R. Bowling et al., RELATIVE FITNESS OF GREENBUG (HOMOPTERA, APHIDIDAE) BIOTYPE-E AND BIOTYPE-I ON SORGHUM, WHEAT, RYE, AND BARLEY, Journal of economic entomology, 91(5), 1998, pp. 1219-1223
Greenbugs, Schizaphis graminum (Rondani),present a well-documented exa
mple of the ability of insects to overcome designed host plant resista
nce. Four greenbug biotypes have been identified on wheat, Triticum ae
stivum L., and 3 on sorghum, Sorghum bicolor (L.) Moench, since greenb
ugs were identified as pests of small grains. Biotype E has been the p
redominant biotype since the mid-1980s. Greenbug biotype I is the most
recent greenbug biotype identified in field plantings of small grains
and may be replacing biotype E. Replacement of biotype E greenbug by
biotype I will depend on the fitness of biotype I on biotype E-resista
nt cultivars. We attempted to predict this event by assessing relative
fitness of the 2 biotypes, defined by life history characteristics on
sorghum, wheat, rye, Secale cereale L., and barley, Hordeum vulgare L
. We used several sorghum cultivars or lines with differ ent reported
levels of resistance to greenbug biotypes E and I, and 1 cultivar or l
ine each of wheat, barley, and rye with reported resistance to biotype
E. Biotype E development time, intrinsic rate of increase (r(m)), and
to a lesser extent number of offspring produced were adversely affect
ed by E-resistant and I-resistant sorghum cultivars or lines, whereas
biotype I was only adversely affected by I-resistant cultivars or line
s. Even on I-resistant cultivars or lines, biotype I outperformed biot
ype E. Wheat line CI 1795 and barley cultivar 'Post', previously ident
ified as resistant to greenbug biotype E, also showed resistance to gr
eenbug biotype I. No differences occurred in the reproductive characte
ristics of greenbugs between E-resistant and E-susceptible rye cultiva
rs, Given these differences in fitness on both E- and I-resistant sorg
hum and the importance of sorghum to greenbug population dynamics in t
he central and northern plains (compared to wheat, barley, and rye), i
t is likely that as increasing acreage is planted to these sorghum cul
tivars biotype I will replace biotype E.