Effects of Neem Extracts on the Feeding, Survival, Longevity and Fecundity of African Bollworm, Helicoverpa Armigera (Hubner) (Lepidoptera: Noctuidae) on Cotton
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Date
2007-07
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Addis Ababa University
Abstract
The effects of neem oil (Nimbecidine 0.03% Aza) and water extracts of neem seed and
leaf were studied each at three different concentration levels on various developmental
stages of African bollworm both under laboratory and field conditions at Werer
Agricultural Research Center. The laboratory study comprised of square dip and larval
immersion experiments, both replicated three times using Completely Randomized
Design. Whereas the field experiment was conducted using a Randomized Complete
Block Design in three replications to verify neem extracts as a botanical insecticide
under field condition. Mean mortality of Helicoverpa armigera larvae ranged from 4.67-
8.00 in square dip experiment and 3.67-6.00 in larval immersion experiment. While
control mortality was 0.33 & 1.00 in square dip and larval immersion experiment,
respectively. Lower number of damaged squares, ranging from 1.00-4.67 were observed
in square dip experiment from different concentration levels of Nimbecidine and water
extracts of neem seed and leaf. Significantly lower mean weight of artificial diet
consumption (0.18-0.68 & 0.43-0.78g) was recorded at 6 & 9 DAT, respectively from
various concentration levels of Nimbecidine and water extracts of neem seed and leaf in
larval immersion experiment. Moreover, higher percent weight loss of ABW larvae, lower
pupal weight, relatively extended duration at the larval stage, higher number of larvalpupal
intermediates, lower number of eggs of which the majority are non-fertile as
compared to the control were recorded from the various concentration levels of water
extracts of neem seed and leaf and Nimbecidine in square dip and larval immersion
experiment. However, results of field experiment have indicated that Nimbecidine and
water extracts of neem seed and leaf have non-significant effect on the survival of ABW
larvae, damaged flowers, squares and bolls in all rounds of spray application and in
combined analysis. Moreover, no yield advantage was obtained from neem extracts.
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Biology