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 4^th and 5^th 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

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 chauffer.  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