Differences Among Beneficial Insect Populations in Sequential Corn Plantings

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

2. Host Farm Cedar Meadow Farm – Holtwood, PA

3. Cropping Techniques Used at Cedar Meadow Farm

4. 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

5. Beneficial insects found in corn systems Chrysopidae Coccinellidae Parasitic Hymenoptera Opilionidae

6. 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?

7. Sampling Methods

8. 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

9. Planting Dates Site 1 – April 15 Site 2 – May 3 (field corn) Site 3 – May 14 Site 4 – June 17

10. Sticky Card Sampling

11. 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

12. 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

13. Vegetative 1 – growth < 25 inches Vegetative 2 – growth > 25 inches Tassel Stage Silk Stage Corn Growth Stages

14. Selection of Populations to Analyze Lacewing eggs were discovered at each site, creating an opportunity for a comparison between lacewing populations in different plantings

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

16. Data Organization

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

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

21. Lacewing Immigration • Each planting experienced lacewing immigration • With each sequential planting, lacewing immigration rates appear to decrease

22. 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

23. Results Calendar day was significantly associated with an increase in Lacewing eggs Each planting had a significant R-Square value April 15 – 0.975 May 3 – 0.843 May 14 – 0.905 June 17 – 0.6559

24. With Linear Regression Lines

25. Possible Explanations • Source-Sink relationships • Lacewing generation time • Pesticide spray schedule • Female lacewings not pressured to move out into new plantings

26. Parasitic Hymenoptera Immigration

28. Parasitic Hymenoptera Immigration To quantify the increasing number of wasps present in each planting, the total number of wasps was summed

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

31. 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 day Output Data (y): Sum of parasitic Hymenoptera

32. R-Square Values • April 15 – 0.889 • May 14 – 0.877 • June 17 – 0.922

33. With Linear Regression Lines

34. 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

35. Predictor Data (x): Calendar day Output Data (y): Sum of lacewing eggs or wasps Co-variable : Planting sequence

36. 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

37. With Linear Regression Lines

38. 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

39. With Linear Regression Lines

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

42. 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

44. 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

45. Analysis of Variance(ANOVA test) GS N Mean V1 3 0.167 V2 3 2.000 T 3 7.000 S 3 9.533 Looks like a trend, but NOT statistically significant (P > .05 & R-Square = .339)

47. Interpretation of Graph Parasitic Hymenoptera density does NOT appear to be influenced by corn growth stage

48. Question 2 Conclusions • Possible trend of increasing lacewing population density with maturing growth stage • No relationship apparent concerning wasp population densities

49. Potential Sources for Error & Misinterpretation • Combination of new and hatched lacewing eggs • Missing data for corn growth stages • Small sample size

50. Thanks go to…. Steve Groff & Cedar Meadow Farm Shelby Fleisher Heather Karsten Jeff Taylor