Weed and herbivorous insect population densities at the broad spatial scale: Ambrosia artemisiifolia L. and Zygogramma suturalis F. (Col., Chrysomelidae)

Abstract

AbstractZ. suturalis was introduced into Russia in 1978 to control against the common ragweed. Weed and insect population densities were estimated in 1988–1989 over 250 km2. Absolute (beetles per m2) density of Z. suturalis was almost linear with the ragweed density (wet weight per m2). Relative (beetles per kg of ragweed) density was independent of ragweed density. Last year's absolute density of Z. suturalis significantly influences current relative insect density, but its influence on the absolute insect density is overpowered by the influence of the current ragweed density. Obviously, just the plant and not the insect is the driving force in their interactions. The introduction results can be considered as establishment and moderate biological success, but not as control success. Host impact is very low because of low relative population density of Z. suturalis. Local patches with high Z. suturalis density, which are usually located in field margins, do not play an important role in total population density determinations. Possibly, field nurseries, i.e. large uncultivated sites grown with ragweed, could be a promising method of Z. suturalis propagation.