What a girl wants: female oviposition preference in Malacosoma americanum.

Abstract

Semelparous animals provide no parental care to their offspring. Instead they must rely on a given environment's conditions to supply resources and sufficient protection for their young. Phytophagous insects are one species that select ovipositioning sites that best increase chances of offspring survival. Malacosoma americanum favors laying its egg masses on host Prunus serotina trees, however, it is unclear why individual hosts of this species are chosen over others. In this study, we investigated possible variables to determine if female moths do in fact have an oviposition site preference, and if so, what criteria they use in host cherry tree selection. We examined tree basal diameter, canopy surface area, density of P. serotina trees within a 3 meter radius of the target tree, leaf water ratio, and leaf nitrogen levels for two sites on the Pellston Plain, MI: one in the shade and one in full sunlight. We found that M. americanum moths oviposited egg masses on trees with higher leaf nitrogen levels (t = 3.921, d.f. =43.8 , p < 0.0001) and trees fully exposed to sunlight (Kruskal-Wallis, p = 0.038). Moths did not select on the basis of basal diameter, canopy surface area, the number of surrounding P. serotina trees, or leaf water content in either location. However, we found that sunlight has a relationship with tree basal diameter (Kruskal-Wallis, p< 0.0001), canopy surface area (Kruskal-Wallis, p< 0.0001), and leaf nitrogen content (t = 3.921, d.f. = 43.8, p = 0.001). From these results we can infer that female M. americanum exhibit individual host P. serotina oviposition preference by favoring trees growing in the sunlight. These preferred host trees were also greater in dimension and higher in nitrogen, indicating possible benefits to ovipositioning moths such as larger and more nutritious food sources. However, we cannot fully determine nor distinguish each linked variable's individual role in female preference.