Table Of ContentGreatBasin Naturalist53(3).pp.310-313
WINTER MORTALm' OF THE RUSSIAN WHEAT APHID
(HOMOPTERA: APHIDIDAE)
ON RANGE GR/VSSES IN NORTHERN UTAH
Frank Me.s.sina'
J.
Keywords:Ru.ssiaitwheataphid,grasses,rungelands. wintermortalitij.
The Russian wheat apliid, Diuraphis nox'ia The overwintering success of D. noxia in
(MorcKilko), is a newly established pest of northern Utah has not been investigated, but
small grains in western North America (Stoet- the typical absence of aphids in earlx spring
zel 1987). This aphid also feeds on several suggests that fall populations are eliminated
native and introduced grasses, including during most winters. In October 1991 I de-
grasses that are widely planted for forage tected a population ofD. noxia on cool-season
improvement or erosion prevention in range- grasses in an experimental garden near Utah
lands (Kindler and Springer 1989, Kindler et State University. I sur\e\ed this population
al. 1991). Recent attention has focused on the throughout the winter and compared the pat-
potential importance ofthese grasses as "over- tern ofmortalit) with local temperature data.
summering" hosts for D. noxia, i.e., as sources
of aphid populations between the summer Materi.\ls and Methods
harvest and fall sowing of winter wheat,
Triticum aestivum L. (Clement et al. 1990, A common garden of six native and intro-
Armstrong et al. 1991). ComparativeK' little duced grass species (Table 1, nomenclature
information is a\ailable on the role ofgrasses follows Barkworth and Dewey 1985) was
as overwintering sites, even though migrants established in 1990 at the Greenville Experi-
from noncrop hosts could cause e.xtensi\'e mental Farm in North Logan, Utah. The gar-
damage to cereals in the spring. In this stud) den consisted of432 plants in six blocks, with
iinestigated the overwintering success of 12 plants per grass species per block. All
I
the Russian wheat aphid on cool-season grass- plants had produced flowering culms and
es in northern Utah. large tussocks byearlyOctober 1991, atwhich
The ability of D. noxio to survive winter time damage caused by the Russian wheat
conditions varies regionally in North America. aphid (e.g., necrotic streaks on leaves) became
Winter mortality may reach 100% at higher apparent on several individuals. Further
latitudes (Butts 1992), so that aphid popula- inspection confirmed the presence of Russian
tions must be reestablished by migrants each wheat aphids within the tighth rolled leaves
season. Such high mortality may stem from a of the newlv produced fall (overwintering)
lack of sexual reproduction (anholocycly) in tillers.
North American populations (Kiriac et al. I estimated the initial extent of the aphid
1990, Stoetzel and Hammon 1992), since a infestation on 15 October 1991 by collecting
sexual generation in the fall is needed to pro- five tillers from each of 18 randoniK' chosen
duce the cold-hardy egg stage. Partheno- plants per grass species. Samples were trans-
genetic females of D. noxia are quite cold- ported to the laboratorv' in plastic bags and
hardy (Harvey and Martin 1988), however, maintained at 5°C for later examination. I
and occasionalK- sin-\ive winter conditions in recorded aphid densitv as 0, 1-100, or >100
northern regions, including Colorado, Idaho, individuals per five tillers. I also noted any
and Alberta (Butts 1992, Feng et al. 1992, winged (alate) adults or nxniphs bearing wing
Hammon and Peairs 1992). pads. Thirty-six of the original 108 plants (6
'DrpartnuiilofBii)l(]g>.L'laliState-Lniwrsity.Ijigan,Utah81322-530.5.
310
1993] NOTI^S 311
Ocg„tTna()b.l11k-11(i1)9r.(w9)i2N,.uoirhI^>hi1t,0w(oi)f p//;-l>.anitiDsXiIirioiaipilISiIuIXlsgrpacsMs' srliix\'cCR.t-insllehresari-n t.<'c^'9^in.iO=;/.3LK-,-(i.,l).,l,-vrftl.,O-aIolvmlerr1a.•g1.-e(,(.s,..'.f,l,.»UroIillmll,ft,|iic;--a.si..ianmjeWisi-t.t1e1.iOlli'l^-
Apliidclensit\ class Rksl ITS
Itost speciesleiilti\ar) 1~1()() >!()() The initial census in October imlicaled that
Agropyrondesertonim aphids had infested all six species of cool-
(Fischerex Link)Scliiiltcs season grasses, with a few plants bearing
(crestedwlieatgrass, 'N'ordan')
>100 aphids per five tillers (Table 1). The
Elynutslanceolatius proportion of plants infested varied signifi-
G((SSocnuralikdbenel^ri\&t-rJ.wCl.ieSantigirtalsis), 10 cPan<tK-.0a2)m;ovnigrtguraalKs-s salplecoifesth(eA'-ii=icha1i4i.0.ridcfeg=ras.5s,
Secar) plant bore aphids, while liussian wheat aphids
were found on less than halfofthe blucbunch
Leymitscinereus wheatgrass plants. Alate adults were found on
(Scribner& Merrill) oiiK 5 of 108 plants, but ininphs bearingwing
A(.GrLeoat\eBasinwiJdrxe, 11 pads were common on all host species. Prior
"Magnar") to this initial census, dail\ minimum tempera-
ture had dropped below free/.ing (down to
Oryzopsishyincnoides -1°C) on onlya single date (Fig. 1).
(Roenier6cScluiltes)
Live aphids remained abundant on each
Ricker 16
(Indianricegrass, grass species on 19 No\ember (Table 2i.
'Palonia') despite several da\s of sub-zero minimum
temperatures in late October and earl\
Pseuduregneriaspicatci November (including a reading of-16°C on 3
(Pursh)A. Line 11
(lihiebniicliwheatgrass, Noxember). On 6 December, 5 da\s after the
Whitniar') minimum temperature had dropped to-2()°C,
each sample contained main dead aphids, but
Thinopyniiii iiitninvdiiiin at least a few li\e aj^hids were found on all
D(Secwhuery)Bark^\. ^- D. H. 12 hosts except Indian ricegrass. No winged
(intennediatepubescent adults were found on this dati' or on any sub-
wheatgrass, 'Luna') sequent date.
Four hosts bore lixe aphids in earl\ Janii-
ar\, but only two (crested wheatgrass and
per i^rass speeies) were then chosen for intermediate piibesceiil wheatgrass) still tlid
monthh samples from Noveml^er 1991 to so b\ inid-Februar> (Table 2). \'c\y cold tem-
April 1992 (dates are listed in Table 2). On peratures wt'ie recorded between these two
each sampling date 1 clipped 10-20 tillers per sampling dates, including a seasonal low of
plant, sometimes after brushing a\va\' snow- -26°C on 21 Januan (Fig. 1). .Most li\f aphids
cover. In the laboratory' I recorded the pies- in the mid-Ficbruaiy samples appeared to be
ence ofany li\'e aphids, which were so deter- in a torpid condition and were unable to right
mined b\' the retention of a pale green bocK themscKt's or walk normalK. Ten aphids that
color and the independent movement of one appeared to walk normalK were placed on
or more appendages. A wider sample ofplants winter wheat seelings ('Hansel' \ariet>) at
was obtained on (S and 21 April 1992: 1 pooled room temperature (these seedlings were
tillers from > 10 indixidual plants per grass known to support a thri\ing laboraton colony
species soas to fill two 4-Lplastic l)ags. of D. noxia). Although a few aphids probed the
Daily temperature data from October to leaves and assumed a feeding stance, all were
April were supplied by the Utah C^limate Cen- dead within 48 h.
ter, which maintains a weather station at DaiK maximum and iiiininuim tempera-
Greenville Farm. To estimate the severit\' of tures were unseasonably high after the Febru-
winter conditions during the sampling period, ary samples were taken, and temperatures
I compared 1991-92 temperature records on remained high throughout the early spring
the Utah State Uni\ersit\ campus ''which is (Fig.l). Despite this apparent iinpro\ement in
312 Great Basin Naturalist [Volume 53
Table2. Presence(+)orabsence (-)ofli\eD. Jioxia apliids from six grasses sampled from No\einl)er 1991 to Ap
1992.
Host-' 19Nov 6Dee 3Jan 11 Feb 11 Mar 2Apr SApr 21 Apr
Crestedwlieatgrass
19931 NOTKS
313
Table 3. Mean dailv minmum, tcmp.ratu.cs fC) per tural Experiment Station and approved a"s'
oiinlosn3t0n\trroatmLOocgtaonb,erUttaoliA.i)ril l!-Wl-y2amioxertheprevi- l-oiu-nal- \(). 4377. i i
