Does the age of the host plant modulate migratory activity of Plutella xylostella?

Ephemeral plants and most tropical crops are available to herbivore insects as irregular and unpredictable patches of resources. Insects that exploit patched habitats usually have well-developed migratory ability, and migration is a fundamental process in the cycle of colonization and extinction of the local populations. We ask here whether Plutella xylostella (Lepidoptera: Yponomeutidae) uses the aging process of the host plant to modulate its migratory activity. The insect was reared in the laboratory on the leaves from the middle estratum (fourth expanded leaves) of cabbage (Brassica oleraceae var. capitata) of various ages, and on leaves from three strata of the mature plant. Females that spent their larval phase in young and tender plants lived for a shorter period of time and laid eggs immediately after metamorphosis. In contrast, mature plants, particularly the new leaves from the superior stratum, favored the development of adult phenotypic traits that occur in migratory forms, such as reduced body size, increased longevity and delayed reproductive activity. We suggest that the lesser nutritional quality and the short temporal persistence of mature plants are selective forces favoring individuals that are better prepared to abandon their habitat soon after emergence. Plutella xylostella may use the predictable ontogenetic changes of the ephemeral host plant to modulate its physiological and behavioral migratory ability.