Environmental Effects: How Environmental Factors Affect Monarch Development
Physiological Changes
|
Environmental Effects
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
Table 1
|
°C
|
°F
|
|
0
|
32
|
|
5
|
41
|
|
10
|
50
|
|
15
|
59
|
|
20
|
68
|
|
25
|
77
|
|
30
|
86
|
|
35
|
95
|
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 at temperatures 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. 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.
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.
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.