Assessment of Infestation levels of Chilo partellus swinhoe(Lepidoptera:Crambidae)on maize and the Impact of its parasitoid cotesia flavipes cameron(Hymenoptera:braconidae)in Sinazongwe District of Zambia
Date
2011-03-31
Authors
Moonga, Nzala Miyanda
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Abstract
The spotted stem borer, Chilo partellus (Swinhoe) is one of the most destructive pests of
maize in the warm, low altitude regions of Zambia. A study was carried out in
Sinazongwe district, which is located at about 600 metres above sea level in the
Southern Province to determine the incidence of C. partellus, damage to maize plants
and the abundance of its natural enemy, Cotesia flavipes. This study was carried out
during the winter cropping seasons of 2005 and 2006 in four locations where previous
releases of C. flavipes had been made. The locations described by intensity of C. flavipes
released were: locality 1; 500-1000 parasitoids, locality 2; 50,000 parasitoids, locality 3;
100,000 parasitoids and locality 4; non-release. These were classified as low, medium,
high and non-release locations respectively. In each location, maize plants were sampled
from sixteen farmers' fields at three different growth stages, namely; knee height,
tasseling and cob maturity. Ten plants were also randomly collected from each farmer's
fields by destructive sampling to assess severity of C. partellus damage.
Analysis of variance (ANOVA) was carried out to determine if there were any
significant differences across the locations and between plant growth stages. The results
showed significant differences (F=7.74; d.f.=3; PO.001) in incidence of C. partellus
across the locations. Similar significant differences were also obtained among the three
plant growth stages (F=63.59; d.f.=2; PO.001). In addition, significant differences were
obtained in respect to the following damage variables; tunnel length (F=12.04; d.f.-3;
PO.001), damage index (F=16.39; d.f.=3; PO.001) and number of exit holes
(F=100.83; d.f.=3; P<0.001) across the locations. Similarly, significant differences were
also obtained at the three plant growth stages in tunnel length (F=115.54; d.f=2;
PO.001), damage index (F=12.04; d.f.=2; P<0.001) and number of exit holes (F=7.96;
d.f.=2; P<0.001). There were however, no significant differences in leaf damage when a
t- test was carried out to compare damage at knee height and tasseling stages across all
the locations. Similarly, there were no significant differences in the number of
parasitized larvae across the locations and at the three maize growth stages. C. partellus
constituted 94.5% and 95.6% of the total stem borer larvae collected from maize plants,
and the remaining 5.9% and 4.4% were Sesamia calamistis in the 2005 and 2006 winter
cropping seasons, respectively.
Results of the present study confirm that C. partellus is the dominant cereal stem borer
in Sinazongwe district and clearly show that C. flavipes is fairly well established in this
agroecosystem. The results indicate however, that at this level of establishment, C.
flavipes did not adequately suppress stem borer populations possibly due to low
parasitism levels at peak stem borer incidence. Follow up studies might be necessary to
clarify this phenomenon.
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Keywords
Lepidoptera , Corn---diseases---pests