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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

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

Organically-managed crucifer field in south Alabama damaged by YMLB

TurnipNapa cabbage

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

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

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?

• 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

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

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

One week after Two weeks after

Results

Laboratory bioassay with four-choice olfactometer

• 10 adults (2-4 days old) per replications

• 20 replicates per experiment per sex

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

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

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

Acknowledgement

• Undergraduate students– Allison Tyler

– David Appel

– Shelia Boyt

• Alabama Agricultural Experiment Station for a seed grant to HYF

Thank you..

Questions?