Differences Among Beneficial Insect Populations in Sequential

Corn Plantings

by

Mika J. Hunter

Host FarmCedar Meadow Farm – Holtwood, PA

Cropping Techniques Used at Cedar Meadow Farm

• Corn is planted throughout the spring and early summer

• Sequential plantings allow corn to be harvested continuously during the summer

• Earliest : April 15

• Latest : ~ June 17

Beneficial insects found in corn systems

Coccinellidae Chrysopidae

Opilionidae Parasitic Hymenoptera

Exploratory Data Analysis Questions

1. Does immigration rate of beneficial insects vary with sequential plantings?

2. Does plant growth stage influence beneficial insect population densities?

Sampling Methods

Selection of sampling sites

• Four different corn fields were selected at the end of May 2003

• Each field was at a different growth stage at the time of selection

Planting Dates

Site 1 – April 15

Site 2 – May 3 (field corn)

Site 3 – May 14

Site 4 – June 17

Sticky Card Sampling

• 2 Sticky cards (single sided) were placed on separate wooden stakes

• Cards were positioned with changing height of corn

• Each stake was separated by a minimum of 150 feet

• Cards were collected and replaced every week for 5 weeks

• Cards were stored in freezer until they could be sorted and identified

Corn Plant Surveying

• 10 corn plants from each site were thoroughly inspected for beneficial insects

• Collected data each week concerning

plant growth stage

insect classification

number of insects

insect life stage

Corn Growth StagesVegetative 1 – growth < 25 inches

Vegetative 2 – growth > 25 inches

Tassel Stage

Silk Stage

Selection of Populations to Analyze

Lacewing eggs were discovered at each site, creating an opportunity for a comparison between lacewing populations in different plantings

Parasitic Hymenoptera were also identified on sticky cards in each site, creating an opportunity for another population comparison

Data Organization

Answering Question 1

Does immigration rate of beneficial insects vary with sequential plantings?

Lacewing Density

0

5

10

15

20

160 170 180 190 200 210 220

Calendar Day

Lace

win

g Eg

g De

nsity

per

10

pla

nts

15-Apr

3-May

14-May

17-Jun

Lacewing Immigration

To quantify the increasing number of lacewings present in each planting, the total number of eggs was summed

Lacewing Immigration

0

10

20

30

40

50

60

70

160 180 200 220

Calendar Day

To

tal n

ew a

nd

hat

ched

eg

gs

per

10

pla

nts

15-Apr

3-May

14-May

17-Jun

Lacewing Immigration

• Each planting experienced lacewing immigration

• With each sequential planting, lacewing immigration rates appear to decrease

Statistical Analysis

• Using SAS, linear regression models were created for each planting. p values <0.05 were considered significant

• Predictor Data (x): Calendar day

• Output Data (y): Sum of lacewing egg

Results

April 15 – 0.975

May 3 – 0.843

May 14 – 0.905

June 17 – 0.6559

Calendar day was significantly associated with an increase in Lacewing eggs

Each planting had a significant R-Square value

Lacewing Immigration

0

10

20

30

40

50

60

70

160 180 200 220

Calendar Day

To

tal n

ew a

nd

hat

ched

eg

gs

per

10

pla

nts

15-Apr

3-May

14-May

17-Jun

pred Apr 15

pred May 3

pred May 14

pred June 17

With Linear Regression Lines

Possible Explanations

• Source-Sink relationships

• Lacewing generation time

• Pesticide spray schedule

• Female lacewings not pressured to move out into new plantings

Parasitic Hymenoptera Immigration

Parasitic Hymenoptera Collection by Calendar Day

0

10

20

30

40

50

60

70

180 190 200 210 220

Calendar Day

Par

asit

ic H

ymen

op

tera

C

oll

ecte

d p

er 2

Sti

cky

Car

ds

14-Apr

14-May

17-Jun

Parasitic Hymenoptera Immigration

To quantify the increasing number of wasps present in each planting, the total number of wasps was summed

Parasitic Hymenoptera Immigration

0

20

40

60

80

100

120

180 190 200 210 220

Calendar Day

Tota

l Par

asiti

c H

ymen

opte

ra

per

2 (s

ingl

e si

ded)

Stic

ky

Car

ds

15-Apr

14-May

17-Jun

Graph Interpretation

Appears that each sequential planting experienced wasp immigration

Possibly similar rates of immigration

Wasp Statistical AnalysisRegression Model

• Calendar day was significantly associated with an increase in wasps

• Each planting had a significant R-Square value

Predictor Data (x): Calendar dayOutput Data (y): Sum of parasitic Hymenoptera

R-Square Values

• April 15 – 0.889

• May 14 – 0.877

• June 17 – 0.922

Parasitic Hymenoptera Immigration

0

20

40

60

80

100

120

180 190 200 210 220

Calendar Day

Tota

l Par

asiti

c H

ymen

opte

ra

per

2 (s

ingl

e si

ded)

Stic

ky

Car

ds

15-Apr

14-May

17-Jun

pred Arpil 15

pred May 14

pred June 17

With Linear Regression Lines

Heterogeneity of Slope Test

To determine if the relationship between calendar day and insect population is influenced by planting sequence, a heterogeneity of slope test was performed for each set of data

Predictor Data (x): Calendar day

Output Data (y): Sum of lacewing eggs or wasps

Co-variable : Planting sequence

Lacewing Results

• Calendar day, sequence, and the interaction of calendar day and sequence significantly influence Lacewing immigration

• Immigration rates differed among sequential planting

• With each sequential planting, lacewing immigration rates appear to decrease

Lacewing Immigration

0

10

20

30

40

50

60

70

160 180 200 220

Calendar Day

To

tal n

ew a

nd

hat

ched

eg

gs

per

10

pla

nts

15-Apr

3-May

14-May

17-Jun

pred Apr 15

pred May 3

pred May 14

pred June 17

With Linear Regression Lines

Wasp Results

• Calendar day, sequence, and the interaction of calendar day and sequence did not significantly influence wasp immigration

• Immigration rates did not significantly vary among sequential planting

Parasitic Hymenoptera Immigration

0

20

40

60

80

100

120

180 190 200 210 220

Calendar Day

Tota

l Par

asiti

c H

ymen

opte

ra

per

2 (s

ingl

e si

ded)

Stic

ky

Car

ds

15-Apr

14-May

17-Jun

pred Arpil 15

pred May 14

pred June 17

With Linear Regression Lines

Answering Question 2

Does plant growth stage influence beneficial insect population densities?

Lacewing Density Organized by Plant Growth Stage

0

4

8

12

16

20

1 2 3 4

Plant Growth Stage

Mea

n Eg

gs P

er 1

0 Pl

ants 1

2

3

4

Graphical Interpretation

• Planting 1: missing data points, but high numbers of lacewings at end of growth stage

• Planting 2 : shows relationship

• Plantings 3 & 4 : does not support relationship seen in planting 2

Lacewing Density Organized by Plant Growth Stage

0

0.5

1

1.5

2

2.5

v1 v2 t s

Plant Growth Stage

Mea

n E

gg

s P

er 1

0 P

lan

ts

3

4

Isolating Graphs to Identify a Trend

Decreasing the scale by a magnitude of 10reveals a trend in plantings 3 & 4 that is comparable to the trend seen in planting 2

Analysis of Variance(ANOVA test)

GS N Mean

V1 3 0.167

V2 3 2.000

T 3 7.000

S 3 9.533Looks like a trend, but NOT statistically significant

(P > .05 & R-Square = .339)

Parasitic Hymenoptera Density Organized by Plant Growth Stage

0

5

10

15

20

25

30

v1 v2 t s

Growth Stage

Mea

n N

um

ber

of

Par

asit

ic

Hym

eno

pte

ra p

er 2

Sti

cky

Car

ds 15-Apr

14-May

17-Jun

Interpretation of Graph

Parasitic Hymenoptera density does

NOT appear to be influenced by corn

growth stage

Question 2 Conclusions

• Possible trend of increasing lacewing population density with maturing growth stage

• No relationship apparent concerning wasp population densities

Potential Sources for Error & Misinterpretation

• Combination of new and hatched lacewing eggs

• Missing data for corn growth stages

• Small sample size

Thanks go to….

Steve Groff & Cedar Meadow Farm

Shelby Fleisher

Heather Karsten

Jeff Taylor