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The management of diamondback moth, Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae), population density on cabbage using chemical and biological control methodsBopape, Malesela Jonas 04 July 2014 (has links)
The diamondback moth, Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae), is a
cosmopolitan insect pest of Brassica crops. In South Africa, there are no action thresholds
for its chemical control which makes it difficult for growers to make informed decisions on
when to apply insecticides and how frequently to apply them in order to achieve optimal
crop yield. To contribute towards optimum application of insecticides against P. xylostella,
this study compared the impact of weekly and bi-weekly applications of a selective
insecticide Dipel® (Bacillus thuringiensis Berliner var. kurstaki) applied at 250 g/ha, and a
broad-spectrum insecticide Dichlorvos (an organophosphate) applied at 1 ml/L against
biological control (Control) on the pest population density on cabbage during October–
December 2011 and March–May 2012. The use of both selective and broad-spectrum
insecticides for experiments enables us to understand if efforts to optimise cabbage yield
depend mainly on effective suppression of P. xylostella densities. Furthermore,
investigations were carried out to determine the impact of these chemicals on parasitism
rates of P. xylostella and species richness of its primary parasitoids.
During the October–December 2011 growing season, the lowest infestation of P. xylostella
occurred on cabbage plots that received weekly application of Dipel and the highest on
untreated control plots. Cabbage weights were negatively related to infestation levels,
implying that weekly application of Dipel yielded bigger cabbage heads. During March–
May 2012, P. xylostella infestations were again higher on the control followed by weekly
and bi-weekly treatments of Dichlorvos, then weekly and bi-weekly applications of Dipel.
Despite the significant differences observed, infestation levels were much lower (< 1 P.
xylostella per plant on average) in all treatments during this season. Consequently no
significant differences in cabbage weights were observed among the treatments. The lower
infestation levels were attributed to higher parasitism levels (≥50 %), especially during the
early stages of crop development.
A total of four parasitic Hymenoptera species were recorded from P. xylostella larvae and
pupae during October–December 2011, while three species were recorded during March–
May 2012. However, Cotesia vestalis (Haliday) (Braconidae) accounted for >80 % of total parasitism levels in all treatments. Parasitism levels were not significantly different among
the treatments in both seasons. Parasitoid species richness was highest on the control.
Although two parasitoid species were recorded in all Dipel and Dichlorvos treatments
during October–December 2011, only one parasitoid species was recorded in the Dipel
treatments during March–May 2012 compared to two species in Dichlorvos treatments.
Although weekly applications of Dipel ensured good yield and crop quality during
October–December, weekly applications of the chemical did not lead to better quality crop
during March–May crop growing season. Thus, it is not necessary to apply insecticides
during periods in which natural mortality of P. xylostella is high due to parasitoids. Since
P. xylostella abundance was a determining factor of crop quality, these results imply that
insect pest management should focus mainly on suppressing its numbers. Furthermore,
there was no evidence that application of either insecticide type had a negative impact on
parasitism rates of P. xylostella. The lower parasitoid species richness on Dipel treated
plots was the consequence of its higher efficiency in suppressing the pest population which
substantially reduced availability of potential hosts for parasitoids, hence only the efficient
C. vestalis was recorded at low host densities / Agriculture and Animal Health / M.Sc. (Agriculture)
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Role of apolipophorin-III in the immediate antibacterial responses of Galleria mellonella larvae (Lepidoptera:Pyralidae)Halwani, Adla E. January 1999 (has links)
No description available.
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Responses of males to a pheromone blend of female Oriental fruit moth with and without E8, E10-dodecadien-1-ol, a peromone component of codling moth (Lepidoptera: Tortricidae)Allred, Darin B. 18 April 1995 (has links)
Graduation date: 1995
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Diamondback moth (Plutella xylostella L.) ; toxicological database, resistance monitoring techniques, and intraplant distributionFongsmut, Anuthep 19 July 1991 (has links)
The diamondback moth (Plutella xylostella L.) is a major
pest of crucifer crops worldwide. It is a particularly
important problem in Southeast Asia where climatic
conditions favor a short generation time and rapid
proliferation. In countries such as Thailand, the
diamondback moth has apparently become resistant to all
classes of insecticides, even the newest ones.
The first part of this thesis is the development of a
computer database of all the available information on
diamondback moth toxicology. About 1,550 records were
extracted from more than 235 published or unpublished
documents. These records include information on the
geographical location of experiments, the insecticide
evaluated, the testing method and the results observed.
Most records in the database are from the last decade, and
are predominantly from Taiwan, Thailand, the USA and
Japan. Trends in the use of various classes of insecticides
can easily be followed. Thirty three records have been
found of insecticide resistance of more than a thousandfold.
An the known mechanisms of resistance are found,
and the diamondback moth has become resistant to all the
classes of insecticides, including Bacillus thuringiensis but
excluding abamectin. Case studies made possible by the
use of the database showed a rapid succession in the use
of 29 insecticides in the last 26 years in a single country
(Thailand). Although this rapid succession is usually
ascribed to the development of resistance, a case study on
the regional differences in resistance to five insecticides
showed marked variations in the level of resistance over
distances of 20 miles or more. The possibility of managing
insecticide resistance at the local level, already suggested
by studies in Hawaii, is thus supported by this analysis.
In the second part of this thesis, the toxicity of Bacillus
thuringiensis var. aizawai and of the bacterial toxin
abamectin was tested by two bioassay techniques on
populations of the diamondback moth from two Chinese
kale fields at locations in Thailand at which the highest
levels of resistance to most insecticides have been
reported. The leaf-dip bioassay was found to be superior to
a residue-vial assay or to the FAO-recommended assay.
More than 70-fold resistance to Bacillus thuringiensis var.
aizawai was observed in the populations of DBM collected
from these two fields, suporting the theory that resistance
resulted in the control failures reported by growers.
Resistance did not explain control failures with abamectin
as no resistance to this compound could be detected.
The third part of this thesis analyzes the intraplant
distribution of the diamondback moth larvae in an effort to
explain the control failures with abamectin on Chinese kale.
Extensive sampling of the various larval instars of the
diamondback moth revealed that a majority of second instar
larvae were sheltered on the young folded leaves of
Chinese kale. The majority of fourth instar larvae and
pupae were found on mature (lower) leaves. Inefficient
spraying practices observed in the field with high volume,
low pressure hydraulic pump sprayers may allow the young
larvae to escape pesticide exposure possibly explaining
control failures in the absence of physiological resistance.
This study shows that resistance in the diamondback
moth is a worldwide problem of major proportions. The
rapid development of resistance to Bacillus thuringiensis in
the field is of practical concern. Resistance management
programs in developing countries should include
mechanisms to optimize insecticide delivery to the
protected habitats of diamondback moth on Chinese kale. / Graduation date: 1992
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Role of apolipophorin-III in the immediate antibacterial responses of Galleria mellonella larvae (Lepidoptera:Pyralidae)Halwani, Adla E. January 1999 (has links)
Apolipophorin-III is a hemolymph protein known for its role in lipid transport. Apolipophorin-III isolated from the hemolymph of last instar larvae of Galleria mellonella bound to the surface of the insect pathogenic Gram-negative bacterium Xenorhabdus nematophilus and to the lipid A moiety of its lipopolysaccharide. This binding reduced the toxicity of the lipopolysaccharide to hemocytes and decreased the inhibitory effect of the lipopolysaccharide on phenoloxidase. Apolipophorin-III also bound to the Gram-positive bacterium Micrococcus lysodeikticus; this enhanced the activity of hen egg lysozyme on the organism as well as the lytic activity of G. mellonella cell-free hemolymph. / The involvement of apolipophorin-III in the immune responses of G. mellonella larvae to lipoteichoic acids, surface components of Gram-positive bacteria, was examined. Lipoteichoic acids from Bacillus subtilis, Enterococcus hirae and Streptococcus pyogenes caused a dose- and time-dependent drop in the total counts of circulating hemocytes and a partial or complete depletion of plasmatocytes depending on the species of lipoteichoic acid. All lipoteichoic acids tested activated phenoloxidase in vitro; however, in vivo, only B. subtilis lipoteichoic acid elevated the phenoloxidase activity while the other two suppressed it. Binding of apolipophorin-III to lipoteichoic acids was demonstrated. Apolipophorin-III prevented the complete depletion of plasmatocytes and depressed the activation of phenoloxidase by lipoteichoic acid from B. subtilis. The concentration of apolipophorin-III in hemolymph two hours post injections of lipopolysaccharides or lipoteichoic acids into larvae of G. mellonella did not change with respect to control insects that received phosphate-buffered saline. The concentration of apolipophorin-III in hemolymph at the end of the feeding larval stage was 8--12 mg/mL of hemolymph. Apolipophorin-III was present in significant amounts in the prepupal, pupal and adult stages. The protein was detected immunologically in hemocyte lysates, plasma and fat body. Non-denaturing polyacrylamide gels and immunoblots of fresh hemolymph suggested that apolipophorin-III is associated with a 77 kDa protein.
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The interaction of surface components of Xenorhabdus nematophilus (Enterobacteriaceae) with the hemolymph of nonimmune larvae of the greater wax moth, Galleria mellonella (Lepidoptera; Galleridae)Maxwell, Philip W. (Philip William) January 1994 (has links)
The following studies were done to identify factors that influence the virulence of Xenorhabdus nematophilus and the interactions of the bacterium with the nonself defence systems of nonimmune Galleria mellonella. Isolates of X. nematophilus that are qualitatively similar in biochemical properties differed significantly in virulence for G. mellonella larvae. The production of enzymes such as proteases could not account for differences in the virulence of the isolates. / Growth conditions, influenced the growth rate and the interactions of the bacterium with nonimmune G. mellonella larvae. In general, X. nematophilus cells grown under aerobic conditions were more susceptible to the nonself defences of G. mellonella larvae than those grown under less than ideal conditions, resulting in increased clearance of the bacteria from the hemolymph (blood) of the insects. Clearance of the bacteria from the hemolymph of the insect was positively correlated with culture condition, culture age, and attachment to insect hemocytes in vitro. / Isolates of X. nematophilus produced flagella and fimbriae when grown under microaerobic and aerobic conditions. The type of fimbriae produced was influenced by culture conditions. The injection of both flagella and fimbriae in picogram quantities into nonimmune G. mellonella caused an increase in total hemocyte counts within these insect larvae. The injection of fimbrial and flagellar antigens into G. mellonella larvae caused changes in the hemocyte types found in circulation in the insect's hemolymph. (Abstract shortened by UMI.)
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Synchrony with host leaf emergence as a component of population dynamics in lepidopteran folivoresHunter, Alison F. (Alison Fiona) January 1991 (has links)
The connection between variable synchrony of insect eclosion with host budburst and variability in insect densities was investigated. Experiments with gypsy moth (Lymantria dispar L.) larvae determined the duration of acceptable foliage after budbreak of nine hardwood species. Four competing conceptual models of environmental influences on the timing of budburst were compared and evaluated. The best budburst model was combined with an eclosion model to estimate the frequency of asynchrony and its correlation with density. Synchrony with budburst has a smaller effect than weather after hatch, on the population size of the gypsy moth, but neither is the driving force behind density changes. However, comparison of traits of 300 species of Macrolepidoptera showed that 50% of outbreak species, but only 24% of nonoutbreak species begin feeding at the time of budburst; this suggests a stronger relation between synchrony and population dynamics than was found with the gypsy moth.
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Biotic barriers to colonizing new hosts by the cinnabar moth Tyria jacobaeae (L.) (Lepidoptera: Arctiidae) /Karac̦etin, Evrim. January 1900 (has links)
Thesis (Ph. D.)--Oregon State University, 2008. / Printout. Includes bibliographical references. Also available on the World Wide Web.
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The management of diamondback moth, Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae), population density on cabbage using chemical and biological control methodsBopape, Malesela Jonas 04 July 2014 (has links)
The diamondback moth, Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae), is a
cosmopolitan insect pest of Brassica crops. In South Africa, there are no action thresholds
for its chemical control which makes it difficult for growers to make informed decisions on
when to apply insecticides and how frequently to apply them in order to achieve optimal
crop yield. To contribute towards optimum application of insecticides against P. xylostella,
this study compared the impact of weekly and bi-weekly applications of a selective
insecticide Dipel® (Bacillus thuringiensis Berliner var. kurstaki) applied at 250 g/ha, and a
broad-spectrum insecticide Dichlorvos (an organophosphate) applied at 1 ml/L against
biological control (Control) on the pest population density on cabbage during October–
December 2011 and March–May 2012. The use of both selective and broad-spectrum
insecticides for experiments enables us to understand if efforts to optimise cabbage yield
depend mainly on effective suppression of P. xylostella densities. Furthermore,
investigations were carried out to determine the impact of these chemicals on parasitism
rates of P. xylostella and species richness of its primary parasitoids.
During the October–December 2011 growing season, the lowest infestation of P. xylostella
occurred on cabbage plots that received weekly application of Dipel and the highest on
untreated control plots. Cabbage weights were negatively related to infestation levels,
implying that weekly application of Dipel yielded bigger cabbage heads. During March–
May 2012, P. xylostella infestations were again higher on the control followed by weekly
and bi-weekly treatments of Dichlorvos, then weekly and bi-weekly applications of Dipel.
Despite the significant differences observed, infestation levels were much lower (< 1 P.
xylostella per plant on average) in all treatments during this season. Consequently no
significant differences in cabbage weights were observed among the treatments. The lower
infestation levels were attributed to higher parasitism levels (≥50 %), especially during the
early stages of crop development.
A total of four parasitic Hymenoptera species were recorded from P. xylostella larvae and
pupae during October–December 2011, while three species were recorded during March–
May 2012. However, Cotesia vestalis (Haliday) (Braconidae) accounted for >80 % of total parasitism levels in all treatments. Parasitism levels were not significantly different among
the treatments in both seasons. Parasitoid species richness was highest on the control.
Although two parasitoid species were recorded in all Dipel and Dichlorvos treatments
during October–December 2011, only one parasitoid species was recorded in the Dipel
treatments during March–May 2012 compared to two species in Dichlorvos treatments.
Although weekly applications of Dipel ensured good yield and crop quality during
October–December, weekly applications of the chemical did not lead to better quality crop
during March–May crop growing season. Thus, it is not necessary to apply insecticides
during periods in which natural mortality of P. xylostella is high due to parasitoids. Since
P. xylostella abundance was a determining factor of crop quality, these results imply that
insect pest management should focus mainly on suppressing its numbers. Furthermore,
there was no evidence that application of either insecticide type had a negative impact on
parasitism rates of P. xylostella. The lower parasitoid species richness on Dipel treated
plots was the consequence of its higher efficiency in suppressing the pest population which
substantially reduced availability of potential hosts for parasitoids, hence only the efficient
C. vestalis was recorded at low host densities / Agriculture and Animal Health / M.Sc. (Agriculture)
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Synchrony with host leaf emergence as a component of population dynamics in lepidopteran folivoresHunter, Alison F. (Alison Fiona) January 1991 (has links)
No description available.
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