Omnivores should aggregate to habitats containing prey and non-prey resources (e.g. plant-provided
foods) that promote their performance. Despite support for this prediction, we lack studies linking
omnivore patch preference in the field, to tangible fitness benefits. This is particularly true for natural
systems, as most studies of omnivory have been conducted in artificial agricultural systems. Here we
assessed the aggregation patterns of an omnivorous salt marsh ladybeetle under field conditions to habitat
patches varying in prey (scale insects) and non-prey (cordgrass pollen) resources. Additionally, we tested
the role of olfactory perception of scale insect-infested cordgrass by ladybeetles in mediating habitat
selection over small spatial scales. We then tested the consequences of habitat selection to ladybeetle fitness
by rearing adult ladybeetles in the laboratory on several separate diets and tracked longevity, egg
production, and larval production. Similarly, we reared larval ladybeetles on the same selection of diets
and tracked larval longevity in response to individual and maternal diet.
Results/Conclusions
Adult ladybeetles preferentially aggregated to habitat patches containing scale insect prey, regardless of
the presence of cordgrass pollen, indicating that scale insects are the preferred food resource for these
insects. Adult aggregation to habitat patches containing scale insects may be facilitated by their ability to
perceive olfactory cues, as adult ladybeetles favored air from scale insect-infested leaves over non-
infested leaves in Y-maze assays. Adult ladybeetles fed both scale insects and cordgrass pollen lived
longer than adult ladybeetles fed single -item diets. However, ladybeetles only reproduced when scale
insects were present in their diets, with no added effect of consuming cordgrass pollen. Larval ladybeetle
longevity was greatest on diets containing scale insects, regardless of the presence of cordgrass pollen.
Our findings suggest that adult ladybeetles preferentially aggregate to habitat patches that enhance their
reproductive output, personal longevity, and the longevity of their offspring. In doing so, adult
ladybeetles increase the local population density of all ladybeetle life stages. At high densities, adult and
larval ladybeetles can suppress scale insect populations (even in the presence of cordgrass pollen) and
indirectly benefit salt marsh primary productivity, resulting in enhanced sediment accretion and spring
regrowth.