Dynamics in the spatial structure of Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)

Integrating global positioning systems technology with a visual canopy survey, a 1-m level of sampling support was used to explore within-field spatial organization of the Colorado potato beetle, Leptinotarsa decemlineata (Say), in potatoes. Spatially referenced counts of adult and large larvae (third and fourth instar) L. decemlineata were made in four ≅1.5-ha untreated potato fields during two Pennsylvania growing seasons. The presence and nature of spatial structure varied with developmental stage. Overwintered, immigrating adults established 'trends' or 'drift' in the mean density, but spatial dependency (covariance structure) was not detected. This, coupled with a high incidence-to-mean density relationship, suggests a within-field dispersive role for the colonizers. Large larvae and F₁ adults, in contrast, displayed spatial dependency (covariance structure), at times accounting for up to ≅45% of the variation. Their relatively lower incidence-to-mean density relationship suggests less within-field mobility during the reproductive phase of the population cycle. These observations imply that, although an insect population's spatial structure may be difficult to characterize due to its dynamic nature, there is a consistent and predictable pattern in L. decemlineata spatial structure that is linked to its population phenology.