Tachinid Flies:
Butterfly Terminators
By Alison Miller
Texas Military Institute, San Antonio, TX
Teacher: Mary Bishop Kennedy
Abstract
Tachinids flies are parasitoids that feed on butterfly larvae. Tachinid larvae burrow
into their host and feed on it from the inside for a few weeks, when they kill their
host and emerge. The tachinid larvae then pupate on the ground and emerge as adult
flies.
In this study I monitored the effects of tachinid and the infection they caus on
queen butterfly larvae. The purpose of this study was to find out how many queen
butterfly larvae are infected with tachinid flies.
I collected 6 queen butterfly larvae and kept them in a plastic container. I fed
the caterpillars milkweed and monitored them for signs of infection, such as looking
lumpy or brownish and moving or eating very little if at all. If signs of infection
were shown, I dissected the butterfly larvae. I recorded and analyzed the data.
I found the rate of infection, the number of fly larvae per caterpillar, and the
percent of infected and healthy caterpillars. 18 tachinid larvae were found in the
6 caterpillars. Results of the analysis showed that 66.6% of the caterpillars were
infected, and 33.3% of the caterpillars remained healthy.
Using the one proportion confidence method, I learned that there is a 30%-100% chance
of picking up an infected caterpillar.
Introduction
Tachinid flies are parasitoids that infect other insects, eventually killing them.
"Parasitoids are insect species which larvae develop as parasites on other insect
species." (www.ento.vt.edu) A female fly starts by laying her eggs on another insect
larva. The fly larvae hatch and burrow into their host, where they live, feeding
off the host. When the tachinid flies are big enough, the host is killed and the
flies emerge. The flies then pupate and emerge as a fully formed adult fly. When
the caterpillar is hanging upside down, getting ready to pupate, the flies kill
the caterpillar and lower themselves to the ground on a thread.
Tachinid flies are classified in the animal kingdom, and the phylum Arthropoda.
Their class is that of the Insecta, and they are in the Diptera order. They are
in the Tachindae family. In this project, I studied the parasitism of a lepidopteran
species, Danaus gillipuss by tachinid flies.
Research Question
How many queen butterfly caterpillars are infected by tachinid fly parasitoids?
Hypotheses
H0: None of the caterpillars will be infected.
Materials and Methods
I collected 4th and 5th instar queen butterfly (Danaus gillipus) larvae in
November, 2004, and kept them in a plastic box. I fed them milkweed and provided
other necessary maintenance. Signs of infection include lumpiness, lethargy, and
a brownish coloring. If the caterpillars showed any of these symptoms I dissected
them and preserved the caterpillar carcass and tachinid larvae in alcohol. I recorded
the rate of infection, number of fly larvae per caterpillar, and the percent of
infected and healthy caterpillars. I used the one proportion confidence method to
analyze the data, which showed that there is a 30%-100% chance of picking up an
infected queen larva.
Results
|
C-1 |
3 |
|
C-2 |
3 |
|
C-3 |
6 |
|
C-4 |
6 |
|
C-5 |
0 |
|
C-6 |
0 |
Analysis of the data revealed that more than half
(66.6%) of the caterpillars were infected. 33.3% of the caterpillars were healthy.
Below is a listing of caterpillars and the number of fly larvae that were found
in each caterpillar. In six caterpillars, a total of 18 tachinid fly larvae were
found, with an average of 3 flies per larva, or 4.5 flies per infected larva. Four
out of 6 larvae were infected, and 2 out of 6 were still healthy.
Discussion
After using the one proportion confidence method, I concluded that there is a 30
- 100% chance of a caterpillar being infected. I therefore disproved my null hypotheses.
My specimens were collected in November of 2004, and cold weather made further collecting
impossible. Because the tachinid population has been developing all year by November,
the tachinid population may be larger at this time of the year, thus increasing
the proportion of infected caterpillars.
Conclusion
Because of the weather, my sample size was limited to 6 queen larvae. 2/3 of the
caterpillars were infected with tachinid fly larvae, and 18 tachinid larvae were
found total.
Future Research
I will find the exact type of Tachinids that are infecting the larvae.
I will collect other species of larvae and compare the infection rates. It will
be interesting to see how high the infection rate is in each species and how environmental
factors contribute to the infection rate.
I will observe the different rates of infection in each season.
Acknowledgements
First and foremost, I'd like to thank my science teacher, Ms. Kennedy. She's been
my mentor throughout the project, and I couldn't have gotten it done without her.
Next I'd like to thank my mom and dad, who have served the combined roles of coach,
cheerleader, and chauffeur. I would also like to thank my friends. You've always
understood and never complained when I had to go work on my project instead of goof
off.
References
- http://www.mlmp.org/results/DeathMilkweed/results_DeathMilkweedTachinid.asp. Retrieved
11/17/04.
- http://www.monarchwatch.org/biology/pred3.htm Retrieved 11/17/04
- http://www.nadsdiptera.org/index.htm Retrieved 11/17/0
- http://www.ento.vt.edu/~sharov/PopEcol/lec10/paras.htmRetrieved 11/17/04
- Borror and White, Insects, Peterson Field Guides, Houghton Mifflin Company, 1970