stat7840 hao wu

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. . . . . . Instar Determination Using Gaussian Mixture Models Hao Wu Department of Entomology and Plant Pathology April 24, 2012

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Page 1: Stat7840 hao wu

. . . . . .

Instar Determination Using Gaussian MixtureModels

Hao Wu

Department of Entomology and Plant Pathology

April 24, 2012

Page 2: Stat7840 hao wu

. . . . . .

Instar

I An instar is a developmental stage of insects, between eachmolt until sexual maturity is reached.(age)

I Insects have exoskeleton(different from us).I Discontinuous growth of exoskeleton (have to molt to increase

size)

I In many cases, the only obvious difference between successiveinstars is the increase in size that occurs after each molt (themolt increment).

Page 3: Stat7840 hao wu

. . . . . .

0

10

20

30

40

2 3 4 5

Histogram of Head With

Head Width of Instars

coun

t

Page 4: Stat7840 hao wu

. . . . . .

The GMMs Assumption

I There are finite numbers of componentsI majority of insects have a fixed number of instar.

I The data within each components can be modeled asGaussian distribution.

I The size of sclertized characters almost do not change in eachinstar.

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The Scatterplot of Ponotum characters

Pronotum Width

Pro

notu

m L

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h

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2 3 4 5

The Scatterplot of Ponotum Length and Head Width

Head Width

Pro

notu

m W

idth

2

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4 6 8 10

The Scatterplot of Ponotum Length and Head Width

Head WidthP

rono

tum

Len

gth

Figure: The Scatterplot of Three characters

Page 5: Stat7840 hao wu

. . . . . .

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4 6 8 10 12 14 16

The Scatterplot of Ponotum characters

Pronotum Width

Pro

notu

m L

engt

h

Page 6: Stat7840 hao wu

. . . . . .

Data Collection

I Period: Jan-Apr.2012

I Variables: Head Width, Pronotum Length and Width.

I 1925 dubia cockroaches.

Page 7: Stat7840 hao wu

. . . . . .

Outliers Detection

The function NNclean in the contributed R package prabclus is aimplementation of the nearest-neighbor method for cluster/noisedetection.This method is used in the instar determination with k = 2.

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4 6 8 10Length

Wid

th

cluster

● 1

2

3

4

5

6

7

Page 8: Stat7840 hao wu

. . . . . .

Model Selection

−20000

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2 4 6 8 10 12

BIC for all models up to 12 components

Number of components

BIC

Models

EII

VII

EEI

VEI

EVI

VVI

EEE

EEV

VEV

VVV

Figure: The BIC plot of each cluster in all models

I Selection:The unconstrained model(”VVV”),7 clusters

I mclustBIC in R package mclust

Page 9: Stat7840 hao wu

. . . . . .

Cluster Analysis

I GMMs based clustering are conducted based on the modelselected by BIC.

I Mclust in R package mclust

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The cluster of Ponotum characters

Pronotum Width

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notu

m L

engt

h

cluster

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The cluster of Ponotum Width and Head Length

Pronotum Width

Hea

d Le

ngth

cluster

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The cluster of Ponotum Length and Head Width

Head Width

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notu

m L

engt

h

cluster

● 1

2

3

4

5

6

7

Figure: The cluster of three characters

Page 10: Stat7840 hao wu

. . . . . .

Result Assessment

Instar 1 Instar 2 Instar 3 Instar 4 Instar 5 Instar 6 Instar 7Length 2.42 2.97 3.83 4.95 6.14 7.48 9.37Width 4.21 5.19 6.44 8.07 9.90 12.17 15.17Head 1.79 2.09 2.49 2.98 3.54 4.22 5.02

Table: The mean of the three characters in each instar

Page 11: Stat7840 hao wu

. . . . . .

More about Instar

According Dyar’s law (Dyar,1890)

InIn−1

= constant

where In = postmolt size , In−1 = premolt size. It can be writtenas:

y = aebx

which is equal to:lny = lna+ bx

the constant growth ratio is eb.

Page 12: Stat7840 hao wu

. . . . . .

Result Assessment

1.0

1.5

2.0

2.5

1 2 3 4 5 6 7

Linear regression for the mean of three characters

Instar Number

Nat

ural

Log

arith

m o

f mea

sure

men

ts

Characters

● Length

Width

Head

Figure: The linear regression of characters in each instar

Page 13: Stat7840 hao wu

. . . . . .

Result Assessment

Geometric sequence

Instar 1 Instar 2 Instar 3 Instar 4 Instar 5 Instar 6 Instar 7 RatioLength 2.42 2.97 3.83 4.95 6.14 7.48 9.37 1.26Width 4.21 5.19 6.44 8.07 9.90 12.17 15.17 1.24Head 1.79 2.09 2.49 2.98 3.54 4.22 5.02 1.19

Table: The mean of the three characters in each instar and growth ratio

Page 14: Stat7840 hao wu

. . . . . .

Conclusion

I The GMMs based clustering methods can be used todeterminate instars of the dubia cockroaches Blapitca dubia.

I The growth rates comply with Dyar’s law.I There are 7 instars in Dubia cockroaches Blapitca dubia.I The growth rates of pronotum length, pronotum width and

head width are 1.26, 1.24, 1.19 respectively.

I The GMMs based clustering methods should be applicable tobe used on other insects, since the dubia cockroaches complywith the same growth model with other insects