differences among beneficial insect populations in sequential corn plantings by mika j. hunter
TRANSCRIPT
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