by David F. Marriott
20 November 2004
Photo © Bill Howell
On July 22, 2004, I noticed a monarch larva from our rearing stock that looked very different. It had eight skin filaments. Within a week I noticed two more larvae with eight filaments. The extra filaments did not appear until the early third instar. I have reared many queen butterflies (Danaus gilippus) which have six filaments. But, after 15 years of rearing tens of thousands of monarchs, I have never seen more than four filaments on the larvae. I have encountered many different aberrations, but never an “eight hair” monarch larva. Some milkweed butterfly species in Africa with multi-skin filaments are common, but not in North America. Below is a brief history of our eight-hair generations:
First Generation: From the three eight-hair larvae noticed in late July (after they emerged as adults), one female adult mated with a non-eight hair larva generation in mid-August. She began laying eggs on August 19th and later produced two eight hair larvae, one male and one female. Possibly more 8 hair larvae were present but we had a greenhouse insecticide problem at the time that terminated some monarch larvae.
Second Generation: The adult female from the first generation mated with a non-8 hair larva generation. She began laying eggs on the 2nd of October. After the female oviposited about 40 eggs she was tagged and released in eastern San Diego County as an inclusion of our migration studies. This female produced four 8 hair larvae. These butterflies are due to emerge in late November. They will be released in a special isolation cage inside our Vivarium for mating purposes. If the climate is warm, they should mate. In addition, there are 12 selected pupae from the same “mother” that did not have 8 hairs as larvae, but they will be used in our experiments. All pupae and adults appeared as normal monarch butterflies. This information sheds light on a possible expression of a recessive trait. We will have more information if the 2nd generation mates and lay eggs.
Photo © Bill Howell
Only one other known example of a monarch larva with more than four skin filaments was discovered on January 5, 2004, in a residential neighborhood in Miami Lakes, Florida. Eleven monarch larvae with six hairs were observed out of about 200 larvae. Four survived to adulthood with no obvious differences to that of a normal monarch. These butterflies were not reared to produce another generation. For more information on this Florida discovery see: “Monarch Butterfly Larvae (Lepidoptera: Nymphalidae) with 3 Tubercle Pairs in South Florida” by Bethany Farrey and Andrew K. Davis (Florida Entomologist, http://www.fcla.edu/FlaEnt/fe873.htm (towards bottom of page) and the PDF is at http://www.fcla.edu/FlaEnt/fe87p408.pdf.)