Oviposition site preference and larval performance
of the aspen leaf miner (Phyllocnistis populiella)

Russell Dennis, Patricia Doak, and Diane Wagner

University of Alaska, Department of Biology and Wildlife, Fairbanks AK 99775 (email: ftred@uaf.edu)

Many plant species produce extrafloral nectaries (EFNs) on their stems, bracts, or leaves. These glands secrete nectar that commonly attracts predaceous mutualists, thereby indirectly protecting the plant from phytophagous insects. In quaking aspen (Populus tremuloides), the proportion of leaves with EFNs to leaves without is highly variable, a phenomenon that offers the opportunity to examine possible defensive effects of EFN expression. As part of a larger study aimed at explaining this variation, we examine the role of EFN expression in oviposition site preference of a current outbreak species, the aspen leaf miner (Phyllocnistis populiella; ALM hereafter). The effects of EFN expression on ALM oviposition are not known, and prior to this study patterns of ALM oviposition have not been precisely measured. Previous studies of variable damage between leaves with and without EFNs have included egg surveys but do not account for possible impacts of egg predation and competition among females for oviposition sites. By experimentally excluding predators and limiting available oviposition sites to one leaf with and one leaf without EFNs, we more accurately investigate individual preference. We hypothesize that 1) adult moths express oviposition site preference for leaves without EFNs, and that 2) this preference confers relatively higher ALM larval survivorship. In the summer of 2009, we conducted 167 choice trials in Fairbanks, AK to test the first of these hypotheses. Female ALMs did not lay significantly more eggs on leaves without EFNs (Wilcoxon signed ranks t = -1.6, p = .0548, n = 40), but females tended to lay the first egg of each trial on a non-EFN leaf (χ2 = 4, p = .046, n = 48). These results are preliminary, and with additional samples in 2010 we plan to further investigate this pattern. The data from this study are intended to provide insight into the interaction between an herbivore and the defensive strategy of its host plant. Current outbreak densities of ALMs in the sub-arctic study region present the opportunity to gather substantial data for this purpose.