Differences Among Beneficial Insect Populations in Sequential Corn Plantings by Mika J. Hunter

Host Farm Cedar 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 Stages Vegetative 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 Immigration To quantify the increasing number of lacewings present in each planting, the total number of eggs was summed

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 – May 14 – June 17 – Calendar day was significantly associated with an increase in Lacewing eggs Each planting had a significant R-Square value

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

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

Graph Interpretation Appears that each sequential planting experienced wasp immigration Possibly similar rates of immigration

Wasp Statistical Analysis Regression Model Calendar day was significantly associated with an increase in wasps Each planting had a significant R-Square value Predictor Data (x): Calendar day Output Data (y): Sum of parasitic Hymenoptera

R-Square Values April 15 – May 14 – June 17 – 0.922

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

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

With Linear Regression Lines

Answering Question 2 Does plant growth stage influence beneficial insect population densities?

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

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

Analysis of Variance (ANOVA test) GSNMean V V T S Looks like a trend, but NOT statistically significant (P >.05 & R-Square =.339)

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