Evol Ecol Res 13: 625-635 (2011)     Full PDF if your library subscribes.

Maintenance of sociality in a communal caterpillar, Eucheira socialis westwoodi (Lepidoptera: Pieridae)

J.J. Sun1 and D.L.A. Underwood2

1Department of Biology, University of California, Riverside, California, USA and 2Department of Biological Sciences, California State University, Long Beach, California, USA

Correspondence: D.L.A. Underwood, Department of Biological Sciences, California State University, Long Beach, CA 90840, USA.
e-mail: dlunderw@csulb.edu


Background: The theory of kin selection fails to explain the maintenance of gregariousness in insects with low levels of relatedness. Alternative proposals suggest that other factors such as group thermodynamic efficiency or predator avoidance are greatly enhanced by insects living socially, and therefore might serve as reinforcements for costly social behaviours exhibited by these species independent of relatedness.

Questions: Do Eucheira socialis westwoodi (Lepidoptera: Pieridae) females place their egg masses near conspecific egg masses? Does the distance between egg masses influence the survival of the larvae hatched from these egg masses? Does group size influence larval foraging success?

Organism: Eucheira socialis westwoodi larvae from naturally occurring colonies in El Madroño, Durango, Mexico.

Methods: We assessed the distribution of egg masses on trees and across trees. Larvae from egg masses oviposited at variable distances from conspecific egg masses were followed until the fourth instar. Differently sized larval groups were constructed and maintained on ‘artificial trees’ using sprigs collected from a single host tree (Arbutus xalapensis: Ericaceae). These were in turn deployed to a semi-natural area. Frequency and duration of foraging of individually marked larvae were recorded daily and subsequently analysed.

Conclusions: Egg masses were significantly clumped on trees and across trees. Larvae from egg masses oviposited near other egg masses coalesced into larger groups and had higher survival rates than larvae from isolated egg masses. Larvae in manipulated groups of 400 individuals fed more frequently and for longer, gained more weight, and had greater survivorship than larvae in smaller groups. These results suggest that larval foraging success serves as reinforcement for the gregarious behaviour seen in E. s. westwoodi larvae and also may drive selection in the oviposition preference of adult females of this species.

Keywords: Eucheira socialis westwoodi, foraging, gregariousness, kin selection, oviposition preference, sex-biased mortality, sociality.

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