How environmental factors affect monarch development

Research on the relationship between monarch development and environmental factors has focused on:

• Short-term, unpredictable environmental changes, and
• Predictable seasonal changes, like decreasing fall temperatures and daylength in the summer range of monarchs.

Short-term Environmental Changes: Effects of Temperature on Larval Development

Several researchers have studied how temperature affects the rate and success of larval development. Rawlins and Lederhouse (1981) and Zalucki (1982) showed that monarch larvae do not develop attemperatures below 10° C or above 34° C (if you are more familiar with degrees Fahrenheit, see table 1). Monarchs generally develop faster at higher temperatures, with those experiencing 27° C taking about 12 days to go through all five instars, and those raised at lower and higher temperatures taking more and less time, respectively. There seems to be a positive relationship between temperature and larval survival at temperatures between 15 and 29° C, while above 29° C survival decreases (Zalucki 1982).

Since larvae tend to develop faster and have higher survival rates at higher temperatures, at least within the range of 15  to 29° C, it would be beneficial for them to be able to increase the temperatures they experience. Females prefer to lay eggs on milkweed plants exposed to the sun (Urquhart 1960, Zalucki 1982), and monarch larvae often select portions of plants that receive direct sunlight (Rawlins and Lederhouse 1981). Larvae also orient their bodies in ways that increase their exposure to the sun’s rays, sometimes increasing their temperature to as much as 8° C above air temperature (Rawlins and Lederhouse 1981). If it is too hot for successful development (above 34° C), larvae will crawl off the milkweed plant and rest in leaf litter, or crawl to the undersides of leaves (Urquhart 1960, Rawlins and Lederhouse 1981).

Temperature may also affect the appearance of larvae. A high school student working in our laboratory in 1998 studied larvae reared at three different temperatures, and found that those reared in cooler temperatures had wider black stripes. She hypothesized that this may help them to absorb heat from the sun more effectively (Larkin 1999).

Other Environmental Influences on Monarch Development

Many researchers have studied the effects of crowding, humidity, hostplant species and quality, and light on development in a wide variety of insect species. Middle School, High School and University researchers in Minnesota and other places have studied how monarchs are affected by a wide variety of environmental conditions.

The condition and species of milkweed eaten by larvae can affect the rate of development and adult size. For example, in their study of diapause induction, Liz Goehring and Karen Oberhauser found that monarch larvae fed older Asclepias syriaca plants developed into larger adults than those fed young plants of the same species. On the other hand, Elaine Dunham found no difference in mass between larvae fed old and young plants, but she did find that larvae fed old plants (click here to read about this study). Beth Lavoie fed larvae milkweed fertilized with varying amounts of nitrogen, and found no difference in mass, but slower growth of larvae fed plants that received less nitrogen (click here to read about this study).

Exposure to light has interesting effects on monarch development. Light can even affect the direction that pupae face; students from Rochester MN found that the larva in its prepupal "J-shape" and the resulting pupa both face away from the light (Does Heat or Light Affect the Direction of the Pre-Pupal "J"?).

Check out lots more Research Projects involving the growth and development of monarchs!
 

References

Chapman, RF. 1982. The insects: structure and function. Third edition. Harvard University Press, Cambridge MA.

Rawlins, JE and RC Lederhouse. 1981. Developmental influences of thermal behavior on monarch caterpillars: an adaptation for migration. J. Kansas Entomol. Soc. 54:387-408.

Scott, JA. 1986. The butterflies of North America. Stanford University Press. Stanford CA.

Urquhart, F. 1960. The monarch butterfly. University of Toronto Press, Toronto Canada.

Zalucki, MP. 1982. Temperature and rate of development in Danaus plexippus and D. chrysippus. J. Australian Entomol. Soc. 21:241-246.