Abstract:
Aphids in unsprayed canola (
Brassica napus
Linnaeus) fields in Isfahan province
(central Iran) were sampled for two growing seasons
, 2011-2013. Sampling unit was a
whole plant and 20 plants were sampled weekly. In t
he laboratory, heat-extraction and
sub-sampling techniques were used to estimate the d
ensity of aphids. To determine the
relationship between population growth rate of the
aphids and degree-days,
linear
regressions were done between log of aphid density
and accumulated degree-days.
Homogeneity tests were done using pairwise comparis
ons between slopes. Aphids'
preference for upper (10-15 cm upper part of stem)
and lower (the rest of stem) parts of
the plant was analyzed using Student’s
t
-test. Aphid fauna included: Cabbage Aphid [CA;
Brevicoryne brassicae
(L.)], Green Peach Aphid [GPA;
Myzus persicae
(Sulzer)], and
Turnip Aphid [TA;
Lipaphis erysimi
(Kaltenbach)]. The GPA developed small population
in comparison with CA and TA and was occasionally f
ound. The population density of
CA and GPA tended to show two peaks, and during flo
wer initiation, population began to
decrease. The average population growth rates of GP
A and CA were 0.001 and 0.003,
respectively. Homogeneity tests indicated that, at
all sites and years, GPA showed reduced
growth rate compared to CA. On average, 36 and 64%
of CA and GPA populations were
found on the lower parts of plants, respectively. T
his indicated that CA preferred upper
part while GPA preferred lower part of the plants.
The obtained results could be used to
make a contribution to systematize the field monito
ring of predominant aphids in canola
crop.
Keywords:
Brevicoryne brassicae
, Canola, Degree-days,
Myzus persicae
, Population growth rate.
