Biology Department

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Effects of Black Walnut Trees on the Epimecis Caterpillar: Soil Interactions

(Effects of Juglans nigra on Epimecis hortaria: Soil Interactions)

The purpose of this experiment is to determine the relationship between black walnut (Juglans nigra) and spicebush (Lindera benzoin) through soil interactions and the affect that this interaction plays on caterpillar (Epimecis hortaria) emergence.

STATE THE PROBLEM :

Black walnut seems to have a negative affect on Epimecis caterpillars, living in the soil below it, by causing them to die before they emerge from the soil as a moth.

MAKE OBSERVATIONS:

  • There appears to be less herbivory (feeding on plants) by the Epimecis on spicebush when it is growing under a walnut tree vs. when it is not growing under walnut.

Background Information (What questions were you trying to answer?):

  • Does the presence of black walnut (Juglans nigra) near spicebush (Lindera benzoin) have a negative impact on the rate of emergence of caterpillars (Epimecis hortaria)?
  • Does the addition of walnut hulls (crushed walnuts) or juglone (a toxic chemical in walnut trees) to non-walnut soil have a negative impact on the rate of emergence of Epimecis caterpillars?

FORM A HYPOTHESIS :

  • The presence of black walnut (Juglans nigra) will decrease the rate of emergence of caterpillars (Epimecis hortaria) from the soil.
  • The addition of crushed walnut hulls or juglone to non-walnut soil will decrease the rate of emergence of caterpillars (Epimecis hortaria).

EXPERIMENT:

Materials:

  • 8 field sites - 4 with spicebush under black walnut trees, 4 with spicebush not under black walnut trees
  • 8 - 5 gallon buckets
  • 5 gallons of soil from each site
  • sieve
  • 8 deli cups
  • water
  • 1 Tbsp measuring device
  • juglone mixture (liquid)
  • walnut hull powder
  • graduated cylinder
  • 8 Epimecis hortaria caterpillars
  • balance
  • incubator

Method:

  1. Determine 4 sites where spicebush grows under walnut trees and 4 sites where no walnut trees are present over spicebush.
    1. Three sites were found at Raker Biological Field Station and Wildlife Sanctuary and one site was created at an Organic Farm
  2. At each of the site a 2 5-gallon buckets was filled with the soil, one with non-walnut soil and the other walnut soil, which led to eight buckets.
  3. These buckets were transported back to lab with covers placed on the top.
  4. In the lab, the soil was sifted to remove all macro (large) matter from the soil.
  5. After being sifted, the soil was placed in deli cups. The deli cups were filled 2/3 full.
  6. The deli cups containing walnut soil were used as a control. One Tbsp of water was added to each cup and the cup was shaken vigorously.
  7. The deli cups containing non-walnut soil were also used as a control. One Tbsp of water was added to each cup and the cup was shaken vigorously.
  8. The non-walnut cups were then randomly selected for additional treatments.
    1. 1/3 of the containers were left with only the water treatment.
    2. 1/3 of the containers had 15mL of walnut hulls and 1 Tbsp of water added. They were then shaken to mix the contents.
    3. 1/3 of the containers had 15 mL of juglone mixture (juglone + water) added and were shaken to mix the contents.
  9. 8 Epimecis caterpillars were collected from the field. Their weight was measured using a balance and recorded. They were then added to the deli cups.(1 per cup)
  10. The deli cups were then placed in an incubator that was set to simulate day and night cycles.
  11. The deli cups were checked daily to see if any of the Epimecis emerged from the soil as moths. This information was then recorded.
  12. You should repeat this set-up at least 3 times so that you have data to compare.

Example of a data table

Example of a Graph (taken from data with serrogate species)

Spodoptera exigua Emergence in Various Soils Measured in Percent

DRAW A CONCLUSION :

Analysis of Data:

The data has shown that the surrogate species, Spodoptera exigua, do in fact have a lower emergence rate when they are below a black walnut tree. The addition treatments have shown a healthy rate of emergence when added to non-walnut soil, which could mean that the chemicals being tested at this point might not be the ones hurting the Epimecis but there are many chemicals in black walnut that we have not yet tested..

Conclusion:

The hypothesis that juglone or walnut hulls are the reason for decreased rates of emergence has been shown to be incorrect since in the non-walnut soil there are actually higher rates of emergence than the control with these addition treatments. The rates of emergence are lower when in the presence of walnut soil in each experiment that has been performed to date.

 

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This material is based upon work supported by the National Science Foundation under Grant No. 0442049.

Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.