Plant abandonment behavior and fitness of monarch larvae (Danaus plexippus) is not influenced by an intraspecific competitor

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Abstract:

Integrating aspects of larval lepidopteran behavior that enhance survival into conservation plans could increase the overall impact of the efforts. We previously recommended that where possible, maintaining 2–4 ramets of closely-spaced common milkweed would support the development of at least one monarch through pupation, based on a seemingly innate behavior in which monarch larvae (Danaus plexippus) abandon their natal milkweed ramet (Asclepias sp.). Here, we explored the impact of intraspecific competition on larval ramet abandonment behavior and fitness of monarch larvae in small artificial milkweed patches.

We observed larvae reared under direct and indirect intraspecific competition, and larvae reared alone.

We found no influence of intraspecific competition; however, our study provides further support that milkweed ramet abandonment is a seemingly innate behavior. This behavior occurs before all of the available leaf biomass on a ramet is consumed and prior to the pre-pupal wandering stage.

Implications for insect conservation: Results from our study suggest that in the absence of predation, parasitism, and interspecific competition, and when sufficient plant biomass is present to support larval development, the presence of an intraspecific competitor does not influence larval behavior or fitness. Based on milkweed ramet abandonment behavior, we continue to suggest maintaining small patches of 2–4 milkweed ramets when possible.