Quantifying the effects of distance and conspecifics on colonization: experiments and models using the loosestrife leaf beetle, Galerucella calmariensis

Abstract

The ability of an insect to disperse to new habitat patches is difficult to quantify, but key to the establishment and persistence of populations. In this study, we examined dispersal of the phytophagous chrysomelid beetle, Galerucella calmariensis, which is currently being introduced into North America for the biological control of purple loosestrife (Lythrum salicaria), an aggressive wetland weed. We used a mark, release, and recapture approach to determine how rates of colonization of host patches by this beetle are influenced by the distance of the patch from the source of dispersers, and by the presence of conspecifics at the patch. We released color-coded beetles at six distances from a long, linear patch of purple loosestrife that was divided into segments with and without conspecifics. We observed initial flight directions as beetles left the release points and collected all beetles that settled at the target patch. We found a bias in initial flight toward the target for distances up to 50 m. Over the 7 days of the experiment, beetles arrived at the target from all release points, including the farthest release point, 847 m away. G. calmariensis was strongly attracted to conspecifics when settling after dispersal; 86% of the 582 recovered beetles came from the segments inhabited by conspecifics. The probability of an individual arriving at the patch declined steeply with release distance. This relationship fits a model in which beetles move in a random direction and stop if they intercept the target patch, and where beetles are lost at a constant rate with distance travelled. The dispersal and patch-colonizing behavior of G. calmariensis is likely to have important consequences for the biological control program against purple loosestrife.

The influence of matrix habitat on Aphthona flea beetle immigration to leafy spurge patches

“…Much of weed biocontrol is conducted on heterogeneous landscapes that are mosaics of weed patches, native and non-native (i.e., crop land) habitats. Once biocontrol agents are established at initial release sites, biocontrol practitioners are interested in the impact of the agent on target weeds, dispersal rates of the agent and the ability of the agent to colonize weed patches some distance from initial release points (e.g., Rees 1990;Mays and Kok 1996;Grevstad and Herzig 1997;McFadyen 1998). Our results indicate that immigration / colonization of weed patches is dependent upon the type of matrix habitat separating source and destination weed patches.…”

Interactions of root and leaf herbivores on purple loosestrife (Lythrum salicaria)

“…Adults form temporary aggregations on host plants (Blossey 1995a;Grevstad and Herzig 1997) and the oviposition period of overwintered females in central New York ranges from mid May to the end of June. Females produce up to 12 eggs/day [clutch size 5.3±0.2 (mean±1 SE); up to 400 eggs/female] with an unlimited food supply (Blossey 1995a).…”

Herbivory strongly influences among-population variation in reproductive output of Lythrum salicaria in its native range

“…In addition, low immigration rates may limit Galerucella densities on islands in the outer part of the archipelago, as these islands are separated by more than 400 m from other islands with L. salicaria populations. The beetle has been reported to disperse up to ~ 850 m across terrestrial habitats when released at various distances away from the nearest host population (Grevstad and Herzig 1997). However, open water may reduce dispersal distances, and dispersal from existing populations may typically be shorter because individuals are strongly attracted to already damaged plants (Hambäck 2010).…”