tobacco wireworm. Injury to sweetpotatoes

by tobacco and gulf wireworms is almost identical

to that caused by the southern potato wireworm.

Melanotus comnvimis (Gyll.) a larger wireworm,

is likely to be the most damaging species in the

more northern sweetpotato growing areas. The

FIGURE 5.—Pupae of the southern potato wireworm

{Oonoderus fallt). ( X 13)

injury it causes is similar to that caused by other

wireworms. but holes are larger and deeper.

FiGUBE 6.—Injury to sweetpotatoes by larvae of the southern potato wirewomi (Oonoderus falli). ( X 1)
INSECTS AFFECTING SWEETPOTATOES

t .1 I

FIGURE 7.—Southern potato wireworm {Gonoderus falU) feeding scars on sweetpotato.

chewed fiber in holes. ( X 8)

Note ragged edges and

CUCUMBER BEETLES

Larvae of the banded cucumber beetle, Diahrotica ialteata LeConte, and the spotted cucumber

beetle, Diabrotica undecimpunctata howardi Barber, feed on the roots of sweetpotatoes. The

spotted cucumber beetle occurs wherever sweetpotatoes are grown east of the Kocky Mountains.

The banded cucumber beetle has become a major

pest of sweetpotatoes in southern Louisiana. Itis

abundant from coastal South Carolina southward

into Florida and westward along the gulf coast

to Texas and also occurs in California. Pitre and

Kantack {S) studied the biology of the banded

cucumber beetle. The spotted cucumber beetle has

been widely studied because it is a pest of corn

and peanuts (/^).

Adults of the banded cucumber beetle are about

a quarter of an inch long and marked with alternating green and yellow bands (fig. 8). They eat

irregular holes in the leaves of sweetpotatoes

(fig. 9). Similar leaf injury by tortoise beetles,

Metriona spp., can be differentiated by holes that

are more uniform in shape and size (fig. 10).

Eggs of the banded cucumber beetle (fig. 11) are

laid m the soil from spring to early autumn. They

hatch in 1 to 2 weeks, depending on the temperature. The larvae are slender and white to pale

yellow. They have brown heads and a darkbrown spot on the last segment of the body (fig.

12). They are soft bodied and their skin, unlike

that of wireworms, is not shiny. Full grown

larvae are i/i to fV^ inch long. The larval stage

lasts from 8 to more than 30 days, depending on

temperatures and the availability of food.

The pupae (fig. 13) are formed in cells just

below the soil surface. They change to adults in

approximately 1 week. Six or seven generations

a year may occur.

Adult spotted cucumber beetles are usually

larger than banded cucumber beetles. Spotted

cucumber beetles have yellowish-green bodies and
AGRICULTURK HANDBOOK 32 9, U.S. DEPARTMENT OF AGRICULTURE

FIGURE 8.—Adult of banded cucumber beetle {Dialrotica

ialteata). (X 10)

black heads, legs, and antennae. The wing covers

are marked with 11 black spots (fig. 14). The

injury to sweetpotato leaves by banded and

spotted cucumber beetles cannot be differentiated.

Eggs, larvae, and pupae of the two species are also

indistinguishable.

Overwintering females of the spotted cucumber

beetle begin laying eggs as soon as the weather

turns warm in the spring. The eggs hatch in

1 to 3 weeks, depending on the temperature. The

larvae become full grown 2 to 4 weeks after hatching, at which time they make cells about 1 inch

below the soil surface where they change to pupae.

In a week or two the pupae change to beetles and

work their way to the soil surface. Usually two

to three generations occur a year.

Cucumber beetle larvae eat small round holes

through the skin of sweetpotato roots, and form

irregularly-shaped enlarged cavities just under

the skin (fig. 15). The larvae seldom tunnel into

the roots as do Systena (p. 10) larvae. The feeding scars are usually in groups rather than

scattered randomly over the root. The original

holes are usually shallow but may be deepened by

later growth of the root. In contrast to wireworms, cucumber beetles often attack sweetpotatoes early in the season. This results in much

healed-hole injury (fig. 16).

y ti

FiGUBE 9.—Injury to sweetpotato foliage by adults of banded cucumber beetle (Diabrotica baltcata). ( X 2)
INSECTS AFFECTING SWEETPOTATOES

FIGURE 10.—Injury to sweetpotato foliage by tortoise beetle (Metriona sp.). (X 2)

FIGURE 11.—Eggs of banded cucumber beetle (DiaWotica

ialteata). (x 10)
AGRICULTURE HANDBOOK 329, U.S. DEPARTMENT OF AGRICULTURE

FiGUKE 12.—Larvae of banded cucumber beetle (Dialrotica halteata). ( X 9)

FIGURE 13.—Pupae of banded cucumber beetle (Diaftroííca PIGUBE 14.—Adult of spotted cucumber beetle (Diahrobalteata). (X 10) tica undecimpunotata howardi). (Xll)
INSECTS AFFECTING SWEETPOTATOES 9

FiQTJBE 15.—Injury to sweetpotatoes by larvae of banded cucumber beetle {Diabrotica halteata). ( X 2)
10 AGRICULTURE HANDBOOK 32 9, U.S. DEPARTMENT OF AGRICULTURE

FIGURE 16.—Healed-hole Injury resulting from early season injury by banded cucumber beetle {Diabrotica ialteata)

larvae. (X %) ,

SYSTENA

The elongate flea beetle, Systena elongata

(Fabricius), the pale-striped flea beetle, Systena

ilanda Melsheimer, and Systena frontalis (Fabricius) feed on sweetpotatoes. Marcovitch (7) described injuries caused by the elongate flea beetle

and mentioned reports of injury by the pale-striped

flea beetle. Cuthbert and Reid (5) reported injury

by Systena frontalis. One or more of these species

probably occur wherever sweetpotatoes are grown.

Adults of the elongate flea beetle are about an

eighth of an inch long and black with longitudinal

white stripes on their backs. They produce characteristic feeding scars on the upper surface of

sweetpotato leaves. Unlike the pale-striped flea

beetle, they usually do not chew entirely through

the leaf unless it is young and tender (fig. 17).

Adults of the pale-striped flea beetle are very

similar to adults of the elongate flea beetle except

that the legs, head, and thorax of the pale-striped

flea beetle are usually not quite as dark. They

feed on sweetpotato leaves and make irregular

holes (fig. 18), which are smaller than those made

by cucumber beetles. Systena frontalis adults

are usually a little larger than the other two

beetles and have no white stripes on their back.

They also eat small holes in the leaves (fig. 19).

The habits and life histories of the three species

are similar, and the immature stages look alike.

These insects have a wide range of hosts including

many weeds. Adults move into sweetpotato fields

during the spring and summer and lay cream to

yellow eggs (fig. 20) in the soil. After a week to

10 days these hatch into white larvae which later

become pale yellow to pale salmon depending on

their food. The larvae are soft bodied and about

three-eighths of an inch long when full grown.

They have brown heads and a fleshy pointed

FIGURE 17.—Adults of elongate flea beetle (Systena

elongata) and injury to sweetpotato foliage. (X 10)
INSECTS AFFECTING SWEETPOTATOES 11

TC—7581

FIGURE 18.—Adult of pale-striped flea beetle (Systena Manda) and injury to sweetpotato foliage. ( X 15)

FIGURE 19.—Adult of Systena frontalis and injury to

sweetpotato foliage. ( X 12 )

FIGURE 20.—Eggs of the elongate flea beetle (Systena

elongata). (X 15)
12 AGRICULTURE HANDBOOK 329, U.S. DEPARTMENT OF AGRICULTURE

FIGURE 21.—Larva of the elongate flea beetle {Systena

elongata). (X 10)

FIGURE 22.—Prepupal larvae and pupae of the elongaite flea

beetle (Systena elongata). (X 10)

TC-7580 TC-7687

FiGUKE 23.—Injury to sweetpotatoes by larvae of the elongate flea beetle (Systena elongata). ( X % )
INSECTS AFFECTING SWEETPOTATOES 13

tubercle on the tail end (fig. 21). The larvae mature in 20 to 30 days, then curl up in a cell made

in the soil and transform into pupae (fig. 22).

The adults emerge in about 1 week. Probably at

least two generations occur a year in the South.

Systena larvae eat small holes through the skin

of sweetpotatoes and make enlarged cavities and

short tunnels just under the skin (fig. 23). Except for these tunnels Systena injury is very similar to that of cucumber beetle larvae, which seldom tunnel into the roots. At harvesttime early

season Systena injury usually appears as shallow

healed scars which tend to be elongate or irregularly shaped (fig. 24) in contrast with those of

cucumber beetle larvae, which are usually round.

In some soils, late-season Systena feeding results

in a large number of small shallow holes in the

roots (fig. 25). This is sometimes referred to as

"pinhole" injury.

FIGURE 24.- -Healed-hole injury resulting from early season feeding by elongate flea beetle {Systena elongata)

larvae. (X 1)

FiGUKE 25.—Pinhole injury resulting from late-season feeding by elongate flea beetle (Systena elongata)

larvae. (X 1)
14 AGRICULTURE HANDBOOK 329, U.S. DEPARTMENT OF AGRICULTURE

SWEETPOTATO FLEA BEETLE

Adults of the sweetpotato flea beetle. Clmetocnema confinis Crotch, have long been recognized as

pests of sweetpotato foliage (10), but the larval

injury to the roots was reported only recently (5).

This insect occurs almost everywhere that sweetpotatoes are grown and lives on bindweed, Convolvulus sp., as well as sweetpotatoes.

The adult beetles are black, about a sixteenth

of an inch long, and characteristically hop away

when disturbed. They eat narrow channels or

grooves in the upper surface of sweetpotato leaves

(fig. 26). This injury is quite characteristic and

easily recognized.

TC-7590

FIGURE 26.—Adults of the sweetpotato flea beetle ( Chaetocnema confluís) and injury to sweetpotato foliage. ( X 7)

FiGUKB 27.—Eggs of the sweetpotato flea beetle ( Ohaetocnema confinis). (X 15)

The adults pass the winter in sheltered locations

in hedgerows and the edges of woods. They move

into sweetpotato fields soon after planting. The

eggs (fig. 27) are laid in the soil and after a few

days hatch into slender white larvae (fig. 28) that

are similar to Diabrotica and Systena larvae but

have no dark spot or fleshy tubercle on their tail

end. When fullgrown the larvae are about threesixteenths of an inch long. They change into

pupae (fig. 28) in the soil. During the warmer

months of the year the entire life cycle of the

sweetpotato flea beetle is completed in about 30

days. A succession of broods occurs during the

spring, summer, and autumn.

Sweetpotato flea beetle larvae make small winding tunnels just under the skin of sweetpotato

roots. These tunnels are nearly invisible at first

but soon darken and can be seen through the skin

(fig. 29). As the roots grow, the skin over the

tunnels splits away leaving shallow scars on the

surface (fig. 30). Although large larval populations of the sweetpotato flea beetle are often found

in sweetpotato plantings, usually they cause little

injury to the harvested roots. Apparently the

larvae feed mostly on the fibrous roots and attack

the enlarged roots only under certain conditions. Sweetpotato varieties diflîer widely in their

susceptibility to economic injury by this insect.

TC-759Î

FIGURE 28.—Larvae (top), prepupal larvae (middle), and

pupae (bottom) of the sweetpotato flea beetle (Chaetocnema confinis). (X 10)
INSECTS AFFECTING SWEETPOTATOES 15

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FIGURE 29.—Injury by larvae of the sweetpotato flea beetle (Ghaetocnema conflnis). ( X 1%)

TC-7594

FiGUEE 30.—Sweetpotato flea beetle {Ghaetocnema conflnis) larval injury as it appears at harvesttime. ( X 1)
16 AGRICULTURE HANDBOOK 329, U.S. DEPARTMENT OF AGRICULTURE

NOTOXUS CALCARATUS

Notoxiis calcaratus Horn and the other members

of the family Anthicidae are sometimes calied the

ant-like flower beetles. Most of them do not damage crops and some prey on other insects. Studies

at Charleston, S.C. {5) disclosed that Notoxus calcaratus larvae sometimes feed on the roots of

sweetpotatoes. The species is widely distributed

and may be responsible for considerable injury

that is attributed to other insects.

The adults (fig. 31) are inconspicuous tan

beetles with brown markings. They are about an

eighth of an inch long and have a characteristic

hornlike projection over their head. No one

knows whether or not the adult beetles feed on

sweetpotato foliage.

The cream-colored larvae resemble small wireworms, but the tail end of their body is conspicuously notched and has no brown markings

PiGUEE 31.—Adult of Notoxus calcaratus. Top photograph shows side view (X 13),

view (X 19).

bottom photograph shows top
INSECTS AFFECTING SWEETPOTATOES 17

TC-7596

FIGURE 32.—Larvae of Notoxus calcaratus. (x 10)

TC-7597

FIGURE 33.—Pupa of Notoxus calcaratus. ( X 22)

(fig. 32). They are about a quarter of an inch

long when fully grown. Little is known about

the life history of this insect. The larvae and

pupae (fig. 33) live in the soil. The larvae appear

to be most abundant in sweetpotato plantings

during the late summer and fall, and much of their

injury occurs shortly before harvest.

Notoxus calcaratus feeding scars on sweetpotato

roots (fig. 34) are similar to those of small wirewornis, but lack the dark discoloration usually

associated with wireworm injury. The feeding

scars are relatively shallow and seldom contain

tunnels.

FIGURE 34.—Injury to sweetpotato by larvae of Notoxus calcaratus. (XI)
18 AGRICULTURE HANDBOOK 32 9, U.S. DEPARTMENT OF AGRICULTURE

GRUBS

Some grub (scarabeid) injury to sweetpotatoes

occurs in most areas where the crop is grown.

There are many species of grubs and undoubtedly

several oí them feed on sweetpotatoes. Cuthbert

and Keid (5) reported injury at Charleston, S.C.

by an introduced species, Plectris aliena Chapin.

White grubs {Phyllophyga spp.) are often reported as pests of sweetpotatoes. These are the

larvae of May beetles or June beetles.

Adults of the various grubs vary in size and

color but all are robust beetles. Many of them

are night flyers and frequently come to lights.

Plectris aliena adults (fig. 35) are light tan, and

their body conformation is typical of most scarabeids.

The eggs (fig. 36) are laid in the soil during the

spring and summer and soon hatch into fleshy

larvae that are typically C-shaped (fig. 37). They

are usually white or cream wdth light-tan heads

and grayish areas on the tail end. The larvae pass

the winter in the soil and change into pupae (fig.

38) the following spring.

Grubs gouge broad shallow areas in sweetpotato roots (fig. 39). Their injury is unlike that

of any other insect except cutworms, but grub

scars are much rougher and frequently shallower.

Since grubs feed upside down in the soil, horizontal roots are injured mostly on the under side.

FIGURE 36.—Eggs of Plectris aliena. (X 10)

FIGURE 35.—Adult of Plectris aliena. (X 7) FIGURE 37.—Larva of Plectris aliena. (X 7)
INSECTS AFFECTING SWEETPOTATOES 19

TC-7602

FIGURE 38.—Pupa of Plcctris aliena. (X 7)

FiGUKE 39.—Injury to sweetpotatoes by larvae of Plectris aliena. ( X 1)
20 AGRICULTURE HANDBOOK 32 9, U.S. DEPARTMENT OF AGRICULTURE

SWEETPOTATO LEAF BEETLE

The sweetpotato leaf beetle, Typophorus nigritws viridicyaneus (Crotch), is a minor but widely

distributed pest of sweetpotatoes. Brannon (1)

studied its biology in North Carolina.

The adults (fig. 40) are metallic bluish-green

beetles about a quarter ,of an inch long. They eat

the leaves of sweetpotatoes by beginning at the

margins and working inward (fig. 41). The eggs

are laid during the spring and summer in clusters

on the underside of the leaves or just beneath the

surface of the soil under sweetpotato plants. The

larvae (fig. 42) are pale yellow or yellow with

brown heads. When mature they are almost a

half of an inch long. The insect passes the winter

as larvae; the pupae are formed in the soil after

the weather becomes warm. Adults emerge during the spring or early summer.

Newly hatched larvae tunnel into the sweetpotato vines and later into the enlarged roots.

Injury to the roots is easily recognized by the large

excrement-filled tunnels that penetrate deeply into

the roots (fig. 43). Frequently the larvae are

found in the tunnels, sometimes a month or more

after harvest.

FIGURE 40.—Adult of sweetpotato leaf beetle ( Typophorui

nigritus viridicyaneus). (X 10)

FIGURE 41.—Sweetpotato leaves and stem showing injury causied by the sweetpotato leaf beetle: A and C, typica

adult injury ; B, injury to vine caused by young larvae.
INSECTS AFFECTING SWEETPOTATOES

TC-7604

PiGUKE 42.—Larva of sweetpotato leaf beetle (Typophorus nigritus viridioycmeus). (x 10)

21

riGURE 43.—Injury to sweetpotato by larvae of sweetpotato leaf beetle {Typophorus nigritus viridicyaneus). (X 1)
22 AGRICULTURE HANDBOOK 329, U.S. DEPARTMENT OF AGRICULTURE

SWEETPOTATO WEEVIL

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t^Sfí

^•;

TC-7606

FIGURE 44.—Adults of sweetpotato weevil {Cylas formicarius elegantulus) and their feeding and egg punctures on|

sweetpotatoes. ( X 6) I

The sweetpotato weevil, Cylas formwarius

elegantulus (Summers), has been studied more

thoroughly than any other insect pest of sweetpotato roots. Cockerham and others (3) studied

its biology in Louisiana, and control methods were

published by the U.S. Department of Agriculture

(11). This weevil is a serious pest of sweetpotatoes but occurs only in certain parts of South

Carolina, North Carolina, Georgia, Florida, Alabama, Mississippi, Louisiana, and Texas.

Adult sweetpotato weevils (fig. 44) are antlike

beetles about a quarter of an inch long. The head

and wing covers are metallic dark blue and the

thorax and legs, bright orange red. The adult

weevil feeds on any exposed part of the sweetpotato plant but prefers the roots. Feeding scars

on the roots consist of tiny shallow holes usually

in patches (fig. 44).

The eggs are laid in specially prepared cavities

in the vines or roots. The egg cavities are similar

to the feeding punctures but may be distinguished

by the mucilaginous covering secreted by the

female. The eggs hatch in about 1 week during

warm weather. The larvae (fig. 45) are white to

ivory with light-brown heads. When full grown

in 2 or 3 weeks they are about three-eighths of an

FIGURE 45.—Larvae (bottom) and pupae of sweetpotato

weevil (Cylas formicarius elegantulus). (X 13)
INSECTS AFFECTING SWEETPOTATOES 23

inch long. The pupae (fig. 45) are found in the

vines or roots. In a week or longer they change

into adult weevils. As many as six or eight generations may be produced in 1 year.

Injury to sweetpotatoes by weevil larvae (fig.

46) can be recognized by tunnels that start just

beneath the skin and become larger as they extend

inward. The tunnels are much smaller than those

of the sweetpotato leaf beetle and frequently contain larvae, pupae, or newly transformed adults.

Adult exit holes (fig. 46) are about the size of a

wooden match stem.

PiGUEE 46.—Injury to sweetpotato by sweetpotato weevil {Cylas formicarius elecjantttlus). Small holes on uncut

surface are adult feeding and egg punctures, and large holes on uncut surface are adult exit holes. Cut area

shows larval tunnels and pupal chambers. (XI)
24 AGRICULTURE HANDBOOK 329, U.S. DEPARTMENT OF AGRICULTURE

OTHER INSECTS

Other insects occasionally feed on the roots of

sweetpotatoes but seldom cause economic loss.

Among these are various kinds of cutworms, the

larvae of which eat large, smooth, open cavities

(fig. 47) usually near the stem end of the roots.

Ambrosia beetles {Scolytld) have been observed

by Kantack {6) to infest sweetpotatoes in

Louisiana.

Larvae of a longhorn beetle (Cerambidd) were

found in the basal portion of sweetpotato vines at

Charleston, S.C.^

Larvae of the American plum borer, Euzophera

seniifuneralis (Walker), were found tunneling

stored sweetpotatoes in North Carolina.^

Mole crickets are frequently reported as insect

pests of sweetpotatoes, but we have found no published description of their injury. The southern

mole cricket, even when abundant, caused no recognizable injury in sweetpotato field-plot experi

ments at Charleston, S.C, between 1961 and 196'

Specimens caged with only sweetpotato roots, livt

for several months but did not feed on the root,

^ Collected by L. R. Morgan, South Carolina Crop Pest

Commission.

^ Personal correspondence from D. A. Mount, surve

entomologist, North Carolina State University Coopera

tive Extension Service in Agriculture and Homi

Elconomics.

FIGURE 47.—Injury to sweetpotato by larva of the variegated cutworm (Peridroma sauoia). ( X 2)
INSECTS AFFECTING SWEETPOTATOES

INJURY FROM CAUSES OTHER THAN INSECTS

25

Sweetpotatoes are subject to certain types of

scarring that may be mistakenly attributed to insect feeding. Perhaps the commonest of these is

injury resulting from decay organisms attacking

the lateral root scars (fig. 48). This injury usually consists of shallow oval areas of darkened

">car tissue arranged in longitudinal rows on the

oots.

Eodents frequently feed on sweetpotatoes in

ae field. The injury they cause can be easily

recognized by the large amount of root consumed

and by their teeth marks (fig. 49).

Enlarged lenticils (fig. 50), a physiological condition caused by periods of excessive soil moisture,

IS sometimes confused with insect injury.

Eoot-knot nematodes frequently injure sweetpotatoes by causing cracking and malformation

of the fleshy roots. The presence of nematodes is

usually revealed by isolated darkened galls in the

flesh of the roots (fig. 51).

FIGURE 48.—Injury to sweetpotatoes caused by decay organisms attacking lateral root soars. (XI)
26 AGRICULTURE HANDBOOK 32 9, U.S. DEPARTMENT OF AGRICULTURE

FiQUBE 49.—Injury to sweetpotatoes by rodents. (X V2)

PiGUEE 50.—Enlarged lenticils on sweetpotato. (X 1)
INSECTS APPECTING SWEETPOTATOES 27

FIGURE 51.—Nematode galls in the flesh of sweetpotato.

(X 2)

LIST OF INSECTS THAT ATTACK SWEETPOTATOES

Î Soientiflc name

Cerambieid

Ghaetocnema conflms Crotch

Conodenus amplicollis ( Gyllenhal)

Oonoderus falli Lane

D'onoderus vesperiinus (Pabricius)

Vylas formicarius elegantulus

(Summers)

Diairotica balteata LeConte

Oiairotioa undecimpunctata

hoioardi Barber

Common name

Longhorn beetles.

Sweetpotato flea beetle.

Gulf wireworm.

Southern potato wirf

worm.

Tobacco wireworm.

Sweetpotato weevil.

Banded cucumber beetle.

Srwtted cucumber beetle.

Scientific name Common name

Euzophera semifuneralis

(Walker) American plum borer.

Mclanotus communia (Gyll.) A wireworm.

Metriona spp Tortoise beetles.

Notoxtts calcaratus Horn An antlike flower beetle

Pcridroma sanoia (Hübner) __ Variegated cutworm.

Plectrla aliena Chapin A grub.

Scolytid Ambrosia beetles.

Sysfena blanda Melsheimer__ Pale-striped flea beetle.

l^!/-itciia elongata (Fabricim)- Elongate flea beetle

Systena frontalis Pabricius_-_ A flea beetle.

Typopliorus nigritus viridicyaneus (Crotch) Sweetpotato leaf beetle.
r 1^

28 AGRICULTURE HANDBOOK 329, U.S. DEPARTMENT OF AGRICULTURE

LITERATURE CITED

(1) BRANNON, L. W.

1938. THE SWEETPOTATO LEAF BEETLE. U.S. Dept.

Agr. Cir. 495, 9 pp., illus.

(2) CocKERHAM, K. L., and DEEN, O. T.

1936. NOTES ON LIFE HISTORY, HABITS AND DISTRIBUTION OF HETERODERES LAURENTII GUER.

Jour. Econ. Ent. 29: 288-296, illus.

(3) DEEN, O. T., CHRISTIAN, M. B., and NEWSOM,

L. D.

1954. THE BIOLOGY OF THE SWEETPOTATO WEEVIL.

La. State Univ. Tech. Bui. 483, 30 pp.

(4) CuTHBERT, F. P., REíD, W. J., JR., and DAY, AUGUSTINE.

1965. THE SOUTHERN POTATO WIREWORM HOW TO

CONTROL IT ON IRISH POTATOES. U.S. Dept.

Agr. Leaflet 534, 8 pp., illus.

(5) and REíD, W. J., JR.

1965. FOUR LITTLE-KNOWN PESTS OF SWEETPOTATO

ROOTS. Jour. Econ. Ent. 58: 581-583, illus.

(6) KANTACK, E. J.

1965. TWENTY YEARS OF COOPERATIVE SWEET POTATO

RESEARCH 1939-1959. Pub. Nat. Sweet Potato Collaborators, pp. 55-64.

(7)

(8)

(9)

(10)

(11)

(12)

MARCOVITCH, S.

1946. INSECTS INJURIOUS TO SWEETPOTATO TUBERS

IN TENNESSEE. Tenn. Agr. Expt. Sta. Bui.

202, 11 pp., illus.

PITRE H. N., JR., and KANTACK, EDMON J.

1962. BIOLOGY OF THE BANDED CUCUMBER BEETLE,

DIABROTICA BALTEATA, IN LOUISIANA. Jour.

Econ. Ent. 55: 904-906.

RABB, R. L.

1963. BIOLOGY OF CONODERUS VESPERTINUS IN T

PIEDMONT SECTION OF NORTH CAROLI

(COLEÓPTERA : ELATERIDAE) . Ann. Eut. S

Amer., 56: 669-675, illus.

SMITH, J. B.

1910. INSECTS INJURIOUS TO SWEET POTATOES

NEW JERSEY. N.J. Agr. Expt. Sta. Bi

229, pp. 3-7, illus.

1960. THE SWEETPOTATO WEEVIL HOW TO CONTROL

IT. U.S. Dept. Agr. Leaflet 431, 8 pp.

1961. THE SOUTHERN CORN ROOTWORM HOW TO CONTROL IT. U.S. Dept. Agr. Leaflet 391, 8 pp.,

illus.

U.S. GOVERNMENT PRINTING OFFICE: 1967 O—249-285