Evol Ecol Res 12: 545-553 (2010)     Full PDF if your library subscribes.

The presence of active larvae delays the emergence of conspecifics in the tupelo leafminer, Antispila nysaefoliella

Candace Low

Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, California, USA

Correspondence: C. Low, Department of Ecology and Evolutionary Biology, Corson Hall, Cornell University, Ithaca, NY 14853-2701, USA.
e-mail: cl754@cornell.edu


Hypothesis: In many systems, density-dependent effects on fitness often can be mitigated with adaptations such as individual mobility or increased competitive ability. However, in sessile or sedentary systems, immobility might preclude individuals from directly choosing their group or patch, thus making it difficult for them to respond to the costs and benefits of group living or variation in density in general. In this study, I test the effect of density on delayed emergence of an effectively sessile species.

Study system: Tupelo leafminer, Antispila nysaefoliella Clemens (Lepidoptera: Heliozelidae), a specialist of black gum, Nyssa sylvatica Marsh (Cornaceae). The study population is located in the northern Shenandoah Valley in Clarke Co., Virginia.

Methods: In 2004 and 2008, I conducted field experiments where I reduced the initial density of larvae on leaves and compared the frequency of occurrence of new larvae after the experimental treatment. In 2008, I also enclosed half of the leaves with fine-mesh bags to exclude compensatory oviposition as a possible cause of subsequent larval emergence.

Prediction and result: The prediction that the removal of active larvae would lead to more occurrences of secondary larval emergence on experimental leaves compared with control leaves was supported in both years of the experiment. The mesh enclosure treatment (2008) had no effect, which suggests that the higher rate of secondary emergence was not due to eggs that were deposited after larvae were removed.

Conclusion: The experimental results demonstrate that the presence of active larvae may suppress the development of conspecific larvae (or unhatched eggs). Therefore, the potential number of A. nysaefoliella larvae on leaves might not be realized immediately at the beginning of the season. Rather, as individuals in the initial cohort die, typically due to parasitism, others may emerge subsequently. Although the mechanism is currently unknown, delayed emergence appears to be associated with larval density.

Keywords: aggregation, competition, delayed hatching, density dependence, hatching asynchrony, life-history timing, plant–insect interactions.

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