AcornStudy

Seed Predation - Acorn Weevils = = =Background= Plants produce vast numbers of seeds that are largely consumed by the various seed eating animals. This is a critical role in plants niche of producer and passing energy and nutrients into the ecosystem. Obviously, some seeds must survive to germinate and produce a seedling that will survive to maturity ensuring the survival of the species, but this is a relatively small percentage of the total production. Of the thousands of acorns produced by an oak tree over its 100+ year life span, only one or two of those acorns will survive to maturity. A wide variety of animals are acorn predators, the obvious candidates include squirrels, woodpeckers, blue jays, turkeys, and deer. However, there are also several insect species that are acorn predators, including the acorn weevil (//Curculio nucum//).

=Acorn Weevil Natural History= The adult female weevil uses her proboscis to drill a hole through the wall of the acorn and into the nut meat (cotyledon) of the acorn. This occurs while the acorns are still green and on the tree. She then turns around and lays an egg into the hole. The egg hatches and the larva feed on the nut meat. After the acorns have masted (fallen to the ground) the larvae will chew their way out of the acorn and dig into the ground where they will pupate for their metamorphosis to the adult phase. The pupa phase can last up to 5 years! For more information see: http://www.cirrusimage.com/beetle_weevil_acorn.htm.

=Video Clips of Acorn Weevils=

media type="custom" key="4527616"media type="custom" key="4527620"media type="custom" key="4527626" An additional source is the PBS/Nature video, The Seedy Side of Plants: http://www.pbs.org/wnet/nature/plants/index.html. This is currently used in 4th grade at the end of a study on seed dispersal.

=Investigation for Students= The relationship between the weevil and the acorn presents some wonderful opportunities for inquiry based learning for young children. Children naturally pick up and explore acorns as they begin to mast in the autumn. The more inquisitive will notice tiny holes on many of the acorns, some children may naturally be compelled to open up the acorns and may discover the larvae or evidence they were there. Acorns that have been the home of a weevil larvae are full of "saw dust" instead of the dense meat of the cotyledons. As the density of the acorn is affected by the consumption of the nut meat, an easy way to identify potentially infested acorns is to float them in a bucket of water. Acorns that are infested will float, while the more dense, uninfested nuts will sink.

Introduction
Lead students in an introductory discussion looking at sample specimens. View clip from Seedy Side. Develop a list of questions for investigation. Develop a methodology for collection and observation.

SmartNotebook File from MW's Introductory lesson (8 Oct 2009)



Acorn Collection
Gather a collection of acorns. Ideally, there would be acorns from several species of oaks and from different locations on campus. The Quad is a good source of acorns and there are several species of oaks growing there. Keep acorns from different locations seperate from each other. One of the questions that can be explored: Is the rate of infestation the same everywhere? Likewise, looking at each species might also yield some interesting findings. Are all species equally attacked by weevils.

Identifying Infested Acorns
There are several methods for identifying potentially infested acorns. This would be an interesting comparison in efficacy. Students may also have their own ideas.


 * ====Method 1: Visual Examination====
 * Students can carefully examine the acorns for the tiny holes made by the female weevil when the egg was laid. Larger holes, about 1/8" in diameter, are often the exit hole of the larvae.
 * ====Method 2: Floaters & Sinkers====
 * As a result of the consumption of the nut meat, those acorns that are infested will be less dense. Place the collected acorns in a bucket of water. Those that are infested will float, while those that are not infested will sink.
 * ====Method 3: Bouncers & Duds====
 * Again, because of the difference in density, whether or not an acorn will bounce when it is dropped can be an indicator of infestation. Drop the acorns from a height of about 1 meter. If they bounce, they are probably not infested. If they are "duds" and do not bounce, that is a good indication of infestation.

Examining Infested Acorns
Once the candidate acorns have been identified, carefully examine the outside of the acorns, looking for the entrance and exit holes. Open the nuts. Nutcrackers, hammers, and hands are all suitable tools for doing this. If hammers and nutcrackers are used, students will need to be cautioned to be careful in breaking open the nuts so that the larvae which may be inside are not crushed. Even if the larvae have already emerged, you want to be careful not to destroy the evidence of their occupancy. The cotyledons may be reduced to a fine "saw dust" material. This is the digested nut meat. Make observations and drawings of the acorns and the larvae. Measurements such as mass and length are also worth making.

Questions

 * Are all oak species equally attacked by weevils?
 * Are weevils equally common across campus?
 * What is the best way to identify infested acorns?

Web References

 * Acorns for Rent: http://www.uky.edu/Ag/Entomology/ythfacts/allyr/yf804.htm
 * Acorn Insects: http://insects.ummz.lsa.umich.edu/MES/notes/entnote20.html