1 semiochemical mediated host plant preference in the yellowmargined leaf beetle, microtheca...
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Semiochemical Mediated Host Plant Preference in the Yellowmargined Leaf beetle, Microtheca ochroloma
Rammohan Rao Balusu and Henry Fadamiro
Department of Entomology and Plant Pathology, Auburn University
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Introduction
Yellowmargined leaf beetle (YMLB), Microtheca ochroloma
(Chrysomelidae) is a pest of cruciferous (Brassicaceae) crops
Cabbage, Turnips, Mustard, Raddish, Collards, etc
Native to South America
First reported in the US
in Mobile, AL in 1947
A serious pest the SEA major problem facing
organic vegetable production
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Damage
Both adults and larvae feed on foliage by first making small holes; later serious defoliation
Defoliation of larvae on turnip Mass attack of adults on napa cabbage
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Organically-managed crucifer field in south Alabama damaged by YMLB
TurnipNapa cabbage
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Mustard greensNapa cabbage
Tet soi B. narinosa
Mizuna B. rapa japonica
TurnipsRadish
TurnipsCollards
LettuceCabbage
Mixed cropping practice of different crucifer vegetables in snow’s bend organic farm in Alabama
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Investigate mechanism of host plant selection and preference in yellowmargined leaf beetle (YMLB)
• Field observations suggest preference among crucifer plants
• Questions:– Do YMLB adults show preference among crucifer plants? – What cues mediate host preference?
• Hypothesis:– Host preference is mediated by plant semiochemicals
Objective
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3 ft
4 ft
4 ft adult beetles
50Turnip
Cabbage
Collards
Napa cabbage
Materials and methods
Greenhouse and laboratory experiments conducted to test host preference
Q. Feeding and Ovipositional preference?
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• Four host plants compared: – cabbage, collards, napa cabbage and turnip
• Experiment (simultaneously) replicated three times (i.e. 3 cages)
• Data collected: – every day for the period of three weeks– number of adults and larvae per plant (up to 21 days) – damage ratings of plants
• Damage ratings based on a scale of 1 to 6: 1 = very light defoliation (< 10%) 2 = light defoliation (10-30%) 3 = moderate defoliation (30-50%)4 = heavy defoliation (50-70%) 5 = very heavy defoliation (70-90%) and 6 = complete (total) defoliation (> 90%)
• Statistical analysis: ANOVA + Tukey HSD test
Materials and methods – greenhouse study
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Day after release
No.
of
Ad
ult
s p
er p
lan
t
0
10
20
30
40
TurnipNapa CabbageCabbageCollards
1 2 3
a
b
cc
a
b
c
a
b
Results: Number of YMLB adults per host plant per day
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Results: Average damage rating caused by YMLB per plant per week
Week0 1 2 3 4
Dam
age
rati
ngs
per
pla
nt
0
1
2
3
4
5
6
7
TurnipNapa CabbageCabbageCollards
a
b
a
b
a
b
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One week after Two weeks after
Results
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Laboratory bioassay with four-choice olfactometer
• 10 adults (2-4 days old) per replications
• 20 replicates per experiment per sex
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Female
Mea
n(±S
E)
no. o
f re
spon
der
s
0
1
2
3
4
5TurnipNapa CabbageCabbageControl
Male
b
a
cc
b
a
c c
Behavioral response of adult YMLB to different crucifer host plants
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Female
Mea
n(±
SE
) no
. of
resp
ond
ers
0
1
2
3
4Turnip Napa CabbageCollardsControl
Male
aba
bc
c
a a
b
b
Behavioral response of adult YMLB to different crucifer host plants
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Summary
• Turnip and napa cabbage are preferred host plants over collard and cabbage
• Olfactory cues play a major role in host plant selection
• Trap crop??????
• Ongoing study is focused on chemistry host plants to identify the possible attractant for YMLB
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Acknowledgement
• Undergraduate students– Allison Tyler
– David Appel
– Shelia Boyt
• Alabama Agricultural Experiment Station for a seed grant to HYF
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Thank you..
Questions?