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cy eniptaerdtmSteanttesof Biological Control of the
gricujture
Animaland Russian Wheat Aphid
PlantHealth
Inspection
Service
ProgramAid
Number1507
Coverphoto: Parasiticwasps sucli as
Diaeretlellarapaekeep Russian wtieataphid
populationsfrom reactiing damaging levels
on small grains and manyothercrops. (Photo
courtesyofJack KellyClark, Universityof
CaliforniaStatewide IPM Project.)
2
—
Populations of most native insects are Origin of the Problem
held in check by parasites, predators,
and disease organisms. But exotic The Russian wheat aphid Diuraphis
—
pests that manage to enterthe United noxia (Mordviiko) originated in south-
States, like the Russian wheat aphid, central Russia and is common in adja-
do not have locally established natural cent countries in Europe, northern
enemies. When the population of such Africa, the Middle East, and Asia. Per-
pests builds to the pointwhere they are haps as a result of expanded interna-
causing economic damage, farmers tional trade in grains during recent
often turn to the use ofchemical insec- decades, this insect has been carried
ticides. Since 1962, the U.S. Depart- into othercountries, including South
ment ofAgriculture (USDA) has been Africa and Chile. In North America, the
wteocrhkniinqguteosdteovseulpopprbeisoslopgeisctasl.coTnthreosle tDhiestrUinbiutteidonStmaatpes,ofaRsuosfsiDaencewmhebaetra1p9h9i2d.in tRhuesseiaralnyw1h9e8a0t'sajpuhsitdnworatshfoifrstMefxoiucnod in
techniques can reduce farmers' depen- (Dataarederivedfromthe National Agricul- City. From this initial infestation, it
dency on insecticides. tural Pest Information System [NAPIS].) spread northward and reached Texas in
In biological control, natural ene- 1986. By 1990, the Russian wheat aphid
mies are used to reduce pes—t popula- when the Russian wheat aphid first was found in 16 Western States and 3
tions to subeconomic levels not appeared in the United States in 1986, Canadian Provinces, but it has not sig-
eradicate pests altogether. Biological APHIS' biological control program was nificantly expanded its North American
control has been successful against already working on a projectto release distribution since then.
many insect pests, including aphids, in natural enemies against otheraphid
North Americafor over a century. pests. This projectformed the basis for
USDA's Animal and Plant Health becoming involved in a more intense,
Inspection Service (APHIS) has been cooperative campaign directed specifi-
cooperatively involved with biological cally againstthe Russian wheat aphid.
control projects for many years. In fact,
3
—
Characteristics of tlie Pest Nature and Cost of the Problem
—
Aphids sometimes called plant lice Like other aphids, the Russian wheat
are small, soft-bodied insects thatfeed aphid feeds on plants by inserting its
on plants by sucking theirjuices. The mouthparts into vasculartissues to tap
Russian wheat aphid is pale green and the flow of nutrient-rich sap. By itself,
usually covered with powdery white wax. such interference with a plant's nutrition
Most individuals are wingless, but large can reduce yields. Butwhile it feeds,
numbers ofwinged forms develop when the Russian wheat aphid also injects a
grain plants mature. Although aphids toxin thatcauses leavesto discolor and
are weakfliers, the wind carries them roll into strawlike tubes that enclosethe
long distances. pests. Heavily infested grain fields may
Three characteristics distinguish the have large areas of stunted and dying
Russian wheat aphid from otheraphids plants.
thatfeed on small grains:
• Stubby, hard-to-see cornicles (twin
projections nearthetip ofthe abdo-
men);
• An apparentdouble tail, especially
when viewed from the side (no other
grain aphids have this);
• Short antennae that are less than half
the length ofthe body.
Russianwheataphidcolonyon damaged
wheatleaf. Atlowerleftisabrown parasit-
ized aphid ("mummy").
Russianwheataphidadultsand nymphs
feeding on agrain leaf.
4
The Russian wheat aphid prefers When afield is initially invaded by coalesce, eventually resulting in large
barley and wheat but also attacks oats. Russian wheat aphid, widely spaced areas of dead ordying plants.
In some infested fields, grain yields patches of plants with characteristic Since the Russian wheat aphid
have dropped by as much as 70 per- symptoms appear. Asthe infestation came to North America, grain farmers
cent. The grain from infested plants progresses, these patches expand and
may also be of lower nutritional quality.
The presence of Russian wheat
aphids in afield is usually revealed by
damageto host plants.
• Infested leaves have whiteto reddish-
purple streaks along the veins.
• The margins of infested leaves roll up
into atube. Rolled leaves may
become so disfigured thattheytake
on acorkscrew appearance.
• Infested plants appearstunted and
produce fewertillers, which often
become prostrate instead of remain-
ing upright.
Russian wheat aphid infestations
usually originate on basal leaves of
tillers, but astillers elongate, aphids
move upward to younger leaves. Moder-
ately infested plants produce smaller
grains and fewergrains per head. When
developing grain heads gettrapped
inside infested terminal leaves, the
heads cannot reach theirfull extension.
Heavily infested plants may die.
Awheatplantshowing Russianwheat aphiddamage.
(Photo courtesyofTexasA& M University.)
5
have controlled it primarily bytlie appli- great concern thatthe initiation of From 1987through the 1988-89
cation of insecticides. However, with the chemical control programs in expansive growing season, crop losses attributable
aphids protected inside rolled-up leaves acreages ofsmall grains may aggravate to Russian wheat aphid infestations in
ofthe host plant, insecticidal control is existing environmental problems orcre- the Western United States totaled
difficult and expensive. Also, there is ate new ones.
Thisdrylandwheatfield in New
Mexicosufferedsignificantdamage
from Russianwheataphid. (APHIS
photoby Bob Flanders.)
5
approximately $221 million, and an addi- The goal of biological control efforts
tional $55 million was expended for con- againstthe Russian wheat aphid in
trol. During the 1989-90 growing North America is to locate, import, and
season, infestations were not as wide- establish effective natural enemies.
spread as in previous years, but yield When successful, this approach will
losses still totaled over $33 million. safely and permanently reduce Russian
Control costs amounted tojust over $1 wheat aphid densities below economi-
million, and the pest exerted an esti- cally significant levels.
mated indirect impact on the community
of over $44 million. These monetary
losses, as well as possible environmen-
tal and social costs, may increase and
will continue to accumulate if more
effective and environmentally appropri-
ate control measures are not developed.
In the native home ofthe Russian
wheat aphid, several species of para-
sites, predators, and pathogens attack
it. These natural enemies probably are
the primary reason why high densities of
the pest rarely develop in these regions.
In newly invaded regions, where no
effective natural enemies exist, the Rus-
Wheat leaves in aplantattacked bythe Rus- sian wheat aphid quickly becomes a
sdieavnelwohpeiantgagprahiindhteeandd.toWrholel,ntrtahpepignrgaitnhehead major pest.
cannot mature properly, yield andqualityare
adverselyaffected.
7
Initial Biological Control in the Westthe sevenspotted lady
Activities beetle (Coccinella septempunctata L.), a
predatorofseveral aphid pests. In
When the Russian wheat aphid first Europe and Asia, this lady beetle is a
invaded Texas, the APHIS Biological common predatorofthe Russian wheat
Control Program was already releasing
Parasiticwasp (Aphidiussp. ovipositing in a
Russian wheataphid.
Adultladybeetle (Cyclonedaancoralissp.]
feeding on agrain aphid. (Photocourtesyof
The larvaofapredaceousfly (Leucopissp.] Max Badgley.)
feeding on Russianwheataphid.
8
