Insects Which Challenge Global Wheat Production - Wheat Science and Trade - page 186

dacloprid, malathion, methyl parathion, para-
thion, and a mix of parathion and methyl parathion
(Royer et al., 1997a).
In addition to the extra costs associated with
the use of insecticides and their potential for con-
tributing to environmental contamination, the
greenbug has demonstrated the ability to develop
resistance to insecticides. Resistance to several
organophosphorous insecticides, including disul-
foton and dimethoate, has been reported in Texas
and Oklahoma (Peters et al., 1975; Teetes et al.,
1975).
The greenbug has a number of natural enemies
(predators and parasitoids) that may suppress
populations during the growing season. Small
parasitic wasps lay eggs inside the body of the
aphid causing the aphid to swell and turn a tan
color as the immature wasp feeds inside. This
swollen, tan-colored aphid is called a mummy. As
with BCOA, some important greenbug predators
include lady beetles, lacewing larvae, and hover
fl y larvae (Royer et al., 1997b).
While insecticides and natural enemies are
important control measures, plant resistance
plays a pivotal role in the development of any
sustainable approach to controlling green-
bug damage in wheat. Insecticides and natural
enemies can be successfully included in an inte-
grated pest management (IPM) approach, with
plant resistance forming the foundation upon
which to build (Quisenberry and Schotzko
1994).

Utilization of host-plant resistance

Efforts to develop greenbug-resistant wheat began
in the 1950s with the identifi cation of greenbug-
resistant DS 28A selected from durum wheat
(Dahms et al., 1955). DS 28A was resistant to
greenbug in the fi eld at the time, and its single
recessive gene was assigned the gene symbol gb
(Curtis et al., 1960). From these initial efforts, a
series of wheat germplasm and cultivars was
developed and released in response to newly iden-
tifi ed greenbug biotypes. Porter et al. (1997)
present details of the reports of biotype identifi ca-
tion and wheat resistance gene development and
deployment.
Tyler et al. (1987) reviewed the status of green-
bug biotypes and sources of resistance in wheat.
They assigned designations for fi ve genes ( gb1 ,
Gb2 , Gb3 , Gb4 , and Gb5 , in which g indicates
recessive inheritance and G indicates dominant
inheritance) for the sources of resistance in the
respective wheat germplasm lines DS 28A,
Amigo, Largo, CI17959, and CI17882. Since that
time, one additional source of resistance has been
reported in wheat. Porter et al. (1991) reported
identifi cation of greenbug biotype G resistance
in a wheat-rye translocation germplasm (GRS-
1201). GRS-1201 has a single, dominant gene
( Gb6 ) located on the 1RS arm of the wheat-rye
translocation chromosome T1AL·1RS (or
1RS·1BL) and is resistant to biotypes B, C, E, G,
and I (Porter et al., 1994). Table 9.2 summarizes

Table 9.2 Greenbug resistance genes
and biotype interactions in wheat.

Greenbug Biotype
BCE FGH I

Resistance
Gene Germplasm Origin K

Reaction to biotype a

DS 28A gb1 T . turgidum

durum

SSSRS SSS

Amigo Gb2 S . cereale RRS S S S SS

Largo Gb3 T . tauschii SRRSS RRR

CI 17959 Gb4 T . tauschii SRRSS SRR

CI 17882 Gb5 T . speltoides SRRSS SRR

GRS 1201 Gb6 S . cereale RRRSR SRR

a R and S indicate resistant and susceptible reactions, respectively.