Abundance and Seasonality of

Insects and its relation with Birds

in a Moist deciduous forest of

Siruvani

Objectives

to describe the Seasonal patterns in insect abundance,

to examine the role of various ecological factors in regulating the insect abundance

Study area

Location– 76o 41’ & 76o 45’ E &

– 10o 56’ & 10o 58’ N

Altitude– 513m from msl

Vegetation– Moist Deciduous

Siruvani forest (Study site)

Teak plantation

Moist deciduous

Annual Rainfall Pattern (Siruvani)

0

500

1000

1500

2000

2500

3000

Rai

nfa

ll (m

m)

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

Mean = 1926mm

Source: TWAD

Methodology

Methods Sweeping Knock down Light trap Transect counting

Overall insect abundance(Sweeping + Light trapping + Knock down)

Insect abundance (method-wise)

0

50

100

150

Coleop

tera

Lepido

ptera

Hemipt

era

Diptera

Orthop

tera

Hymen

opter

a

Others

Lig

ht tr

ap

Sw

eepi

ng

Kno

ck d

own

Light trap Sweeping Knock down

Species richness (method-wise)

0

5

10

15

20

25

No.

IT

Us

/ sam

ple

Light trap Sweeping Knock down

Winter Summer Wet 1 Wet 2

Relative abundance in different habitats

Teak plantation24%

Riverine37%

Moist deciduous39%

Pattern of abundance fluctuation in different habitats

0

100

200

300

400

Teak plantation

Riverine

Moist deciduous

Teak plantation Riverine Moist deciduous

Species richness

0

5

10

15

20

25

No.

of I

TU

s/ s

ampl

e

S-W Monsoon N-E Monsoon Winter Summer

Moist deciduous Riverine Teak plantation

Composition of Insect Community

Others10.5% Hymenoptera

23.3%

Lepidoptera16.2%

Coleoptera15.0%

Hemiptera11.0%

Orthoptera11.2%

Diptera12.7%

Seasonal abundance of Insects

N-E Monsoon20%

Winter23%

Summer27%

S-W Monsoon30%

Seasonal abundance of insect groups

N-E M. Winter Summer S-W M Total

Orthoptera 20.6% 35.4% 15.2% 28.9% 100%

Lepidoptera 17.4% 38.2% 8.4% 36.0% 100%

Hemiptera 18.8% 28.5% 21.6% 31.2% 100%

Diptera 26.2% 14.7% 8.6% 50.5% 100%

Hymenoptera 23.5% 27.3% 19.7% 29.5% 100%

Coleoptera 19.7% 12.3% 24.2% 43.8% 100%

Abundance fluctuation in Diptera

0

50

100

150

200

250

300

Sep-9

4

Oct-94

Nov-9

4

Dec-9

4

Jan-

95

Feb-9

5

Mar-

95

Apr-9

5

May

-95

Jun-

95Ju

l-95

Aug-9

5

Sep-9

5

Oct-95

Nov-9

5

Dec-9

5

Jan-

96

Feb-9

6

Mar-

96

Apr-9

6

May

-96

Jun-

96Ju

l-96

Aug-9

6

Abu

ndan

ce (

No.

/Mon

th)

Order Factors affecting abundance Coleoptera Rainfall (+ve) & Flowers (-ve) Diptera Temperature (-ve) Hemiptera - Hymenoptera - Lepidoptera - Orthoptera Bird abundance (+ve)

Factors affecting insect abundance (Step-wise Regression)

= Seasonal fluctuation Significant = Seasonal fluctuation insignificant

Temporal fluctuation in Rainfall & Insect abundance

0

200

400

600

800

1000

1200

Sep

-94

Oct

-94

Nov

-94

Dec

-94

Jan-

95Fe

b-95

Mar

-95

Apr

-95

May

-95

Jun-

95Ju

l-95

Aug

-95

Sep

-95

Oct

-95

Nov

-95

Dec

-95

Jan-

96Fe

b-96

Mar

-96

Apr

-96

May

-96

Jun-

96Ju

l-96

Aug

-96

Ins

ec

ts (

nu

mb

er)

& R

ain

fall

(mm

)

Rain fall Insect abundance

0

50

100

150

200

250

300

0 50 100 150 200 250 300 350

Birds

Coleo

ptera R = -0.601 (P =

0.02)

Abundance of Birds & Insects

0

25

50

75

100

125

150

175

0 25 50 75 100 125 150 175 200 225 250 275 300 325

BirdsO

rtho

pter

a

R = 0.438 (P = 0.03)

Coleoptera (-ve) Orthoptera +ve

Lepidoptera

Hemiptera

Hymenoptera

Diptera

Conclusions

Abundance SW Monsoon > Summer > Winter > NE Monsoon Moist deciduous > Riverine > Teak plantation

Role of Environmental factors Overall Insect abundance - Temperature (-ve) Coleoptera - Rainfall & Number of rainy days Diptera - Humidity & Number of rainy days Orthoptera - Bird abundance (-ve) Hemiptera Hymenoptera Lepidoptera

Seasonal fluctuation NS,