PARENT SESSION
Poster Session 30: Invertebrate Ecology
Thursday, August 11, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal
Developmental plasticity in the forest tent caterpillar: life history consequences of a threshold size for pupation.
Etilé, Elsa*,1, Despland, Emma2, 1 Université du Québec à Montréal, Montréal, Québec, Canada2 Concordia University, Montréal, Québec, Canada
ABSTRACT- In insects, size and age at adult emergence depend on larval growth occuring in discrete steps or instars. We examine the patterns of growth of forest tent caterpillars (Malacosoma disstria Hübner) in order to determine the factors that influence the number of instars that larvae undergo before pupation, to examine the mechanisms underlying plasticity in larval development and to evaluate the fitness consequences of this plasticity. All caterpillars were reared under the same conditions; at each moult, the date, the head capsule width and the mass of the freshly moulted insect were recorded. Logistic regression analysis showed that a threshold size (measured either as mass or head capsule width) must be reached at the beginning of an instar for pupation to occur at the next molt. Females exhibited the same growth rate as males but a higher threshold for pupation: females thus often underwent more instars than males and attained higher pupal mass. An increase in the number of larval instars occurred via a decrease in growth rate, and led to an increase in larval development time with no change in pupal mass. The combination of a threshold size for pupation and discrete growth steps can amplify slight differences in growth rate and lead to unpredictable relationships between growth rate, pupal mass and larval development time, such as those observed in other flush feeding insects. Understanding the mechanisms controlling discrete larval growth and the onset of metamorphosis is essential to the study of insect life history.
Key words: developmental plasticity, Lepidoptera, critical weight, larval stadia