Helicoverpa zea The Corn Earworm Valley Springs High School 10th grade Pre-AP Biology
Experiment One Problem: How long is the life cycle of the corn ear worm? Hypothesis: After doing extensive research, we hypothesized that the life cycle of the corn ear worm would last approximately 30 days.
Procedure • We followed the instructions that came with the corn ear worms. • We watched the corn ear worms grow. • We recorded data on a daily basis, excluding the weekends and days we were on break.
Survival Rate • We started out with 72 corn ear worm larvae. • 47 of those pupated, and 27 of those emerged as adults. • Therefore, 65% of the worms pupated, and 38% survived to adulthood.
Growth Rate • The average growth of the female worms was 2.8 centimeters. • The average growth of the males was 2 centimeters. • The overall average growth was 2.4 centimeters.
Male vs. Female • Of the larvae that pupated, 30 were identified as males, and 17 were identified as females. Therefore, 64% of the worms were males, and 36% were females. • We wondered if we were accurate at telling the difference. Our growth data showed that females were larger than the males – could this be right?
So, we did some more research. Differences between males and females of the same species is known as sexual dimorphism. • In most animals, males are bigger than females. But, in 80% of insects, the females are larger. • Yeah! Our data supports that idea.
Life Cycle • The average length of the life cycle for our worms was 54 days. • The average length of the life cycle for the male was 56 days. • The average length of the life cycle for the female was 52 days.
Reproduction • We were not successful in producing a second generation. We thought we had done everything correctly, so we researched factors that affect reproduction. • According to our research, temperature affects the life cycle of the corn ear worm. In places where the temperature is higher, the life cycle is shorter and there are three or more generations. In places where the temperature is low, the life cycle is longer and there are generally only one or two generations of worms.
Reproduction Continued • During the day, our classroom was kept at a constant temperature (70-75 degrees). Therefore, the worms should have grown normally. When they didn’t, we couldn’t figure out what was wrong. • A few weeks into our experiment, Mrs. Bogle came back to her classroom at night. Much to her surprise, the room was freezing. Apparently, our janitor likes to work in “arctic conditions”. • We now knew that our worms were growing in cold temperatures, and therefore would not have many generations.
Analysis/Conclusion • Our data did not support our hypothesis. The life cycle took almost twice as long as we had expected. • Because the temperature in our classroom was too low, our worms were unable to grow properly. Therefore, we were not successful in producing a second generation.
Fountain of Youth? • One of our larvae never pupated. It is still alive. • We thought we had found the fountain of youth, or maybe it was the preservative in the soy food. • We consulted the experts. Dr. Lopez explained that the larva is in diapause, an overwintering stage. This can be induced by temperatures around 19 degrees C (about 66 degrees F). • This might also explain our low survival rate and zero reproductive rate.
Experiment Two • Problem: Since temperature obviously affects the life cycle of the corn ear worm, what would happen if we applied heat to the larvae? • Hypothesis: If we applied heat to several larvae, then these larvae would pupate much faster.
Procedure • Obtain corn ear worm larvae from Dr. Wilson. • Place the larvae (inside their containers) under a heat lamp. • Observe the larvae on a daily basis, noting how long it took for them to pupate.
The new larvae pupated much faster. • The average life cycle of the new worms was ten days shorter than that of the original corn ear worms.
Roasted Larvae? • While some of our larvae developed correctly, we had a few casualties along the way. • Some of our worms were a little too close to the light. The result? They burned. • Despite these casualties, four made it to the pupa stage, and one made it to adulthood. • These numbers might sound low to you, but they were a large improvement from our first set of larvae.
Analysis/Conclusion • Our data supported our hypothesis. By placing our larvae under the heat lamp, we were able to produce more pupated worms at a faster rate. • Therefore, our data supports the idea that temperature affects the life cycle of the corn ear worm.
Experiment Three • Problem: What would the larvae do if there were to be a shortage of corn? • Hypothesis: If we placed the larvae on other various foods, then they would adapt their eating habits, and eat whatever was given to them.
Procedure • We ordered a few more larvae. • Students were asked to bring in various foods of their choice. • Each group was assigned at least one worm. They were then asked to empty the soy food from the larvae containers, and replace the soy food with their chosen food. • The worms were then observed to see how well they survived on the new foods.
There were many different kinds of foods chosen for our worms. • These foods included: strawberries, grapes, tomatoes, sweet potatoes, corn, bananas, lettuce, and oranges. • The worms survived on all of the foods that we tried. • In addition, some of them changed color according to what they ate.
Drowned Larvae • We did have one problem. • Instead of staying on top of the new foods like we had thought they would, the larvae climbed down into the containers. • The result? They drowned.
Not long after we discovered our first problem, Dr. Wilson came to visit our class. • We asked him what to do about our drowning worms. He suggested that we place a piece of sponge under the food, so that it would soak up the juices before the larvae could drown. • Much to our surprise, the larvae quit eating the foods we had placed in the containers. • Instead, they ate the sponge!
Analysis/Conclusion • Our data supported our hypothesis. • When we took away their food and gave them something different, they adapted their eating habits. They ate whatever was given to them. • We concluded that the larvae could survive on almost any food crop.
Friend or Foe? • In our classroom, the corn ear worm became our friend. We even named each one. • However, we did learn that in the agricultural community, the corn ear worm can be a major foe. In the larval stage, they can ruin hundreds of crops – thus causing farmers to lose thousands of dollars.
Furthermore, in warm climates they reproduce quickly. There can be new generations each month. • They can also survive on almost any food crop.